Identification of Genes Involved in the Differentiation of R7y and R7p Photoreceptor Cells in .

The R7 and R8 photoreceptor cells of the compound eye mediate color vision. Throughout the majority of the eye, these cells occur in two principal types of ommatidia. Approximately 35% of ommatidia are of the pale type and express in R7 cells and in R8 cells. The remaining 65% are of the yellow type and express in R7 cells and in R8 cells. The specification of an R8 cell in a pale or yellow ommatidium depends on the fate of the adjacent R7 cell. However, pale and yellow R7 cells are specified by a stochastic process that requires the genes , and To identify additional genes involved in this process we performed genetic screens using a collection of 480 transposon insertion strains. We identified genes in gain of function and loss of function screens that significantly altered the percentage of expressing R7 cells (%) from wild-type. 36 strains resulted in altered % in the gain of function screen where the insertion strains were crossed to a driver line. 53 strains resulted in altered % in the heterozygous loss of function screen. 4 strains showed effects that differed between the two screens, suggesting that the effect found in the gain of function screen was either larger than, or potentially masked by, the insertion alone. Analyses of homozygotes validated many of the candidates identified. These results suggest that R7 cell fate specification is sensitive to perturbations in mRNA transcription, splicing and localization, growth inhibition, post-translational protein modification, cleavage and secretion, signaling, ubiquitin protease activity, GTPase activation, actin and cytoskeletal regulation, and Ser/Thr kinase activity, among other diverse signaling and cell biological processes.