Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia and flagellar axoneme (PubMed:34715025). Plays a key role in the assembly or attachment of the inner dynein arm to microtubules in sperm flagella and tracheal cilia (By similarity). Forms filamentous polymers in the walls of ciliary and flagellar microtubules (PubMed:34715025). May interact with CCDC172. Colocalized with CCDC172 at the perinuclear region. Expressed in trachea multiciliated cells. Tyrosine phosphorylated. Belongs to the tektin family.