The apical ectoplasmic specializations is not only responsible for linking the spermatid to the Sertoli cell but also for the translocation of spermatids through the seminiferous epithelium and for the timely release of spermatozoa into the lumen on completion of spermiogenesis. The basal Sertoli-Sertoli junctional complex establishes a blood-testis barrier (BTB), which separates the basal, spermatogonia-containing compartment of the seminiferous epithelium from the immune-privileged, adluminal compartment. The BTB functions primarily to limit paracellular diffusion and to shield haploid germ cells from autoimmune recognition.
These barrier functions are thought to be mediated by occludins, claudins, and junctional adhesion molecules present at tight junctions. It has been suggested that the formation and maintenance of tight junctions of both classical epithe-lia and endothelia of the blood-brain barrier are dependent on cadherin-based zonulae adherens. In addition, Fukuhara et al. have now shown that in cultured epithelial cells, nectin-mediated adhesion is also required for the formation of tight junctions.