THE BROAD-COMPLEX DIRECTLY CONTROLS A TISSUE-SPECIFIC RESPONSE TO THESTEROID-HORMONE ECDYSONE AT THE ONSET OF DROSOPHILA METAMORPHOSIS

In Drosophila, all of the major metamorphic transitions are regulated by changes in the titer of the steroid hormone ecdysone. Here we exami ne how a key regulator of metamorphosis and primary ecdysone response gene, the Broad-Complex, transmits the hormonal signal to one of its t argets, the Sgs-4 glue gene. We show that Broad-Complex RNAs accumulat e in mid third instar larval salivary glands prior to Sgs-4 induction, as expected for the products of a gene that regulates the timing of S gs-4 activation. The Broad-Complex codes for a family of zinc finger t ranscriptional regulators. We have identified a number of binding site s for these proteins in sequences known to regulate the timing of Sgs- 4 induction, and have used these sites to derive a binding consensus f or each protein. Some of these binding sites are required in vivo for Sgs-4 activity. In addition, rbp(+), a genetically defined Broad-Compl ex function that is required for Sgs-4 induction, acts through these B road-Complex binding sites. Thus, the Broad-Complex directly mediates a temporal and tissue-specific response to ecdysone as larvae become c ommitted to metamorphosis.