Morphology, proliferation, and differentiation of undifferentiated spermatogonia in the Chinese hamster and the ram.

Abstract

AbstractThe population of undifferentiated spermatogonia was studied in whole mounted seminiferous tubules of the Chinese hamster and the ram. The morphology of the differentiating spermatogonia in the ram is also described.The nuclear morphology of the undifferentiated spermatogonia was found to vary considerably. 3H‐thymidine labeling studies in the Chinese hamster revealed that this variability is associated with the phases of the cell cycle. In both animals the undifferentiated spermatogonia were found to lie isolated (As), paired (Apr), or in groups of four, eight, or sixteen cells (Aal). We described how the varying morphology can be used to identify the composing clones of a cluster of undifferentiated spermatogonia.Cell counts performed throughout the whole cycle of the seminiferous epithelium revealed a very similar pattern of proliferation in the Chinese hamster and the ram. The number of As + Apr spermatogonia remained constant throughout the epithelial cycle. However, the occurrence of labeled and mitotic cells showed that As, Apr as well as Aal spermatogonia do proliferate. In both animals the mitotic activity of the undifferentiated spermatogonia is very low during the lifespan of A2 spermatogonia but increases considerably among A3, staying high among Intermediate spermatogonia. Thereafter, mitotic activity subsides to a lower level until the cycle repeats itself. Clones of 16 Aal in the Chinese hamster only exceptionally divide further.The results in the ram are incompatible with a scheme of stem cell renewal in which the A1 spermatogonia derive from A2 spermatogonia (Hochereau‐de Reviers et al., 1976). It is proposed that in the ram, like in rodents, the As spermatogonia are the spermatogonial stem cells and that the A1 spermatogonia derive quantitatively from the undifferentiated spermatogonia at each epithelial cycle.It could be calculated from the number of newly formed clones that both in the Chinese hamster and the ram, on the average, each As spermatogonium will have to divide several times during one epithelial cycle.Unlike in rodents, in the ram differentiation into A1 spermatogonia brings about a distinct morphologic change enabling us to observe that some Apr and rarely As spermatogonia transform into A1 spermatogonia. Thus, all undifferentiated spermatogonia are able to differentiate into A1 but the chance for this to occur increases strongly with the clonal size.