Preventing erosion of X-chromosome inactivation in human embryonic stem cells

Cloutier et al. discover that human embryonic stem cells (hESCs) cultured with media containing inhibitors of GSK3 proteins undergo erosion of X-chromosome inactivation, which equalizes X-linked gene expression between females and males. The findings inform the faithful culture of hESCs. X-chromosome inactivation is a paradigm of epigenetic transcriptional regulation. Female human embryonic stem cells (hESCs) often undergo erosion of X-inactivation upon prolonged culture. Here, we investigate the sources of X-inactivation instability by deriving new primed pluripotent hESC lines. We find that culture media composition dramatically influenced the expression of XIST lncRNA, a key regulator of X-inactivation. hESCs cultured in a defined xenofree medium stably maintained XIST RNA expression and coating, whereas hESCs cultured in the widely used mTeSR1 medium lost XIST RNA expression. We pinpointed lithium chloride in mTeSR1 as a cause of XIST RNA loss. The addition of lithium chloride or inhibitors of GSK-3 proteins that are targeted by lithium to the defined hESC culture medium impeded XIST RNA expression. GSK-3 inhibition in differentiating female mouse embryonic stem cells and epiblast stem cells also resulted in a loss of XIST RNA expression. Together, these data may reconcile observed variations in X-inactivation in hESCs and inform the faithful culture of pluripotent stem cells.

Automated summary

Cloutier et al. discovered that inhibitors of GSK3 proteins in the culture medium can reduce X-chromosome inactivation in human embryonic stem cells, leading to equal expression of X-linked genes between females and males. These findings are significant for the faithful culture of hESCs.