The Drosophila Genes disconnected and disco-related Are Redundant With Respect to Larval Head Development and Accumulation of mRNAs From Deformed Target Genes

Abstract

HOM-C/hox genes specify body pattern by encoding regionally expressed transcription factors that activate the appropriate target genes necessary for differentiation of each body region. The current model of target gene activation suggests that interactions with cofactors influence DNA-binding ability and target gene activation by the HOM-C/hox proteins. Currently, little is known about the specifics of this process because few target genes and fewer cofactors have been identified. We undertook a deficiency screen in Drosophila melanogaster in an attempt to identify loci potentially encoding cofactors for the protein encoded by the HOM-C gene Deformed (Dfd). We identified a region of the X chromosome that, when absent, leads to loss of specific larval mouthpart structures producing a phenotype similar to that observed in Dfd mutants. The phenotype is correlated with reduced accumulation of mRNAs from Dfd target genes, though there appears to be no effect on Dfd protein accumulation. We show that these defects are due to the loss of two functionally redundant, neighboring genes encoding zinc finger transcription factors, disconnected and a gene we call disco-related. We discuss the role of these genes during differentiation of the gnathal segments and, in light of other recent findings, propose that regionally expressed zinc finger proteins may play a central role with the HOM-C proteins in establishing body pattern.