LAUSR

This study was a single time‐point mapping of various immunostaining patterns revealed with the proliferating cell nuclear antigen (PCNA) PC10 antibody in spermatogonia at the immature pole of the testis of the Blue shark (Prionace glauca). Scattered in the stroma of the germinal ridge that demarcates the immature pole's outer boundary were nests of variously immunoreactive A‐spermatogonia, each flanked by a fusiform cell. Spermatocysts were assembled from niche‐derived stromal cells, displaced A‐progenitors, and their progeny, which showed one of two main immunostaining patterns (i.e., an uneven light brown/globular and homogeneous dark [hod] brown appearance). The testes of wild‐caught Prionace showed two conditions, namely, extensive multinucleate cell death (MNC) near the mitosis–meiosis transition or an early recovery phase from the latter showing vacuolated areas. Both the proportion of cysts with immature Bhod‐spermatogonia and the frequency of mitotic figures in such cysts in the early recovery testis condition were significantly higher than the comparable parameters in MNC testis condition. Moreover, the post‐MNC recovery phase revealed a decrease in the proportion of immature cysts with uneven light brown/globular‐like spermatogonia. The protracted spread of a cell cycle signal in an anatomically discrete, syncytially connected spermatogonial clone manifests as different PCNA immunoreactivities.