University of Rome TOR Vergata

Laboratory for the study of mouse primordial germ cells

Prof. Massimo De Felici

The life history of PGCs

in the mouse and human embryo

Primordial germ cells (PGCs) are the founders of the gametes. They arise at the earliest stages of embryonic development and migrate to the gonadal ridges, where they differentiate into oogonia/oocytes in the ovary and prospermatogonia in the testis. One of the most  fascinating characteristic of these cells is their double nature of highly specialised cells that, at the same time, maintain their differentiation totipotency to pass on to gametes. How this is realised is not known. However, over the last two decades important aspects of PGC development and differentiation have been revealed.

           In the mouse embryo, a cluster of about 50 PGCs can be detected using histochemistry staining for alkaline phosphatase enzyme or other markers (i.e. Stella. Oct4) in gastrulating embryos around 7-7.25 days post coitum (dpc) in the extraembryonic mesoderm at the base of the amniotic fold. From this region, PGCs spread into the mesoderm of the primitive streak, and the endoderm of the yolk sac and hind gut. At 10 dpc, they begin to move by active migration up the dorsal mesentery and into the gonadal ridges where, around 12.5 dpc, they differentiate into oogonia/oocytes and prospermatogonia in the ovary and testis, respectively.

In the human embryo, PGCs can be recognised at around 3 weeks of gestation in the mesoderm/endoderm of the yolk sac. Following the morphogenetic movements of the embryo during the 4th week they enter into the embryo engulfed in the wall of the hind gut. Between 5th-6th week they migrate from the gut tube via the dorsal mesentery to the gonadal ridges. PGCs continue to multiply by mitosis during their migration and after arrival into the gonadal ridges. Around the end of 6th week testicular differentiation of the gonads become apparent with the formation of testicular cords by differentiating Sertoli cells; PGCs can be now called prospermatogonia. Similarly, in the female proliferating PGCs within the differentiating ovary (8-26 weeks) are called oogonia.