Proliferation of spermatogonia and Sertoli cells in maturing mice

Spermatogonial proliferation was studied in mice from day 13 p.p. when the seminiferous epithelium is incomplete, until week 12 p.p. when a steady state at adult levels has been attained. Counts of undifferentiated, A1 and intermediate spermatogonia and primary spermatocytes in stages IV and IX of the cycle of the seminiferous epithelium were made in whole mounted seminiferous tubules. Sertoli cell proliferation was studied in a separate series from 6 to 14 days p.p. employing the 3H-thymidine labeling index. It appeared that 1. Sertoli cell proliferation stops at day 12 whereafter the cells obtain their adult appearance; 2. The numbers of stem cell spermatogonia and the production of differentiating A1 spermatogonia increase almost twofold between day 13 and week 12; 3. The efficiency of the divisions of the differentiating A1-B spermatogonia is similar to that in the adult throughout this period; 4. At all ages studied, the cell counts revealed an almost constant numerical relationship between Sertoli cells and germ cells, which suggests a function of Sertoli cells in the regulation of spermatogonial proliferation.