Testicular somatic cells plays an integral role in the maintenance and control of spermatogenesis. Analysis of somatic cell-cell interactions within the testis has demonstrated that testicular peritubular cells secrete P-Mod-S, a locally derived, nonmitogenic paracrine factor. P-Mod-S the functions of Sertoli cells maintains germinal cell development. P-Mod-S has been shown to stimulate Sertoli cells to a greater degree than any single regulatory agent known to influence the cell. Therefore, peritubular cell-Sertoli cell interactions, mediated via P-Mod-S, is postulated to play a critical role in the maintenance and control of testicular function. The goals of this research proposal are:1) determine the mechanism of action of P-Mod-S on the Sertoli cell;2) determine the effects of P-Mod-S on the expression of Sertoli cell genes important for testicular function; and 3) identify and initially characterize the P-Mod-S receptor. The completion of these goals will provide additional understanding of the paracrine factor P-Mod-S and its significance in the maintenance and control of spermatogenesis. Thus, further investigation of the testicular paracrine factor P-Mod-S, will provide information needed for the potential future design of agents to act on the testis as a contraceptive or for the prevention of infertility.