TET knockout cells transit between pluripotent states and exhibit precocious germline entry

TET1, TET2 and TET3 are DNA demethylases with critical roles in development and differentiation. To assess the contributions of TET proteins to cell function during early development, single and compound knockouts of Tet genes in mouse pluripotent embryonic stem cells (ESCs) were generated. Here we show that TET proteins are not required to transit between naïve, formative and primed pluripotency. Moreover, ESCs with double-knockouts of Tet1 and Tet2 or triple-knockouts of Tet1, Tet2 and Tet3 are phenotypically indistinguishable. These TET-deficient ESCs exhibit differentiate defects; they fail to activate somatic gene expression and retain expression of pluripotency transcription factors. Therefore, TET1 and TET2, but not TET3 act redundantly to facilitate somatic differentiation. Importantly however, TET-deficient ESCs can differentiate into primordial germ cell-like cells (PGCLCs), and do so at high efficiency in the presence or absence of PGC-promoting cytokines. Moreover, acquisition of a PGCLC transcriptional programme occurs more rapidly in TET-deficient cells. These results establish that TET proteins act at the juncture between somatic and germline fates: without TET proteins, epiblast cell differentiation defaults to the germline.