Distinct pluripotent stem cells can be generated from different mouse embryonic cell types: embryonic stem cells (ESCs) from the inner cell mass(ICM); epiblast stem cells (EpiSCs) from the ICM-derived epiblast; and embryonic germ cells (EGCs) from primordial germ cells (PGCs). Since PGCs originate from the epiblast in vivo, what is the relationship between EpiSCs and PGCs? On ,Katsuhiko Hayashi and Azim Surani now report that EpiSCs can generate unlimited amounts of PGCs. By monitoring the expression of a Blimp1(the key PGC determinant) reporter transgene in EpiSCs, they show that self-renewing EpiSCs, unlike ESCs, spontaneously generate a continuous stream of PGCs, some of which differentiate into oocyte-like cells when co-cultured with female gonadal cells. These PGCs can also de-differentiate into pluripotent cells that resemble EGCs rather than EpiSCs, indicating that the epigenetic memory of the EpiSCs and PGCs has been erased. As mouse EpiSCs resemble human ESCs, this study could provide an inroad into studying both early human and mouse germ cell development.
