THE SEVENLESS SIGNALING CASSETTE MEDIATES DROSOPHILA EGF RECEPTOR FUNCTION DURING EPIDERMAL DEVELOPMENT

In Drosophila, Drk, an SH2 adaptor protein, Sos, a putative activator of Ras1, Ras1, raf and rolled/MAP kinase have been shown to be require d for signalling from the sevenless and the torso receptor tyrosine ki nase. From these studies, it was unclear whether these components act in a single linear pathway as suggested by the genetic analysis or whe ther different components serve to integrate different signals. We hav e analyzed the effects of removing each of these components during the development of the adult epidermal structures by generating clones of homozygous mutant cells in a heterozygous background. Mutations in ea ch of these signalling components produce a very similar see of phenot ypes. These phenotypes resemble those caused by loss-of-function mutat ions in the Drosophila EGF receptor homolog (DER). It appears that the se components form a signalling cassette, which mediates all aspects o f DER signalling but that is not required for other signalling process es during epidermal development.