Gene regulation in time and space during X-chromosome inactivation

X chromosome inactivation in mammals involves chromosome-wide gene silencing at one X chromosome in cells of females, a process that requires complex spatiotemporal regulation. Recent findings provide new insights into the mechanisms and dynamics of X chromosome inactivation and the accompanying 3D reshaping of the chromosome. X-chromosome inactivation (XCI) is the epigenetic mechanism that ensures X-linked dosage compensation between cells of females (XX karyotype) and males (XY). XCI is essential for female embryos to survive through development and requires the accurate spatiotemporal regulation of many different factors to achieve remarkable chromosome-wide gene silencing. As a result of XCI, the active and inactive X chromosomes are functionally and structurally different, with the inactive X chromosome undergoing a major conformational reorganization within the nucleus. In this Review, we discuss the multiple layers of genetic and epigenetic regulation that underlie initiation of XCI during development and then maintain it throughout life, in light of the most recent findings in this rapidly advancing field. We discuss exciting new insights into the regulation of X inactive-specific transcript (XIST), the trigger and master regulator of XCI, and into the mechanisms and dynamics that underlie the silencing of nearly all X-linked genes. Finally, given the increasing interest in understanding the impact of chromosome organization on gene regulation, we provide an overview of the factors that are thought to reshape the 3D structure of the inactive X chromosome and of the relevance of such structural changes for XCI establishment and maintenance.

Automated summary

This article reviews the recent advances in understanding the mechanisms of X chromosome inactivation (XCI) and the accompanying chromosome reshaping. It discusses the genetic and epigenetic regulation underlying the initiation and maintenance of XCI, focusing on the role of XIST, the silencing of X-linked genes, and the structural changes of the inactive X chromosome.