Required for cell fusion events during development including the fusion of anchor cells (AC), vulval A and vulval D rings, and late epidermal seam cells (PubMed:17488621). Required for amphid sheath cell fusion induced by entry into dauer stage (PubMed:21350017). Expressed in amphid sheath cells. First expressed in embryonic hyp5 cells and then during larval development in pharyngeal muscles, uterine rings, head and tail neurons, sheath cells of chemo-sensory neurons, and in male neurons. Expressed in AC, vulval D rings and uterine seam cells in cell fusion events during development. Egg laying defective phenotype. AC fail to fuse in the majority of worms (PubMed:17488621). RNAi-mediated knockdown in a daf-7 e1372 mutant background causes a severe defect in amphid sheath cell fusion induced by entry into dauer stage (PubMed:21350017). Belongs to the EFF/AFF cell fusogen family.