Cell nucleus: Wikis

  
  

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HeLa cells stained for DNA with the Blue Hoechst dye.
^ The cells are stained with a dye called methylene blue.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ The nucleus is counterstained for DNA (DAPI stain, blue fluorescence).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ (P to T) Spermatogenesis in Schistocerca gregaria (locust) stained blue for DNA with DAPI (blue fluorescence) and labelled for rDNA (pTa71, digoxigenin-FITC, green/cyan fluorescence).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.The central and rightmost cell are in interphase, thus their entire nuclei are labeled.^ In Petunia hybrida root tip meristematic nuclei, there are four rDNA sites, two are active through most of the interphase stages of the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The dynamic organisation of interphase nuclei during cell differentiation and with changing cell activity, p.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Nuclei of the apical cell are haploid and spherical with a large central nucleolus.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

On the left a cell is going through mitosis and its DNA has condensed ready for division.
.
Schematic of typical animal cell, showing subcellular components.
^ Schematic drawing of the structure of a typical bacterial cell of the bacillus type.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ (A to C) Three examples of wild-type interphase cells that show the typical tight association between the MTOC (marked with arrowheads) and nucleus.
  • Microtubule-Nucleus Interactions in Dictyostelium discoideum Mediated by Central Motor Kinesins -- Tikhonenko et al. 8 (5): 723 -- Eukaryotic Cell 10 February 2010 13:013 UTC ec.asm.org [Source type: Academic]

^ The plot shows that cells with rapid sags toward rest (short ) had deeper sags (small b/a ) and had undershoots with two components.
  • Cholinergic Modulation of Stellate Cells in the Mammalian Ventral Cochlear Nucleus -- Fujino and Oertel 21 (18): 7372 -- Journal of Neuroscience 10 February 2010 13:013 UTC www.jneurosci.org [Source type: Academic]

Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles
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Entry of material into the nucleus through phagocytosis.
^ Entering the nucleus through the pores are the nucleotide building blocks of DNA and RNA, as well as adenosine triphosphate , which provides the energy for synthesizing genetic material.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

The phagosome travels from the cell membrane to the nucleus, and then is engulfed by the nucleus, releasing its contents.
.In cell biology, the nucleus (pl.^ Systems biology in the cell nucleus .
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Viruses and the Nucleus is an invaluable resource for students of virology, microbiology and cell biology as well as for those who work within the industry.
  • Wiley::Viruses and the Nucleus 10 February 2010 13:013 UTC eu.wiley.com [Source type: Academic]

^ Biology breaks cell types into eukaryotic (those with a defined nucleus) and prokaryotic (those with no defined nucleus).
  • Biology4Kids.com: Cell Structure: Cell Nucleus 10 February 2010 13:013 UTC www.biology4kids.com [Source type: FILTERED WITH BAYES]

.nuclei; from Latin nucleus or nuculeus, meaning kernel), also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells.^ A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated.
  • NCBO BioPortal: Cell Cycle Ontology (S. cerevisiae) - nucleus 10 February 2010 13:013 UTC bioportal.bioontology.org [Source type: FILTERED WITH BAYES]

^ Eukaryotes have cells that contain nuclei .

^ Generally, eukaryotic cells contain membrane-bound organelles in addition to the membrane-bound nuclei .

.It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes.^ RNA: replicated from DNA - The organization of cells .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Such cells can be induced to form embryos.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ The genetic information of cells - - DNA: the genetic material .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.The genes within these chromosomes are the cell's nuclear genome.^ Chromosome territories, nuclear architecture and gene regulation in mammalian cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ More work is needed to relate changing cell activity and the expression of genes in development to specific organizational properties of the nucleus, including the intranuclear distribution of genes and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Mutational decay and age of chloroplast and mitochondrial genomes transferred recently to angiosperm nuclear chromosomes.
  • Experimental Reconstruction of Functional Gene Transfer from the Tobacco Plastid Genome to the Nucleus -- Stegemann and Bock 18 (11): 2869 -- THE PLANT CELL 10 February 2010 13:013 UTC www.plantcell.org [Source type: Academic]

.The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression — the nucleus is therefore the control center of the cell.^ We therefore sought to design an experimental strategy that would allow us to directly test for functionalization of transferred organellar genes in the nucleus.
  • Experimental Reconstruction of Functional Gene Transfer from the Tobacco Plastid Genome to the Nucleus -- Stegemann and Bock 18 (11): 2869 -- THE PLANT CELL 10 February 2010 13:013 UTC www.plantcell.org [Source type: Academic]

^ More work is needed to relate changing cell activity and the expression of genes in development to specific organizational properties of the nucleus, including the intranuclear distribution of genes and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ These differences presumably represent differing specific or total activities of the different cell types.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and separates its contents from the cellular cytoplasm, and the nuclear lamina, a meshwork within the nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole.^ They both have a cell membrane, nucleus and a cytoplasm composed of many of the same organelles.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ The nuclear membrane is a double membrane .

^ The nuclear membranes outer membrane is in contact with the cytoplasm .

.Because the nuclear membrane is impermeable to most molecules, nuclear pores are required to allow movement of molecules across the envelope.^ Connecting the interior volume of a nucleus with the external cytoplasm are numerous pores that form a fluid-filled bridge that crosses the nuclear membrane .

^ Osmosis : Movement of water molecules from a region of high concentration to a region of lower concentration through a differentially permeable cell membrane.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ The entire envelope is perforated by numerous nuclear pores.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.These pores cross both of the membranes, providing a channel that allows free movement of small molecules and ions.^ These molecules have special amino acid sequences on their surface that signal admittance by the nuclear pore complexes.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Connecting the interior volume of a nucleus with the external cytoplasm are numerous pores that form a fluid-filled bridge that crosses the nuclear membrane .

^ Osmosis : Movement of water molecules from a region of high concentration to a region of lower concentration through a differentially permeable cell membrane.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

.The movement of larger molecules such as proteins is carefully controlled, and requires active transport regulated by carrier proteins.^ The control of DNA condensation is mediated via protein- chromatin interactions and influenced by epigenetic phenomena such as histone acetylation ( 76 ) and DNA methylation ( 89 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ This movement involves carrier proteins (channels) in the cell membrane and requires energy in the form of ATP (adenosine triphosphate).
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ Electrophoresis A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance.^ See also: cell , gene , gene expression , chromosome Return to Top .
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ See also: cell , chromosome , gene expression , trisomy .
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Lower limit of propulsive forces required for nuclear organelles to undergo processive transport in intranuclear region of mouse embryonic tissue cell .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

.Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes.^ The nucleus of the average human cell is only 6 micrometres (6 × 10 −6 metre) in diameter, yet it contains about 1.8 metres of DNA. This is distributed among 46 chromosomes , each consisting of a single DNA molecule about 40 mm (1.5 inches) long.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing.
  • NCBO BioPortal: Cell Cycle Ontology (S. cerevisiae) - nucleus 10 February 2010 13:013 UTC bioportal.bioontology.org [Source type: FILTERED WITH BAYES]

^ Animal cells and plant cells contain membrane-bound organelles, including a distinct nucleus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.The best known of these is the nucleolus, which is mainly involved in the assembly of ribosomes.^ As is well known, ribosomes are not assembled in the cytoplasm but in the nucleolus, well away from the site of translation – of both host- and mitochondrion-derived ribosomal proteins.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.

Contents

History

Oldest known depiction of cells and their nuclei by Antonie van Leeuwenhoek, 1719.
Drawing of a Chironomus salivary gland cell published by Walther Flemming in 1882. The nucleus contains Polytene chromosomes.
The nucleus was the first organelle to be discovered. .The probably oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632 – 1723).^ Antonie van Leeuwenhoek, detail of a portrait by Jan Verkolje; in the Rijksmuseum, Amsterdam.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.He observed a "Lumen", the nucleus, in the red blood cells of salmon[1].^ Each spherical spore has a diameter of about 1/200 mm (5 µm), slightly smaller than a human red blood cell (7.5 µm).
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ Red Cell Disorders: Peripheral Blood Clues to Nonneoplastic Conditions .
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

^ Decreased DNA synthesis causes the nucleus in the developing red cells to mature at a slower than normal rate.
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

.Unlike mammalian red blood cells, those of other vertebrates still possess nuclei.^ Red blood cells are 1/2 to 2/3 as large as white blood cells, contain no nucleus, and are Gram negative.
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

^ On the other hand, quantitative in vivo microscopy methods provide the first glimpse of how DNA, RNA and proteins behave inside the nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Hypertonic and Hypotonic : When comparing two solutions, such as the inside of a red blood cell (RBC) with the solution they are placed in, the solution with the greater salt concentration is hypertonic, while the solution with the lower salt concentration is hypotonic.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

The nucleus was also described by Franz Bauer in 1804[2] and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. .Brown was studying orchids microscopically when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer.^ It has been difficult to find such a ganglion cell in primate retina but they they have been reported in the koniocellular layers of the primate lateral geniculate nucleus.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

^ The head contains a nucleus covered by an outer cap called the acrosome which stores enzymes needed to penetrate the cellular and glycoprotein layers surrounding the egg.
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^ Interestingly, PCD is first observed in the nucleus, many of the defining features of PCD centre on nuclear morphology, and the nucleus is the last structure to disappear with the death of the cell.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[3] He did not suggest a potential function. .In 1838 Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "Cytoblast" (cell builder).^ ErbB4, a member of the EGF receptor family, plays an important role in mammary gland development and controls cell proliferation and differentiation.
  • Met, the Hepatocyte Growth Factor Receptor, Localizes to the Nucleus in Cells at Low Density -- Pozner-Moulis et al. 66 (16): 7976 -- Cancer Research 10 February 2010 13:013 UTC cancerres.aacrjournals.org [Source type: Academic]

^ It is thought that both groups of cells play a role in form vision.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

^ The presence of Met in the nucleus indicates that it may play a role in enhancing signaling of the full-length Met receptor or may be indicative of a novel signaling pathway.
  • Met, the Hepatocyte Growth Factor Receptor, Localizes to the Nucleus in Cells at Low Density -- Pozner-Moulis et al. 66 (16): 7976 -- Cancer Research 10 February 2010 13:013 UTC cancerres.aacrjournals.org [Source type: Academic]

.He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view having already described cells multiplying by division and believing that many cells would have no nuclei.^ It would be reasonable to assume that if they have no nucleus, they have no use for nor capacity to make new ribosomes either It most likely is not important to know.
  • sieve tube cells - no ribosomes ? | DAT Discussions | Student Doctor Network 10 February 2010 13:013 UTC forums.studentdoctor.net [Source type: General]

^ The organization of chromosomes in cells at division has been unclear, and many data obtained before the 1990s are contradictory (see, e.g., references 9 , 41 , 151 , and 155 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ I nevertheless acknowledge that one can make a strong case by asking how the integrity of the genome was maintained in a cell that already developed cytoskeletal dynamics and membrane traffic [ 4 ].
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

.The idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak (1852) and Rudolf Virchow (1855) who decisively propagated the new paradigm that cells are generated solely by cells ("Omnis cellula e cellula").^ He had followed Sherington's work on the spinal cord where the idea of excitation and inhibition between nerve cells first evolved.
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^ CaCo2 cells were generously donated by the laboratory of Dr. Jon Morrow (Yale University School of Medicine, New Haven, CT).
  • Met, the Hepatocyte Growth Factor Receptor, Localizes to the Nucleus in Cells at Low Density -- Pozner-Moulis et al. 66 (16): 7976 -- Cancer Research 10 February 2010 13:013 UTC cancerres.aacrjournals.org [Source type: Academic]

.The function of the nucleus remained unclear.^ Their function was and remains unclear, though they were not thought to be associated with active DNA replication, transcription, or RNA processing.

[4]
.Between 1876 and 1878 Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus.^ Pronucleus The nucleus of a sperm or egg prior to fertilization.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ The discovery of Herbst ( 20 ), who showed that calcium-free sea water separated the individual blastomeres of the sea urchin egg from each other, makes it possible to isolate each single blastomere and to follow its fate.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

^ Figure 1 Two figures from plates II and III of Boveri's definitive 1907 publication on the development of dispermic sea urchin eggs.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

.This was the first time it was suggested that an individual develops from a (single) nucleated cell.^ The cultured cells, synchronized to develop together, divided four or five times before losing their nuclei and becoming immature red blood cells.
  • Whitehead Institute - How red blood cells nuke their nuclei 10 February 2010 13:013 UTC www.wi.mit.edu [Source type: Academic]

^ This was obtained by a digitized fluorescence approach at the single cell level, using Hoechst dye as a probe with a high affinity to nucleic acids.
  • Welcome to IEEE Xplore 2.0: Double pulse approach of electropulsation: a fluorescence analysis of the nucleus perturbation at the single cell level 10 February 2010 13:013 UTC ieeexplore.ieee.org [Source type: Academic]

^ Through the evolutionary process man has developed into a species that can now fight back against the intrusion of harmful single cell organisms.

.This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "Monerula", a structureless mass of primordial mucus ("Urschleim").^ More work is needed to relate changing cell activity and the expression of genes in development to specific organizational properties of the nucleus, including the intranuclear distribution of genes and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The changes that occur are never as dramatic as can occur during development and are perhaps restricted to a certain framework established for the cell type.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Gross reorganization of the nucleus is probably associated with a changing cellular role, as occurs during cell differentiation and development, the subject of the following sections of the review.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time.^ After a few minutes, the green drained from the nucleus back into the cell proper, only to return again after some time.
  • ERK's got rhythm: Protein that controls cell growth found to cycle in and out of cell nucleus | Eureka! Science News 10 February 2010 13:013 UTC esciencenews.com [Source type: Academic]
  • ERK's got rhythm: Protein that controls cell growth found to cycle in and out of cell nucleus 10 February 2010 13:013 UTC www.biologynews.net [Source type: Academic]
  • PNNL: News - ERK's got rhythm 10 February 2010 13:013 UTC www.pnl.gov [Source type: Academic]
  • Featured Article - Video: ERK's got rhythm - Growth controller found to cycle in and out of cell nucleus 10 February 2010 13:013 UTC www.labspaces.net [Source type: Academic]
  • ERK's got rhythm: Protein that controls cell growth found to cycle in and out of cell nucleus | Science Blog 10 February 2010 13:013 UTC www.scienceblog.com [Source type: Academic]

^ After summarizing the results, Section 5 discusses some implications for cell nucleus ultrastructure and for applications.
  • Cell Nucleus Ultrastructure and Chromosome Aberrations 10 February 2010 13:013 UTC math.berkeley.edu [Source type: Academic]

^ Conversely the egg cell may be fertilized by the Silver Honey Bantam sperm cell and the polar nucleus may be fertilized by the X18G sperm cell.
  • Detection of an unfertilized polar nucleus with a fertilized egg cell 10 February 2010 13:013 UTC www.agron.missouri.edu [Source type: Academic]

.However, Hertwig confirmed his observation in other animal groups, e.g.^ However the biggest division is between the cells of the prokaryote kingdom (the bacteria) and those of the other four kingdoms (animals, plants, fungi and protoctista), which are all eukaryotic cells.

^ However, unlike the other 12 Dictyostelium kinesin motors, Kif9 does not group with previously recognized kinesin families ( 38 ).
  • Microtubule-Nucleus Interactions in Dictyostelium discoideum Mediated by Central Motor Kinesins -- Tikhonenko et al. 8 (5): 723 -- Eukaryotic Cell 10 February 2010 13:013 UTC ec.asm.org [Source type: Academic]

amphibians and molluscs. Eduard Strasburger produced the same results for plants (1884). .This paved the way to assign the nucleus an important role in heredity.^ Taken together, these experiments suggest that components within the cytoplasm, not DNA content of the nucleus, play an important role in nuclear size control.
  • Active Mechanism Locks In The Size Of A Cell's Nucleus 10 February 2010 13:013 UTC www.sciencedaily.com [Source type: FILTERED WITH BAYES]
  • The Rockefeller University - Newswire: Active mechanism locks in the size of a cell�s nucleus 10 February 2010 13:013 UTC newswire.rockefeller.edu [Source type: Academic]
  • The Rockefeller University - Newswire: Active mechanism locks in the size of a cell�s nucleus 10 February 2010 13:013 UTC newswire.rockefeller.edu [Source type: Academic]

^ RNA (Ribonucleic acid) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ The arcuate nucleus has a key role in the regulation of feeding behaviour, through two important populations of centrally projecting neurons: .
  • Arcuate nucleus - encyclopedia article - Citizendium 10 February 2010 13:013 UTC en.citizendium.org [Source type: Academic]
  • Arcuate nucleus - encyclopedia article - Citizendium 10 February 2010 13:013 UTC locke.citizendium.org [Source type: Academic]

In 1873 August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity. .The function of the nucleus as carrier of genetic information became clear only later, after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century; the chromosome theory of heredity was developed.^ It is specialised to carry genetic information.
  • More about Animal Cells 10 February 2010 13:013 UTC www.purchon.com [Source type: FILTERED WITH BAYES]

^ The nucleus directs activities of the cell and carries genetic information from generation to generation.

^ Chromosomes carry the genes, the units of heredity.
  • Eukaryotic Cells- Biology 102 Course - CarolGuze.com 10 February 2010 13:013 UTC www.carolguze.com [Source type: Academic]

[4]

Structures

.The nucleus is the largest cellular organelle in animals.^ The nucleus is the largest cellular organelle .

^ The nucleus is the largest membrane-bound organelle.
  • Plant cells vs. Animal cells - Biology Online 10 February 2010 13:013 UTC www.biology-online.org [Source type: Academic]

^ The nucleus is a cellular organelle that contains the genomic DNA. The nucleus is surrounded by a nuclear envelope consisting of a double layer of membranes.

[5] .In mammalian cells, the average diameter of the nucleus is approximately 6 micrometers (μm), which occupies about 10% of the total cell volume.^ Fraction of nucleus out of total mesophyll cell volume .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ Percent of nucleus volume out of total cell volume .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ Volume of nucleus of Hela cell .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

[6] .The viscous liquid within it is called nucleoplasm, and is similar in composition to the cytosol found outside the nucleus.^ The DNA within the nucleus is found as DNA-protein structures called chromatin .

^ There are similarities to polyploid nuclei, including associations of homologous and heterologous chromosomes and substantial structural reorganization of the nucleus from that found in cycling cells.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Cytoplasmic trait A genetic characteristic in which the genes are found outside the nucleus, in chloroplasts or mitochondria.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

[7] It appears as a dense, roughly spherical organelle.

Nuclear envelope and pores

.The eukaryotic cell nucleus.^ Cell Nucleus The cell nucleus is the trademark of any eukaryotic cell.
  • Labeled Animal Cell Diagram 10 February 2010 13:013 UTC www.buzzle.com [Source type: Academic]

^ Do eukaryotic cells have a nucleus?
  • Do prokaryotic cells have a nucleus? Do eukaryotic cells have a nucleus? - Yahoo!7 Answers 10 February 2010 13:013 UTC au.answers.yahoo.com [Source type: General]

^ A nucleus can be found in eukaryotic cells.
  • WikiAnswers - What type of cell has a nucleus 10 February 2010 13:013 UTC wiki.answers.com [Source type: FILTERED WITH BAYES]

.Visible in this diagram are the ribosome-studded double membranes of the nuclear envelope, the DNA (complexed as chromatin), and the nucleolus.^ Organization of chromatin fibre - - The nuclear envelope .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Simple and complex nuclear loci created by newly transferred chloroplast DNA in tobacco.
  • Experimental Reconstruction of Functional Gene Transfer from the Tobacco Plastid Genome to the Nucleus -- Stegemann and Bock 18 (11): 2869 -- THE PLANT CELL 10 February 2010 13:013 UTC www.plantcell.org [Source type: Academic]

^ Find this article online Itoh N, Shimizu N (1998) DNA replication-dependent intranuclear relocation of double minute chromatin.
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

Within the cell nucleus is a viscous liquid called nucleoplasm, similar to the cytoplasm found outside the nucleus.
.
A cross section of a nuclear pore on the surface of the nuclear envelope (1).
^ Specifically, the section 'Evolution of a selective hydrogel sieve at nuclear pores' illustrates how recent experimental results [ 37 , 38 ] shed light on the stepwise evolution of nuclear pore selectivity.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ In the section, 'Evolution of a selective hydrogel sieve at nuclear pores', the statement is made that nuclear localization signals 'mimicked the sequences used by karyopherins to recognise host-RPs'.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ The entire envelope is perforated by numerous nuclear pores.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

Other diagram labels show (2) the outer ring, (3) spokes, (4) basket, and (5) filaments.
.The nuclear envelope otherwise known as nuclear membrane consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometers (nm).^ The nuclear envelope is a double membrane composed of an outer and an inner phospholipid bilayer.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Protein-extracts, 20–50 µg, were first separated by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and were then transferred onto polyvinylidene fluoride membrane.
  • PLoS ONE: Modulation of Akt and ERK1/2 Pathways by Resveratrol in Chronic Myelogenous Leukemia (CML) Cells Results in the Downregulation of Hsp70 10 February 2010 13:013 UTC www.plosone.org [Source type: Academic]

^ This in turn would have triggered a selective pressure to create a barrier separating the eukaryotic ribosome factory from the mitochondrial ribosome factory (the nuclear membrane).
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

.The nuclear envelope completely encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm.^ The nucleus is separated from the rest of the cell and the cytoplasm by a double...
  • nucleus – FREE nucleus information | Encyclopedia.com: Find nucleus research 10 February 2010 13:013 UTC www.encyclopedia.com [Source type: Academic]

^ Nuclear Envelope - this is a double membrane structure that encloses the nucleus.
  • The Contents of the Nucleus: A Look at the Structure and Function of the Cell Nucleus 10 February 2010 13:013 UTC www.brighthub.com [Source type: Academic]

^ A. Separates the cytoplasm of the cell from its environment .

[8] .The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes.^ The rough endoplasmic reticulum - - The Golgi apparatus .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Roug h endoplasmic reticulum (rough ER) .

^ The rough appearance of rough endoplasmic reticulum is due to the presence of ribosomes on the membrane.

.The space between the membranes is called the perinuclear space and is continuous with the RER lumen.^ The space within the ER (lumen) is continuous with the space between the two membranes of the nucleus .

^ Plant cells contain membrane-bound organelles, including fluid-filled spaces, called vacuoles, that …[Credits : Encyclopædia Britannica, Inc.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Upon fusion with the plasma membrane (a process known as exocytosis ), the lumen of the transport vesicle (a.k.a., secretory vesicle in this context) is continuous with the outside of the cell .

.Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins.^ Entering the nucleus through the pores are the nucleotide building blocks of DNA and RNA, as well as adenosine triphosphate , which provides the energy for synthesizing genetic material.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The entire envelope is perforated by numerous nuclear pores.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ At the local level, dynamic binding significantly affects the behavior of proteins because it provides the basis for regulatory events through combinatorial, competitive networks of interactions.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast) to 100 proteins (in vertebrates).[5] .The pores are 100 nm in total diameter; however, the gap through which molecules freely diffuse is only about 9 nm wide, due to the presence of regulatory systems within the center of the pore.^ The pores are 100 nm in total diameter; however, the gap through which molecules freely diffuse is only about 9 nm wide, due to the presence of regulatory systems within the center of the pore.

^ The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast ) to 100 proteins (in vertebrate s).

^ The nucleus of the average human cell is only 6 micrometres (6 × 10 −6 metre) in diameter, yet it contains about 1.8 metres of DNA. This is distributed among 46 chromosomes , each consisting of a single DNA molecule about 40 mm (1.5 inches) long.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.This size allows the free passage of small water-soluble molecules while preventing larger molecules, such as nucleic acids and larger proteins, from inappropriately entering or exiting the nucleus.^ The ICD of the nucleus has a complex of proteins and nucleic acids.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Current data suggest that the nucleus of each cell type has a structured framework within which local changes in the organization and distribution of proteins and nucleic acids can occur with changing cell activity.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ RNA (Ribonucleic acid) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.These large molecules must be actively transported into the nucleus instead.^ These large molecules must be actively transported into the nucleus instead.

^ The large, membrane-bounded organelle that contains the genetic material , in the form of multiple linear DNA molecules organized into structures called chromosomes .
  • Nucleus - definition from Biology-Online.org 10 February 2010 13:013 UTC www.biology-online.org [Source type: FILTERED WITH BAYES]

^ Microinjection of anti-NS2 antibodies into infected cells inhibited   MeSH: Active Transport, Cell Nucleus   [Hold mouse button down for author info.
  • WikiGenes - Active Transport, Cell Nucleus 10 February 2010 13:013 UTC www.wikigenes.org [Source type: Academic]

.The nucleus of a typical mammalian cell will have about 3000 to 4000 pores throughout its envelope,[9] each of which contains a donut-shaped, eightfold-symmetric ring-shaped structure at a position where the inner and outer membranes fuse.^ The nucleus and cell membrane are clearly visible.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ The nucleus of the average human cell is only 6 micrometres (6 × 10 −6 metre) in diameter, yet it contains about 1.8 metres of DNA. This is distributed among 46 chromosomes , each consisting of a single DNA molecule about 40 mm (1.5 inches) long.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Animal cells and plant cells contain membrane-bound organelles, including a distinct nucleus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

[10] .Attached to the ring is a structure called the nuclear basket that extends into the nucleoplasm, and a series of filamentous extensions that reach into the cytoplasm.^ Attached to the ring is a structure called the nuclear basket that extends into the nucleoplasm, and a series of filamentous extensions that reach into the cytoplasm.

^ The structures of the envelope where it opens to the cytoplasm are called the nuclear pores (NUCLEAR PORE).
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ You’re inside a cell, milling around in the aqueous molecular crowd called the cytoplasm , and you’d like to get into the nucleus.
  • Projects in Scientific Computing 2006 (PSC) 10 February 2010 13:013 UTC www.psc.edu [Source type: Academic]

.Both structures serve to mediate binding to nuclear transport proteins.^ Both structures serve to mediate binding to nuclear transport proteins.

^ MTASs mediate interaction with microtubules directly or with components of the motor proteins dynein or kinesin, which mediate transport along microtubules towards the nucleus or cell periphery respectively.
  • Getting to the Heart of a Tumour Cell: Targeting the nucleus | Research & Development | Issue 5, 2007 | Pharma Focus Asia 10 February 2010 13:013 UTC www.pharmafocusasia.com [Source type: Academic]

^ The inner surface has a protein lining called the nuclear lamina, which binds to chromatin and other nuclear components.
  • Molecular Expressions Cell Biology: Plant Cell Structure - Nucleus 10 February 2010 13:013 UTC micro.magnet.fsu.edu [Source type: Academic]

[5]
.Most proteins, ribosomal subunits, and some RNAs are transported through the pore complexes in a process mediated by a family of transport factors known as karyopherins.^ Each is a complex protein consisting of many subunits.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The complexes also regulate the export from the nucleus of RNA and subunits of ribosomes .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Entering the nucleus through the pores are the nucleotide building blocks of DNA and RNA, as well as adenosine triphosphate , which provides the energy for synthesizing genetic material.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.Those karyopherins that mediate movement into the nucleus are also called importins, while those that mediate movement out of the nucleus are called exportins.^ Controls movement of materials in/out of nucleus .
  • Cells The building Bricks of Life - Cell Theory - Williamsclass Middle School Science 10 February 2010 13:013 UTC www.williamsclass.com [Source type: Academic]

^ Those karyopherins that mediate movement into the nucleus are also called importins, while those that mediate movement out of the nucleus are called exportins.

^ You’re inside a cell, milling around in the aqueous molecular crowd called the cytoplasm , and you’d like to get into the nucleus.
  • Projects in Scientific Computing 2006 (PSC) 10 February 2010 13:013 UTC www.psc.edu [Source type: Academic]

.Most karyopherins interact directly with their cargo, although some use adaptor proteins.^ Most karyopherins interact directly with their cargo, although some use adaptor proteins.

^ Despite its modest appearance, cytoplasm provides the stage for some of the cell's most important functions, including protein synthesis, energy production, and cell growth and replication.
  • Teachers' Domain: Nucleus, Cytoplasm, Membrane 10 February 2010 13:013 UTC www.teachersdomain.org [Source type: FILTERED WITH BAYES]

^ MTASs mediate interaction with microtubules directly or with components of the motor proteins dynein or kinesin, which mediate transport along microtubules towards the nucleus or cell periphery respectively.
  • Getting to the Heart of a Tumour Cell: Targeting the nucleus | Research & Development | Issue 5, 2007 | Pharma Focus Asia 10 February 2010 13:013 UTC www.pharmafocusasia.com [Source type: Academic]

[11] .Steroid hormones such as cortisol and aldosterone, as well as other small lipid-soluble molecules involved in intercellular signaling can diffuse through the cell membrane and into the cytoplasm, where they bind nuclear receptor proteins that are trafficked into the nucleus.^ The nucleus and cell membrane are clearly visible.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ They both have a cell membrane, nucleus and a cytoplasm composed of many of the same organelles.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ Cells ingest molecules through their plasma membranes.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.There they serve as transcription factors when bound to their ligand; in the absence of ligand many such receptors function as histone deacetylases that repress gene expression.^ The specificity of transcription factors contributes to differences in the gene expression of different types of cells.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Resveratrol was found to modulate the function of HSF1 as a transcription factor for Hsp70 in K562 cells [11] .
  • PLoS ONE: Modulation of Akt and ERK1/2 Pathways by Resveratrol in Chronic Myelogenous Leukemia (CML) Cells Results in the Downregulation of Hsp70 10 February 2010 13:013 UTC www.plosone.org [Source type: Academic]

^ Mapping global histone acetylation patterns to gene expression.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[5]

Nuclear lamina

.In animal cells, two networks of intermediate filaments provide the nucleus with mechanical support: the nuclear lamina forms an organized meshwork on the internal face of the envelope, while less organized support is provided on the cytosolic face of the envelope.^ Intermediate filaments The cell matrix and cell-to-cell communi...
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Organization of chromatin fibre - - The nuclear envelope .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The nuclear envelope - Genetic organization of the nucleus .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores.^ The nuclear envelope is a double-membrane structure.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC mac122.icu.ac.jp [Source type: Academic]

^ Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores.

^ Nuclear envelope and pores .

[6]
.The nuclear lamina is mostly composed of lamin proteins.^ The inner surface of the nuclear envelope has a protein lining called the nuclear lamina, which binds to chromatin and other contents of the nucleus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.Like all proteins, lamins are synthesized in the cytoplasm and later transported into the nucleus interior, where they are assembled before being incorporated into the existing network of nuclear lamina.^ RNA is synthesized in the nucleus but then travels into the cytoplasm where it functions in the synthesis of proteins.

^ Instead, he opted to examine how nuclear proteins are targeted to the nucleus after being synthesized in the cytoplasm.
  • Calm in the STORm : The Scientist Careers 10 February 2010 13:013 UTC www.the-scientist.com [Source type: FILTERED WITH BAYES]

^ Ribosomal proteins are made in cytoplasm, must be transported back into nucleus.
  • BIOLOGY 107 Lecture Notes. Cell structure and function 10 February 2010 13:013 UTC www.sp.uconn.edu [Source type: FILTERED WITH BAYES]

[12][13] .Lamins are also found inside the nucleoplasm where they form another regular structure, known as the nucleoplasmic veil,[14] that is visible using fluorescence microscopy.^ PubMed ] Gustafsson MG. Nonlinear structured-illumination microscopy: Wide-field fluorescence imaging with theoretically unlimited resolution.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ Find this article online Gustafsson MG (2005) Nonlinear structured-illumination microscopy: Wide-field fluorescence imaging with theoretically unlimited resolution.
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

.The actual function of the veil is not clear, although it is excluded from the nucleolus and is present during interphase.^ Distribution of snRNPs, splicing factor SC-35 and actin in interphase nuclei: immunocytochemical evidence for differential distribution during changes in functional states.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[15] .The lamin structures that make up the veil bind chromatin and disrupting their structure inhibits transcription of protein-coding genes.^ One gene makes one protein.
  • DNA and proteins are the molecules of the cell nucleus. 10 February 2010 13:013 UTC www.dnaftb.org [Source type: Academic]

^ The lamin structures that make up the veil bind chromatin and disrupting their structure inhibits transcription of protein-coding genes.

^ It is a deoxyribonucleic acid (DNA) attached to a protein (primarily histone) structure base and is the carrier of the genes in inheritance.
  • nucleus - NDI Foundation 10 February 2010 13:013 UTC www.ndif.org [Source type: Academic]

[16]
.Like the components of other intermediate filaments, the lamin monomer contains an alpha-helical domain used by two monomers to coil around each other, forming a dimer structure called a coiled coil.^ When a red cell precursor contains too much iron, the siderotic granules form a ring around the nucleus and the resulting cells are referred to as ring sideroblasts.
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

^ The components of various other nuclear structures have recently also been cataloged.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ The brain has now separated the two major forms of contrast, spectral versus energy contrast to use them as independent variables to create color.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

.Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer called a protofilament.^ The second is nuclear reorganization without polyploidy, where nuclei reorganize their structure to form novel arrangements of proteins and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ This base pairing joins the two strands of the molecule much as rungs join the two sides of a ladder, and the chemical bonding of the base pairs twists the doubled strands into a spiral, or helical, shape.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Four of them, called H2A, H2B, H3, and H4, contribute two molecules each to form an octamer, an eight-part core around which two turns of DNA are wrapped.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament.^ Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament.

^ Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer called a protofilament.

^ An actin filament consists of two chains of globular actin monomers twisted to form a helix.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC www.emc.maricopa.edu [Source type: Academic]

.These filaments can be assembled or disassembled in a dynamic manner, meaning that changes in the length of the filament depend on the competing rates of filament addition and removal.^ Microtubules are small cylindrical fibers that change in length by assembling and disassembling.

^ In the region of very low doses, the change in this fraction is the only meaning of "lower dose-rate."
  • CHAPTER 20, Number of Primary Electron-Tracks per Cell-Nucleus, per Rad of Dose Received from Various Sources of Radiation, RADIATION-INDUCED CANCER FROM LOW-DOSE EXPOSURE 10 February 2010 13:013 UTC www.ratical.org [Source type: Academic]

^ The concept of dose rate loses its meaning at these very low doses because it depends only on the time in which a single particle traverses a cell" ( Bar85 ).
  • CHAPTER 20, Number of Primary Electron-Tracks per Cell-Nucleus, per Rad of Dose Received from Various Sources of Radiation, RADIATION-INDUCED CANCER FROM LOW-DOSE EXPOSURE 10 February 2010 13:013 UTC www.ratical.org [Source type: Academic]

[6]
Mutations in lamin genes leading to defects in filament assembly are known as laminopathies. The most notable laminopathy is the family of diseases known as progeria, which causes the appearance of premature aging in its sufferers. .The exact mechanism by which the associated biochemical changes give rise to the aged phenotype is not well understood.^ Therman ( 149 ) reviewed several mechanisms that give rise to polyploidy.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Many studies have reported that both oligonucleotides and MBs can be rapidly taken up by the nucleus, although the mechanism is not well understood ( 16 , 20 , 30 ).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ Within the nucleolus, increased rDNA transcription is associated with an altered distribution of rDNA heterochromatin ( 142 ) as well as changing size and number of nucleoli ( 86 ) and nucleolus ultrastructure ( 78 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[17]

Chromosomes

.
A mouse fibroblast nucleus in which DNA is stained blue.
^ The nucleus is counterstained for DNA (DAPI stain, blue fluorescence).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ (D) The nucleus is counterstained with DAPI (blue fluorescence) for DNA. Note the two spherical nucleoli (arrows).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The intensity of the blue coloration gives an indication of overall DNA condensation levels across the nucleus.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

The distinct chromosome territories of chromosome 2 (red) and chromosome 9 (green) are visible stained with fluorescent in situ hybridization.
.The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes.^ Recombinant clone Clone containing recombinant DNA molecules.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ This specialized structure is involved in the replication and stability of linear DNA molecules.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Structural organization of the nucleus - - DNA packaging .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well defined chromosomes familiar from a karyotype.^ DNA is linear and associated with proteins to form chromatin .

^ During cell division, they move the chromosomes into the newly-forming cells.

^ The cell division cycle - - Controlled proliferation .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.A small fraction of the cell's genes are located instead in the mitochondria.^ A small fraction of the cell's genes are located instead in the mitochondria .

^ Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs (RNA, MESSENGER).
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ Coiled bodies preferentially associate with U4, U11, and U12 small nuclear RNA genes in interphase HeLa cells but not with U6 and U7 genes.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

.There are two types of chromatin.^ There are two types of chromatin.

^ There are two major types of photoreceptors in most vertebrate eyes, rods and cones.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

^ There are two main types of cell division: mitosis and meiosis.∗ .
  • NYSTEM Glossary 10 February 2010 13:013 UTC stemcell.ny.gov [Source type: Academic]

.Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell.^ Chromosomes are structures in the cells that contain genes.
  • Leukemia & Lymphoma Society - Chronic Myelogenous Leukemia 10 February 2010 13:013 UTC www.leukemia-lymphoma.org [Source type: Academic]

^ Contain DNA (about 1% of total DNA in the cell).
  • cell 10 February 2010 13:013 UTC www.bsu.edu [Source type: Academic]

^ Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell.

[18] .The other type, heterochromatin, is the more compact form, and contains DNA that are infrequently transcribed.^ During DNA replication, the heterochromatin moved to the nuclear interior, decondensed, and replicated to form linear chromatids.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The interphase distribution of satellite DNA-containing heterochromatin in mouse nuclei.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.This structure is further categorized into facultative heterochromatin, consisting of genes that are organized as heterochromatin only in certain cell types or at certain stages of development, and constitutive heterochromatin that consists of chromosome structural components such as telomeres and centromeres.^ However, this is not the only function of this cell structure.
  • Animal Cells 10 February 2010 13:013 UTC www.animalcells.net [Source type: FILTERED WITH BAYES]

^ Chromosomes are structures in the cells that contain genes.
  • Leukemia & Lymphoma Society - Chronic Myelogenous Leukemia 10 February 2010 13:013 UTC www.leukemia-lymphoma.org [Source type: Academic]

^ The dynamics of chromosome organization and gene regulation.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]
  • Spector Lab 10 February 2010 13:013 UTC spectorlab.cshl.edu [Source type: Academic]

[19] .During interphase the chromatin organizes itself into discrete individual patches,[20] called chromosome territories.^ The study of interphase nuclear organization and the distribution of chromatin has been a subject of interest for over 100 years ( 23 , 24 , 131 ), yet there is little general consensus about the significance of organization patterns, especially concerning the intranuclear locations of individual chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Rabl's model of interphase chromosome arrangement tested in chinese hamster cells by premature chromatin condensation and laser UV microbeam analysis.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Chromosome order in HeLa cells changes during mitosis and early G1, but is stably maintained during subsequent interphase stages.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[21] .Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.^ Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.

^ Active and inactive genes localize preferentially in the periphery of chromosome territories.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ For example, when examining the X chromosome territory, single 2D optical sections consistently showed a smaller diameter for the inactive X than for its active counterpart, suggesting a smaller inactive X territory volume.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

[22]
.Antibodies to certain types of chromatin organization, particularly nucleosomes, have been associated with a number of autoimmune diseases, such as systemic lupus erythematosus.^ Nucleosomes: the subunits of chromatin - - - Organization of chromatin fibre .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The nucleus is organized around chromatin through the action of the Ran GTPase system that is universally present in eukaryotes [ 9 , 10 ].
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ Virus-specific basic phosphoproteins associated with herpes simplex virus type 1 (HSV-1) particles and the chromatin of HSV-1 infected cells.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

[23] .These are known as anti-nuclear antibodies (ANA) and have also been observed in concert with multiple sclerosis as part of general immune system dysfunction.^ D–E ) TAP protein was pulled down with anti-TAP antibody from nuclear extract of influenza A virus-infected 293T cells.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ Comparing nuclear disintegration in these tissues with that in cells undergoing complete PCD is likely to shed much light on the nuclear processes involved and on PCD in general.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Rabbit anti-NS1 polyclonal antibody was generously provided by Prof. J. Ortín [Centro Nacional de Biotecnolog ’a (CSIC), Madrid, Spain].
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

[24] .As in the case of progeria, the role played by the antibodies in inducing the symptoms of autoimmune diseases is not obvious.^ Identification of cellular elements present in a direct clinical smear is important because most of these elements play an important role in the disease process.
  • Epithelial cell Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

Nucleolus

An electron micrograph of a cell nucleus, showing the darkly stained nucleolus.
.The nucleolus is a discrete densely stained structure found in the nucleus.^ There are similarities to polyploid nuclei, including associations of homologous and heterologous chromosomes and substantial structural reorganization of the nucleus from that found in cycling cells.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Prokaryote Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Eukaryote Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.It is not surrounded by a membrane, and is sometimes called a suborganelle.^ The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.
  • Cells and DNA - Genetics Home Reference 10 February 2010 13:013 UTC ghr.nlm.nih.gov [Source type: Academic]

^ The axoneme is surrounded by cell membrane (which is called the sheath ).
  • cell 10 February 2010 13:013 UTC www.bsu.edu [Source type: Academic]

^ DNA is, surrounded by a double membrane called the nuclear envelope .

.It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA).^ Host ribosomes were assembled around chromatin because assembly was seeded on the transcribing host rRNAs.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ DNA wrapped around clusters of histone proteins to form nucleosomes, which can coil to form …[Credits : Encyclopædia Britannica, Inc.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ These include ribosomal RNA ( rRNA ), which forms part of the ribosomes and is exported to the cytoplasm to help translate the information in mRNA into proteins.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.These regions are called nucleolar organizer regions (NOR).^ In human lymphocytes, these changes are accompanied by a loss of association of chromosome 15 ( 103 ) and of nucleolar organizing regions ( 145 ) on chromosomes 13, 14, 15, 21, and 22.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Nucleolar organizing region A part of the chromosome containing rRNA genes.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes.^ Ribosomes are assembled in a region called the nucleolus .

^ Cell Nucleolus [M0003766] Within most types of eukaryotic CELL NUCLEUS, a distinct region, not delimited by a membrane, in which some species of rRNA (RNA, RIBOSOMAL) are synthesized and assembled into ribonucleoprotein subunits of ribosomes.
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ The nucleolus 13 is the structure in the nucleus where ribosomal RNA is transcribed and ribosomal subunits are assembled 8.

.The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association.^ The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association.

^ One of these rapidly trafficking nucleolar RNAs is the signal recognition particle (SRP) RNA, and further results indicate that the nucleolus is a site of SRP RNA processing or ribonucleoprotein assembly prior to export to the cytoplasm.
  • Movement and localization of RNA in the cell nucleus -- PEDERSON 13 (9002): 238 -- The FASEB Journal 10 February 2010 13:013 UTC www.fasebj.org [Source type: Academic]

^ There may be one or more nucleoli nu KLEE o lus(nucleolus): these structures are associated with regions of the DNA which code for special RNA and proteins.

.This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.^ This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.

^ As a result, the differentiation of cells can occur without the loss or irreversible inactivation of unnecessary genes, an observation that is reinforced by the presence of specific genes in a range of adult tissues.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association.

[25]
.The first step in ribosomal assembly is transcription of the rDNA, by a protein called RNA polymerase I, forming a large pre-rRNA precursor.^ On the other hand, quantitative in vivo microscopy methods provide the first glimpse of how DNA, RNA and proteins behave inside the nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ The nuclear export of cellular mRNA is mediated by several proteins that bind to mRNA and to pre-mRNA precursors ( 3 ).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ First, a modified nucleotide is added to the start of the RNA molecule by a reaction called capping.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.This is cleaved into the subunits 5.8S, 18S, and 28S rRNA.[26] The transcription, post-transcriptional processing, and assembly of rRNA occurs in the nucleolus, aided by small nucleolar RNA (snoRNA) molecules, some of which are derived from spliced introns from messenger RNAs encoding genes related to ribosomal function.^ RNA polymerase I synthesizes three of the four types of rRNA (called 18S, 28S, and 5.8S RNA); therefore it is active in the nucleolus, where the genes encoding these rRNA molecules reside.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Higher level organisation of individual gene transcription and RNA splicing.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Ribosomal gene transcription is organised in foci within nucleolar components.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.The assembled ribosomal subunits are the largest structures passed through the nuclear pores.^ The assembled ribosomal subunits are the largest structures passed through the nuclear pores.

^ Structure of the nuclear envelope and nuclear pores.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC www.emc.maricopa.edu [Source type: Academic]
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC mac122.icu.ac.jp [Source type: Academic]

^ This model, termed the exomembrane hypothesis, suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits.

[5]
.When observed under the electron microscope, the nucleolus can be seen to consist of three distinguishable regions: the innermost fibrillar centers (FCs), surrounded by the dense fibrillar component (DFC), which in turn is bordered by the granular component (GC).^ They propose that surround antagonism from the H2 horizontal cell turns L cone off-center midget bipolar cells into S cone-on/L cone-off cells and L cone-on/S cone-off cells.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

^ The precise location of actively transcribing genes within the nucleolus is still a matter of controversy, although transcription probably occurs in the dense fibrillar component associated with the fibrillar centers ( 117 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ An electron microscopic study of the nucleolus-organising regions at some stages of the cell cycle (G0 period, G2 period, mitosis).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Transcription of the rDNA occurs either in the FC or at the FC-DFC boundary, and therefore when rDNA transcription in the cell is increased more FCs are detected.^ Transcription of the rDNA occurs either in the FC or at the FC-DFC boundary, and therefore when rDNA transcription in the cell is increased more FCs are detected.

^ This concentration differential does not occur outside the porous, rigid cell wall, therefore its rectangular shape remains intact.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ Indeed, similar levels of irradiance have been previously used (in non-FCS studies) on cells in Drosophila embryos with no detectable adverse effects (30) .
  • Movement and localization of RNA in the cell nucleus -- PEDERSON 13 (9002): 238 -- The FASEB Journal 10 February 2010 13:013 UTC www.fasebj.org [Source type: Academic]

Most of the cleavage and modification of rRNAs occurs in the DFC, while the latter steps involving protein assembly onto the ribosomal subunits occurs in the GC.[26]

Other subnuclear bodies

Subnuclear structure sizes
Structure name Structure diameter
Cajal bodies 0.2–2.0 µm[27]
PIKA 5 µm[28]
PML bodies 0.2–1.0 µm[29]
Paraspeckles 0.2–1.0 µm[30]
Speckles 20–25 nm[28]
.Besides the nucleolus, the nucleus contains a number of other non-membrane delineated bodies.^ Besides the nucleolus, the nucleus contains a number of other non-membrane delineated bodies.

^ The most controversial model, known as viral eukaryogenesis, posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus.

^ Not all living cells have nuclei, only eukaryotes have a nucleus, prokaryotes such as bacteria have no nucleus, or any other double membraned organelles.
  • What Is The Function Of A Nucleus? - Blurtit 10 February 2010 13:013 UTC www.blurtit.com [Source type: General]

.These include Cajal bodies, Gemini of coiled bodies, polymorphic interphase karyosomal association (PIKA), promyelocytic leukaemia (PML) bodies, paraspeckles and splicing speckles.^ All coiled bodies are associated with the nucleolus (O).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ However in differentiated haploid cells of the thallus, all nuclei have two coiled bodies associated with the nucleolus (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Coiled bodies preferentially associate with U4, U11, and U12 small nuclear RNA genes in interphase HeLa cells but not with U6 and U7 genes.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

.Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not uniform mixture, but rather contains organized functional subdomains.^ Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not uniform mixture, but rather contains organized functional subdomains.

^ Results show that chromosome territories are rather open structures consisting of domains that contain highly compacted chromatin and a considerable volume of interchromatin space.
  • Structure and Functional Organisation of the Cell Nucleus - Swammerdam Institute for Life Sciences - University of Amsterdam 10 February 2010 13:013 UTC www.science.uva.nl [Source type: Academic]

^ However, little is known about the nature of synaptic transmission during a time when brain stem trigeminal neurons are consolidating whisker-specific patterns.
  • Electrophysiological Properties and Synaptic Responses of Cells in the Trigeminal Principal Sensory Nucleus of Postnatal Rats -- Lo et al. 82 (5): 2765 -- Journal of Neurophysiology 10 February 2010 13:013 UTC jn.physiology.org [Source type: Academic]

[29]
.Other subnuclear structures appear as part of abnormal disease processes.^ Other subnuclear structures appear as part of abnormal disease processes.

^ Sometimes, this is normal, other times, this is due to diseases or to defective process of preparation and staining of the smear.
  • The Blood Cells 10 February 2010 13:013 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ The contradiction construed here by Driesch which, in addition to other considerations, leads him to postulate an "autonomy of living processes," appears to me not to exist in reality.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

.For example, the presence of small intranuclear rods have been reported in some cases of nemaline myopathy.^ Some examples of DNA use are to establish paternity in child support cases; establish the presence of a suspect at a crime scene, and identify accident victims.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.This condition typically results from mutations in actin, and the rods themselves consist of mutant actin as well as other cytoskeletal proteins.^ Autosomal recessive conditions require two mutations to show themselves.
  • Genetics and Neuromuscular Diseases 10 February 2010 13:013 UTC www.mda.org [Source type: FILTERED WITH BAYES]

^ Actin filaments are long, thin fibers composed of 2 chains of protein wrapped around each other.

^ Autosomal dominant conditions require only one mutation to show themselves.
  • Genetics and Neuromuscular Diseases 10 February 2010 13:013 UTC www.mda.org [Source type: FILTERED WITH BAYES]

[31]

Cajal bodies and gems

.A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies (CB), whose diameter measures between 0.2 µm and 2.0 µm depending on the cell type and species.^ Modified VP22 localizes to the cell nucleus during synchronized herpes simplex virus type 1 infection.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ Coiled bodies preferentially associate with U4, U11, and U12 small nuclear RNA genes in interphase HeLa cells but not with U6 and U7 genes.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ A more sophisticated version of this type of approach is to use cross-pair correlation, a statistical measure used to investigate correlations between two sets of point-like objects.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

[27] .When seen under an electron microscope, they resemble balls of tangled thread[28] and are dense foci of distribution for the protein coilin.^ When foci colocalize with -coilin, they are termed coiled bodies.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[32] .CBs are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.^ RNA synthesis - - Processing of mRNA .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Similar studies are beginning to reveal patterns of different modifications in relation to gene activity and organization (Bernstein et al., 2005 ; Schubeler et al., 2004 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Coiled bodies preferentially associate with U4, U11, and U12 small nuclear RNA genes in interphase HeLa cells but not with U6 and U7 genes.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

[27]
.Similar to Cajal bodies are Gemini of coiled bodies, or gems, whose name is derived from the Gemini constellation in reference to their close "twin" relationship with CBs.^ In derived cells behind the apex, which do not divide, a single coiled body is additionally observed.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Coiled bodies have an intimate relationship with the nucleolus (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Gall JG, Bellini M, Wu Z, and Murphy C, "Assembly of the Nuclear Transcription and Processing Machinery: Cajal Bodies (Coiled Bodies) and Transcriptosomes" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

.Gems are similar in size and shape to CBs, and in fact are virtually indistinguishable under the microscope.^ Gems are similar in size and shape to CBs, and in fact are virtually indistinguishable under the microscope.

^ Similar to Cajal bodies are Gemini of coiled bodies, or gems, whose name is derived from the Gemini constellation in reference to their close "twin" relationship with CBs.

[32] .Unlike CBs, gems do not contain small nuclear ribonucleoproteins (snRNPs), but do contain a protein called survivor of motor neurons (SMN) whose function relates to snRNP biogenesis.^ The removal of introns, called RNA splicing , appears to be mediated by small nuclear ribonucleoprotein particles (snRNP’s).
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ This suggests that the nucleocytoplasmic transport of both influenza A virus intron-containing and intronless mRNAs should be related to the function of RNAP-II. As the viral NS1 protein was reported involved in cellular intron-containing mRNA splicing and nuclear export, we also examined its cellular distribution in ActD-treated MDCK cells to investigate if it was also associated with influenza A virus mRNAs.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ [Web of Science] [Medline] Qiu Y, Krug RM. The influenza virus NS1 protein is a poly(A)-binding protein that inhibits nuclear export of mRNAs containing poly(A).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

Gems are believed to assist CBs in snRNP biogenesis,[33] though it has also been suggested from microscopy evidence that CBs and gems are different manifestations of the same structure.[32]

PIKA and PTF domains

.PIKA domains, or polymorphic interphase karyosomal associations, were first described in microscopy studies in 1991. Their function was and remains unclear, though they were not thought to be associated with active DNA replication, transcription, or RNA processing.^ Their specific function remains unclear.
  • SIU SOM Histology GI 10 February 2010 13:013 UTC www.siumed.edu [Source type: Academic]

^ RNA: replicated from DNA - The organization of cells .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ DNA: the genetic material - - RNA: replicated from DNA .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

[34] .They have been found to often associate with discrete domains defined by dense localization of the transcription factor PTF, which promotes transcription of snRNA.^ Han J, Kim D, and Morris KV, "Promoter-associated RNA is required for RNA-directed transcriptional gene silencing in human cells" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

^ Perhaps there is also a diffusable factor from the meiocytes or the tapetal cells which promotes the homologue associations.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ In human cycling cells, heterochromatin is often found either attached to or associated with the nuclear envelope, as well as at internal locations (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[35]

PML bodies

Promyelocytic leukaemia bodies (PML bodies) are spherical bodies found scattered throughout the nucleoplasm, measuring around 0.2–1.0 µm. .They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains.^ PML NBs, PML nuclear bodies.
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

^ They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains.

^ Contains information on nucleus structure and function, including nuclear transport, and subnuclear domains .

.They are often seen in the nucleus in association with Cajal bodies and cleavage bodies.^ They are often seen in the nucleus in association with Cajal bodies and cleavage bodies.

^ Number of cajal bodies in HeLa cell nucleus .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ They have been found to often associate with discrete domains defined by dense localization of the transcription factor PTF, which promotes transcription of snRNA .

.It has been suggested that they play a role in regulating transcription.^ It has been suggested that they play a role in regulating transcription.

^ On T lymphocytes CD26 regulates expression of ADA on the cell surface, with the CD26/ADA complex playing a key role in the catalytic removal of local adenosine to regulate immune system function [ 2 ].
  • Cancer Cell International | Full text | Localization of CD26/DPPIV in nucleus and its nuclear translocation enhanced by anti-CD26 monoclonal antibody with anti-tumor effect 10 February 2010 13:013 UTC www.cancerci.com [Source type: Academic]

^ Han M-H, Goud S, Song L, and Fedoroff N, "The Arabidopsis double-stranded RNA-binding protein HYL1 plays a role in microRNA-mediated gene regulation" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

[29]

Paraspeckles

Discovered by Fox et al. in 2002, paraspeckles are irregularly shaped compartments in the nucleus' interchromatin space.[36] .First documented in HeLa cells, where there are generally 10–30 per nucleus,[37] paraspeckles are now known to also exist in all human primary cells, transformed cell lines and tissue sections.^ (D and E) Sectioned nucleus from a wheat meristematic cell.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ When the barrelette cell was depolarized ( 50 mV) after hyperpolarization ( 120 mV), there was a hyperpolarizing notch before the first spike (Fig.
  • Electrophysiological Properties and Synaptic Responses of Cells in the Trigeminal Principal Sensory Nucleus of Postnatal Rats -- Lo et al. 82 (5): 2765 -- Journal of Neurophysiology 10 February 2010 13:013 UTC jn.physiology.org [Source type: Academic]

^ Comparing nuclear disintegration in these tissues with that in cells undergoing complete PCD is likely to shed much light on the nuclear processes involved and on PCD in general.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[38] .Their name is derived from their distribution in the nucleus; the "para" is short for parallel and the "speckles" refers to the splicing speckles to which they are always in close proximity.^ Sometimes referred to as interchromatin granule clusters, speckles are rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing.

^ Similar to Cajal bodies are Gemini of coiled bodies, or gems, whose name is derived from the Gemini constellation in reference to their close "twin" relationship with CBs.

^ At the present time, no sophisticated nucleus-wide, function-defined model of compartment distributions exists, and therefore test procedures refer to simple null distributions.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]
  • PLoS Computational Biology: Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ploscompbiol.org [Source type: Academic]

[37]
.Paraspeckles are dynamic structures that are altered in response to changes in cellular metabolic activity.^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Current data suggest that the nucleus of each cell type has a structured framework within which local changes in the organization and distribution of proteins and nucleic acids can occur with changing cell activity.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Dynamic changes to patterns of chromatin condensation are associated with altered cell activity and the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.They are transcription dependent[36] and in the absence of RNA Pol II transcription, the paraspeckle disappears and all of its associated protein components (PSP1, p54nrb, PSP2, CFI(m)68 and PSF) form a crescent shaped perinucleolar cap in the nucleolus.^ All coiled bodies are associated with the nucleolus (O).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ However in differentiated haploid cells of the thallus, all nuclei have two coiled bodies associated with the nucleolus (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Han J, Kim D, and Morris KV, "Promoter-associated RNA is required for RNA-directed transcriptional gene silencing in human cells" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

.This phenomenon is demonstrated during the cell cycle.^ It is this axis that varies during the cell cycle.
  • Three-dimensional organization of the mammalian nucleus in normal and tumor cells. 10 February 2010 13:013 UTC atlasgeneticsoncology.org [Source type: Academic]

^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Characterisation of the nucleolar organising regions during the cell cycle in two varieties of Petunia hybrida as visualised by fluorescence in situ hybridisation and silver staining.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.In the cell cycle, paraspeckles are present during interphase and during all of mitosis except for telophase.^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Chromosome order in HeLa cells changes during mitosis and early G1, but is stably maintained during subsequent interphase stages.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Premature chromosome condensation (PCC) A method of studying chromosomes in the interphase stage of the cell cycle.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.During telophase, when the two daughter nuclei are formed, there is no RNA Pol II transcription so the protein components instead form a perinucleolar cap.^ In contrast, during mitosis, the nuclear skeleton depolymerizes, transcription ceases, proteins become phosphorylated (e.g., histone H1), and there is increased adhesiveness between factories and nucleosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ It has been reported that a group of nucleoplasmic proteins, mostly RNA-binding proteins, relocalize from the nucleoplasm to a specific nucleolar cap during transcriptional inhibition ( 46 ).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ See more articles cited in this paragraph Fluorescent labeling of nascent RNA reveals transcription by RNA polymerase II in domains scattered throughout the nucleus.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

[38]

Splicing speckles

.Sometimes referred to as interchromatin granule clusters or as splicing-factor compartments, speckles are rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing.^ Proteomic analysis of interchromatin granule clusters.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ The role of speckles and foci is still a matter of debate (for a review, see reference 95 ), but it is likely that the distribution of splicing factors is dynamic, with mRNA being transcribed and processed at the gene locus, and that splicing factors shuttle from speckles in the ICD. Coiled bodies are not found in some cell types ( 160 ), and they do not colocalize with pre-mRNA, poly(A) mRNA, the splicing factor SC-35 and DNA. This indicates that they too are probably not directly involved in splicing but may be involved in snRNP storage, maturation, or transport ( 95 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The first nuclear structure to be analyzed in this manner was the interchromatin granule cluster (IGC), which constitutes the major fraction of the splicing factor compartments (Mintz et al., 1999 ; Saitoh et al., 2004 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[39] .Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.^ Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs; and each protein has unique functions.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.

^ These proteins include helicase s that unwind the double-stranded DNA molecule to facilitate access to it, RNA polymerase s that synthesize the growing RNA molecule, topoisomerase s that change the amount of supercoil ing in DNA, helping it wind and unwind, as well as a large variety of transcription factor s that regulate expression.

[40]

Function

.The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.^ Main The nature and function of cells .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression .

^ Regulatory region or sequence A DNA base sequence that controls gene expression.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes.^ The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryote s.

^ At high concentrations of fructose-6-phosphate , a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus, [33] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.

^ We therefore sought to design an experimental strategy that would allow us to directly test for functionalization of transferred organellar genes in the nucleus.
  • Experimental Reconstruction of Functional Gene Transfer from the Tobacco Plastid Genome to the Nucleus -- Stegemann and Bock 18 (11): 2869 -- THE PLANT CELL 10 February 2010 13:013 UTC www.plantcell.org [Source type: Academic]

Cell compartmentalization

.The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary.^ The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary.

^ The nuclear envelope - Genetic organization of the nucleus .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The nucleus is spheroid in shape and separated from the cytoplasm by a double membrane called the nuclear envelope .
  • Cell (biology) - Hwiki 10 February 2010 13:013 UTC hwiki.fzk.de [Source type: Academic]

.This is important for controlling processes on either side of the nuclear membrane.^ This is important for controlling processes on either side of the nuclear membrane.

^ The many results described here suggest that chromatin, chromosome, and nuclear organization are important to the control of development and differentiation; the central question is, what is that role?
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Image:RanGTPcycle.png Macromolecules , such as RNA and proteins , are actively transported across the nuclear membrane in a process called the Ran - GTP nuclear transport cycle.

.In some cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway.^ In some cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway.

^ In any case, some of the cytoplasm remains visible, generally in a lateral position.
  • The Blood Cells 10 February 2010 13:013 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ These findings suggest that the influenza A virus mRNA may be exported from the nucleus by the cellular TAP/p15 pathway with NS1 protein and RNAP-II participation.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

.This regulatory mechanism occurs in the case of glycolysis, a cellular pathway for breaking down glucose to produce energy.^ This regulatory mechanism occurs in the case of glycolysis , a cellular pathway for breaking down glucose to produce energy.

^ Metabolism has two distinct divisions: catabolism , in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism , wherein the cell uses energy and reducing power to construct complex molecules and perform other biological functions.
  • Cell (biology) - Hwiki 10 February 2010 13:013 UTC hwiki.fzk.de [Source type: Academic]

^ Enzymes in the walls if the mitochondria use oxygen to break down glucose and other nutrients to release energy.

Hexokinase is an enzyme responsible for the first the step of glycolysis, forming glucose-6-phosphate from glucose. .At high concentrations of fructose-6-phosphate, a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus,[41] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.^ At both levels, protein factors are believed to perform the regulation—for example, by binding to special promoter DNA regions flanking the transcribed gene.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ More work is needed to relate changing cell activity and the expression of genes in development to specific organizational properties of the nucleus, including the intranuclear distribution of genes and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Gene product The biochemical material, either RNA or protein, resulting from expression of a gene.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

[42]
.In order to control which genes are being transcribed, the cell separates some transcription factor proteins responsible for regulating gene expression from physical access to the DNA until they are activated by other signaling pathways.^ Some cells have no contact with other cells .

^ The specificity of transcription factors contributes to differences in the gene expression of different types of cells.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Oncogenes activate other genes that increase cell division rate.

.This prevents even low levels of inappropriate gene expression.^ This prevents even low levels of inappropriate gene expression.

^ The expression of a gene is regulated at many different levels.
  • Structure and Functional Organisation of the Cell Nucleus - Swammerdam Institute for Life Sciences - University of Amsterdam 10 February 2010 13:013 UTC www.science.uva.nl [Source type: Academic]

^ One of these levels is epigenetic regulation, which involves heritable changes in gene expression that occur without a change in DNA sequence.
  • Structure and Functional Organisation of the Cell Nucleus - Swammerdam Institute for Life Sciences - University of Amsterdam 10 February 2010 13:013 UTC www.science.uva.nl [Source type: Academic]

.For example in the case of NF-κB-controlled genes, which are involved in most inflammatory responses, transcription is induced in response to a signal pathway such as that initiated by the signaling molecule TNF-α, binds to a cell membrane receptor, resulting in the recruitment of signalling proteins, and eventually activating the transcription factor NF-κB. A nuclear localisation signal on the NF-κB protein allows it to be transported through the nuclear pore and into the nucleus, where it stimulates the transcription of the target genes.^ Cells ingest molecules through their plasma membranes.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Signal receptors - - Cellular response .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Oscillations in NF-kappaB signaling control the dynamics of gene expression.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[6]
.The compartmentalization allows the cell to prevent translation of unspliced mRNA.[43] Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins.^ Eukaryotic cells contain membrane-bound organelles, including a clearly defined nucleus, …[Credits : Encyclopædia Britannica, Inc.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Proteins involved in pre-mRNA splicing can be dispersed and can occur as speckles and foci with patterns depending on cell activity or type.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Antisense Nucleic acid that has a sequence exactly opposite to an mRNA molecule made by the body; binds to the mRNA molecule to prevent a protein from being made.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation.^ The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation.

^ The lower diffusion rate of NA mRNA in the cytoplasm compared with that in the nucleus may due to the association of NA mRNA with cytoplasmic microtubules and the anchoring of NA mRNA on the ER membrane for translation.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ As ribosomes are located outside the nucleus, mRNA produced needs to be exported.

.Without the nucleus ribosomes would translate newly transcribed (unprocessed) mRNA resulting in misformed and nonfunctional proteins.^ The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation.

^ Without the nucleus ribosomes would translate newly transcribed (unprocessed) mRNA resulting in misformed and nonfunctional proteins.

^ It would be reasonable to assume that if they have no nucleus, they have no use for nor capacity to make new ribosomes either It most likely is not important to know.
  • sieve tube cells - no ribosomes ? | DAT Discussions | Student Doctor Network 10 February 2010 13:013 UTC forums.studentdoctor.net [Source type: General]

Gene expression

.
A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts.
^ Han J, Kim D, and Morris KV, "Promoter-associated RNA is required for RNA-directed transcriptional gene silencing in human cells" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

^ PubMed ] Xing Y, Johnson CV, Dobner PR, Lawrence JB. Higher level organization of individual gene transcription and RNA splicing.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ Active genes dynamically colocalize to shared sites of ongoing transcription.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

"Begin" indicates the 3' end of the DNA, where new RNA synthesis begins; "end" indicates the 5' end, where the primary transcripts are almost complete.
.Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein.^ DNA repair genes Genes encoding proteins that correct errors in DNA sequencing.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Complementary DNA (cDNA) DNA that is synthesized in the laboratory from a messenger RNA template.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ As ribosomes are located outside the nucleus, mRNA produced needs to be exported.

.As ribosomes are located outside the nucleus, mRNA produced needs to be exported.^ As ribosomes are located outside the nucleus, mRNA produced needs to be exported.

^ Nevertheless, the mechanisms by which influenza virus mRNAs are exported from the nucleus and the roles of viral NS1 protein in influenza A virus intronless mRNA export are still unclear.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ These findings suggest that the influenza A virus mRNA may be exported from the nucleus by the cellular TAP/p15 pathway with NS1 protein and RNAP-II participation.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

[44]
.Since the nucleus is the site of transcription, it also contains a variety of proteins which either directly mediate transcription or are involved in regulating the process.^ The membrane contains proteins that have a variety of functions.

^ Since the nucleus is the site of transcription, it also contains a variety of proteins which either directly mediate transcription or are involved in regulating the process.

^ At high concentrations of fructose-6-phosphate , a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus, [33] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.

.These proteins include helicases that unwind the double-stranded DNA molecule to facilitate access to it, RNA polymerases that synthesize the growing RNA molecule, topoisomerases that change the amount of supercoiling in DNA, helping it wind and unwind, as well as a large variety of transcription factors that regulate expression.^ Transcription factor A protein that binds to regulatory regions and helps control gene expression.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Promoter A DNA site to which RNA polymerase will bind and initiate transcription.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Regulation of genetic expression - - Regulation of RNA synthesis .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

[45]

Processing of pre-mRNA

.Newly synthesized mRNA molecules are known as primary transcripts or pre-mRNA. They must undergo post-transcriptional modification in the nucleus before being exported to the cytoplasm; mRNA that appears in the nucleus without these modifications is degraded rather than used for protein translation.^ Ribosomal proteins are synthesized in the cytoplasm and transported to the nucleus for subassembly in the nucleolus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The nucleus must not only synthesize the mRNA for many thousands of proteins, but it must also regulate the amounts synthesized and supplied to the cytoplasm.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ NS1 protein was reported to interact with influenza A viral transcription–replication complexes in infected cells ( 47 ) and be cross-linked to influenza A mRNAs in cytoplasm for enhancement of viral protein translation ( 48 , 49 ).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

.The three main modifications are 5' capping, 3' polyadenylation, and RNA splicing.^ In higher organisms there are three main RNA polymerases, designated I, II, and III (or sometimes A, B, and C).
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.While in the nucleus, pre-mRNA is associated with a variety of proteins in complexes known as heterogeneous ribonucleoprotein particles (hnRNPs).^ Proteins involved in pre-mRNA splicing can be dispersed and can occur as speckles and foci with patterns depending on cell activity or type.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ He suggested that loops are connected to transcription factories that are fixed on a nuclear skeleton and contain transcription factors, RNA polymerases, and pre-mRNA splicing complexes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The arrays were interpreted to lie within, and be part of, the ICD. Similar ICDs have been revealed in cultured mammalian cells as a reticular network of ribonuclear particles associated with pre-mRNA splicing ( 146 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Addition of the 5' cap occurs co-transcriptionally and is the first step in post-transcriptional modification.^ Addition of the 5' cap occurs co-transcriptionally and is the first step in post-translational modification.

^ Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post-transcriptional modification is complete.

^ This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.

.The 3' poly-adenine tail is only added after transcription is complete.^ The 3' poly- adenine tail is only added after transcription is complete.

.RNA splicing, carried out by a complex called the spliceosome, is the process by which introns, or regions of DNA that do not code for protein, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule.^ Base One of the molecules that form DNA and RNA molecules.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Thousands of nucleotides are linked to form a DNA or RNA molecule.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Exon The protein-coding DNA sequence of a gene.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.^ This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.

^ However, this tour covered only the highlights; there are many other fascinating processes that occur within cells.
  • Inside the Cell: Chapter 1: An Owner's Guide to the Cell - National Institute of General Medical Sciences 10 February 2010 13:013 UTC publications.nigms.nih.gov [Source type: FILTERED WITH BAYES]

^ Reductionist approaches have been spectacularly successful at dissecting at the molecular level many of the key processes that occur within the nucleus, particularly gene expression.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[5] .Many pre-mRNAs, including those encoding antibodies, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences.^ In contrast, not cellular intronless H2a mRNA but spliced β-actin mRNA was detected from the infected coimmunoprecipitation sample pulled down by anti-NS1 antibody ( Figure 9 A and B).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ Mammalian nuclei contain foci which are highly enriched in components of the pre-mRNA splicing machinery.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The nuclear export of cellular mRNA is mediated by several proteins that bind to mRNA and to pre-mRNA precursors ( 3 ).
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

This process is known as alternative splicing, and allows production of a large variety of proteins from a limited amount of DNA.

Dynamics and regulation

Nuclear transport

Macromolecules, such as RNA and proteins, are actively transported across the nuclear membrane in a process called the Ran-GTP nuclear transport cycle.
.The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes.^ Number of nuclear pores per nucleus .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ Template:Main The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes.

^ At high concentrations of fructose-6-phosphate , a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus, [33] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.

.Although small molecules can enter the nucleus without regulation,[46] macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit.^ Trotochaud AE, and Wassarman KM, "A highly conserved 6S RNA structure is required for regulation of transcription" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

^ Han M-H, Goud S, Song L, and Fedoroff N, "The Arabidopsis double-stranded RNA-binding protein HYL1 plays a role in microRNA-mediated gene regulation" .
  • Current Research Focusing on Euchromatin Within the Cell Nucleus. 10 February 2010 13:013 UTC www.euchromatin.net [Source type: Academic]

^ A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule).
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

."Cargo" proteins that must be translocated from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals which are bound by importins, while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins.^ A number of virus proteins, such as the immediate-early proteins ICP0 ( 13 , 30 ) and ICP27 ( 19 , 28 ), the DNA replication protein encoded by gene UL9 ( 27 ), and the capsid protein VP19C ( 40 ), have been shown to contain classical nuclear localization signals (NLSs), which are defined in the primary amino acid sequence of these proteins ( 15 , 32 ).
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ However, at the start of M phase and prior to nuclear envelope breakdown, cyclin B1 is phosphorylated at its amino terminus, resulting in the creation of a nuclear import signal followed by the rapid translocation of the protein from the cytoplasm to the nucleus ( 16 ).
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ [Abstract/ Free Full Text] Kang Y, Cullen BR. The human tap protein is a nuclear mRNA export factor that contains novel RNA-binding and nucleocytoplasmic transport sequences.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

The ability of importins and exportins to transport their cargo is regulated by GTPases, enzymes that hydrolyze the molecule guanosine triphosphate to release energy. .The key GTPase in nuclear transport is Ran, which can bind either GTP or GDP (guanosine diphosphate) depending on whether it is located in the nucleus or the cytoplasm.^ A key selective force during the autogenous origin of the nucleus could have been the need to segregate ribosome factories from the cytoplasm where ribosomal proteins (RPs) of the protomitochondrium were synthesized.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ ER or peroxisomes, the nucleus is not a topologically separated compartment in the eukaryotic cytoplasm since the nucleoplasm and the cytoplasm are continuous through the nuclear pores.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ I rather suspect, given the noisy nature of nuclear transport, that DNA binding proteins started to be transported after or along with RPs with minimal or no modification of their basic motifs.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

.Whereas importins depend on RanGTP to dissociate from their cargo, exportins require RanGTP in order to bind to their cargo.^ RanGTP dependent karyopherin-RP dissociation reduces chimerism .
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ RanGTP dissociated the karyopherin-cargo complexes that traversed the pores at the nuclear side.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

[11]
.Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus.^ These ribosomes are produced in the nucleus and pass into he cytoplasm through the pores in the nuclear membrane.

^ Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus.

^ HCF-dependent nuclear import of VP16.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

.Inside the nucleus, RanGTP acts to separate the cargo from the importin, allowing the importin to exit the nucleus and be reused.^ Inside the nucleus, RanGTP acts to separate the cargo from the importin, allowing the importin to exit the nucleus and be reused.

^ These nuclear pores allow chemical messages to exit and enter the nucleus.
  • Inside the Cell: Chapter 1: An Owner's Guide to the Cell - National Institute of General Medical Sciences 10 February 2010 13:013 UTC publications.nigms.nih.gov [Source type: FILTERED WITH BAYES]

^ Whereas importins depend on RanGTP to dissociate from their cargo, exportins require RanGTP in order to bind to their cargo.

.Nuclear export is similar, as the exportin binds the cargo inside the nucleus in a process facilitated by RanGTP, exits through the nuclear pore, and separates from its cargo in the cytoplasm.^ Nuclear export is similar, as the exportin binds the cargo inside the nucleus in a process facilitated by RanGTP, exits through the nuclear pore, and separates from its cargo in the cytoplasm.

^ Number of nuclear pores per nucleus .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus.

.Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post-transcriptional modification is complete.^ Moreover, the association of NS1 with influenza A virus intronless mRNAs in the nucleus could not be simply interpreted by the inhibition of NS1 on virus mRNA, like the roles of NS1 protein in NS1 and NS2 mRNAs export.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

^ HIV-1 mRNA species that are otherwise excluded from the cell cytoplasm Functional dissection of the HIV-1 Rev trans-activator--derivation of a trans-dominant repressor of Rev function.
  • WikiGenes - Active Transport, Cell Nucleus 10 February 2010 13:013 UTC www.wikigenes.org [Source type: Academic]

^ The colocalization of NS1 protein and M2 mRNA might be correlated with NS1 inhibition of the splicing and export of intron-containing mRNAs, but the colocalization of intronless NA mRNA with NS1 protein was very surprising.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

.This quality-control mechanism is important due to the these molecules' central role in protein translation; mis-expression of a protein due to incomplete excision of exons or mis-incorporation of amino acids could have negative consequences for the cell; thus incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation.^ RNA (Ribonucleic acid) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ The term granulocyte is due to the presence of granules in the cytoplasm of these cells.
  • The Blood Cells 10 February 2010 13:013 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ This quality-control mechanism is important due to the these molecules' central role in protein translation; mis-expression of a protein due to incomplete excision of exons or mis-incorporation of amino acids could have negative consequences for the cell; thus incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation.

[5]

Assembly and disassembly

.
An image of a newt lung cell stained with fluorescent dyes during metaphase.
^ Characterisation of the nucleolar organising regions during the cell cycle in two varieties of Petunia hybrida as visualised by fluorescence in situ hybridisation and silver staining.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Segmentation of fluorescence microscopy images for quantitative analysis of cell nuclear architecture.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ Metaphase A stage in mitosis or meiosis during which the chromosomes are aligned along the equatorial plane of the cell.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.The mitotic spindle can be seen, stained green, attached to the two sets of chromosomes, stained light blue.^ Centromere A specialized chromosome region to which spindle fibers attach during cell division.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ (P to T) Spermatogenesis in Schistocerca gregaria (locust) stained blue for DNA with DAPI (blue fluorescence) and labelled for rDNA (pTa71, digoxigenin-FITC, green/cyan fluorescence).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Meiosis results in four rather than two daughter cells, each with a haploid set of chromosomes.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

All chromosomes but one are already at the metaphase plate.
.During its lifetime a nucleus may be broken down, either in the process of cell division or as a consequence of apoptosis, a regulated form of cell death.^ Translocation of GFP-22 from cytoplasm to nucleus during cell division.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ Cell division is the process by which cells reproduce themselves.

^ Biological context of   MeSH: Active Transport, Cell Nucleus   [Hold mouse button down for author info.
  • WikiGenes - Active Transport, Cell Nucleus 10 February 2010 13:013 UTC www.wikigenes.org [Source type: Academic]

.During these events, the structural components of the nucleus—the envelope and lamina—are systematically degraded.^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ During cell division these molecules become tightly coiled into individual rodlike structures called chromosomes .

^ These examples show that nuclear polyploidy is involved in development and that during the course of cell differentiation, the nucleus can enlarge its DNA content in different ways.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.During the cell cycle the cell divides to form two cells.^ Such eggs almost always divide, as I have described previously ( 8 ), into two cells, each with one large and one small nucleus.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Nuclear Division in Megakaryocytes Megakaryocytes differ from other cell lines because the nucleus divides during mitosis but the cytoplasm does not.
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

.In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets.^ Lower limit of propulsive forces required for nuclear organelles to undergo processive transport in intranuclear region of mouse embryonic tissue cell .
  • Search BioNumbers - The Database of Useful Biological Numbers 10 February 2010 13:013 UTC bionumbers.hms.harvard.edu [Source type: Academic]

^ A subcellular fraction isolated by ultracentrifugation or other separation techniques must first be isolated so that a process can be studied free from all of the complex side reactions that occur in a cell.
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ In this case, there is no guarantee, or even the possibility, that all cells will be supplied with a portion of all the different qualities represented by the individual chromosomes.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

.This occurs by the replicated chromosomes, the sister chromatids, attaching to microtubules, which in turn are attached to different centrosomes.^ Synteny Genes occurring in the same order on chromosomes of different species.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ DNA replication-timing analysis of human chromosome 22 at high resolution and different developmental states.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

.The sister chromatids can then be pulled to separate locations in the cell.^ The sister chromatids at metaphase can be seen to separate but not to segregate, leading to chromosomes in "ski pairs" ( 11 ).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ During Anaphase the centromere of each chromatid pair splits, and the kinetochore microtubules shorten and pull one of each duplicated chromosome to opposite ends of the cell.

.In many cells the centrosome is located in the cytoplasm, outside the nucleus, the microtubules would be unable to attach to the chromatids in the presence of the nuclear envelope.^ Chloroplast chromosome Circular DNA found in the photosynthesizing organelle (chloroplast) of plants instead of the cell nucleus where most genetic material is located.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ RNA (Ribonucleic acid) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ A common way for a nucleus to differentiate in development is by undergoing many rounds of DNA synthesis without an accompanied cell division, i.e., a process of nuclear polyploidization.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[47] .Therefore the early stages in the cell cycle, beginning in prophase and until around prometaphase, the nuclear membrane is dismantled.^ Higher plants have a life cycle that includes an alternation of generations between a haploid stage and a diploid stage, and it is interesting that early land plants are thought to have had a dominant haploid generation.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The next key step in the evolution of nuclear compartmentalisation was the development of a membrane network around chromatin from the secretory endomembrane system of the protoeukaryote.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

[14] .Likewise, during the same period, the nuclear lamina is also disassembled, a process regulated by phosphorylation of the lamins.^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The cell cycle-dependent nuclear import of v-Jun is regulated by phosphorylation of a serine adjacent to the nuclear localisation signal.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ A key emerging contributor to genome function and regulation is the spatial and temporal arrangement of the genome and gene expression processes in nuclear space (Misteli, 2001 ; Spector, 2003 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[48] .Towards the end of the cell cycle, the nuclear membrane is reformed, and around the same time, the nuclear lamina are reassembled by dephosphorylating the lamins.^ Cytoplasm - between cell and nuclear membranes.

^ (DONE--NMS) The nuclear envelope is similar to the cell membrane, but instead of protecting all the organelles in the cell, it protects the genetic material inside the nucleus.
  • SlideSix :: Cell_Project_Emma_Noland_Kuresha 10 February 2010 13:013 UTC slidesix.com [Source type: FILTERED WITH BAYES]

^ ER lumen forms a continues "internal canal" system that runs from the cell membrane to the nuclear envelope.
  • cell 10 February 2010 13:013 UTC www.bsu.edu [Source type: Academic]

[48]
.However, in dinoflagellates the nuclear envelope remains intact, the centrosomes are located in the cytoplasm, and the microtubules come in contact with chromosomes, whose centromeric regions are incorporated into the nuclear envelope (the so-called closed mitosis with extranuclear spindle).^ This is one of the main reasons why the nuclear positioning of compartments such as centromeres, telomeres, genes, and chromosome territories has been studied so intensely.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ However, this may not be the case in all tissues, for example in tapetal cells of the wheat anther (see "Nuclear differentiation and the distribution of chromatin and chromosomes" below).
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Draft sequence data are mostly in the form of 10,000 base pair-sized fragments whose approximate chromosomal locations are known.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

In many other protists (e.g. ciliates, sporozoans) and fungi the centrosomes are intranuclear, and their nuclear envelope also does not disassemle during cell division.
.Apoptosis is a controlled process in which the cell's structural components are destroyed, resulting in death of the cell.^ Cellular Structures [M0356640] Components of a cell.
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ Following from this, I will show how nuclear structure can change with changing cellular activity in processes that do not involve developmental change, e.g., events that can occur during the cell cycle.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ It is an important process used by some white blood cells phagocytes to destroy bacteria that enter the body.

.Changes associated with apoptosis directly affect the nucleus and its contents, for example in the condensation of chromatin and the disintegration of the nuclear envelope and lamina.^ Organization of chromatin fibre - - The nuclear envelope .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The nuclear envelope - Genetic organization of the nucleus .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The inner surface of the nuclear envelope has a protein lining called the nuclear lamina, which binds to chromatin and other contents of the nucleus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.The destruction of the lamin networks is controlled by specialized apoptotic proteases called caspases, which cleave the lamin proteins and thus degrade the nucleus' structural integrity.^ It has implications for how proteins interact with the genome globally as well as locally and thus for the system-level behavior of the nucleus and the genome.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

Lamin cleavage is sometimes used as a laboratory indicator of caspase activity in assays for early apoptotic activity.[14] .Cells that express mutant caspase-resistant lamins are deficient in nuclear changes related to apoptosis, suggesting that lamins play a role in initiating the events that lead to apoptotic degradation of the nucleus.^ Suggest that the name of this, here and in the neurolex wiki list, should be changed to "olfactory bulb (main) periglomerular cell", to be consistent with the other olfactory bulb cells.
  • Cell Types With Definitions - NeuroLex 10 February 2010 13:013 UTC neurolex.org [Source type: Academic]

^ Our previous studies of cells infected with HSV-1 expressing GFP-22 had suggested that during virus infection VP22 was exclusively cytoplasmic ( 8 ).
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ Nuclear chromatin structure in relation to cell differentiation and cell activation in the cap and quiescent centre of Zea mays L. J. Exp.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[14] Inhibition of lamin assembly itself is an inducer of apoptosis.[49]
.The nuclear envelope acts as a barrier that prevents both DNA and RNA viruses from entering the nucleus.^ The nuclear envelope - Genetic organization of the nucleus .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ These nuclear pores allow chemical messages to exit and enter the nucleus.
  • Inside the Cell: Chapter 1: An Owner's Guide to the Cell - National Institute of General Medical Sciences 10 February 2010 13:013 UTC publications.nigms.nih.gov [Source type: FILTERED WITH BAYES]

^ Entering the nucleus through the pores are the nucleotide building blocks of DNA and RNA, as well as adenosine triphosphate , which provides the energy for synthesizing genetic material.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

.Some viruses require access to proteins inside the nucleus in order to replicate and/or assemble.^ Later on, some viruses have finally managed to replicate inside the eukaryotic nucleus.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ Localisation of the herpes simplex virus type 1 major capsid protein VP5 to the cell nucleus requires the abundant scaffolding protein VP22a.
  • Cytoplasm-to-Nucleus Translocation of a Herpesvirus Tegument Protein during Cell Division -- Elliott and O'Hare 74 (5): 2131 -- The Journal of Virology 10 February 2010 13:013 UTC jvi.asm.org [Source type: Academic]

^ Crm1 p pathway and functions in both mammalian cells and yeast A novel nuclear export activity in HIV-1 matrix protein required for viral replication.
  • WikiGenes - Active Transport, Cell Nucleus 10 February 2010 13:013 UTC www.wikigenes.org [Source type: Academic]

.DNA viruses, such as herpesvirus replicate and assemble in the cell nucleus, and exit by budding through the inner nuclear membrane.^ Interphase The period in the cell cycle when DNA is replicated in the nucleus; followed by mitosis.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ ER or peroxisomes, the nucleus is not a topologically separated compartment in the eukaryotic cytoplasm since the nucleoplasm and the cytoplasm are continuous through the nuclear pores.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ Such specialization of component genomes may be mediated through DNA methylation or other genomic imprinting mechanism.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.This process is accompanied by disassembly of the lamina on the nuclear face of the inner membrane.^ Nuclear Lamina [M0406410] A lattice of fibrils which covers the entire inner surface of the nuclear envelope and interlinks nuclear pores (NUCLEAR PORE).
  • MeSH Semantic Type: Cell Component [T026] 10 February 2010 13:013 UTC www.slicksurface.com [Source type: Academic]

^ Sun-1 recently has been identified in Dictyostelium ( 67 ) as an inner nuclear membrane component of the KASH/SUN pathway of transnuclear linkers ( 21 , 57 , 62 ).
  • Microtubule-Nucleus Interactions in Dictyostelium discoideum Mediated by Central Motor Kinesins -- Tikhonenko et al. 8 (5): 723 -- Eukaryotic Cell 10 February 2010 13:013 UTC ec.asm.org [Source type: Academic]

^ The nuclear envelope is a double membrane composed of an outer and an inner phospholipid bilayer.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

[14]

Anucleated and polynucleated cells

.
Human red blood cells, like those of other mammals, lack nuclei.
^ See more articles cited in this paragraph Chromosomes exhibit preferential positioning in nuclei of quiescent human cells.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ One of the most obvious examples of nuclear differentiation without polyploidy is found in mammalian blood cell types, where nuclei can be highly lobed (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Transcription-dependent spatial arrangements of CFTR and adjacent genes in human cell nuclei.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

This occurs as a normal part of the cells' development.
.Although most cells have a single nucleus, some eukaryotic cell types have no nucleus, and others have many nuclei.^ In humans and other eukaryotes, replication occurs in the cell nucleus.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ On the other hand, quantitative in vivo microscopy methods provide the first glimpse of how DNA, RNA and proteins behave inside the nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Dynamics of single mRNPs in nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

.This can be a normal process, as in the maturation of mammalian red blood cells, or a result of faulty cell division.^ It is generally assumed that polyploidy occurs to amplify genes without the energetically demanding process of cell division.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ One of the most obvious examples of nuclear differentiation without polyploidy is found in mammalian blood cell types, where nuclei can be highly lobed (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ A common way for a nucleus to differentiate in development is by undergoing many rounds of DNA synthesis without an accompanied cell division, i.e., a process of nuclear polyploidization.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Anucleated cells contain no nucleus and are therefore incapable of dividing to produce daughter cells.^ Such eggs almost always divide, as I have described previously ( 8 ), into two cells, each with one large and one small nucleus.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

^ Animal cells and plant cells contain membrane-bound organelles, including a distinct nucleus.
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ The first cleavage spindle therefore contains 36 elements each of which divides into half, so that each daughter cell similarly contains 36.
  • Developmental Biology 8e Online: On Multipolar Mitosis as a Means of Analysis of the Cell Nucleus 10 February 2010 13:013 UTC 8e.devbio.com [Source type: FILTERED WITH BAYES]

.The best-known anucleated cell is the mammalian red blood cell, or erythrocyte, which also lacks other organelles such as mitochondria and serves primarily as a transport vessel to ferry oxygen from the lungs to the body's tissues.^ One of the most obvious examples of nuclear differentiation without polyploidy is found in mammalian blood cell types, where nuclei can be highly lobed (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ One unique feature of the mammalian cell nucleus is the presence of structural and functional domains that lack membrane boundaries (Lamond and Earnshaw, 1998 ; Matera, 1999 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ The simulations try to approximate such a situation, mitochondria serve as a 'sink' and mitochondrial RP import is modelled as a flux.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

Erythrocytes mature through erythropoiesis in the bone marrow, where they lose their nuclei, organelles, and ribosomes. .The nucleus is expelled during the process of differentiation from an erythroblast to a reticulocyte, which is the immediate precursor of the mature erythrocyte.^ Gross reorganization of the nucleus is probably associated with a changing cellular role, as occurs during cell differentiation and development, the subject of the following sections of the review.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ A common way for a nucleus to differentiate in development is by undergoing many rounds of DNA synthesis without an accompanied cell division, i.e., a process of nuclear polyploidization.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ These examples show that nuclear polyploidy is involved in development and that during the course of cell differentiation, the nucleus can enlarge its DNA content in different ways.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[50] The presence of mutagens may induce the release of some immature "micronucleated" erythrocytes into the bloodstream.[51][52] .Anucleated cells can also arise from flawed cell division in which one daughter lacks a nucleus and the other has two nuclei.^ On the other hand, quantitative in vivo microscopy methods provide the first glimpse of how DNA, RNA and proteins behave inside the nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ There are similarities to polyploid nuclei, including associations of homologous and heterologous chromosomes and substantial structural reorganization of the nucleus from that found in cycling cells.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ However in differentiated haploid cells of the thallus, all nuclei have two coiled bodies associated with the nucleolus (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Polynucleated cells contain multiple nuclei.^ Eukaryotes have cells that contain nuclei .

^ The volume so occupied can be regarded as if it were all occupied by cells containing no relevant nuclei.
  • CHAPTER 20, Number of Primary Electron-Tracks per Cell-Nucleus, per Rad of Dose Received from Various Sources of Radiation, RADIATION-INDUCED CANCER FROM LOW-DOSE EXPOSURE 10 February 2010 13:013 UTC www.ratical.org [Source type: Academic]

^ All these results suggest that both intron-containing and intronless influenza A virus mRNAs are exported from MDCK cell nuclei by a CRM1 independent pathway.
  • Imaging and characterizing influenza A virus mRNA transport in living cells -- Wang et al. 36 (15): 4913 -- Nucleic Acids Research 10 February 2010 13:013 UTC nar.oxfordjournals.org [Source type: Academic]

.Most Acantharean species of protozoa[53] and some fungi in mycorrhizae[54] have naturally polynucleated cells.^ The question whether the Rabl configuration is a feature of dividing cells in all species requires some consideration.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

.Other examples include the intestinal parasites in the genus Giardia, which have two nuclei per cell.^ On the other hand, quantitative in vivo microscopy methods provide the first glimpse of how DNA, RNA and proteins behave inside the nuclei of living cells.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Independent assortment During meiosis each of the two copies of a gene is distributed to the germ cells independently of the distribution of other genes.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ However in differentiated haploid cells of the thallus, all nuclei have two coiled bodies associated with the nucleolus (Fig.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

[55] .In humans, skeletal muscle cells, called myocytes, become polynucleated during development; the resulting arrangement of nuclei near the periphery of the cells allows maximal intracellular space for myofibrils.^ See more articles cited in this paragraph Chromosomes exhibit preferential positioning in nuclei of quiescent human cells.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ Transcription-dependent spatial arrangements of CFTR and adjacent genes in human cell nuclei.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ This can be the result of a mutation during development or fusion of embryos at an early developmental stage.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

[5] .Multinucleated cells can also be abnormal in humans; for example, cells arising from the fusion of monocytes and macrophages, known as giant multinucleated cells, sometimes accompany inflammation[56] and are also implicated in tumor formation.^ For example, in human T cells the distribution and relative quantities of acetylated histones H3 and H4 have been mapped across the genome (Roh et al., 2005 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[57]

Evolution

.As the major defining characteristic of the eukaryotic cell, the nucleus' evolutionary origin has been the subject of much speculation.^ However, in the present manuscript, Gáspár Jékely adopts an alternative scenario, in which the eukaryotic nucleus originated relatively recently, i.e.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ Gross reorganization of the nucleus is probably associated with a changing cellular role, as occurs during cell differentiation and development, the subject of the following sections of the review.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ The origin of the nucleus is a central problem about the origin of eukaryotes.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

.Four major theories have been proposed to explain the existence of the nucleus, although none have yet earned widespread support.^ During the 1980s, Lynn Margulis proposed the theory of endosymbiosis to explain the origin of mitochondria and chloroplasts from permanent resident prokaryotes.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC www.emc.maricopa.edu [Source type: Academic]

^ DNA replication; e) ATP synthesis Which of these cellular organelles have their own DNA? a) chloroplast; b) nucleus; c) mitochondrion; d) all of these The theory of ___ was proposed to explain the possible origin of chloroplasts and mitochondria.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC www.emc.maricopa.edu [Source type: Academic]

^ Because the neurons in the lateral geniculate nucleus responded similarly to what was found in the retina, attention went to striate cortex to explain opponent color theory by physiology.
  • Webvision: Color Vision. by Peter Gouras 10 February 2010 13:013 UTC webvision.med.utah.edu [Source type: Academic]

[58]
.The theory known as the "syntrophic model" proposes that a symbiotic relationship between the archaea and bacteria created the nucleus-containing eukaryotic cell.^ In humans and other eukaryotes, replication occurs in the cell nucleus.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Proteomics in the cell nucleus The mammalian cell nucleus contains an estimated 20% of all cellular proteins (Simpson et al., 2000 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ In the case of NF- B, quantitative live-cell imaging has shown that persistent asynchronous oscillations between the nucleus and cytoplasm are required for NF- B target gene expression.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

.It is hypothesized that the symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus.^ Considering the absence of homologues of the NCP proteins in Archaea or Bacteria, it is likely that the nucleus originated in a specific pre-eukaryotic lineage of organisms either ancestral or sister group of Archaea.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ At this stage, which is similar to the situation in modern eukaryotes, the nucleus is fully defined compositionally.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

.This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria.^ According to the endosymbiont hypothesis, bacteria may be the progenitors of cellular organelles such as chloroplasts and mitochondria.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ Chloroplasts, like Gram-negative bacteria , mitochondria , and cyanobacteria, divide by binary fission .

^ Google Search )] [ mitochondria ( Online Biology Book )] [ origin and evolution of the related organelles: mitochondrion, chloroplast, and peroxisome ( The Society for the Study of the Origin and Evolution of Life )] [ index ] .

[59] .The archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins, including histones.^ This supports autogenous scenarios for the origin of the nucleus [ 3 ].
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ More work is needed to relate changing cell activity and the expression of genes in development to specific organizational properties of the nucleus, including the intranuclear distribution of genes and chromosomes.
  • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

^ Intriguingly, gene regions that have similar modification patterns are co-regulated, which supports the notion of a combinatorial code (Kurdistani et al., 2004 ).
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

.Observations that myxobacteria are motile, can form multicellular complexes, and possess kinases and G proteins similar to eukarya, support a bacterial origin for the eukaryotic cell.^ In situ hybridization Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

[60]
.A second model proposes that proto-eukaryotic cells evolved from bacteria without an endosymbiotic stage.^ Many Gram-negative bacteria, as well as Gram-positive bacteria generate their ATP via cellular respiration , by mechanisms very similar to how the mitochondria of eukaryotic cells generate ATP, also via cellular respiration .

^ The presence of a nucleus distinguishes the eukaryotic cells of multicellular organisms from the prokaryotic , one-celled organisms such as bacteria .
  • cell (biology) :: The nucleus -- Britannica Online Encyclopedia 10 February 2010 13:013 UTC www.britannica.com [Source type: Academic]

^ Eukaryotic cells arose through the uptake of free-living bacteria by endosymbiosis and their gradual conversion into organelles (plastids and mitochondria).
  • Experimental Reconstruction of Functional Gene Transfer from the Tobacco Plastid Genome to the Nucleus -- Stegemann and Bock 18 (11): 2869 -- THE PLANT CELL 10 February 2010 13:013 UTC www.plantcell.org [Source type: Academic]

.This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures.^ The components of various other nuclear structures have recently also been cataloged.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Systematic mapping of DNA replication sites The structural state of chromatin has also been implicated in nuclear functions other than gene expression.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

^ Prokaryote Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

[61] .A similar proposal states that a eukaryote-like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell.^ Accurate quantitative description of nuclear compartment spatial organisation in static cells is only the first step toward an overall understanding of how the cell nucleus functions.
  • Quantitative Analysis of Cell Nucleus Organisation 10 February 2010 13:013 UTC www.ncbi.nlm.nih.gov [Source type: Academic]

^ A crucial first step towards an integrated view of the nucleus and its compartments is the generation of a protein inventory for each domain ( Fig.
  • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

[62]
.The most controversial model, known as viral eukaryogenesis, posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus.^ Localize Determination of the original position (locus) of a gene or other marker on a chromosome.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ In humans and other eukaryotes, replication occurs in the cell nucleus.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Prokaryote Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

.The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes).^ Western blot A technique used to identify and locate proteins based on their ability to bind to specific antibodies.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Two strands of DNA are held together in the shape of a double helix by the bonds between base pairs.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

^ Antisense Nucleic acid that has a sequence exactly opposite to an mRNA molecule made by the body; binds to the mRNA molecule to prevent a protein from being made.
  • http://www.ornl.gov/TechResources/Human_Genome/glossary/glossary.html 10 February 2010 13:013 UTC www.ornl.gov [Source type: Academic]

One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator".[63] Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes.[64][65] It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis.[66]
.Finally, a very recent proposal suggests that traditional variants of the endosymbiont theory are insufficiently powerful to explain the origin of the eukaryotic nucleus.^ I agree with Gáspár Jékely that one should propose a positive selection pressure for the origin of the nucleus.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ In the framework of the mixed origin of eukaryotes, Gáspár Jékely proposes an elegant explanation for the origin of the nucleus, suggesting that the nuclear membrane emerged progressively to prevent the formation of hybrid, less efficient, ribosomes, containing a mixture of proto-eukaryotic and bacterial ribosomal proteins.
  • Biology Direct | Full text | Origin of the nucleus and Ran-dependent transport to safeguard ribosome biogenesis in a chimeric cell 10 February 2010 13:013 UTC www.biology-direct.com [Source type: Academic]

^ During the 1980s, Lynn Margulis proposed the theory of endosymbiosis to explain the origin of mitochondria and chloroplasts from permanent resident prokaryotes.
  • CELLS II: CELLULAR ORGANIZATION 10 February 2010 13:013 UTC www.emc.maricopa.edu [Source type: Academic]

.This model, termed the exomembrane hypothesis, suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits.^ The nucleus and cell membrane are clearly visible.
  • Lab Manual Exercise # 1 10 February 2010 13:013 UTC waynesword.palomar.edu [Source type: FILTERED WITH BAYES]

^ The nuclear membranes inner membrane lines the interior volume of the nucleus .

^ Mononuclear - A cell having a single nucleus.
  • Nucleus Information and Courses from MediaLab, Inc. 10 February 2010 13:013 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

[67]

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Further reading

  • Goldman, Robert D.; Gruenbaum, Y; Moir, RD; Shumaker, DK; Spann, TP (2002). ."Nuclear lamins: building blocks of nuclear architecture". Genes & Dev. 16 (16): 533–547. doi:10.1101/gad.960502.^ Protein dynamics: implications for nuclear architecture and gene expression.
    • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

    ^ Chromosome territories, nuclear architecture and gene regulation in mammalian cells.
    • Systems biology in the cell nucleus -- Gorski and Misteli 118 (18): 4083 -- Journal of Cell Science 10 February 2010 13:013 UTC jcs.biologists.org [Source type: Academic]

    PMID 11877373.
     
A review article about nuclear lamins, explaining their structure and various roles
  • Görlich, Dirk; Kutay, U (1999). ."Transport between the cell nucleus and the cytoplasm". Ann.^ The interchromosomal domain (ICD), occurring between the chromosome domains, is thought to be an important structural and functional compartment of the cycling cell nucleus ( 160 ).
    • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

    Rev. Cell Dev. Biol.
    15 (15): 607–660. doi:10.1146/annurev.cellbio.15.1.607. PMID 10611974.
     
A review article about nuclear transport, explains the principles of the mechanism, and the various transport pathways
  • Lamond, Angus I.; Earnshaw, WC (1998-04-24). ."Structure and Function in the Nucleus". Science 280 (5363): 547–553. doi:10.1126/science.280.5363.547.^ Smith PH, Rhode WS (1989) Structural and functional properties distinguish two types of multipolar cells in the ventral cochlear nucleus.
    • Cholinergic Modulation of Stellate Cells in the Mammalian Ventral Cochlear Nucleus -- Fujino and Oertel 21 (18): 7372 -- Journal of Neuroscience 10 February 2010 13:013 UTC www.jneurosci.org [Source type: Academic]

    PMID 9554838.
     
A review article about the nucleus, explaining the structure of chromosomes within the organelle, and describing the nucleolus and other subnuclear bodies
A review article about the evolution of the nucleus, explaining a number of different theories
  • Pollard, Thomas D.; William C. Earnshaw (2004). Cell Biology. Philadelphia: Saunders. ISBN 0-7216-3360-9. 
A university level textbook focusing on cell biology. Contains information on nucleus structure and function, including nuclear transport, and subnuclear domains

External links

.
  • cellnucleus.com Website covering structure and function of the nucleus from the Department of Oncology at the University of Alberta.
  • The Nuclear Protein Database Information on nuclear components.
  • The Nucleus Collection in the Image & Video Library of The American Society for Cell Biology contains peer-reviewed still images and video clips that illustrate the nucleus.
  • Nuclear Envelope and Nuclear Import Section from Landmark Papers in Cell Biology, Joseph G. Gall, J. Richard McIntosh, eds., contains digitized commentaries and links to seminal research papers on the nucleus.^ (D and E) Sectioned nucleus from a wheat meristematic cell.
    • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

    ^ Structure and function in the nucleus.
    • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

    ^ Other important components of the nucleus, particularly nucleolar ultrastructure and proteins involved in ribosomal DNA (rDNA) transcription, rRNA splicing, packaging, and export (for reviews, see references 116 and 141 ), the nuclear envelope including the nuclear pores (essential for compartmentalizing the nucleus and enabling import into and export from the nucleus [for a review, see reference 62 ]), and nuclear lamins occurring on the inner face of the nuclear envelope (involved in maintaining nuclear shape and anchoring chromatin at the nuclear periphery in animal nuclei [for a review, see reference 124 ]) are not covered here.
    • Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells -- Leitch 64 (1): 138 -- Microbiology and Molecular Biology Reviews 10 February 2010 13:013 UTC mmbr.asm.org [Source type: Academic]

    Published online in the Image & Video Library of The American Society for Cell Biology
  • Cytoplasmic patterns generated by human antibodies

Gallery of nucleus images


cells stained for DNA with the  Blue Hoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left a cell is going through mitosis and its DNA has condensed ready for division.]]

s: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles]]

In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel) is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression — the nucleus is therefore the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and separates its contents from the cellular cytoplasm, and the nuclear lamina, a meshwork within the nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole. Because the nuclear membrane is impermeable to most molecules, nuclear pores are required to allow movement of molecules across the envelope. These pores cross both of the membranes, providing a channel that allows free movement of small molecules and ions. The movement of larger molecules such as proteins is carefully controlled, and requires active transport regulated by carrier proteins. Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance.

Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best known of these is the nucleolus, which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.

Contents

History

[[File:|thumb|left|upright=1.5|Oldest known depiction of cells and their nuclei by Antonie van Leeuwenhoek, 1719.]] salivary gland cell published by Walther Flemming in 1882. The nucleus contains Polytene chromosomes. ]] The nucleus was the first organelle to be discovered. The probably oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632 – 1723). He observed a "Lumen", the nucleus, in the red blood cells of salmon[1]. Unlike mammalian red blood cells, those of other vertebrates still possess nuclei. The nucleus was also described by Franz Bauer in 1804[2] and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids microscopically when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer.[3] He did not suggest a potential function. In 1838 Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "Cytoblast" (cell builder). He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view having already described cells multiplying by division and believing that many cells would have no nuclei. The idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak (1852) and Rudolf Virchow (1855) who decisively propagated the new paradigm that cells are generated solely by cells ("Omnis cellula e cellula"). The function of the nucleus remained unclear.[4]

Between 1876 and 1878 Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a (single) nucleated cell. This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "Monerula", a structureless mass of primordial mucus ("Urschleim"). Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other animal groups, e.g. amphibians and molluscs. Eduard Strasburger produced the same results for plants (1884). This paved the way to assign the nucleus an important role in heredity. In 1873 August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity. The function of the nucleus as carrier of genetic information became clear only later, after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century; the chromosome theory of heredity was developed.[4] I like lizards.

Structures

The nucleus is the largest cellular organelle in animals.[5] In mammalian cells, the average diameter of the nucleus is approximately 6 micrometers (μm), which occupies about 10% of the total cell volume.[6] The viscous liquid within it is called nucleoplasm, and is similar in composition to the cytosol found outside the nucleus.[7] It appears as a dense, roughly spherical organelle.

Nuclear envelope and pores

-studded double membranes of the nuclear envelope, the DNA (complexed as chromatin), and the nucleolus. Within the cell nucleus is a viscous liquid called nucleoplasm, similar to the cytoplasm found outside the nucleus.]] on the surface of the nuclear envelope (1). Other diagram labels show (2) the outer ring, (3) spokes, (4) basket, and (5) filaments.]]

The nuclear envelope otherwise known as nuclear membrane consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometers (nm). The nuclear envelope completely encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm.[8] The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes. The space between the membranes is called the perinuclear space and is continuous with the RER lumen.

Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins. The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast) to 100 proteins (in vertebrates).[5] The pores are 100 nm in total diameter; however, the gap through which molecules freely diffuse is only about 9 nm wide, due to the presence of regulatory systems within the center of the pore. This size allows the free passage of small water-soluble molecules while preventing larger molecules, such as nucleic acids and larger proteins, from inappropriately entering or exiting the nucleus. These large molecules must be actively transported into the nucleus instead. The nucleus of a typical mammalian cell will have about 3000 to 4000 pores throughout its envelope,[9] each of which contains a donut-shaped, eightfold-symmetric ring-shaped structure at a position where the inner and outer membranes fuse.[10] Attached to the ring is a structure called the nuclear basket that extends into the nucleoplasm, and a series of filamentous extensions that reach into the cytoplasm. Both structures serve to mediate binding to nuclear transport proteins.[5]

Most proteins, ribosomal subunits, and some RNAs are transported through the pore complexes in a process mediated by a family of transport factors known as karyopherins. Those karyopherins that mediate movement into the nucleus are also called importins, while those that mediate movement out of the nucleus are called exportins. Most karyopherins interact directly with their cargo, although some use adaptor proteins.[11] Steroid hormones such as cortisol and aldosterone, as well as other small lipid-soluble molecules involved in intercellular signaling can diffuse through the cell membrane and into the cytoplasm, where they bind nuclear receptor proteins that are trafficked into the nucleus. There they serve as transcription factors when bound to their ligand; in the absence of ligand many such receptors function as histone deacetylases that repress gene expression.[5]

Nuclear lamina

In animal cells, two networks of intermediate filaments provide the nucleus with mechanical support: the nuclear lamina forms an organized meshwork on the internal face of the envelope, while less organized support is provided on the cytosolic face of the envelope. Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores.[6]

The nuclear lamina is mostly composed of lamin proteins. Like all proteins, lamins are synthesized in the cytoplasm and later transported into the nucleus interior, where they are assembled before being incorporated into the existing network of nuclear lamina.[12][13] Lamins are also found inside the nucleoplasm where they form another regular structure, known as the nucleoplasmic veil,[14] that is visible using fluorescence microscopy. The actual function of the veil is not clear, although it is excluded from the nucleolus and is present during interphase.[15] The lamin structures that make up the veil bind chromatin and disrupting their structure inhibits transcription of protein-coding genes.[16]

Like the components of other intermediate filaments, the lamin monomer contains an alpha-helical domain used by two monomers to coil around each other, forming a dimer structure called a coiled coil. Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer called a protofilament. Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament. These filaments can be assembled or disassembled in a dynamic manner, meaning that changes in the length of the filament depend on the competing rates of filament addition and removal.[6]

Mutations in lamin genes leading to defects in filament assembly are known as laminopathies. The most notable laminopathy is the family of diseases known as progeria, which causes the appearance of premature aging in its sufferers. The exact mechanism by which the associated biochemical changes give rise to the aged phenotype is not well understood.[17]

Chromosomes

nucleus in which DNA is stained blue. The distinct chromosome territories of chromosome 2 (red) and chromosome 9 (green) are visible stained with fluorescent in situ hybridization.]]

The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.

There are two types of chromatin. Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell.[18] The other type, heterochromatin, is the more compact form, and contains DNA that are infrequently transcribed. This structure is further categorized into facultative heterochromatin, consisting of genes that are organized as heterochromatin only in certain cell types or at certain stages of development, and constitutive heterochromatin that consists of chromosome structural components such as telomeres and centromeres.[19] During interphase the chromatin organizes itself into discrete individual patches,[20] called chromosome territories.[21] Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.[22]

Antibodies to certain types of chromatin organization, particularly nucleosomes, have been associated with a number of autoimmune diseases, such as systemic lupus erythematosus.[23] These are known as anti-nuclear antibodies (ANA) and have also been observed in concert with multiple sclerosis as part of general immune system dysfunction.[24] As in the case of progeria, the role played by the antibodies in inducing the symptoms of autoimmune diseases is not obvious.

Nucleolus

of a cell nucleus, showing the darkly stained nucleolus.]]

The nucleolus is a discrete densely stained structure found in the nucleus. It is not surrounded by a membrane, and is sometimes called a suborganelle. It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA). These regions are called nucleolar organizer regions (NOR). The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes. The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association. This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.[25]

The first step in ribosomal assembly is transcription of the rDNA, by a protein called RNA polymerase I, forming a large pre-rRNA precursor. This is cleaved into the subunits 5.8S, 18S, and 28S rRNA.[26] The transcription, post-transcriptional processing, and assembly of rRNA occurs in the nucleolus, aided by small nucleolar RNA (snoRNA) molecules, some of which are derived from spliced introns from messenger RNAs encoding genes related to ribosomal function. The assembled ribosomal subunits are the largest structures passed through the nuclear pores.[5]

When observed under the electron microscope, the nucleolus can be seen to consist of three distinguishable regions: the innermost fibrillar centers (FCs), surrounded by the dense fibrillar component (DFC), which in turn is bordered by the granular component (GC). Transcription of the rDNA occurs either in the FC or at the FC-DFC boundary, and therefore when rDNA transcription in the cell is increased more FCs are detected. Most of the cleavage and modification of rRNAs occurs in the DFC, while the latter steps involving protein assembly onto the ribosomal subunits occur in the GC.[26]

Other subnuclear bodies

Subnuclear structure sizes
Structure name Structure diameter
Cajal bodies 0.2–2.0 µm [27]
PIKA 5 µm [28]
PML bodies 0.2–1.0 µm [29]
Paraspeckles 0.2–1.0 µm [30]
Speckles 20–25 nm [28]

Besides the nucleolus, the nucleus contains a number of other non-membrane delineated bodies. These include Cajal bodies, Gemini of coiled bodies, polymorphic interphase karyosomal association (PIKA), promyelocytic leukaemia (PML) bodies, paraspeckles and splicing speckles. Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not uniform mixture, but rather contains organized functional subdomains.[29]

Other subnuclear structures appear as part of abnormal disease processes. For example, the presence of small intranuclear rods have been reported in some cases of nemaline myopathy. This condition typically results from mutations in actin, and the rods themselves consist of mutant actin as well as other cytoskeletal proteins.[31]

Cajal bodies and gems

A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies (CB), whose diameter measures between 0.2 µm and 2.0 µm depending on the cell type and species.[27] When seen under an electron microscope, they resemble balls of tangled thread[28] and are dense foci of distribution for the protein coilin.[32] CBs are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.[27]

Similar to Cajal bodies are Gemini of coiled bodies, or gems, whose name is derived from the Gemini constellation in reference to their close "twin" relationship with CBs. Gems are similar in size and shape to CBs, and in fact are virtually indistinguishable under the microscope.[32] Unlike CBs, gems do not contain small nuclear ribonucleoproteins (snRNPs), but do contain a protein called survivor of motor neurons (SMN) whose function relates to snRNP biogenesis. Gems are believed to assist CBs in snRNP biogenesis,[33] though it has also been suggested from microscopy evidence that CBs and gems are different manifestations of the same structure.[32]

PIKA and PTF domains

PIKA domains, or polymorphic interphase karyosomal associations, were first described in microscopy studies in 1991. Their function was and remains unclear, though they were not thought to be associated with active DNA replication, transcription, or RNA processing.[34] They have been found to often associate with discrete domains defined by dense localization of the transcription factor PTF, which promotes transcription of snRNA.[35]

PML bodies

Promyelocytic leukaemia bodies (PML bodies) are spherical bodies found scattered throughout the nucleoplasm, measuring around 0.2–1.0 µm. They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains. They are often seen in the nucleus in association with Cajal bodies and cleavage bodies. It has been suggested that they play a role in regulating transcription.[29]

Paraspeckles

Discovered by Fox et al. in 2002, paraspeckles are irregularly shaped compartments in the nucleus' interchromatin space.[36] First documented in HeLa cells, where there are generally 10–30 per nucleus,[37] paraspeckles are now known to also exist in all human primary cells, transformed cell lines and tissue sections.[38] Their name is derived from their distribution in the nucleus; the "para" is short for parallel and the "speckles" refers to the splicing speckles to which they are always in close proximity.[37]

Paraspeckles are dynamic structures that are altered in response to changes in cellular metabolic activity. They are transcription dependent[36] and in the absence of RNA Pol II transcription, the paraspeckle disappears and all of its associated protein components (PSP1, p54nrb, PSP2, CFI(m)68 and PSF) form a crescent shaped perinucleolar cap in the nucleolus. This phenomenon is demonstrated during the cell cycle. In the cell cycle, paraspeckles are present during interphase and during all of mitosis except for telophase. During telophase, when the two daughter nuclei are formed, there is no RNA Pol II transcription so the protein components instead form a perinucleolar cap.[38]

Splicing speckles

Sometimes referred to as interchromatin granule clusters or as splicing-factor compartments, speckles are rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing.[39] Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.[40]

Function

The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle. The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes.

Cell compartmentalization

The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary. This is important for controlling processes on either side of the nuclear membrane. In some cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway. This regulatory mechanism occurs in the case of glycolysis, a cellular pathway for breaking down glucose to produce energy. Hexokinase is an enzyme responsible for the first the step of glycolysis, forming glucose-6-phosphate from glucose. At high concentrations of fructose-6-phosphate, a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus,[41] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.[42]

In order to control which genes are being transcribed, the cell separates some transcription factor proteins responsible for regulating gene expression from physical access to the DNA until they are activated by other signaling pathways. This prevents even low levels of inappropriate gene expression. For example in the case of NF-κB-controlled genes, which are involved in most inflammatory responses, transcription is induced in response to a signal pathway such as that initiated by the signaling molecule TNF-α, binds to a cell membrane receptor, resulting in the recruitment of signalling proteins, and eventually activating the transcription factor NF-κB. A nuclear localisation signal on the NF-κB protein allows it to be transported through the nuclear pore and into the nucleus, where it stimulates the transcription of the target genes.[6]

The compartmentalization allows the cell to prevent translation of unspliced mRNA.[43] Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins. The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation. Without the nucleus ribosomes would translate newly transcribed (unprocessed) mRNA resulting in misformed and nonfunctional proteins.

Gene expression

File:Transcription label
A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. "Begin" indicates the 3' end of the DNA, where new RNA synthesis begins; "end" indicates the 5' end, where the primary transcripts are almost complete.

Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to be exported.[44]

Since the nucleus is the site of transcription, it also contains a variety of proteins which either directly mediate transcription or are involved in regulating the process. These proteins include helicases that unwind the double-stranded DNA molecule to facilitate access to it, RNA polymerases that synthesize the growing RNA molecule, topoisomerases that change the amount of supercoiling in DNA, helping it wind and unwind, as well as a large variety of transcription factors that regulate expression.[45]

Processing of pre-mRNA

Newly synthesized mRNA molecules are known as primary transcripts or pre-mRNA. They must undergo post-transcriptional modification in the nucleus before being exported to the cytoplasm; mRNA that appears in the nucleus without these modifications is degraded rather than used for protein translation. The three main modifications are 5' capping, 3' polyadenylation, and RNA splicing. While in the nucleus, pre-mRNA is associated with a variety of proteins in complexes known as heterogeneous ribonucleoprotein particles (hnRNPs). Addition of the 5' cap occurs co-transcriptionally and is the first step in post-transcriptional modification. The 3' poly-adenine tail is only added after transcription is complete.

RNA splicing, carried out by a complex called the spliceosome, is the process by which introns, or regions of DNA that do not code for protein, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule. This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.[5] Many pre-mRNAs, including those encoding antibodies, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences. This process is known as alternative splicing, and allows production of a large variety of proteins from a limited amount of DNA.

Dynamics and regulation

Nuclear transport

s, such as RNA and proteins, are actively transported across the nuclear membrane in a process called the Ran-GTP nuclear transport cycle.]]

The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes. Although small molecules can enter the nucleus without regulation,[46] macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit. "Cargo" proteins that must be translocated from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals which are bound by importins, while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins. The ability of importins and exportins to transport their cargo is regulated by GTPases, enzymes that hydrolyze the molecule guanosine triphosphate to release energy. The key GTPase in nuclear transport is Ran, which can bind either GTP or GDP (guanosine diphosphate) depending on whether it is located in the nucleus or the cytoplasm. Whereas importins depend on RanGTP to dissociate from their cargo, exportins require RanGTP in order to bind to their cargo.[11]

Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus. Inside the nucleus, RanGTP acts to separate the cargo from the importin, allowing the importin to exit the nucleus and be reused. Nuclear export is similar, as the exportin binds the cargo inside the nucleus in a process facilitated by RanGTP, exits through the nuclear pore, and separates from its cargo in the cytoplasm.

Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post-transcriptional modification is complete. This quality-control mechanism is important due to the these molecules' central role in protein translation; mis-expression of a protein due to incomplete excision of exons or mis-incorporation of amino acids could have negative consequences for the cell; thus incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation.[5]

Assembly and disassembly

lung cell stained with fluorescent dyes during metaphase. The mitotic spindle can be seen, stained green, attached to the two sets of chromosomes, stained light blue. All chromosomes but one are already at the metaphase plate. ]]

During its lifetime a nucleus may be broken down, either in the process of cell division or as a consequence of apoptosis, a regulated form of cell death. During these events, the structural components of the nucleus—the envelope and lamina—are systematically degraded.

During the cell cycle the cell divides to form two cells. In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets. This occurs by the replicated chromosomes, the sister chromatids, attaching to microtubules, which in turn are attached to different centrosomes. The sister chromatids can then be pulled to separate locations in the cell. In many cells the centrosome is located in the cytoplasm, outside the nucleus, the microtubules would be unable to attach to the chromatids in the presence of the nuclear envelope.[47] Therefore the early stages in the cell cycle, beginning in prophase and until around prometaphase, the nuclear membrane is dismantled.[14] Likewise, during the same period, the nuclear lamina is also disassembled, a process regulated by phosphorylation of the lamins.[48] Towards the end of the cell cycle, the nuclear membrane is reformed, and around the same time, the nuclear lamina are reassembled by dephosphorylating the lamins.[48]

However, in dinoflagellates the nuclear envelope remains intact, the centrosomes are located in the cytoplasm, and the microtubules come in contact with chromosomes, whose centromeric regions are incorporated into the nuclear envelope (the so-called closed mitosis with extranuclear spindle). In many other protists (e.g. ciliates, sporozoans) and fungi the centrosomes are intranuclear, and their nuclear envelope also does not disassemle during cell division.

Apoptosis is a controlled process in which the cell's structural components are destroyed, resulting in death of the cell. Changes associated with apoptosis directly affect the nucleus and its contents, for example in the condensation of chromatin and the disintegration of the nuclear envelope and lamina. The destruction of the lamin networks is controlled by specialized apoptotic proteases called caspases, which cleave the lamin proteins and thus degrade the nucleus' structural integrity. Lamin cleavage is sometimes used as a laboratory indicator of caspase activity in assays for early apoptotic activity.[14] Cells that express mutant caspase-resistant lamins are deficient in nuclear changes related to apoptosis, suggesting that lamins play a role in initiating the events that lead to apoptotic degradation of the nucleus.[14] Inhibition of lamin assembly itself is an inducer of apoptosis.[49]

The nuclear envelope acts as a barrier that prevents both DNA and RNA viruses from entering the nucleus. Some viruses require access to proteins inside the nucleus in order to replicate and/or assemble. DNA viruses, such as herpesvirus replicate and assemble in the cell nucleus, and exit by budding through the inner nuclear membrane. This process is accompanied by disassembly of the lamina on the nuclear face of the inner membrane.[14]

Anucleated and polynucleated cells

Although most cells have a single nucleus, some eukaryotic cell types have no nucleus, and others have many nuclei. This can be a normal process, as in the maturation of mammalian red blood cells, or a result of faulty cell division.

Anucleated cells contain no nucleus and are therefore incapable of dividing to produce daughter cells. The best-known anucleated cell is the mammalian red blood cell, or erythrocyte, which also lacks other organelles such as mitochondria and serves primarily as a transport vessel to ferry oxygen from the lungs to the body's tissues. Erythrocytes mature through erythropoiesis in the bone marrow, where they lose their nuclei, organelles, and ribosomes. The nucleus is expelled during the process of differentiation from an erythroblast to a reticulocyte, which is the immediate precursor of the mature erythrocyte.[50] The presence of mutagens may induce the release of some immature "micronucleated" erythrocytes into the bloodstream.[51][52] Anucleated cells can also arise from flawed cell division in which one daughter lacks a nucleus and the other has two nuclei.

Polynucleated cells contain multiple nuclei. Most Acantharean species of protozoa[53] and some fungi in mycorrhizae[54] have naturally polynucleated cells. Other examples include the intestinal parasites in the genus Giardia, which have two nuclei per cell.[55] In humans, skeletal muscle cells, called myocytes, become polynucleated during development; the resulting arrangement of nuclei near the periphery of the cells allows maximal intracellular space for myofibrils.[5] Multinucleated cells can also be abnormal in humans; for example, cells arising from the fusion of monocytes and macrophages, known as giant multinucleated cells, sometimes accompany inflammation[56] and are also implicated in tumor formation.[57]

Evolution

As the major defining characteristic of the eukaryotic cell, the nucleus' evolutionary origin has been the subject of much speculation. Four major theories have been proposed to explain the existence of the nucleus, although none have yet earned widespread support.[58]

The theory known as the "syntrophic model" proposes that a symbiotic relationship between the archaea and bacteria created the nucleus-containing eukaryotic cell. It is hypothesized that the symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus. This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria.[59] The archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins, including histones. Observations that myxobacteria are motile, can form multicellular complexes, and possess kinases and G proteins similar to eukarya, support a bacterial origin for the eukaryotic cell.[60]

A second model proposes that proto-eukaryotic cells evolved from bacteria without an endosymbiotic stage. This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures.[61] A similar proposal states that a eukaryote-like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell.[62]

The most controversial model, known as viral eukaryogenesis, posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus. The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes). One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator".[63] Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes.[64][65] It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis.[66]

Finally, a very recent proposal suggests that traditional variants of the endosymbiont theory are insufficiently powerful to explain the origin of the eukaryotic nucleus. This model, termed the exomembrane hypothesis, suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits.[67]

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  67. ^ de Roos AD (2006). [Expression error: Unexpected < operator "The origin of the eukaryotic cell based on conservation of existing interfaces"]. Artif Life 12 (4): 513–523.. doi:10.1162/artl.2006.12.4.513. PMID 16953783. 

Further reading

  • Goldman, Robert D.; Gruenbaum, Y; Moir, RD; Shumaker, DK; Spann, TP (2002). [Expression error: Unexpected < operator "Nuclear lamins: building blocks of nuclear architecture"]. Genes & Dev. 16 (16): 533–547. doi:10.1101/gad.960502. PMID 11877373. 
A review article about nuclear lamins, explaining their structure and various roles
A review article about nuclear transport, explains the principles of the mechanism, and the various transport pathways
  • Lamond, Angus I.; Earnshaw, WC (1998-04-24). [Expression error: Unexpected < operator "Structure and Function in the Nucleus"]. Science 280 (5363): 547–553. doi:10.1126/science.280.5363.547. PMID 9554838. 
A review article about the nucleus, explaining the structure of chromosomes within the organelle, and describing the nucleolus and other subnuclear bodies
A review article about the evolution of the nucleus, explaining a number of different theories
  • Pollard, Thomas D.; William C. Earnshaw (2004). Cell Biology. Philadelphia: Saunders. ISBN 0-7216-3360-9. 
A university level textbook focusing on cell biology. Contains information on nucleus structure and function, including nuclear transport, and subnuclear domains

External links

Gallery of nucleus images


Simple English

stained for DNA with the blue Hoechst dye. The middle and right cells are in interphase, so their entire nuclei are labeled. On the left a cell is going through mitosis and its DNA has condensed, ready for division.]]

-dotted double membranes of the nuclear envelope, the DNA complex, and the nucleolus.]] A cell nucleus is the part of the cell which contains the genetic code, the DNA, and the RNA. The nucleus is small and round, and it works as the cell's control center. It contains x-shaped "duffel bags" called chromosomes, and inside the chromosomes are DNA strands. The human body contains billions of cells, which vary from blood cells that carry oxygen from one part of the body to another, nerve cells which create reactions that stimulate feelings and data, and skin cells that protect the cells underneath.

Some animals (like amoebas) consist of only one cell with the same basic materials as multi-cellular organisms.

Cell nuclei are only found in eukaryotes. They were first found by Antonie van Leeuwenhoek in the 17th century. Bacteria and Archaea are single-celled organisms of quite a different type: they are prokaryotes, and their cells do not have nuclei.

References


Citable sentences

Up to date as of December 28, 2010

Here are sentences from other pages on Cell nucleus, which are similar to those in the above article.








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