Proliferative activity of the developing seminiferous epithelium during prespermatogenesis in the golden hamster testis measured by bromodeoxyuridine labeling.

Bromodeoxyuridine (BrdU)-labeling was used to study the cell kinetics of the developing seminiferous epithelium in the testes of golden hamsters aged 10.5 to 27.5 days post conception (dpc), i.e., during a period beginning one developmental day before testicular differentiation (11.5 dpc) and extending to the appearance of the first "mature" spermatogonia. Supporting (Sertoli) cells continuously proliferate throughout the period studied. Labeling indices amount to about 30% between the 10.5th and 16.5th dpc, and subsequently decrease to levels below 10% on the 26.5th and 27.5th dpc. Germ cells (prespermatogonia) proliferate between the 10.5th and 15.5th dpc and again, after a period of mitotic quiescence, from the 24.5th dpc onwards. This pattern of prespermatogonial proliferation substantiates and further specifies the successive appearance of M-prespermatogonia (10.5th to 15.5th dpc: proliferating), T1-prespermatogonia (16.5th to 23.5th dpc: quiescent), and T2-prespermatogonia (24.5th to 27.5th dpc: proliferating). Thus, the M-prespermatogonial phase of germ cell proliferation is shown to commence at least 24 h before testicular differentiation. Transitions from M- to T1-phase and from T1- to T2-phase are rather abrupt. Both the latter observation and the comparison with oogonial development in the female at the corresponding time (onset of meiosis) indicate the presence of an underlying control mechanism operative during prespermatogenic development. Due to different nuclear staining patterns, the BrdU-labeling method allows temporal subdivision of the S-phase, thus opening up prospects of more detailed cell-kinetic analyses of the seminiferous epithelium.