HORMONAL INDUCTION OF DOPA DECARBOXYLASE IN THE EPIDERMIS OF DROSOPHILA IS MEDIATED BY THE BROAD-COMPLEX

The 2B5 early pufflocus corresponds to the Broad-Complex (BR-C) and en codes a family of transcription factors whose members are induced by t he molting hormone ecdysone. Mutations in the br subcomplementation gr oup substantially reduce the levels of Dopa decarboxylase (DDC) in the epidermis of mature third instar larvae but not in mature second inst ar organisms. Enzyme levels are normal in the central nervous system o f the two mutants examined. The specificity of these effects suggests that a product of the BR-C locus mediates the rapid appearance of DDC in mature third instar larvae experiencing an elevated titer of ecdyso ne. The likely identity of this protein has been confirmed by pursuing the observation that the br(28) allele is caused by the insertion of a P element into the Z2 DNA-binding domain. Both the transcript and a protein carrying this domain are present in the epidermis and a BR-C r ecombinant protein carrying the Z2 finger binds to the first intron of the Ddc gene. Five binding sites have been identified within the intr on by DNAase I footprinting and a core consensus sequence has been der ived which shares some identity with the consensus binding site of the Z2 protein to the Sgs-4 regulatory region. Our demonstration that Dde is a target of BR-C in the epidermis is the first direct evidence of a role for this early gene in a tissue other than the salivary glands. The data reinforce the idea that BR-C, which clearly mediates a saliv ary gland-specific response to ecdysone, may play a widespread role in the hormone's activation of gene cascades in other target tissues.