Two anti-radial spoke monoclonal antibodies inhibit Chlamydomonas axonemal motility by different mechanisms.

In the 9 + 2 axoneme, radial spokes are structural components attached to the A-tubules of the nine outer doublet microtubules. They protrude toward the central pair microtubule complex with which they have transient but regular interactions for the normal flagellar motility to occur. Flagella of Chlamydomonas mutants deficient in entire radial spokes or spoke heads are paralyzed. In this study the importance of two radial spoke proteins in the flagellar movement is exemplified by the potent inhibitory action of two monoclonal antibodies on the axonemal motility of demembranated-reactivated Chlamydomonas models. We show that one of these proteins is localized on the stalk of the radial spokes, whereas the other is a component of the head of the same structure and most likely correspond to radial spoke protein 2 and 1, respectively. Fine motility analysis by videomicrography further indicates that these two anti-radial spoke protein antibodies at low concentration affect motility of demembranated-reactivated Chlamydomonas by changing the flagellar waveform without modifying axonemal beat frequency. They also modify wave amplitude differently during motility inhibition. This brings more direct evidence for the involvement of both radial spoke stalk and head in the fine tuning of the waveform during flagellar motility.