Plays a role in spermiogenesis and fertilization. Located throughout the subacrosomal area (PubMed:27488028). Testis-specific (PubMed:27488028). Increases in the third week postnatal and gradually increased until the adult stage (PubMed:27488028). Deficient mice develop and grow normally. Knockout males, but not females, exhibit subfertile capacity. Deficient mice are characterized by abnormal sperm head shape and a failure of sperm-egg fusion (PubMed:27488028).