Cross regulation of decapentaplegic and Ultrabithorax transcription in the embryonic visceral mesoderm of Drosophila.

The Drosophila decapentaplegic gene (dpp) encodes a TGF-beta family member involved in signal transduction during embryonic midgut formation. The shortvein (shv) class of cis-regulatory dpp mutants disrupt expression in parasegments 4 and 7 (ps4 and ps7) of the embryonic visceral mesoderm (VM) surrounding the gut and cause abnormalities in gut morphogenesis. We demonstrate that cis-regulatory elements directing expression in ps4 and ps7 are separable and identify DNA fragments that generate ps4 and ps7 expression patterns using reporter gene constructs. dpp reporter gene expression in both ps4 and ps7 is autoregulated as it requires endogenous dpp+ activity. Reporter gene ps7 expression requires the wild-type action of Ultra-bithorax (Ubx), and abdominal-A. Furthermore, the expression of certain Ubx reporter genes is coincident with dpp in the VM. Both the mis-expression of Ubx reporter genes in the developing gastric caecae at ps4 and its normal expression in ps7 are dependent upon endogenous dpp+ activity. We conclude that dpp both responds to and regulates Ubx in ps7 of the visceral mesoderm and that Ubx autoregulation within this tissue may be indirect as it requires more components than have previously been thought.