Essential for male fertility. Plays an important role in spermatogenesis and regulates sperm motility by controlling the development of the flagellar bending of sperm (PubMed:24339785). Testis-specific. Exclusively expressed in testicular germ cells while it is not present in mature sperm (at protein level). Males are either infertile due to a lack of sperm resulting from spermatogenic arrest, or subfertile due to impaired sperm motility. The motility defect is caused by altered Ca(2+) regulation of the flagellar beat of sperm. Truncated N-terminus.