On the origin of the human germline.

Abstract

In mice, primordial germ cells (PGCs), the precursors of eggs and sperm, originate from pre-gastrulation post-implantation embryos. By contrast, the origin of human PGCs (hPGCs) has been less clear and has been difficult to study due to the technical and ethical constraints that limit direct studies on human embryos. In recent years, however, in vitro simulation models using human pluripotent stem cells, together with surrogate non-rodent mammalian embryos, have provided insights and experimental approaches to address this question. Here, we review these studies, which suggest that the posterior epiblast and/or the nascent amnion in pre-gastrulation human embryos is a likely source of hPGCs, and that a different gene regulatory network controls PGCs in humans compared to the mouse. Such studies on the origins and mechanisms of hPGC specification prompt further consideration of the somatic cell fate decisions that occur during early human development.