Directional transport and active retention of Dpp/BMP create wing vein patterns in Drosophila

► Dpp is directionally moved from LVs to PCV by a facilitated transport mechanism. ► Dpp mobility is tightly restricted by active retention mechanism in LVs. ► The active retention of Dpp requires both Tkv and positive feedback mechanism. ► The position of PCV is prepatterned in a Dpp signal-independent manner. ► Combination of long- and short-range signals allows ligands to form vein patterns.