Mechanism of Mouse Germ Cell Specification: A Genetic Program Regulating Epigenetic Reprogramming

Abstract

Specification of germ cells and their segregation fromsomatic neighbors is one of the most decisive events ofearly development in animals. There are two key routes tothe initiation of the germ cell lineage. One is through theinheritance of preformed germ cell determinants or germplasm as observed in Drosophila melanogaster andCaenorhabditis elegans (Eddy 1975; Wylie 1999). Theother route, which is sometimes referred to as the stemcell model, occurs in the mouse, where a group ofpluripotent cells are first established with seeminglyequivalent potential from which both germ cells and somatic cells are derived (McLaren 1999; Saitou et al.2003). These two modes of germ cell specification are referred to as preformation and epigenesis, respectively(Fig. 1). Although preformation is observed in mostmodel organisms, it is apparently a less dominant modeof germ cell specification, and epigenesis may be ancestral to the Metazoa (Extavour and Akam 2003)...