Germ Cell-Intrinsic and -Extrinsic Factors Govern Meiotic Initiation in Mouse Embryos

Retinoic acid ( RA) is an essential extrinsic inducer of meiotic initiation in mammalian germ cells. However, RA acts too widely in mammalian development to account, by itself, for the cell- type and temporal specificity of meiotic initiation. We considered parallels to yeast, in which extrinsic and intrinsic factors combine to restrict meiotic initiation. We demonstrate that, in mouse embryos, extrinsic and intrinsic factors together regulate meiotic initiation. The mouse RNA- binding protein DAZL, which is expressed by postmigratory germ cells, is a key intrinsic factor, enabling those cells to initiate meiosis in response to RA. Within a brief developmental window, Dazl- expressing germ cells in both XX and XY embryos actively acquire the ability to interpret RA as a meiosis- inducing signal.