Genetic dissection of cell fate specification in the developing eye of Drosophila

The specification of the R7 photoreceptor cell in each ommatidium of the developing eye of Drosophila is dependent on the activation of the sevenless (sev) receptor tyrosine kinase on the R7 precursor by its membrane-bound ligand, boss, on the neighboring R8 cell. The genetic dissection of the signalling pathway activated by the sev receptor has uncovered a highly conserved signal transduction cascade, known as the Ras/MAP kinase cascade, which is used by various receptor tyrosine kinases for a number of different developmental decisions. The type of cellular response is at least in part dependent on the nature of the nuclear factors present in the cells when this signalling cascade is activated. (C) 1996 Academic Press Ltd