Human Embryonic Stem Cells and Germ Cell Development

Abstract

Embryonic stem cells (ESCs) are derived from the inner cell mass (ICM) of blastocysts and are characterized by the ability to differentiate into the three primary germ layers. Evidence shows, however, that the cells of the ICM and derived ESCs are not identical. Expression of early germ cell-specific markers in undifferentiated ESCs and the ability of ESCs to differentiate into functional germ cells in vitro suggest that early germ cells and ESCs may be closely related cell types. Proteins such as Dazl, Pumilio, and Nanos are essential for specification, maintenance, and maturation of the germ cell population and are conserved from invertebrates to vertebrates. Homologs of these RNA-binding proteins have recently been identified in human germ cells as well as in human ESCs, suggesting a role in differentiation of ESCs towards the germ cell lineage. This review summarizes properties of ESCs and germ cells and highlights the importance of protein complex formation in differentiation of ESCs towards the germ cell lineage.