Sertoli cell ectoplasmic specializations in the seminiferous epithelium ofthe testosterone-suppressed adult rat

The Sertoli cell ectoplasmic specialization is a unique junctional structur e involved in the interaction between elongating spermatids and Sertoli cel ls. We have previously shown that suppression of testicular testosterone in adult rats by low-dose testosterone and estradiol (TE) treatment causes th e premature detachment of step 8 round spermatids from the Sertoli cell. Be cause these detaching round spermatids would normally associate with the Se rtoli cell via the ectoplasmic specialization, we hypothesized that ectopla smic specializations would be absent in the seminiferous epithelium of TE-t reated rats, and the lack of this junction would cause round spermatids to detach. In this study, we investigated Sertoli cell ectoplasmic specializat ions in normal and TE-treated rat testis using electron microscopy and loca lization of known ectoplasmic specialization-associated proteins (espin, ac tin, and vinculin) by immunocytochemistry and confocal microscopy, In TE-tr eated rats where round spermatid detachment was occurring, ectoplasmic spec ializations of normal morphology were observed opposite the remaining step 8 spermatids in the epithelium and, importantly, in the adluminal Sertoli c ell cytoplasm during and after round spermatid detachment. When higher dose s of testosterone were administered to promote the reattachment of all step 8 round spermatids, newly elongating spermatids associated with ectoplasmi c specialization proteins within 2 days. We concluded that the Sertoli cell ectoplasmic specialization structure is qualitatively normal in TE-treated rats, and thus the absence of this structure is unlikely to be the cause o f round spermatid detachment. We suggest that defects in adhesion molecules between round spermatids and Sertoli cells are likely to be involved in th e testosterone-dependent detachment of round spermatids from the seminifero us epithelium.