The developmental process of spermatogenesis in mammals results in formation of cells highly differentiated in structure and function. The goals are to understand the intrinsic and extrinsic mechanisms that regulate the function of these cells and the stage-specific expression of genes for germ cell-specific proteins. It is hypothesized that such proteins are responsible for unique structural and functional characteristics of sperm and spermatogenic cells. We are using monoclonal antibodies to identify, localize, and isolate such proteins, and will use recombinant DNA methods to clone and characterize their genes. Cytoskeletal proteins of the sperm flagellum have been identified that appear to be germ cell-specific intermediate filament (IF) proteins. Some of these proteins are synthesized in spermatocytes, while others are first present in spermatids. They are recognized by antibodies to IF proteins of somatic cells but also have unique antigenic and biochemical properties. These proteins appear to be products of temporally regulated genes expressed only in spermatogenesis. Other studies are examining the influence of somatic cells on germ cell function and gene expression. In vitro studies have shown that chemotaxis is involved in migration of primordial germ cells (PGC) to the-genital ridges. It was also found that an enzyme and an antigen are lost from the surface of PGC after they enter the ridges. In addition, the spermatozoon must interact with the epididymis to gain the ability to fertilize. During this process, the sperm surface is modified by glycoproteins secreted by the epididymal epithelium. These glycoproteins are being isolated and characterized to identify their roles in sperm maturation. Related studies are concerned with purification of a Sertoli cell product which stabilizes binding of some of these epididymal glycoproteins to the sperm surface until near the time of fertilization.