Abstract
The identification of receptor tyrosine kinases in Drosophila has provided an opportunity to study the requirement for these proteins during the development of a multicellular organism. Genetic analysis of the function of the Drosophila epidermal growth factor (EGF) receptor homolog (DER) has revealed an extremely diverse set of roles for this protein throughout the life cycle of the organism, for example in eye development and in the establishment of dorsoventral polarity in the oocyte. We discuss the possible basis for the pleiotropic activity of DER, and the similarities and differences in the function of the homologous proteins in other invertebrates and vertebrates.
