Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating. Regulates motility patterns of both 9+0 and 9+2 motile cilia through differential localization and recruitment of axonemal dynein components. Required for centriolar satellite integrity and non-motile cilium assembly. Required for motile cilium formation. Through its role in beating of primary cilia, involved in the establishment of organ laterality during embryogenesis. Required for sperm flagellum biogenesis and is essential for male fertility 