Inhibitor of tracheal branching that restricts branch budding by antagonizing the BNL-FGF pathway (BNL: branchless, an fgf inducer of branching). Acts as an antagonist of EGFR-mediated signaling in the eye (where it is important for cell determination) midline glia, chordotonal organs, wing and ovarian follicle cells. Interacts with DRK and RasGAP1 proteins of the Ras pathway. In ovary, expressed from stage 7 of oogenesis in the posterior follicle cells and during stage 9 when the follicle cells migrate posteriorly over the oocyte nucleus, expression is seen in the dorsal and lateral cells and is excluded from the ventral cells. Once the migration of follicle cells is complete expressed in the dorsal-anterior corner of the egg chamber. Expressed in the embryonic tracheal system, developing eye imaginal disk, embryonic chordotonal organ precursors, midline glia and wing imaginal disk. By the BNL-FGF pathway in the tracheal system and by the egf receptor pathway in the wing imaginal disk and the follicle cells of the ovary. The Cys-rich domain is responsible for the localization of the protein to the plasma membrane. Pupal lethal. Mutant embryos and larvae show ectopic tracheal branching. Belongs to the sprouty family.