Ras Signal Transduction Pathway in Drosophila Eye Development

Abstract

Ras plays a central role downstream from many receptor tyrosine kinases (RTKs) which function in diverse cellular processes (for review, see Schlessinger 1993). In the Drosophila eye, Ras1 is required for the fate determination of all photoreceptors (Simon et al. 1991). The Drosophila compound eye is composed of an orderly array of 800 unit eyes, or ommatidia (Wolff and Ready 1993). Each ommatidium contains 8 photoreceptor neurons, R1-R8, as well as 4 lens-secreting cone cells, and 7 other accessory cells. Although little is known about the role of Ras1 in the development of R1-6 and R8, its role in the determination of photoreceptor R7 has been extensively studied (for review, see Dickson and Hafen 1994; Krämer and Cagan 1994; Zipursky and Rubin 1994). Ras1 transduces the signal initiated by Sevenless (Sev), a RTK expressed in a subset of cells including the presumptive R7 precursor (Tomlinson et al. 1987; Bowtell et...