Capture of mouse and human stem cells with features of formative pluripotency [mouse, RNA-Seq 2]

Pluripotent cells emerge as a naïve founder population in the blastocyst, acquire capacity for germline and soma formation, and then undergo lineage priming. Mouse embryonic stem (ES) cells and epiblast stem cells (EpiSCs) respectively represent the initial naïve and final primed phases of pluripotency. Here we investigated the intermediate formative stage. Using minimal exposure to specification cues, we derived stem cells from formative mouse epiblast. Unlike ES cells or EpiSCs, formative stem (FS) cells responded directly to germ cell induction. They colonised somatic tissues and germline in chimaeras. Whole transcriptome analyses showed similarity to pre-gastrulation formative epiblast. Signal responsiveness and chromatin accessibility features reflect lineage capacitation. Furthermore, FS cells showed distinct transcription factor dependencies, relying critically on Otx2. Finally, FS cell culture conditions applied to human naïve cells or embryos supported expansion of similar stem cells, consistent with a conserved staging post on the trajectory of mammalian pluripotency.