Gradient formation of the TGF-beta homolog Dpp

Secreted morphogens such as the Drosophila TGF-beta homolog Decapentaplegic (Dpp) are thought to spread through target tissues and form long-range con centration gradients providing positional information. Using a GFP-Dpp fusi on, we monitored a TGF-beta family member trafficking in situ throughout th e target tissue and forming a long-range concentration gradient. Evidence i s presented that long-range Dpp movement involves Dpp receptor and Dynamin functions. We also show that the rates of endocytic trafficking and degrada tion determine Dpp signaling range. We propose a model where the gradient i s formed via intracellular trafficking initiated by receptor-mediated endoc ytosis of the ligand in receiving cells with the gradient slope controlled by endocytic sorting of Dpp toward recycling versus degradation.