Localizes in the intracellular space in testicular germ cells and sperm. Detected also on the cell surface in post-meiotic round spermatids. In cauda epididymal sperm relocates during the acrosome reaction from the inner-acrosomal membrane onto the equatorial segment surface, on which sperm-oocyte fusion occurs. Colocalizes with IZUMO1 at the inner-acrosomal membrane. Detected in testis and in a mixture of spermatogenic cells at various stages (testicular germ cells). Not detected in heart, brain, spleen, lung, liver, skeletal muscle and kidney. Mice are normal with no alterations in fertility, body size and behavior.