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156:. These modifications are also found in other types of DNA, but much less frequently. Cytosine methylation is the most common type, although it is not found in all eukaryotes. In humans there is increased methylation at the centromeres and telomeres, which are composed of constitutive heterochromatin. These modifications can persist through both mitosis and meiosis and are
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DNA in the center of the nucleus where it can be actively transcribed. During mitosis it is believed that constitutive heterochromatin is necessary for proper segregation of sister chromatids and centromere function. The repeat sequences found at the pericentromeres are not conserved throughout many
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domains are regions of DNA found throughout the chromosomes of eukaryotes. The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes. In humans there is significantly more constitutive
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These regions are highly condensed and epigenetically modified to prevent transcription. For the genes to be transcribed, they must have a mechanism to overcome the silencing that occurs in the rest of the heterochromatin. There are many proposed models for how the genes in these regions are
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Genetic disorders that result from mutations involving the constitutive heterochromatin tend to affect cell differentiation and are inherited in an autosomal recessive pattern. Disorders include
55:. The regions that stain darker are regions of constitutive heterochromatin. The constitutive heterochromatin stains darker because of the highly condensed nature of the DNA.
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Histone modifications are one of the main ways that the cell condenses constitutive heterochromatin. The three most common modifications in constitutive heterochromatin are
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Constitutive heterochromatin was thought to be relatively devoid of genes, but researchers have found more than 450 genes in the heterochromatic DNA of
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Constitutive heterochromatin is found more commonly in the periphery of the nucleus attached to the nuclear membrane. This concentrates the
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Some cancers are associated with anomalies in constitutive heterochromatin and the proteins involved in its formation and maintenance.
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When genes are placed near a region of constitutive heterochromatin, their transcription is usually silenced. This is known as
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heterochromatin found on chromosomes 1, 9, 16, 19 and Y. Constitutive heterochromatin is composed mainly of high copy number
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Yasuhara, Jiro C.; Wakimoto, Barbara T. (2006-06-01). "Oxymoron no more: the expanding world of heterochromatic genes".
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Angell, Roslyn R.; Jacobs, Patricia A. (1975-12-01). "Lateral asymmetry in human constitutive heterochromatin".
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48:, but their repeat composition makes them difficult to sequence, so only small regions have been sequenced.
174:(HP1). HP1 is involved in the chromatin condensing process that makes DNA inaccessible for transcription.
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Bártová, Eva; KrejÄŤĂ, Jana; HarniÄŤarová, Andrea; Galiová, Gabriela; Kozubek, Stanislav (2008-08-01).
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expressed, including the insulation, denial, integration, exploitation, and TE restraining models.
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is linked to hypomethylation of the genome and especially of satellite regions.
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repeats. In humans these regions account for about 200Mb or 6.5% of the total
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Possible models for expression of genes found in constitutive heterochromatin.
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modifications for regulation, while telomeres show more conserved sequences.
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C-banding of a human female karyotype showing constitutive heterochromatin
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Visualization of constitutive heterochromatin is possible by using the
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253:"Constitutive heterochromatin formation and transcription in mammals"
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of the cell cycle and does not participate in meiotic recombination.
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General model for duplication of heterochromatin during cell division
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Saksouk, Nehmé; Simboeck, Elisabeth; Déjardin, Jérôme (2015-01-15).
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66:, and which does not stain when using the C-banding technique.
468:"Epigenetic Codes for Heterochromatin Formation and Silencing"
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Atlas of
Genetics and Cytogenetics in Oncology and Haematology
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Lomberk, Gwen; Wallrath, Lori; Urrutia, Raul (2006-01-01).
517:"Histone Modifications and Nuclear Architecture: A Review"
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Constitutive heterochromatin is not to be confused with
62:, which is less condensed, less stable, and much less
170:that methylates H3K9, providing a binding site for
137:Constitutive heterochromatin is replicated late in
466:Richards, Eric J.; Elgin, Sarah C. R. (2002).
521:Journal of Histochemistry & Cytochemistry
437:"Heterochromatin, from Chromosome to Protein"
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435:Marie-Geneviève Mattei and Judith Luciani.
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574:"The Heterochromatin Protein 1 family"
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312:T. Strachan and A. Read (2004).
318:. Garland Publishing. pp.
197:is linked to a decrease in the
86:Heterochromatin vs. euchromatin
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485:10.1016/S0092-8674(02)00644-X
32:known as satellite repeats,
25:Constitutive heterochromatin
258:Epigenetics & Chromatin
150:histone H3-Lys9 methylation
125:Replication and epigenetics
115:position-effect variegation
95:species and depend more on
60:facultative heterochromatin
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315:Human Molecular Genetics 3
411:10.1016/j.tig.2006.04.008
172:heterochromatin protein 1
168:histone methyltransferase
591:10.1186/gb-2006-7-7-228
533:10.1369/jhc.2008.951251
146:histone hypoacetylation
105:Drosophila melanogaster
203:non-Hodgkin's lymphoma
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272:10.1186/1756-8935-8-3
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154:cytosine methylation
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447:on 27 October 2015
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152:(H3K9), and
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46:human genome
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223:"C-Banding"
92:euchromatic
64:polymorphic
632:Categories
584:(7): 228.
451:9 November
345:Chromosoma
232:2015-12-02
227:web.udl.es
209:References
97:epigenetic
42:transposon
643:Telomeres
600:1465-6906
541:0022-1554
494:0092-8674
365:0009-5915
281:1756-8935
158:heritable
618:17224041
559:18474937
502:11909520
419:16690158
381:10118235
299:25788984
201:, while
178:Diseases
78:Function
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320:256–295
290:4363358
164:SUV39H1
139:S phase
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472:Cell
453:2015
415:PMID
369:PMID
361:ISSN
324:ISBN
295:PMID
277:ISSN
186:and
36:and
638:DNA
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