Making Germ Cells from Human Embryonic Stem Cells

Abstract

Human embryonic stem cells are proliferating, self-renewing cells that have the great potential of differentiating into diverse cell types in vivo and in vitro. Investigations on human embryonic stem cells have allowed us to probe critical early stages of development, including the mechanisms of pluripotency, lineage specification, the formation and differentiation of specific cell and tissue types, and the underlying molecular and genetic mechanisms. In addition to the three main tissue lineages, embryonic stem cells can also give rise to the germ cell lineage, which produces the male or female gametes. With the difficulties of studying early human germ cell development in vivo, stem cells can provide a unique model and window into human germ cell differentiation. Further, as infertility is quite common in humans, most often due to defects in sperm and egg quantity or quality, embryonic stem cells and the recently discovered induced pluripotent stem cells might one day provide clinical applications for the treatment of infertility and reproductive disorders. Thus, stem cells have the great potential to revolutionize regenerative and reproductive medicine and numerous cutting-edge investigations and techniques are underway. This chapter summarizes our current understanding of the earliest events of human germ cell formation and gamete differentiation both in vivo and in vitro and the genetic requirements of this process as resolved from both human and animal studies. We also review the current literature on the formation of germ cells from embryonic stem cells and, finally, discuss needed future improvements and clinical implications of this work.