A screen for dominant modifiers of ro(Dom), a mutation that disrupts morphogenetic furrow progression in drosophila, identifies groucho and hairless as regulators of atonal expression

ro(Dom) is a dominant allele of rough (ro) that results in reduced eye size due to premature arrest in morphogenetic furrow (MF) progression. We found that the ro(Dom) stop-furrow phenotype was sensitive to the dosage of gene s known to affect retinal differentiation, in particular members of die hed gehog (hh) signaling cascade. We demonstrate that ro(Dom) interferes with H h's ability to induce the retina-specific proneural gene atonal (ato) in th e MF and that normal eye size can be restored by providing excess Ato prote in. We used ro(Dom) as a sensitive genetic background in which to identify mutations that affect hh signal transduction or regulation of ato expressio n. In addition to mutations in several unknown loci, we recovered multiple alleles of groucho (gro) and Hairless (H). Analysis of their phenotypes in somatic clones suggests that both normally act to restrict neuronal cell fa te in the retina, although they control different aspects of ate's complex expression pattern.