The long-term objectives of the proposed research are the development of a better understanding of cellular functions and interactions in the testis and the influence of the somatic cells on the maintenance and control of spermatogenesis. Specifically those interactions between seminiferous peritubular cells and Sertoli cells mediated via soluble peptides will be examined. Four specific aims are proposed: 1) to sequence and develop a molecular cDNA probe for the paracrine factor produced by peritubular cells (P) which modulates (Mod) Sertoli cell (S) function, PModS; 2) to elucidate the mechanism of action of PModS and examine the effects of PMOdS on various Sertoli cell functions; 3) to elucidate the hormonal and developmental regulation of PModS production and immunoneutralize PModS and transforming growth factors alpha and beta in the seminiferous tubule. The peritubular cells and Sertoli cells utilized in the study will be isolated from rat testes. Results of the proposed research will provide information on peritubular cell-Sertoli cell interactions, the hormonal control of these interactions, and the influence of these cellular interactions on the maintenance and control of spermatogenesis. Information from the proposed studies is essential for the future design of male contraceptives and fertility agents. In addition, the research will provide insight into general mesenchymal-epithelial cell interactions which are important for the physiology of many different tissues.