The drosophila genes disconnected and disco-related are redundant with respect to larval head development and accumulation of mRNAs from deformed target genes

HOM-C/hox genes specify body pattern by encoding regionally expressed trans cription factors that activate the appropriate target genes necessary? for differentiation of each body region. The current model of target gene activ ation suggests that interactions with cofactors influence DNA-binding abili ty 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 f ewer cofactors hale been identified. We undertook a deficiency screen in Dr osophila melanogaster in an attempt to identify loci potentially encoding c ofactors for the protein encoded by the I IOM-C gene Deformed (Dfd). We ide ntified a region of the X chromosome that, when absent, leads to loss of sp ecific lan al mouthpart structures producing a phenotype similar to that ob served in Dfd mutants. The phenotype is correlated with reduced accumulatio n of mRNAs from Dfd target genes, though there appears to Le no effect on D fd protein accumulation. We show that these defects are due to the loss of two functionally redundant, neighboring genes encoding zinc finger transcri ption factors, disconnected and a gene rye call disco-related. We discuss t ie role of these genes during differentiation of the gnathal segments and, in light of other recent findings, propose that regionally expressed zinc f inger proteins may play a central role with the HOM-C proteins in establish ing body pattern.