Fig. 7.

A proposed model for germ cell commitment in mammals. The germline comprises all cells whose descendants include gametes. At fertilization, the totipotent zygote has the capacity to give rise to all cell lineages. As development proceeds, extraembryonic and somatic lineages differentiate away from the germline. PGCs (blue cells) are induced from the epiblast, preserving the germline, but also maintaining a broad developmental potential. At PGC colonization of the gonads, expression of a germ cell program—marked by DAZL—is induced in germline cells by the genital ridge. Our studies show that DAZL is necessary for the restriction of developmental potential in the germline, resulting in the determination of germ cells (pink cells). Determined germ cells then undertake gametogenesis and must cycle through fertilization to reestablish totipotency and continue the germline cycle in a new diploid individual. ExE, extraembryonic ectoderm.