MUTATIONS DISRUPTING NEURONAL CONNECTIVITY IN THE DROSOPHILA VISUAL-SYSTEM

The photoreceptor neurons (R cells) of the Drosophila compound eye ela borate a precise array of neuronal connections in the brain. These pro jections exhibit target specificity and create topographic maps (retin otopy). We have screened histologically for mutations disrupting R cel l connectivity in developing tissue. Eighty mutations were isolated fr om over 6000 ethylmethane sulfonate-mutagenized lines. Characterizatio n of these mutations included genetic mosaic analysis to determine whe ther the gene is required in the retina or in the optic ganglia. Most mutations were found to affect connectivity indirectly by disrupting d evelopment more generally in the eye or brain. Genes were identified a s candidates for playing direct roles in R cell connectivity by affect ing axonal outgrowth (eddy), target recognition (limbo and nonstop), a nd retinotopy (limbo).