SERTOLI-CELL - UPDATE ON THE CONCEPT OF N URSING CELL

The seminiferous epithelium is certainly one of the most complex tissu es. Within this epithelium, the unique strategic position the Sertoli cell allows it to receive, integrate, and emit all the signals require d for the spermatogenic process to or from the extratubular compartmen t (e.g., FSH, testosterone), the peritubular cells (e.g., P-Mod-S), an d germ cells themselves. At all stages of sexual maturation, Sertoli c ells and germ cells have developed a formidable set of communication d evices involved in attachment, displacement, cell shaping, and cell-ce ll transfer of molecules and cellular materials. The location of Serto li cells allows them to coordinate germ cell activity in both the tran sversal and the longitudinal axes of the seminiferous tubule. The Sert oli cell barrier and Sertoli cell products creates the physical and ch emical microenvironments required for the completion of each of the di fferent steps of spermatogenesis. In addition to the production of the tubular fluid, the Sertoli cell secretes several molecules directly o r indirectly implicated in germ cell control : proteins, peptides and steroid(s) involved in germ cell proliferation, differentiation and me tabolism, transport/binding proteins, proteases, extracellular matrix components, energy metabolites, antiproteases, and various membrane co mponents. Sertoli cell polarization results from the existence of Sert oli cell-Sertoli cell occluding junctions. The products required for t he mitotic phase of spermatogenesis may principally be secreted basall y, whereas those required for meiotic division, spermiogenesis and spe rm cells may preferentially be secreted apically. Changes in the compo sition of the germ cell complement and in germ cell size and shape, as well as germ cell divisions and migration, profoundly affect Sertoli cell morphology and function. Plasma membrane molecules, germ cell sol uble factors, and transfer of germ cell materials (e.g., residual bodi es shed by late spermatids at the time of spermiation), are most proba bly the agents and mechanisms involved in germ cell regulation of Sert oli cell function. Progress is crucially needed for understanding the function and regulation of the Sertoli cell, given that the etiology o f male infertility is still so poorly understood and that there is a g reat social demand for mastering all facets of spermatogenesis : induc tion and stimulation (pathologists), protection (e.g., against antican cer therapy), and contraception.