Editing X-inactivation (section)

===Silencing===
The inactive X chromosome does not express the majority of its genes, unlike the active X chromosome. This is due to the silencing of the Xi by repressive [[heterochromatin]], which compacts the Xi DNA and prevents the expression of most genes.

Compared to the Xa, the Xi has high levels of [[DNA methylation]], low levels of [[histone acetylation]], low levels of [[histone H3]] lysine-4 [[histone methylation|methylation]], and high levels of histone H3 lysine-9 methylation and H3 lysine-27 methylation mark which is placed by the [[Polycomb recruitment in X chromosome inactivation|PRC2 complex recruited by Xist]], all of which are associated with gene silencing.<ref>{{cite journal | vauthors = Ng K, Pullirsch D, Leeb M, Wutz A | title = Xist and the order of silencing | journal = EMBO Reports | volume = 8 | issue = 1 | pages = 34–9 | date = January 2007 | pmid = 17203100 | pmc = 1796754 | doi = 10.1038/sj.embor.7400871 | format = Review Article | quote = [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1796754/ Table 1 Features of the inactive X territory] }} – Originated from;<br />{{cite journal | vauthors = Chow JC, Yen Z, Ziesche SM, Brown CJ | title = Silencing of the mammalian X chromosome | journal = Annual Review of Genomics and Human Genetics | volume = 6 | pages = 69–92 | year = 2005 | pmid = 16124854 | doi = 10.1146/annurev.genom.6.080604.162350 }}<br />{{cite journal | vauthors = Lucchesi JC, Kelly WG, Panning B | title = Chromatin remodeling in dosage compensation | journal = Annual Review of Genetics | volume = 39 | pages = 615–51 | year = 2005 | pmid = 16285873 | doi = 10.1146/annurev.genet.39.073003.094210 | citeseerx = 10.1.1.328.2992 }}</ref> [[PRC2]] regulates [[chromatin]] compaction and [[chromatin remodeling]] in several processes including the [[DNA damage (naturally occurring)|DNA damage]] response.<ref name="pmid28758948">{{cite journal |vauthors=Veneti Z, Gkouskou KK, Eliopoulos AG |title=Polycomb Repressor Complex 2 in Genomic Instability and Cancer |journal=Int J Mol Sci |volume=18 |issue=8 |pages= 1657|date=July 2017 |pmid=28758948 |pmc=5578047 |doi=10.3390/ijms18081657 |doi-access=free }}</ref> Additionally, a histone variant called macroH2A ([[H2AFY]]) is exclusively found on [[nucleosome]]s along the Xi.<ref name="Costanzi1998">{{cite journal | vauthors = Costanzi C, Pehrson JR | title = Histone macroH2A1 is concentrated in the inactive X chromosome of female mammals | journal = Nature | volume = 393 | issue = 6685 | pages = 599–601 | date = June 1998 | pmid = 9634239 | doi = 10.1038/31275 | bibcode = 1998Natur.393..599C | s2cid = 205001095 }}</ref><ref name="Costanzi2000">{{cite journal | vauthors = Costanzi C, Stein P, Worrad DM, Schultz RM, Pehrson JR | title = Histone macroH2A1 is concentrated in the inactive X chromosome of female preimplantation mouse embryos | journal = Development | volume = 127 | issue = 11 | pages = 2283–9 | date = June 2000 | doi = 10.1242/dev.127.11.2283 | pmid = 10804171 | url = http://dev.biologists.org/cgi/reprint/127/11/2283.pdf }}</ref>