Localizes in the acrosomal region of early elongating spermatids. During late stages of elongating spermatids, no longer detected in the acrosomal region, while it mainly localizes in the cytoplasm. Incorporated into the midpiece of spermatids and is also present in the mitochondrial sheath of mature spermatozoa. Mainly expressed in spermatocytes and spermatids in testis. First detected in 18-day-old mice (at protein level).