Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating. Morpholino knockdown of the protein causes strong ciliopathy phenotypes, including pronephric cysts, axis curvature, left-right asymmetry defects and hydrocephalus. Cilia length and number appear normal, but outer dynein arms are missing and cilia are paralyzed.