Required for initial steps of body morphogenesis (PubMed:11877381). May play a role in egg laying and yolk protein clatherin-mediated endocytosis by oocytes during oogenesis (PubMed:19798448). Plays a role in the formation of muscle connections, also called muscle arm extensions, between the body wall and the motor axons in the dorsal and ventral cord (PubMed:27123983). Interacts with gex-3. Enriched at cell boundaries. Embryonic lethal with cells differentiating, but failing to become organized (PubMed:11877381). The external hypodermal cells fail to spread over and enclose the embryo, but instead cluster on the dorsal side (PubMed:11877381). In one study, animals are viable and there is defective extension of body wall muscle connections or arms towards the ventral nerve cord (PubMed:27123983). In this same study, double knockout with madd-3 results in severe muscle arm extension defects (PubMed:27123983). RNAi-mediated knockdown results in reduced egg laying and in defective endocytosis by oocytes characterized by an accumulation of aggregated yolk protein in the pseudocoelomatic space (PubMed:19798448). Belongs to the CYFIP family.