A CREB-binding site as a target for decapentaplegic signalling during Drosophila endoderm induction

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Abstract
Decapentaplegic (Dpp) is an extracellular signal of the transforming growth factor‐β family with multiple functions during Drosophila development. For example, it plays a key role in the embryo during endoderm induction. During this process, Dpp stimulates transcription of the homeotic genes Ultrabithorax in the visceral mesoderm and labial in the subjacent endoderm. Here, we show that a cAMP response element (CRE) from an Ultrabithorax enhancer mediates Dpp‐responsive transcription in the embryonic midgut, and that endoderm expression from a labial enhancer depends on multiple CREs. Furthermore, the Drosophila CRE‐binding protein dCREB‐B binds to the Ultrabithorax CRE, and ubiquitous expression of a dominant‐negative form of dCREB‐B suppresses CRE‐mediated reporter gene expression and reduces labial expression in the endoderm. Therefore, a CREB protein may act as a nuclear target, or as a partner of a nuclear target, for Dpp signalling in the embryonic midgut.