Wu, J. et al. Nature 521, 316–321 (2015).

Embryonic stem cells derived from the mouse inner cell mass and epiblast stem cells (EpiSCs) from the post-implantation embryo (corresponding to 'primed' human embryonic stem cells) represent two time points in development. Wu et al. reasoned that spatial positioning in the early embryo may also define other distinct stem cell populations. By optimizing epiblast cell culture conditions, they identified stable, region-selective pluripotent stem cells (rsEpiPSCs) that resemble EpiSCs but selectively engraft to the posterior of epiblast-stage embryos. rsEpiPSCs are derived with perfect success, and they proliferate more rapidly and show high cloning efficiencies compared with traditional EpiSCs. The new cell type has distinct transcriptional, methylation and metabolic profiles. Similar culture conditions can derive human rsEpiPSCs. The ease of isolating and manipulating these cells makes them valuable for future stem cell work.