FIG. 1.

Hypothetical model depicting the radial spoke as a mechanochemical transducer extending between the central pair apparatus and outer doublet microtubules, anchored near the base of the inner arm dynein. In this model, the signal input includes calcium binding and/or mechanical strain induced by transient interaction of the spoke head with the central apparatus as microtubules slide (54) or as the central pair rotates (35). Transduction output, at the junction between the spoke stalk and doublet microtubule, is predicted to include localized control of axonemal protein phosphorylation and localized regulation of dynein-driven microtubule sliding. cAMP, cyclic AMP; DRC, dynein regulatory complex.