Isolation and expression of scabrous, a gene regulating neurogenesis in Drosophila

Mutations in the Drosophila scabrous (sea) gene affect eye and bristle development, leading to irregular spacing of ommatidia and bristle duplications in the adult fly. We have cloned the sea gene by P-element tagging. The sea transcription unit is 12 kb and consists of four exons that are joined in a 3.2-kb mRNA. In an enhancer trap screen we have isolated several P[lacZ] insertions close to the sea transcription start site. We have examined the expression pattern of sea by in situ hybridization to sea transcripts, by β-galactosidase localization in the P[lacZ] lines, and by immunocytochemistry with an anti-sca antiserum. During embryogenesis, sea is expressed in a dynamic pattern associated with neural development. During imaginal development, sea is mainly expressed in the R8 photoreceptor precursor cells in the eye imaginal disc and in sensory organ precursor cells in other discs. In the wing disc, sea expression is coextensive with the anlagen for bristles and is controlled by genes of the achaete-scute complex. Based on its loss-of-function phenotype, expression pattern, and the predicted structure of its product, a secreted peptide with homology to the fibrinogen gene family, we propose that sea encodes a signal involved in lateral inhibition within individual domains of the developing nervous system.