The Role of Xist in X-Chromosome Dosage Compensation

In each somatic cell of a female mammal one X chromosome is transcriptionally silenced via X-chromosome inactivation (XCI), initiating early in development. Although XCI events are conserved in mouse and human postimplantation development, regulation of X-chromosome dosage in preimplantation development occurs differently. In preimplantation development, mouse embryos undergo imprinted form of XCI, yet humans lack imprinted XCI and instead regulate gene expression of both X chromosomes by dampening transcription. The long non-coding RNA Xist/XIST is expressed in mouse and human preimplantation and postimplantation development to orchestrate XCI, but its role in dampening is unclear. In this review, we discuss recent advances in our understanding of the role of Xist in X chromosome dosage compensation in mouse and human.