| Summary: | Tubulobulbar complexes are cytoskeleton-related membrane structures that develop at sites of intercellular attachment in the mammalian seminiferous epithelium. At apical junctions between Sertoli cells and spermatids the structures internalize adhesion junctions and are a component of the sperm release mechanism. Here I explore the possibility that tubulobulbar complexes that form at the ‘blood-testis barrier’ are sub-cellular machines that internalize basal junction complexes. Electron microscopy reveals that morphologically identifiable tight and gap junctions are present in basal tubulobulbar complexes in rats. In addition, immunological probes for claudin-11 (CLDN11), connexin-43 (GJA1), and nectin-2 (PVRL2) react with linear structures at the light level that I interpret as tubulobulbar complexes, and probes for early endosome antigen 1 (EEA1) and Rab5 (RAB5A) react in similar locations. Significantly, fluorescence staining patterns for actin and claudin-11 indicate that the amount of junction present is dramatically reduced over the time period that tubulobulbar complexes are known to be most prevalent during spermatogenesis. I also demonstrate, using electron microscopy and fluorescence microscopy, that tubulobulbar complexes develop at basal junctions in primary cultures of Sertoli cells. These structures not only morphologically resemble their in vivo counterparts, but they also contain junction proteins. I use this culture system together with transfection techniques to show that junction proteins from one transfected cell project into and are likely internalized by adjacent non-transfected cells as predicted by the junction internalization hypothesis. On the basis of my findings I present a new model for basal junction remodeling as it relates to spermatocyte translocation in the seminiferous epithelium.
|
|---|
