GENETIC DISSECTION OF SIGNAL-TRANSDUCTION MEDIATED BY THE SEVENLESS RECEPTOR TYROSINE KINASE IN 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 by boss, a protein expressed on the membra ne of the neighboring R8 cell. Constitutive activation of the sev rece ptor results in a dosage dependent increase in the number of R7 cells per ommatidium. Genetic screens have been used to identify mutations t hat alter the efficiency of signal transduction. Subsequent molecular characterization of the corresponding genes has led to the identificat ion of a number of proteins involved in transducing the signal from th e receptor to the nucleus. In contrast to the receptor and its ligand, these components are shared between different signal transduction pat hways not only in Drosophila but are also homologous to components inv olved in signal transduction in other organisms.