Monoallelic gene targeting in hypoblast stem cells reveals X chromosome inactivation

We recently isolated hypoblast stem cells (HypoSC), which are related to embryonic stem (ES) cells. ES cells efficiently perform homologous recombination (HR) and lack X chromosome inactivation (Xi), but it is unknown whether the same applies to HypoSC. Using the X-linked hypoxanthine phosphoribosyl transferase (HPRT) gene, we find that HypoSC perform HR with similar frequency as ES cells. Monoallelic targeting in female HypoSC eliminated HPRT gene expression, implying epigenetic inactivation of the other allele. Although density-induced differentiation complicated selection, the targeted clones maintained their original properties. These results will facilitate targeted genetic manipulation of HypoSC and the study of Xi.

► We demonstrate homologous recombination (HR) in hypoblast stem cells (HypoSC).
► We targeted the X-linked hypoxanthine phosphoribosyl transferase (HPRT) gene.
► Targeting efficiency was high, similar to that seen in embryonic stem cells.
► In female HypoSC, the non-targeted HPRT allele was not expressed.
► Thus HypoSC efficiently perform HR and likely exhibit X chromosome inactivation.