Cubitus interruptus Requires Drosophila CREB-Binding Protein To Activate wingless Expression in the Drosophila Embryo

Abstract

ABSTRACT CREB-binding protein (CBP) serves as a transcriptional coactivator in multiple signal transduction pathways. The Drosophila homologue of CBP, dCBP, interacts with the transcription factors Cubitus interruptus (CI), MAD, and Dorsal (DL) and functions as a coactivator in several signaling pathways during Drosophila development, including the hedgehog ( hh ), decapentaplegic ( dpp ), and Toll pathways. Although dCBP is required for the expression of the hh target genes, wingless ( wg ) and patched ( ptc ) in vivo, and potentiates ci -mediated transcriptional activation in vitro, it is not known that ci absolutely requires dCBP for its activity. We used a yeast genetic screen to identify several ci point mutations that disrupt CI-dCBP interactions. These mutant proteins are unable to transactivate a reporter gene regulated by ci binding sites and have a lower dCBP-stimulated activity than wild-type CI. When expressed exogenously in embryos, the CI point mutants cannot activate endogenous wg expression. Furthermore, a CI mutant protein that lacks the entire dCBP interaction domain functions as a negative competitor for wild-type CI activity, and the expression of dCBP antisense RNAs can suppress CI transactivation in Kc cells. Taken together, our data suggest that dCBP function is necessary for ci -mediated transactivation of wg during Drosophila embryogenesis.