Cell-cell interactions, cell adhesion and inductive interactions play an important role in many development and physiological processes of higher eukaryotes, including the process of human embryo implantation. In humans, a novel cell adhesion complex, consisting of the proteins bystin, trophinin and tastin, has been identified that is thought to link with the cytoskeleton and function in embryo implantation. While trophinin and tastin sequences have not been identified outside of mammals, bystin-like genes have been conserved through evolution and are found in yeast, worms, zebrafish and the fruit fly, Drosophila melanogaster. Our recent studies on the Drosophila bystin ortholog, termed bys, have shown that bys is essential for viability of the organism and that bys mRNA is expressed in tissues that undergo cell-cell interactions, cell-adhesion, convergent extension and inductive interactions during development. This data suggests that Drosophila bys may have a novel function in processes that are essential to development and cell interactions. To fully understand the role of bys in development, it will be necessary to carry out experiments designed to understand the contribution of bys at various life stages and in specific tissues. The overall goals of this proposal are to carry out a functional analysis of bys in Drosophila. To begin this analysis, we will molecularly characterize newly induced bys mutations using PCR, Southern blots and DNA sequencing. To determine if the bys mutations may represent hypomorphic or null alleles, we will examine bys mRNA and/or protein expression in bys mutant animals. Further experiments are designed to characterize the phenotypes of bys mutant embryos. Because bys is expressed maternally, at various stages of embryogenesis and in larval tissues, we will carry out mosaic analyses to determine later functions of bys. This work will not only shed light on a novel developmentally important gene in Drosophila, but may also be applicable to understanding the function of the human bystin.