X-chromosome inactivation (XCI) in mammals relies on XIST, a long noncoding transcript that coats and silences the X chromosome in cis. Vallot et al. have discovered a long noncoding RNA, XACT, that is expressed from and coats the active X chromosome in human pluripotent cells. In the absence of XIST, XACT is expressed from both X chromosomes in humans but not in mice, suggesting a unique role for XACT in the control of human XCI initiation.
Posted by Nicola Brunetti-Pierri, MD