Migration and proliferation of primordial germ cells in the rat

Information about early primordial germ cell (PGC) formation and migration in rats is lacking. In utero developed and in vitro cultivated whole rat embryos were studied on days 10-13 postcoitum (p.c.). The development of the PGCs was investigated in serial sections stained for alkaline phosphatase activity. On postcoital day 10, PGCs were found in the invaginating visceral yolk sac endoderm and at the base of the allantois. At day 11 p.c. PGCs were mostly found in the ventral and lateral gut wall or in the mesenchyme between the gut and the future genital ridges. At day 12 p.c. most of the PGCs (94%) could be localised in the mesenchyme or in the future genital ridges. On postcoital day 13 almost all PGCs had reached the now-well-developed genital ridges. Quantitative measurements showed an increase in the number of PGCs from 84 at day 10 p.c. up to 2,768 at day 13 p.c. Only slight differences were found between in vivo and in vitro embryos with respect to the number of PGCs and their developmental pattern. The in vitro culture of whole rat embryos enables the discrimination between the effects of indirect (maternal) and direct action of PGC-toxic agents.