Central pair apparatus enhances outer‐arm dynein activities through regulation of inner‐arm dyneins

The beating of eukaryotic cilia and flagella is controlled by multiple species of inner-arm and outer-arm dyneins. To clarify the regulation on axonemal beating by nucleotide conditions and central-pair microtubules, microtubule sliding in disintegrating Chlamydomonas axonemes of various mutants and in vitro microtubule gliding by isolated axonemal dyneins were examined. In the in vitro motility assays with outer-arm dyneins (alphabeta and gamma), microtubule translocation velocity decreased at high concentrations of ATP, while this inhibition was canceled by the simultaneous presence of ADP or ribose-modified analogues, mantATP/ADP. In contrast, motility of inner-arm dyneins was rather insensitive to these nucleotides. The velocity of sliding disintegration in axonemes lacking the central pair was less than that in wild-type axonemes at high ATP concentrations, but was overcome by the presence of ADP or mantATP/ADP. While these nucleotides did not activate the sliding velocity in other mutant axonemes, they increased the extent of sliding, except for axonemes lacking outer-arm dynein. Experiments with axonemes lacking inner-arm dynein f using casein kinase 1 inhibitor suggest that the regulation of outer-arm dynein by the central pair is effected through the activation of inner-arm dynein f, and possibly by other interactions. These results indicate that the central pair activates outer-arm dyneins on specific outer-doublet, resulting in amplification of the axonemal bending force.