Undifferentiated spermatogonia and their role in the seasonally fluctuating spermatogenesis in the mink, Mustela vison.

Three classes of spermatogonia were discerned: undifferentiated A spermatogonia (Ais, Apr, Aal), differentiated A spermatogonia (A1, A2) and differentiated B spermatogonia (B1, B2). Cell counts performed throughout the seminiferous epithelial cycle in the breeding season revealed that the number of undifferentiated A spermatogonia was lowest in the presence of differentiated A1 and A2 spermatogonia during stages I-II to III-IV. In the non-breeding season a highly significant increase in the number of undifferentiated spermatogonia occurred in an animal with moderate germ cell loss exclusively at stages I-II to III-IV, when the A1 and A2 spermatogonia degenerated. In three other animals involved in severe cell loss, enhanced proliferation of undifferentiated spermatogonia was much greater than in the animal mentioned above. These result suggest the presence of a feedback mechanism between undifferentiated and differentiated spermatogonia, which may be considered to play an important role in regulating seasonal changes in spermatogonial proliferation.