Required for vesicle docking or fusion during acrosome biogenesis. May play a role in RNA trafficking or localization. Interacts with FCHO1 (By similarity). Interacts with EPS15R and EPS15. Associated with the cytosolic surface of proacrosomic vesicles of early round spermatids. Highly expressed during spermiogenesis. Contains FG repeats. O-glycosylated. Mice have a normal life-span and show no apparent abnormalities. Females display normal fertility but males are infertile due to a lack of acrosome in their spermatozoa.