Microarray analysis of R7 and R8 targeting

The formation of neuronal connections requires the precise guidance of developing axons towards their targets. In the Drosophila visual system, photoreceptor neurons (R cells) project from the eye into the brain. These cells are grouped into some 750 clusters comprised of eight photoreceptors or R-cells each. R cells fall into three classes, R1-R6, R7 and R8. Posterior R8 cells are the first to project axons into the brain. How these axons select a specific pathway is not known. Here, we used a microarray-based approach to identify genes expressed in R7 and R8 neurons as they extend into the brain. We used microarray analysis to measure gene expression changes when the transcription factor Runt is misexpressed in eye discs and conversely when eye discs are rendered mutant for the Senseless transcription factor.