Podosome‐like tubulobulbar complexes internalize intact junctions in the seminiferous epithelium

Abstract

Tubulobulbar complexes are actin‐rich double‐plasma membrane protrusions with associated vesicles that form at intercellular junctions in the seminiferous epithelium of the mammalian testis. One role that has been proposed for these 'podosome‐like' structures is that they internalize 'intact' intercellular junctions during the translocation of spermatocytes through basal junction complexes between Sertoli cells, and during sperm release from Sertoli cells at the apex of the epithelium. If tubulobulbar complexes internalize junctions, then components of tubulobulbar complexes that contain junction proteins also should be associated with endosomal markers. In this study, we probed apical tubulobular complexes in fixed epithelial fragments of rat and mouse testes for adhesion molecules (alpha‐6 integrin in rat, and nectin 2&3 in mouse) and early endosomal markers (Rab 5 in rat and EEA1 in mouse). The antibody to Rab 5 labeled the distal ends of tubulobulbar complexes that also labeled strongly with the antibody to alpha‐6 integrin. EEA1 surrounded vesicles at the ends of tubulobulbar complexes that also were positive for nectin 2 and nectin 3. These results are consistent with the proposal that tubulobulbar complexes are subcellular machines that internalize intact intercellular junctions in the testes.Grant Funding SourceNSERC