We propose to analyze the cell surface molecules necessary for normal determination and differentiation using the fruit fly, Drosophila melanogaster. The objective of the research is to elucidate basic principles in the development of higher organisms, including man. Our long-range interests are in understaning intercellular interactions such as adhesion, induction, and intercellular communication, which are involved in morphogenesis and pattern formation. A strategy is proposed which uses genetics to link the biochemical characterization of molecules involved in cell-cell adhesion to their role(s) in vivo. Cultured cells and embryonic cells will be studied with respect to cell-cell adhesion, cell sorting in mixed aggregates, myoblast fusion. Assays will be developed to test the effects of blocking antibody reagents of these intercellular interaction in vitro. Immunochemical methods will characterize the specific cell surface antigens involved and facilitate a search for genetic variance with alteration in those molecules. By developing a system to characterize inter-cellular interaction in the development of an organism where genetic methodology can be applied, we will have the opportunity to obtain temperature sensitive mutants to study the roles of specific cell surface molecules in vivo.