Primordial germ cell proliferation in fetal testes in mouse strains with high and low incidences of congenital testicular teratomas.

The development of genital ridges in mouse strains were compared with high and low susceptibility to teratocarcinogenesis. The number of dividing primordial germ cells (PGC) was low at 12 days of gestation. The number increased sharply at 13 days and decreased precipitously by 15 days of gestation. The period of high mitotic activity closely paralleled the period of susceptibility to experimentally induced teratocarcinogenesis. Testes that had a long proliferative period had a higher incidence of teratomas than those that had a short proliferative period. A group of fetuses was identified that had markedly fewer than normal PGC. The incidence of teratomas in this group was very high, and nearly all growths were bilateral.