Epigenetic regulation during the differentiation of stem cells to germ cells.

Gametogenesis is an essential process to ensure the transfer of genetic information from one generation to the next. It also provides a mechanism by which genetic evolution can take place. Although the genome of primordial germ cells (PGCs) is exactly the same with somatic cells within an organism, there are significant differences between their developments. For example, PGCs eventually undergo meiosis to become functional haploid gametes, and prior to that they undergo epigenetic imprinting which greatly alter their genetic regulation. Epigenetic imprinting of PGCs involves the erasure of DNA methylation and the reestablishment of them during sperm and oocyte formation. These processes are necessary and important during gametogenesis. Also, histone modification and X-chromosome inactivation have important roles during germ cell development. Recently, several studies have reported that functional sperm or oocytes can be derived from stem cells in vivo or in vitro. To produce functional germ cells, induction of germ cells from stem cells must recapitulate these processes similar to endogenous germ cells, such as epigenetic modifications. This review focuses on the epigenetic regulation during the process of germ cell development and discusses their importance during the differentiation from stem cells to germ cells.