Nanometer scale vibration in mutant axonemes of Chlamydomonas

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Abstract
Flagellar axonemes of sea urchin sperm display high frequency (200–400 Hz) vibration with nanometer scale amplitudes in the presence of ATP [Kamimura and Kamiya, 1992: J. Cell Biol. 116:1443–1454]. To investigate how various axonemal components affect the vibration, we examined vibration in wild‐type and mutant axonemes of Chlamydomonas. At 1 mM ATP, wild‐type axonemes underwent vibration at 100–650 Hz with amplitudes of 4–40 nm. This vibration was similar to, but less regular than, that in sea urchin sperm. Axonemes of the mutants ida1 and ida4 lacking part of the inner arm dynein underwent vibrations indistinguishable from that of wild‐type. The mutant oda1 lacking the entire outer arm underwent vibration at about half the wild‐type frequency. Unexpectedly, the paralyzed mutants pf18 lacking the central pair and pf14 lacking the radial spokes displayed vibration with significantly higher frequencies and smaller amplitudes than those in the wild‐type vibration. These results indicate that the high‐frequency vibration is common to many kinds of mutant axonemes that lack various axonemal substructures, but that its manner is sensitive to the presence of outer arm dynein and the central pair/radial spoke system. Simultaneous measurements of amplitude and frequency in wild‐type and mutant axonemes suggest that the velocity of microtubule sliding in vibrating axonemes is lower than the velocity of sliding under load‐free conditions. The velocity is particularly low in pf18. A possible mechanism is proposed to explain the lower sliding velocity and vibration amplitude in the pf18 axoneme, based on an assumption that central pair/radial spoke system may work to regulate the switching of two antagonizing forces within the axoneme.