D-Fos, a target gene of Decapentaplegic signalling with a critical role during Drosophila endoderm induction.

The Drosophila endoderm is patterned by the signals Decapentaplegic and Wingless secreted from the visceral mesoderm. This induction culminates in a precise pattern of spatially restricted expression of labial, a selector gene with a role in cell type specification in the larval midgut. Here, we show that Decapentaplegic signalling induces elevated expression of the Drosophila AP-1 transcription factor D-Fos in a slightly broader endodermal region than labial. This induction occurs in parallel to, and independently of, that of labial. Furthermore, we present evidence that D-Fos is required for labial induction in the embryo as well as for maintenance of labial expression through larval stages; and that D-Fos is critical for cellular differentiation in the larval gut. We propose that Decapentaplegic, by inducing D-Fos, broadly defines an endodermal region which thus becomes predisposed to express labial, and that D-Fos cooperates with signal-activated response factors to confer the precise pattern of labial expression in this region.