Loss of Sertoli-Germ Cell Adhesion Determines the Rapid Germ Cell Elimination During the Seasonal Regression of the Seminiferous Epithelium of the Long Hairy Armadillo Chaetophractus villosus.

The armadillo Chaetophractus villosus is a seasonal breeder whose seminiferous epithelium undergoes rapid regression with massive germ cell loss leaving the tubules with only Sertoli cells and spermatogonia. Here, we addressed the question of whether this regression entails 1) the disassembly of cell-junctions (immunolocalization of nectin-3, Cadm1, N-cadherin and beta-catenin and transmission electron microscopy, TEM); 2) apoptosis (immunolocalization of Cytochrome C and Caspase 3 and TUNEL assay) and 3) the involvement of Sertoli cells in germ cells phagocytosis (TEM). We showed a dramatic reduction in the extension of vimentin filaments associated with desmosome-like junctions at the interface between Sertoli and germ cells and an increased diffusion of the immunosignals of nectin-3, Cadm1, N-cadherin and beta-catenin. Together, these results suggest loss of Sertoli-germ cells adhesion which, in turn, might determine post-meiotic cell sloughing at the beginning of epithelium regression. Then, loss of Sertoli-germ cells adhesion triggers cell death. Cytochrome C is released from mitochondria, but whilst post-meiotic cells were negative to late apoptotic markers, at advanced regression, spermatocytes were positive to all apoptotic markers. TEM analysis showed cytoplasmic engulfment of cell debris and lipid droplets within Sertoli cells, a sign of their phagocytic activity which contributes to the elimination of the residual meiocytes still present in the latest regression phases. These findings are novel and add new players to the mechanisms of seminiferous epithelium regression occurring in seasonal breeders and introduce the armadillo as an interesting model for studying seasonal spermatogenesis.