Distribution of the spermatogonial subpopulations during the stages of the epithelial cycle and their relative position along the basal membrane of the seminiferous tubules

The function of the seminiferous epithelium is maintained by the biological activity of spermatogonial stem cells (SSCs), which are essential for the maintenance of spermatogenesis and for the continuous production of sperm. In literature, little is known about the location of SSCs and the spermatogonial stem niche, and whether these aspects are evolutionarily preserved between species. In rodents it has been shown that undifferentiated spermatogonia (including SSCs), are not randomly distributed in the seminiferous tubule, but in specific stages of the seminiferous epithelium cycle (SEC), they are preferentially located in the areas of the tubule close to the interstitial areas and not in the tubule-tubule contact regions. Herein, using testicular tissue samples from Macaca Fascicularis, we analyzed for the first time in primates the topological localization of undifferentiated spermatogonia (undiff-SPG) in seminiferous tubules, identified by IF and IHC analysis using specific markers. Interestingly, the analysis of the relative position of undiff-SPG subsets along the basal membrane with the respect to the interstitial tissue, revealed significant differences. PIWIL4+ and NANOS3+ undiff-SPG are randomly distributed along the basal compartment of the seminiferous tubules in all stages, while GFRA1+ undiff-SPG show different distribution in relation to the stages of the cycle. GFRA1+ undiff-SPG are preferentially localized in regions facing the interstitium in the first half of the cycle while they preferentially occupy tubule-tubule contact regions in the second one. This data could provide important information on the function of the spermatogonial compartment in primates.