THE SH2-CONTAINING TYROSINE PHOSPHATASE CORKSCREW IS REQUIRED DURING SIGNALING BY SEVENLESS, RAS1 AND RAF

The sevenless gene encodes a receptor tyrosine kinase which is require d for the development of the R7 photoreceptor cell in each ommatidium of the Drosophila eye, We have previously used a sensitized genetic sc reen to identify mutations, designated Enhancers of sevenless (E(sev)) , which affect genes that encode components of the sevenless signaling pathway, Here, we report that one of these mutations, E(sev)1A(e0P) i s a dominantly inhibiting allele of corkscrew, which encodes an SH2 do main-containing protein tyrosine phosphatase (Perkins et al., 1992), W e show that corkscrew function is essential for sevenless signaling an d that expression of a membrane-targeted form of corkscrew can drive R 7 photoreceptor development in the absence of sevenless function, Furt hermore, we have used the dominantly inhibiting corkscrew allele to ex amine the role of corkscrew during signaling by activated forms of Ras 1 and Raf, Our analysis indicates that corkscrew function is still req uired during signaling by activated Ras1 and Raf proteins, These resul ts define a function for corkscrew that is either downstream of Ras1 a ctivation or in a parallel pathway that acts with activated Ras1/Raf t o specify R7 photoreceptor development.