The topographical distribution of spermatogonial subpopulations during the cycle of seminiferous epithelium in <i>Macaca Fascicularis</i>

The maintenance of mammalian spermatogenesis depends on the intricate molecular and cellular interactions between spermatogonial stem cells and their cognate niche in the seminiferous epithelium of the testis. To sustain the continuous production of sperm, spermatogonia proliferate and differentiate under the control of various niche factors, promoting either self-renewal or commitment to spermatogonial differentiation. Single-cell RNA sequencing analyses have identified different subpopulations of spermatogonia in primates based on the expression of specific marker genes (PIWIL4, GFRA1, NANOS3 and KIT). However, the spatial distribution of the different spermatogonial subpopulations and their relationship with the niche has not been described yet. Here, we investigate the topological localization of spermatogonia in primates. To this end, immunohistochemical stainings for PIWIL4, GFRA1, NANOS3 and KIT were performed on Bouin fixed samples of Macaca fascicularis and quantitatively analyzed. Strauss's linear selectivity index (Linear Index, Li) was employed to assess the regional distribution of spermatogonial subpopulations in the basal compartment of seminiferous tubules. Remarkably, PIWIL4+ spermatogonia showed a random distribution along the basal compartment across all the stages of the seminiferous epithelium cycle. In contrast, GFRA1+, NANOS3+ and KIT+ spermatogonia displayed stage-dependent localization patterns. The spatial organization of different spermatogonial subpopulations, appeared coordinated with the cycle of the seminiferous epithelium, suggesting a dynamic regulation of spermatogonial behavior throughout the process of sperm production. Our study contributes to the growing body of literature aimed at deciphering the complexities of SSC biology and the regulation of spermatogenesis in mammalian species, with implications for understanding male fertility.