Kinetics of gametogenesis. II. Comparative autoradiographic studies of oogonia and multiplying prospermatogonia of the Wistar rat.

In the rat the last generation of oogonia and multiplying prospermatogonia (M-prospermatogonia), frequently arranged in synchronized clusters, enters mitosis on about day 17 post conception (p.c.). The duration of the S-phase D-S-Duration and the minimal generation time Tmin of both kinds of "gonia" were determined by the method of labeled mitoses (22 female and 22 male fetuses derived from 11 pregnant rats were sacrificed from 2 to 22 h after a single i.p. injection of 3H-thymidine on day 17 p.c.). Three curves, derived from the labeled prophases, metaphases and the postmitotic descendents of oogonia and M-prospermatogonia--oocytes and primary transitional prospermatogonia (T1-prospermatogonia)--were evaluated. It was demonstrated that the curves as well as the calculated values of D-S-Duration and Tmin are very similar for oogonia and M-prospermatogonia. D-S-Duration ranged from about 10 to 12.5h (10 h read off from the curves of labeled metaphases), Tmin from 16.5 to 18 h (16.5 h read off from the curves of labeled metaphases).