Pachytene spermatocyte and round spermatid binding to Sertoli cells in vitro

Spermatogenic cells differentiate in vivo while in continuous contact with the Sertoli cell. During differentiation, the spermatogenic cells and Sertoli cells form a number of morphologically distinct stage-specific adhesions. We describe an in vitro assay system for studying the adhesion of spermatogenic cells to Sertoli cell monolayers. Mixed populations of spermatogenic cells or enriched fractions of pachytene spermatocytes and round spermatids were labelled with the vital dye, fluorescein diacetate, prior to their addition to Sertoli cell monolayers so that the adhesion of viable spermatogenic cells could be quantified. Using this assay system, the number of pachytene spermatocyte and round spermatid binding sites on the Sertoli cell monolayer were similar, but the kinetics of binding were different. Pachytene spermatocytes were able to inhibit significantly round spermatid binding, while round spermatids did not significantly inhibit pachytene spermatocyte binding. After coculture for 24-48 h, spermatocytes form junctional structures with Sertoli cells that are similar to desmosome-like junctions. These results suggest that pachytene spermatocytes and round spermatids bind to Sertoli cells by different mechanisms.