May negatively regulate Notch-induced cell proliferation in the eye-head primordium. May act in leg and wing primordia to negatively regulate body-wall specifying genes and thereby promote appendage formation. Required for tracheal development. Self-associates. Interacts with gro and noc. Expressed in tracheal pit cells from stage 11. At stage 12, expression becomes restricted to lateral anterior and posterior tracheal branches. Expressed in the highly proliferative region of the eye-head primordium. Expressed in the distal regions of leg and wing imaginal disks. Belongs to the Elbow/Noc family.