Mammalian X-chromosome inactivation and the XIST gene

X-chromosome inactivation is a unique developmental event that results in the cis-limited transcriptional inactivation of most genes on one of the two X chromosomes in female mammals. Studies in both human and mouse have demonstrated that X inactivation requires the presence in cis of a locus, the X-inactivation center, that is thought to be involved in the initiation and/or spreading of the inactivation signal in early development. Identification and characterization of a gene, XIST, which is located at or near the X-inactivation center and which is expressed specifically from the inactive X chromosome in both humans and mouse, suggests that it may be involved in X inactivation.