DIRECT AND LONG-RANGE ACTION OF A DPP MORPHOGEN GRADIENT

During development of the Drosophila wing, the decapentaplegic (dpp) g ene is expressed in a stripe of cells along the anteroposterior compar tment boundary and gives rise to a secreted protein that exerts a long -range organizing influence on both compartments. Using clones of cell s that express DPP, or in which DPP receptor activity has been constit utively activated or abolished, we show that DPP acts directly and at long range on responding cells, rather than by proxy through the short -range induction of other signaling molecules. Further, we show that t wo genes, optomotor-blind and spalt are transcriptionally activated at different distances from DPP-secreting cells and provide evidence tha t these genes respond to different threshold concentrations of DPP pro tein. We propose that DPP acts as a gradient morphogen during wing dev elopment.