Molecular mechanisms mediating testicular cell adhesions and intraepithelial germ cell translocations remain largely unexplored. In this proposal, the investigator hypothesizes that L-selectin expressed on the surfaces of Sertoli cells is directly involved in germ cell-Sertoli cell adhesion and germ cell translocation in the seminiferous epithelium. He proposes that binding of L-selectin to fucosylated ligands on germ cells triggers a signaling pathway involving small GTPases which alter actin polymerization and thus mediate rearrangements of the Sertoli cell cytoskeleton which are necessary for proper movement of germ cells through the epithelium. Four SA's are proposed. First, the hypothesis that transcription and translation of Sertoli cell L-selectin are related to important changes in Sertoli cells necessary for spermatogenesis will be tested by looking for stage-specific expression of L-selectin and by examining its developmental timing, particularly as related to Sertoli junction formation. Second, the investigator will ask whether L-selectin interacts with cytoskeletal-associated proteins, whether it is partially cleaved by its activation, and whether this causes alteration of the activity of small GTPases, thus regulating actin polymerization. In the third aim, the investigator will test the hypothesis that testicular L-selectin modulates Sertoli cell tight junctions via its interaction with the cytoskeleton and the resultant changes in GTPase activity. Finally, the specific fucosylated Lewis-like molecules on germ cells which serve as L-selectin ligands will be identified and the PI will determine whether exposure of Sertoli cells to these compounds causes changes in their small GTPases, rearrangements in the actin cytoskeleton and changes in tight junctions.