Plays a role in the formation of the central complex of ciliary and flagellar axonemes. Homodimer (PubMed:27486783). Interacts with SUN5 (By similarity). Localizes both to epithelial motile cilium and the sperm flagellum (PubMed:27486783). In spermatids, rapidly enriched in the coupling apparatus with the elongation of the spermatid. Tightly attached to the implantation fossa during the maturation of the spermatid. In mature spermatzoa evenly distributed along the flagellum (By similarity). Specifically expressed in testis and trachea. The disease is caused by variants affecting the gene represented in this entry.