Derivation and Differentiation of Human Embryonic Germ Cells

Embryonic germ (EG) cells are pluripotent stem cells derived from primordial germ cells (PGCs) that arise in the late embryonic and early fetal period of development. Embryonic stem (ES) cells were first derived from the inner cell mass of mouse pre-implantation embryos, and EG cells were initially derived from mouse PGCs. Subsequently, EG cells have been derived from chicken, pig, and human PGCs. Pig, chicken, and mouse EG cells have been demonstrated to contribute to experimentally produced chimeric animals, including germline transmission in the latter two species. Human EG cells can be derived from PGCs by using methods similar to those used to derive mouse EG cultures. Like mouse embryonic stem and EG cells, human EG cells require leukemia inhibitory factor (LIF) for proliferation as undifferentiated stem cells. Unlike mouse EG cells, however, human EG cells do not readily lose their dependence on exogenous cytokines and factors supplied by the feeder layer, and they have a higher frequency of spontaneous differentiation into embryoid bodies (EBs). Although EBs are a loss to the pluripotent stem cell population, they are a source of cells expressing markers of mature cellular phenotypes, as well as their presumed progenitors and precursors. Cells that retain a high capacity for cell proliferation and express makers of multiple lineages can be isolated from EBs, and can be used in a variety of in vitro and in vivo differentiation paradigms. The current challenges are to match individual EB-derived (EBD) cultures to desired endpoints, and to enrich or purify populations of cells within EBD cultures to more specifically address biological requirements. © 2009