Adapter protein which modulates signaling mediated by several receptor tyrosine kinases such as sev and Ack (PubMed:8462097, PubMed:22615583, PubMed:8462098). Required for proper signaling by sevenless (PubMed:8462097, PubMed:8462098). May act to stimulate the ability of Sos to catalyze Ras1 activation by linking sevenless and Sos in a signaling complex (PubMed:8462097, PubMed:8462098). Required for functional and morphological integrities of the scolopidia, sensory neurons and the antennal mechanosensory and motor center (AMMC) brain neuropil (PubMed:30610177). Required for Ack-dependent suppression of apoptosis in the eye (PubMed:22615583). Interacts with autophosphorylated sev via SH2 domain and Sos, Dos and Dab via SH3 domains (PubMed:12128212, PubMed:8462097, PubMed:8462098, PubMed:9671493). Binds to tyrosine phosphorylated Dab via the SH2 domain (PubMed:9671493). Interacts with phosphorylated Ack (PubMed:22615583). Localizes at the presynaptic terminal. Found mainly in the developing eye and in the antennal disk. Also observed in other imaginal disks tested and in the embryo. Expressed in Johnston's organ, the hearing organ, neurons (at protein level) (PubMed:30610177). Embryonically lethal (PubMed:30610177). Loss in Johnston's organ causes scolopidium abnormalities (PubMed:30610177). Belongs to the GRB2/sem-5/DRK family.