Cilium- and flagellum-specific protein that plays a role in axonemal structure organization and motility (By similarity). Involved in the regulation of the size and morphology of cilia. Required for axonemal microtubules polyglutamylation (By similarity). Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme. Widely expressed, with highest levels in testis and lowest in muscle. Expressed at high levels in germinal vesicle stage oocytes at the mRNA level. Expression progressively decreases until blastocyst stage (PubMed:15803458). Detected in later embryonic stages from 9.5 to 19.5 dpc. At 11.5 dpc, the expression is widespread, with no preference for any particular organ or structure (PubMed:8688464). Belongs to the CFAP20 family.