Initial phases of the rat testis differentiation in vitro.

Rat gonadal primordia with their supporting mesonephroi were explanted in vitro at the undifferentiated stage (12 days 16 h after fertilization), at the outset of testicular differentiation (13 days 9 h) or when already containing seminiferous cords. The younger foetuses were sexed with the sex chromatin test in the amniotic membrane. The basal medium was CMRL 1066 and the culture period, 1 to 4 days. Testicular differentiation resulted from the appearance of large clear cells, the primordial Sertoli cells, and from their aggregation into seminiferous cords. Addition of 15% foetal calf serum to the medium prevented the differentiation of seminiferous cords, but large clear cells appeared. In testes from 14- or 15-day-old foetuses, the seminiferous cords disintegrated under the influence of serum. The serum did not prevent the differentiation of Sertoli cells, but impaired organogenesis or maintenance of the early seminiferous cords. The results support previous histological observations on the initial stages of testicular differentiation.