Dyneins are cellular proteins that function as transporters. They function by moving along the microtubules. Axonemal dyneins are present in cells that contain cilia and flagella and cause the sliding of microtubules that is characteristic of the motion associated with these organelles. The radial spokes are another set of proteins that are regularly spaced along the cilia and flagella and form a connection between the central microtubule pair and the dynein motor. Thus, the radial spokes, with their multisubunit stalk and head carry out a signal transduction between the microtubules and the dynein motor. Evidence suggests that the radial spokes regulate dynein-induced movement and govern cilia and flagella waveform, with the central pair-radial spoke interactions determining bend direction and shape (waveform), and radial spoke-inner dynein arm interactions influencing velocity. The RSPH9 gene codes for the RSPH9 protein, which, by homology is predicted to be a radial spoke protein. This homology is based on proteins in the alga Chlamydomonas reinhardtii and other ciliates.
Mutations in RSPH9 have been shown to cause a form of primary ciliary dyskinesia (CILD12). This condition is characterized by axonemal abnormalities of motile cilia. Specifically, respiratory infections, chronic inflammation, bronchiectasis, reduced fertility in affected males, and situs inversus in about half of affected patients, are noticed.