Flagellar oscillation: new vibes from beads

Abstract

The oscillatory mechanism of eukaryotic flagella and cilia remains one of the mysteries of cell biology. It has been difficult to dissect the oscillation functionally when its coupling to the bending of the flagellum has been required to provide a read-out of the functioning of the oscillator. A way around this difficulty is now provided by work from several laboratories, involving the attachment of submicrometer diameter beads to microtubules as indicators of dynein-driven movement of microtubules. No one considers the flagellar oscillator to be a purely biochemical oscillator, since its frequency, and other properties of flagellar bending waves, can be significantly altered by external mechanical influences (reviewed by Brokaw, 1989a). Flagella can be described as highpowered mechanochemical oscillators that operate at the subcellular level. The oscillatory mechanism of the dynein-microtubule system in flagella is therefore comparable to that of the myosin-actin system of insect fibrillar flight muscle (Pringle, 1957). However, flagella oscillate at frequencies ranging from less than 1 cycle per second to more than 100 cycles per second, with microtubule sliding amplitudes of 100 nm or more, while fibrillar muscles oscillate at frequencies up to 1000 cycles per second, but with local amplitudes usually of the order of 10 nm.