Deficiency (Df) lines for all four chromosomes obtained from the Bloomington stock center were used to identify dominant modifiers of mutant dVCP in a genetic screen. For the primary screen, balanced virgin female dVCP R152H (recombined with Gmr GAL4) flies were crossed with Df/Balancer males from 270 deficiency lines and progeny were examined for changes in eye phenotype (including color, ommatidia structure and bristle formation). At least ten progeny were examined and scored on a twenty-point scale. Eyes were examined for the presence of: supernumerary inter-ommatidial bristles (IOBs), IOBs with abnormal orientation, necrotic patches, a decrease in size, retinal collapse, fusion of ommatidia, disorganization of ommatidial array and loss of pigmentation. Points were added if: there was complete loss of IOBs (+1), more than 3 small or 1 large necrotic patch (+1), retinal collapse extended to the midline of the eye (+1) or beyond (+2), loss of ommatidial structure in less than 50% (+1) or more than 50% (+2) of the eye, and if pigmentation loss resulted in change of eye color from red to orange (+1) or pale orange/white (+2). Gmr, GAL4, UAS dVCP R152H / Balancer served as an internal control. In a secondary screen to filter nonspecific modifiers of cell death, deficiencies defined as hits (either enhancing or suppressing the dVCP mutant phenotype) were then crossed with flies expressing the pro-apoptotic gene Reaper (recombined with Gmr GAL4). Any hits that similarly affected dVCP R152H and Reaper in the secondary screen were excluded from further study due to the possibility of non–specific anti-apoptotic effects. As regions of interest were identified from the primary and secondary screens, additional Df lines were obtained that overlapped with interacting deficiencies to verify and refine the position of potential modifiers. For the final step of gene identification, individual RNAi lines corresponding to the genes within the candidate intervals were obtained from the Vienna Drosophila RNAi Center. Gmr GAL4, UAS dVCP R152H females were crossed with males from the RNAi lines and the progeny eyes were evaluated for changes. A modifier was defined as an RNAi line that replicated the enhancement or suppression of the corresponding deficiency.