Dally encodes a cell-surface heparan sulfate proteoglycan that can potentiate signalling through the Decapentaplegic (Dpp) pathway during fly development. However, the exact function of Dally during wing development has remained unclear. Fujise and co-workers now shed some light on this function. On , they report that Dally might play at least two roles in the formation of the Dpp gradient in the developing wing: by regulating the sensitivity of cells to Dpp in a cell-autonomous fashion, perhaps by acting as a co-receptor for Dpp,stabilizing the protein and so enhancing Dpp signalling; and by affecting Dpp distribution in a non-autonomous manner, possibly by sequestering Dpp –a known heparin-binding protein. These combined effects of Dally, the authors propose, determine the shape and activity of the Dpp wing gradient.
