Germ cell specification in mammals

PGCs, primordial germ cells, are germ cell precursors which arise early in development in mammals and lower organisms. In lower organisms, the ‘germ plasm’, the accumulation of granular cytoplasmic components containing ribonucleoproteins and RNAs, is inherited maternally, hence the PGCs form by ‘preformation’. Mammals, on the other hand, do not inherit material but induce germ cells in epiblast (~E6.0) by BMP4 signaling and various epigenetic modifications, by ‘epigenesis’. The germ cells go through more changes and migrate to gonadal ridges, where they serve as gametogonia. In order to underdtand the mechanism of PGC specification and their scientific/clinical value, in vitro techniques have been developed as well as in vivo. In this paper, we will explore how gametes are formed, how germ cells are specified and how they migrate. Finally we will go through the advancements in embryonic stem cell and embryonic germ cell cultures.