GENETIC-ANALYSIS OF THE SEVENLESS SIGNAL-TRANSDUCTION PATHWAY OF DROSOPHILA

The specification of the R7 photoreceptor cell fate in the developing eye of Drosophila depends on the local activation of the sevenless (se v) receptor tyrosine kinase (RTK) by boss, a protein expressed on the membrane of the neighboring R8 cell. Constitutive activation of the se v receptor results in a dosage dependent increase in the number of R7 cells per ommatidium. Genetic screens have been used to identify mutat ions that alter the efficiency of signal transduction. Subsequent mole cular characterization of the corresponding genes has led to the ident ification of a number of proteins involved in transducing the signal f rom the receptor to the nucleus. In contrast to the receptor and its l igand, these components are shared between different signal transducti on pathways not only in Drosophila but homologous components are also involved in signal transduction in other organisms.