Current view of the potential roles of proteins enriched on the inactive X chromosome

Abstract

X chromosome inactivation (X-inactivation) is triggered by X-linked noncoding Xist RNA, which is expressed asymmetrically from one of the two X chromosomes in females and coats it in cis to induce chromosome-wide silencing. Xist RNA is thought to play a role as a platform in recruiting proteins involved in gene silencing and heterochromatinization, which mediate serial changes in epigenetic modification of the chromatin. During the last two decades, many proteins have been shown to be enriched on the inactivated X chromosome in mouse and human. Although the biological significance of most of them for X-inactivation has not been fully established, extensive studies of these proteins should provide a better understanding of the molecular basis of how X-inactivation mediated by Xist RNA is regulated. Here, we review the potential roles of some of these proteins in the stepwise process of Xist RNA-mediated chromosome silencing.

Density imaging of heterochromatin in live cells using orientation-independent-DIC microscopy

“…The pericentric foci that we investigated as described above are a model of constitutive heterochromatin. Therefore, to ascertain the generality of our findings, we examined inactivated human X chromosomes, a classic facultative heterochromatin model ( Wutz, 2011 ; Nakajima and Sado, 2014 ; Smeets et al. , 2014 ; da Rocha and Heard, 2017 ; Jegu et al.…”

“…Importantly, under specific developmental or environmental conditions, facultative heterochromatin can lose its condensed structure and become transcriptionally active. A famous process involving facultative heterochromatin is X-inactivation, through which one of the copies of the X chromosome present in female mammals is transcriptionally silenced, creating a Barr body ( Wutz, 2011 ; Nakajima and Sado, 2014 ; Smeets et al. , 2014 ; da Rocha and Heard, 2017 ; Jegu et al.…”