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Topic: Heterochromatin

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	Heterochromatin - Wikipedia, the free encyclopedia
		Heterochromatin is believed to serve several functions, from gene regulation to the protection of the integrity of chromosomes; all of these roles can be attributed to the dense packing of DNA, which makes it less accessible to protein factors that bind DNA or its associated factors.
		Heterochromatin is generally stably inherited; when a cell divides the two daughter cells will typically contain heterochromatin within the same regions of DNA, resulting in epigenetic inheritance.
		An example of facultative heterochromatin is X-chromosome inactivation in female mammals: one X chromosome is packaged in facultative heterochromatin and silenced, while the other X chromosome in packaged in euchromatin and expressed.
	en.wikipedia.org /wiki/Heterochromatin (896 words)

	Heterochromatin (Site not responding. Last check: 2007-10-09)
		In both flies and humans, heterochromatin is concentrated in large (Megabase-sized) blocks, predominantly in the centric and subtelomeric regions of all chromosomes.
		Heterochromatin is not inert, and is essential for cell and organismal viability in multicellular eukaryotes.
		Genes required for viability and fertility reside in heterochromatin, as are elements required for normal chromosomal inheritance.
	taputea.lbl.gov /research/het/heterochromatin.html (137 words)

	Eu- and Heterochromatin (Site not responding. Last check: 2007-10-09)
		Heterochromatin is less abundant, relative to euchromatin, in the large nuclei of active cells (right, upper) than in the small nuclei of resting cells, such as small lymphocytes (right, lower).
		Heterochromatin is not being transcribed and consists, in part, of satellite DNA.
		Heterochromatin around centromeres may be condensed because transcripts of its DNA induce transcriptional gene silencing (ref).
	opbs.okstate.edu /~melcher/MG/MGW1/MG1131.html (318 words)

	Heterochromatin definition - Medical Dictionary definitions of popular medical terms (Site not responding. Last check: 2007-10-09)
		Heterochromatin: Chromosomal material that is darkly staining and tightly coiled throughout the cell cycle and that is, for the most part, genetically inactive.
		Constitutive heterochromatin is fixed and irreversible in form and function.
		Chromosomes 1, 9, 16 and the Y chromosome contain regions of constitutive heterochromatin.
	www.medterms.com /script/main/art.asp?articlekey=3736 (202 words)

	Genome Biology \| Full text \| RNAi hushes heterochromatin
		The heterochromatin of eukaryotic genomes is concentrated at and around centromeres and plays a central role in the maintenance of genome integrity through regulation of both gene expression and chromosome segregation [1,2].
		Centric heterochromatin is required for cohesion between sister centromeres, which ensures proper chromosome segregation at mitosis [3,4].
		The heterochromatin protein 1 (HP1) homolog Swi6 then binds to the methylated lysine 9 of histone H3 [10] and spreads the silent heterochromatin structure (with methylated lysine 9) to surrounding sequences [12].
	genomebiology.com /2002/3/12/reviews/1035 (2521 words)

	Elgin Lab: Heterochromatin Abstracts
		Several alleles of each gene were tested for their affect using 118E-10, a line carrying our P element in the fourth chromosome pericentric heterochromatin, and 39C-12, a line carrying our P element in the banded portion of the fourth chromosome.
		However, genes normally active within heterochromatin (rolled and light) do not show this pattern, suggesting that the altered chromatin structure observed is associated with regions that are silent, rather than being a property of the domain as a whole.
		When the hsp26 transgene is found within heterochromatin, the packaging is altered to a more uniform nucleosome array, apparently reflecting the surrounding heterochromatin; a model of the nucleosome array consistent with the present data is shown.
	www.biology.wustl.edu /faculty/elgin/hetchrom.html (1645 words)

	Interactive Fly, Drosophila
		Surprisingly, whereas GAGA factor retains its association with the heterochromatin throughout the cell cycle, a significant fraction of HP1 is dispersed throughout the spindle around the segregating chromosomes during mitosis.
		Heterochromatin protein 1 is required for the normal expression of two heterochromatin genes in Drosophila.
		Heterochromatin protein 1 (HP1) is associated with induced gene expression in Drosophila euchromatin.
	www.sdbonline.org /fly/polycomb/hp1-4.htm (3818 words)

	Emil Heitz: (1892-1965): Chloroplasts, Heterochromatin, and Polytene Chromosomes.
		Heterochromatin in Bryophyta: Using the liverwort Pellia epiphylla (Jungermaniidae) and exploiting prophases, metaphases and telophases as well as interphase nuclei, HEITZ found evidence that identical chromosome sections are constantly heterochromatic (heteropycnotic).
		Nevertheless, the density of genes in a chromosome is related to the longitudinal differentiation in euchromatin and heterochromatin.
		Longitudinal differentiation in euchromatin and proximal heterochromatin is evident in metaphase configuration.
	www.euchromatin.net /Zacharias1.htm (4976 words)

	Heterochromatin: stable and unstable invasions at home and abroad -- Fahrner and Baylin 17 (15): 1805 -- Genes and ...
		For key components of the heterochromatin machinery, mammalian pericentromeric components are indicated in purple, Schizosaccharomyces pombe centromeric components in orange, and those present in both in fl.
		However, the REST/NRSF-CoRest complex recruits the heterochromatin machinery discussed in the text (indicated by a shaded green and yellow rectangle) to a limited region encompassing, and silencing (red X), all five genes, thus forming a localized domain of facultative heterochromatin surrounded on both sides by euchromatin (thin fl line).
		The bottom panel shows, as discussed in the text, that during subsequent cell renewal, this microcosm of heterochromatin is fully reversed (left), remains as a microcosm of heterochromatin for an intermediate level of reversible gene silencing (middle), or is recruited to large domains of late replicating heterochromatin, resulting in a permanently silenced state (right).
	www.genesdev.org /cgi/content/full/17/15/1805 (4634 words)

	A CAF-1 dependent pool of HP1 during heterochromatin duplication
		Candidate factor(s) involved in the inheritance of heterochromatin domains must fulfill at least two criteria: (i) they must be present during replication and (ii) they must permit a link between nucleosome formation and proteins, such as HP1, involved in defining the higher order structure of pericentric heterochromatin.
		The part of the heterochromatin domain that is subject to disruption during replication seems to be restricted to the periphery, thus explaining how the overall stability could be preserved.
		Left: In the presence of p150CAF-1 (si cont), replicating pericentric heterochromatin is represented with a replication-independent pool of HP1 (RI-HP1, large light green circle) in the inner region interacting with RNA (fl), and a replication-specific pool of HP1 at the periphery (RS-HP1, small dashed green circles) colocalizing with p150CAF-1 (red circles).
	www.nature.com /emboj/journal/v23/n17/full/7600362a.html (7300 words)

	Heterochromatin in Animals and Plants. Similarities and Differences -- Avramova 129 (1): 40 -- PLANT PHYSIOLOGY
		The repetitive DNA in heterochromatin is usually methylated, in accordance with a predicted repressive function.
		A paradigm for an epigenetic silencing mechanism is the repression of the homeotic genes.
		Grunstein M (1998) Yeast heterochromatin: regulation of its assembly and inheritance by histones.
	www.plantphysiol.org /cgi/content/full/129/1/40 (5439 words)

	Euchromatin Network Home Page.
		Heitz (1929) originally described as heterochromatin that portion of the nuclear chromatin which demonstrated its allocycly by maintaining a condensed state while the remainder of the nuclear chromatin was extending to what he termed the euchromatin state.
		Euchromatin 10nm (100 A.) microfibrils are ultrastructurally continuous with those in heterochromatin condensations (Frenster, 1965a), and are present in all diploid interphase animal cells examined (Frenster et al, 1974).
		These genetic, cytological, biochemical and biophysical studies all strongly support the current view that heterochromatin represents repressed segments of chromosomal DNA while euchromatin represents active segments, and are an expression of the degree of nuclear differentiation within individual differentiated cells (Frenster, 1972; Nakatsu et al, 1974: Frenster, 1974).
	www.euchromatin.net (647 words)

	High- and Low-mobility Populations of HP1 in Heterochromatin of Mammalian Cells -- Schmiedeberg et al. 15 (6): 2819 -- ...
		Quantitative FRAP analysis for all HP1 isoforms was performed in euchromatin (B), and heterochromatin (C).
		of a subfraction of GFP-HP1 molecules in heterochromatin.
		Heterochromatin, HP1 and methylation at lysine 9 of histone H3 in animals.
	www.molbiolcell.org /cgi/content/full/15/6/2819 (6626 words)

	Conservation of Heterochromatin Protein 1 Function -- Wang et al. 20 (18): 6970 -- Molecular and Cellular Biology
		Heterochromatin represents a cytologically visible state of heritable gene repression.
		Heterochromatin protein 1, a known suppressor of position-effect variegation, is highly conserved in Drosophila.
		Heterochromatin protein 1 modifies mammalian PEV in a dose- and chromosomal-context-dependent manner.
	mcb.asm.org /cgi/content/full/20/18/6970 (7543 words)

	Heterochromatin and chromosome evolution: a FISH probe of Cebus apella paraguayanus (Primate: Platyrrhini) developed by ...
		Heterochromatin and chromosome evolution: a FISH probe of Cebus apella paraguayanus (Primate: Platyrrhini) developed by chromosome microdissection
		Neotropical Primate karyotypes are highly variable, particularly in the heterochromatic regions, not only regarding the amount of heterochromatin, but also the composition.
		We propose that the heterochromatin observed in CAPp and CAPn is specific for these species.
	www.funpecrp.com.br /gmr/year2005/vol4-4/gmr0178_abstract.htm (224 words)

	Heterochromatin protein 1 distribution during development and during the cell cycle in Drosophila embryos -- Kellum et ...
		Heterochromatin protein 1 distribution during development and during the cell cycle in Drosophila embryos -- Kellum et al.
		is associated with the heterochromatin at the chromocenter of polytene
		heterochromatin protein 1 in the heterochromatin of the chromosomes was
	jcs.biologists.org /cgi/content/abstract/108/4/1407 (956 words)

	Euchromatin and Heterochromatin
		Euchromatin and heterochromatin are very typical examples of chromosome regions that are generally treated as segments.
		Since the demarkation of eu- and heterochromatin is such a typical component of karyotype analysis, MicroMeasure treats this type of analysis separately from other segment types (up to 12 additional segment types may be defined: see Using Segments for more information).
		Like all other structures, regions of eu-and heterochromatin must be marked along chromosomes as they are encountered.
	www.colostate.edu /Depts/Biology/MicroMeasure/Help/heteu.html (193 words)

	Drosophila Heterochromatin Protein 1 (HP1)/Origin Recognition Complex (ORC) Protein Is Associated with HP1 and ORC and ...
		Drosophila Heterochromatin Protein 1 (HP1)/Origin Recognition Complex (ORC) Protein Is Associated with HP1 and ORC and Functions in Heterochromatin-induced Silencing -- Shareef et al.
		HOAP Colocalizes with Subfractions of HP1 and ORC in Heterochromatin
		James, T.C., and Elgin, S.C.R. Identification of a nonhistone chromosomal protein associated with heterochromatin in Drosophila melanogaster and its gene.
	www.molbiolcell.org /cgi/content/full/12/6/1671 (8636 words)

	Heterochromatin: Abstracts
		transgene is found within heterochromatin, the packaging is altered to a more uniform nucleosome array, apparently reflecting the surrounding heterochromatin; a model of the nucleosome array consistent with the present data is shown.
		The relationship between Arp4 and heterochromatin protein 1 (HP1) was investigated by labeling embryos and larval tissues with antibodies to Arp4 and HP1.
		Arp4 and HP1 exhibit almost superimposable heterochromatin localization patterns, remain associated with the heterochromatin throughout prepupal development, and exhibit similar changes in localization during the cell cycle.
	www.biologie.uni-hamburg.de /b-online/ibc99/wustl/faculty/elgin/abstracts1.html (919 words)

	Association of Lsh, a Regulator of DNA Methylation, with Pericentromeric Heterochromatin Is Dependent on Intact ...
		Association of Lsh, a Regulator of DNA Methylation, with Pericentromeric Heterochromatin Is Dependent on Intact Heterochromatin -- Yan et al.
		heterochromatin is not altered in the absence of Lsh, despite
		Higher-order structure in pericentric heterochromatin involves a distinct pattern of histone modification and an RNA component.
	mcb.asm.org /cgi/content/full/23/23/8416 (6277 words)

	Unraveling heterochromatin - Nature Genetics (Site not responding. Last check: 2007-10-09)
		Together, these data suggest that the higher-order arrangement of pericentric heterochromatin is dependent not only on the presence of H3 Lys9 methylation and HP1, but on an unknown RNA component as well (Fig.
		Interestingly, the enzyme(s) responsible for mediating H3 Lys9 methylation at the inactive X chromosome is not known, but it is presumed that the structural formation and subsequent inactivation of this chromatin may be mediated, in part, by this enzyme's ability to recruit an H3 Lys9 methylation−specific binding factor, aside from HP1.
		It is uncanny that many fundamental parallels, such as the presence of RNA and H3 Lys9 methylation, exist between these two types of condensed heterochromatin, yet they seem to be functionally and structurally distinct (Fig.
	www.nature.com /ng/journal/v30/n3/full/ng0302-241.html (1360 words)

	Distinct Cytoplasmic and Nuclear Fractions of Drosophila Heterochromatin Protein 1: Their Phosphorylation Levels and ...
		Increased phosphorylation of HP1, a heterochromatin-associated protein of Drosophila, is correlated with heterochromatin assembly.
		Identification of a nonhistone chromosomal protein associated with heterochromatin in Drosophila melanogaster and its gene.
		Heterochromatin protein 1 is required for correct chromosome segregation in Drosophila embryos.
	www.jcb.org /cgi/content/full/142/2/307 (7356 words)

	Heterochromatin banding patterns in Rutaceae-Aurantioideae--a case of parallel chromosomal evolution -- Guerra et al. ...
		Heterochromatin banding patterns in Rutaceae-Aurantioideae--a case of parallel chromosomal evolution -- Guerra et al.
		Heterochromatin banding patterns in Rutaceae-Aurantioideae—a case of parallel chromosomal evolution
		of heterochromatin dispersion, proposed by Schweizer and Loidl
	www.amjbot.org /cgi/content/full/87/5/735 (5617 words)

	Dynamic relocation of epigenetic chromatin markers reveals an active role of constitutive heterochromatin in the ...
		Dynamic relocation of epigenetic chromatin markers reveals an active role of constitutive heterochromatin in the transition from proliferation to quiescence -- Grigoryev et al.
		be strongly influenced by the presence of pericentromeric heterochromatin.
		Horsley, D., Hutchings, A., Butcher, G. and Singh, P. M32, a murine homologue of Drosophila heterochromatin protein 1 (HP1), localizes to euchromatin within interphase nuclei and is largely excluded from constitutive heterochromatin.
	jcs.biologists.org /cgi/content/full/117/25/6153 (5801 words)

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