D-FOS, A TARGET GENE OF DECAPENTAPLEGIC SIGNALING WITH A CRITICAL ROLE DURING DROSOPHILA ENDODERM INDUCTION

The Drosophila endoderm is patterned by the signals Decapentaplegic an d Wingless secreted from the visceral mesoderm. This induction culmina tes 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, me show that Decapentaplegic signalling induces elevated expression of the Drosophila AP-1 transcription factor D-Fos in a sli ghtly broader endodermal region than labial. This induction occurs in parallel to, and independently of, that of labial. Furthermore, we pre sent evidence that D-Fos is required for labial induction in the embry o as well as for maintenance of labial expression through larval stage s; and that D-Fos is critical for cellular differentiation in the larv al gut. We propose that Decapentaplegic, by inducing D-Fos, broadly de fines an endodermal region which thus becomes predisposed to express l abial, and that D-Fos cooperates with signal-activated response factor s to confer the precise pattern of labial expression in this region.