Exit from Naive Pluripotency Induces a Transient X Chromosome Inactivation-like State in Males

A hallmark of naive pluripotency is the presence of two active X chromosomes in females. It is not clear whether prevention of X chromosome inactivation (XCI) is mediated by gene networks that preserve the naive state. Here, we show that robust naive pluripotent stem cell (nPSC) self-renewal represses expression of Xist, the master regulator of XCI. We found that nPSCs accumulate Xist on the male X chromosome and on both female X chromosomes as they become NANOG negative at the onset of differentiation. This is accompanied by the appearance of a repressive chromatin signature and partial X-linked gene silencing, suggesting a transient and rapid XCI-like state in male nPSCs. In the embryo, Xist is transiently expressed in males and in females from both X chromosomes at the onset of naive epiblast differentiation. In conclusion, we propose that XCI initiation is gender independent and triggered by destabilization of naive identity, suggesting that gender-specific mechanisms follow, rather than precede, XCI initiation. [Display omitted] •A robust naive pluripotent transcription factor network abolishes expression of Xist•Xist accumulates on the male X and both female Xs at the onset of differentiation•Males undergo transient and rapid partial XCI•Male XCI is triggered by downregulation of the naive identity Silva and colleagues report that the initiation of X chromosome inactivation takes place in males and on both X chromosomes in females. This is transient and rapid and is triggered by downregulation of naive pluripotent transcription factors during the onset of differentiation.