Plays a role in guidance and morphology of central and peripheral axons and in synaptic morphology. Also required for formation of cell membrane protrusions and for bristle development (PubMed:12818175, PubMed:14588242, PubMed:15269173, PubMed:15385157). Plays a role in regulating mitochondrial activity, energy metabolism and membrane potential which maintains normal gamma-aminobutyric acid (GABA) signaling and ensures normal social behavior (PubMed:32200800). Interacts with Fmr1 and Rac1. Component of the WAVE complex composed of Hem/Kette, Scar/Wave and Sra-1/Cyfip where it binds through its C-terminus directly to Hem. Accumulates in central axons and motor neuron terminals. In the embryo, expressed mainly in the gut and in the developing central nervous system where high levels of expression are found in the CNS neuropile. Expression in the gut diminishes as development proceeds (at protein level). In the adult, expressed specifically in the nervous system. Expressed throughout the life cycle with no major peaks of expression. In the embryo, uniquitously and highly expressed at precellular and cellular blastoderm stages. Flies display pupal lethality with defects in axon growth, branching and pathfinding, synaptic length and organization of the neuromuscular junction. They also display defects in cell morphology with cells exhibiting a starfish-like shape with multiple slender cell extensions and loss of actin filaments at the cell periphery (PubMed:12818175, PubMed:14588242, PubMed:15269173). RNAi-mediated knockdown in gamma-aminobutyric acid (GABA)ergic neurons, or specifically in the anterior paired lateral (APL) neurons or in the antennal lobe local interneurons (LNs), results in feeding-dependent socialization defects (PubMed:32200800). Belongs to the CYFIP family.