The overall objective of this project is to elucidate the mechanism of action of FSH upon the mammalian testis and thus provide a link between hormonal modulation of genetic information and the physiologic function of the organ involved. The specific tasks involved are to determine the cellular site of action of FSH within the testis and the sequence of biochemical events which are set into motion soon after this hormone interacts with the target cell. Finally, these initial biochemical events will be related to the later actions of this gonadotrophin such as changes in structure and spermatogenic function of the gonad. In order to partially fulfill these goals we will: (1) determine the role of cyclic AMP on the testicular response to FSH by studying adenylate cyclase in isolated membranes and protein kinase activation; (2) determine specific protein substrate for the protein kinase and determine how phosphorylation alters function of the proteins; (3) investigate possible effects of FSH on the kinetics of spermatogenesis; (4) localize the testicular target cells for FSH; (5) isolate and purify the protein factors required for initiation of protein synthesis and determine the effect of FSH on their activity; (6) utilize a cell-free translation system to examine the accumlation of specific mRNA during testis development; (7) study changes in gene restriction during postnatal maturation of the testis and the influence of hormones on nuclear gene expression utilizing techniques of chromatin analysis and nucleic acid hybridization.