Loss of sex-determining region Y-box 2 (Sox2) captures embryonic stem cells in a primed pluripotent state

Two main pluripotent cell lines can be established from the preimplantation and postimplantation mouse embryo as naïve embryonic stem cells (ESCs) and primed epiblast stem cells (EpiSCs), respectively. Although the two pluripotent states are interconvertible, the molecular mechanism controlling the transition between naïve and primed pluripotency remains to be fully elucidated. Here, by performing a CRISPR-based loss-of-function screen in ESCs, we identify Sox2 involved in the repression of lineage-specification marker brachyury (T). Upon Sox2 ablation in ESCs, two populations of cells mutually exclusive for CDX2 (trophectoderm marker) and T expression can be observed. T-positive cells display features resembling the salient characteristics of EpiSCs including molecular and functional properties. By using genetic ablation approach, we show that acquisition and maintenance of primed pluripotency in Sox2 null T-positive cells heavily depend on fibroblast growth factor (Fgf) and Nodal, which is produced in an autocrine manner in these cells. We further demonstrate that Sox3 compensates for the absence of Sox2 in maintaining the primed state of Sox2-null pluripotent cells. Establishment of Sox2-deficient pluripotent cells will enable the elucidation of the mechanisms controlling the transition of cells between different states of pluripotency.