Beating flagella power the movement of various eukaryotic cells. They are driven by the axoneme, a structure that usually comprises a central pair (CP) of singlet microtubules and nine surrounding doublets linked by dynein motors. Productive flagellar beating involves sequential activation and inactivation of these motors. Rotation of the CP is widely thought to regulate these changes but, on , Keith Gull and colleagues reveal that the CP does not rotate in trypanosome axonemes. Using the paraflagellar rod as an external reference, the authors demonstrate that the CP axis in trypanosomes is kept constant relative to this extra-axonemal structure. They then show that the orientation of the CP is dependent on an intact basal body (which anchors the axoneme to the cell) and influenced by physical contacts made by the CP along its length by knocking down several flagellar and basal body proteins (e.g. δ-tubulin) by RNAi. The authors conclude that, although CP rotation might regulate dynein-driven flagellar beating in some species, flagellar beating can also be regulated by other means.
