Heterochromatin


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Related to Heterochromatin: Facultative heterochromatin, Constitutive heterochromatin

heterochromatin

[¦hed·ə·rō′krō·məd·ən]
(cell and molecular biology)
Specialized chromosome material which remains tightly coiled even in the nondividing nucleus and stains darkly in interphase.

Heterochromatin

 

portions of the chromosomes that remain thickened in the interval between cell divisions, that is, in the interphase (as opposed to other portions called euchromatin). Heterochromatin is sometimes closely associated with the nucleolus, forming a sort of ring or casing around it. During mitosis the heterochromatin is colored more or less darkly than the euchromatin (the phenomenon of positive or negative heteropycnosis). Heterochromatin is especially characteristic of sex chromosomes of many animal species. Heteropycnotic areas can be obtained experimentally, for example, through the action of low temperature. It is theorized that heterochromatin does not contain genes that control the development of the organism.

M. E. ASPIZ

References in periodicals archive ?
The classification proposed by Imai (1991) is based on heterochromatin location and details in chromosome size mainly among similar karyotypes are not highlighted, especially when the species have low amount of heterochromatin.
Our study connects the dots between Werner syndrome and heterochromatin disorganization, outlining a molecular mechanism by which a genetic mutation leads to a general disruption of cellular processes by disrupting epigenetic regulation," says Izpisua Belmonte.
Constitutive heterochromatin distribution in monocentric and polycentric chromosomes.
Using mouse models, they demonstrated that in the absence of the two proteins, heterochromatin collapsed into the nuclear centre.
Although the mechanisms involved in this heterochromatin loss and DNA size reduction are unknown, several processes have been proposed in other organisms, such as unequal exchange and spontaneous deletion in nonessential DNA (16,32).
Heterochromatin in yeast forms at the telomeres and propagates centromerically for about 3-4 kilobases.
What we've discovered," says Bauchan, "is that some yellow-flowered (Falcata) alfalfas, which carry genes for winter hardiness, stand persistence, and resistance to bacterial wilt, have a lower amount of heterochromatin than some of the standard, purple-flowered alfalfas.
Methylation of Lysine-9 of Histone H3: Role in Heterochromatin Modulation and Tumorigenesis
Mitosis-specific phosphorylation of histone H3 initiates primarily within pericentromeric heterochromatin during G2 and spreads in an ordered fashion coincident with mitotic chromosome condensation.
The aims of this proposal are: 1) To determine which BET proteins are important for heterochromatin maintenance; 2) To determine the mechanism of action of the key BET protein(s) in epigenetic silencing; 3) To analyse chromatin changes resulting from inhibiting of the key BET protein(s) in the selected cancer cell lines.
TFL2/LHP1, the plant homologue of animal HP1, surprisingly does not primarily localize to heterochromatin but it participates in the regulation of specific genes in euchromatic regions.
Loss of the Suv39h histone methyltransferases impairs mammalian heterochromatin and genome stability.