Involved in fertilization by facilitating sperm penetration of the zona pellucida. May promote spermatocyte apoptosis, thereby limiting sperm production. In adults, may reduce testosterone synthesis in Leydig cells. Is not essential either for development or fertility. Interacts with SLXL1; Co-localize in seminiferous tubules. Interacts with SLY. Localized specifically to the crescent shaped acrosome at the apex of the sperm head. More highly expressed in adult testis than in fetal testis. Exclusively expressed in the testis (at protein level). Intense expression in stages II, III and IV of spermatogenesis, whereas expression is lower in stage I. Abnormal expression in testes of patients with male infertility. Contains a N-terminal domain similar to that of the N-terminal section of DKK3. N-glycosylated during spermatogenesis. Not N-glycosylated in mature sperm.