The long-term objectives of the proposed work are to dissect the roles of calcium regulation in sperm development and mature sperm function. The initial studies proposed here concern the role(s) of a newly identified calcium-binding protein implicated in calcium-regulatory events in the testis. The protein, termed Androcam, is specifically expressed in the testis and appears to be evolutionarily conserved from insects to mammals. The characteristics of Androcam indicate that it is a calcium sensor-a protein that converts transient changes in intracellular calcium into changes in cellular responses as a result of calcium-induced changes in its protein-protein interactions. Two major approaches to understanding Androcam function will be pursued: i) the disruptions in spermatogenesis and mature sperm function produced by mutations to the Androcam gene of Drosophila melanogaster will be analyzed; ii) the protein interaction partners of Androcam, both in the calcium-bound and calcium-free state will be identified in the same organism. Prior studies already allow the prediction that two types molecular motor proteins may be Androcam targets. The Androcam homologs in other species will also be isolated with a particular view to pursuing studies of Androcam-related proteins in mammalian species.