May play an important role in spermatogenesis and/or testis development. Highly expressed in testis. Transcripts can be found in primary and secondary spermatocytes, and spermatids, but the protein itself is only detected in spermatids. No expression in Leydig cells, spermatogonia, or sperm. Very weak expression in the heart, kidney, spleen, thymus and ovary. Expressed as early as day 6 postpartum (dpp), with higher expression in the adult testis. Was originally thought to be the H-Y antigen. It is uncertain whether Met-1 or Met-11 is the initiator.