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During mitosis it is believed that constitutive heterochromatin is necessary for proper segregation of sister chromatids and centromere function. [6] The repeat sequences found at the pericentromeres are not conserved throughout many species and depend more on epigenetic modifications for regulation, while telomeres show more conserved sequences.
All cells of a given species package the same regions of DNA in constitutive heterochromatin, and thus in all cells, any genes contained within the constitutive heterochromatin will be poorly expressed. For example, all human chromosomes 1, 9, 16, and the Y-chromosome contain large regions of constitutive heterochromatin. In most organisms ...
The family of heterochromatin protein 1 (HP1) ("Chromobox Homolog", CBX) consists of highly conserved proteins, which have important functions in the cell nucleus.These functions include gene repression by heterochromatin formation, transcriptional activation, regulation of binding of cohesion complexes to centromeres, sequestration of genes to the nuclear periphery, transcriptional arrest ...
Function [ edit ] CENPA is a protein which epigenetically defines the position of the centromere on each chromosome, [ 7 ] determining the position of kinetochore assembly and the final site of sister chromatid cohesion during mitosis .
Establishment of sister chromatid cohesion is the process by which chromatin-associated cohesin protein becomes competent to physically bind together the sister chromatids. In general, cohesion is established during S phase as DNA is replicated, and is lost when chromosomes segregate during mitosis and meiosis .
This nuclear protein moves to the centromeres during mitosis and functions as a histone methyltransferase, methylating lysine-9 of histone H3. Overall, it plays a vital role in heterochromatin organization, chromosome segregation , and mitotic progression. [ 6 ]
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[49] [50] [47] Senescent cells undergo chromatin landscape modifications as constitutive heterochromatin migrates to the center of the nucleus and displaces euchromatin and facultative heterochromatin to regions at the edge of the nucleus.