Two classes of spermatogonial stem cells in the monkey (Cercopithecus aethiops)

Abstract

To analyze the behavior of spermatogonia in the monkey, the cytological features, topographical arrangement and frequency of the two classes of type A (A 1, A 2) and the four classes of type B (B 1–B 4) spermatogonia were determined in dissected tubules, fixed in Carnoy, stained with hematoxylin and mounted “in toto.” The capacity of spermatogonia to divide was also analyzed in radioautographed testicular sections from an animal injected with tritiated thymidine. The type A 1 spermatogonia, characterized by nuclei containing deeply stained, finely granulated chromatin, were found to be non‐dividing elements. The type A 2 spermatogonia, characterized by nuclei showing palely stained, coarsely granular chromatin, all divided in stages IX–X of the cycle of the seminiferous epithelium to yield equal numbers of new type A 2 cells and type B 1 spermatogonia. The type B 1, as the other type B cells, were characterized by nuclei containing granules or flakes of deeply stained chromatin. While the type A 2 spermatogonia remained dormant until stage IX of the following cycle, the type B 1 cells all divided during stage XII to yield twice their number of type B 2 spermatogonia. These, in stage II, divided to give twice as many type B 3, which, in stage IV, divided to produce twice as many type B 4 spermatogonia. Lastly, in stage VI, the latter elements all divided to yield spermatocytes. Thus, the type A 1 spermatogonia, did not appear to be actively involved in the production of spermatocytes and were tentatively considered as “reserve stem cells;” the type A 2 spermatogonia, were identified as “renewing stem cells.”