Science 333, 456–459 (2011)

Credit: © 2011 AAAS

Cilia and flagella — tail-like protrusions that some cells have — can undergo self-sustained beating patterns that drive active cell motion. In eukaryotic cells, the core of these protrusions consists of an ordered bundle of microtubules and, among hundreds of proteins, dynein motors. Dyneins cause neighbouring microtubules to slide against each other by walking on a microtubule while being attached to an adjacent one. Elastic connectors between microtubules transform sliding into bending, and the regulated activity of thousands of dyneins causes oscillatory beating. Zvonimir Dogic and colleagues have now found a minimal in vitro system that mimics the beating patterns of cilia. The system is composed of microtubules, clusters of kinesin motors and a non-adsorbing polymer. Entropic depletion of the polymer drives microtubule bundling, whereas microtubule–kinesin interactions cause the bundled microtubules to beat as in native cilia. Surprisingly, dense arrays of active bundles spontaneously beat in sync, just as ciliary fields do. Such a minimal system could serve to further decipher the mechanistic origin of the synchronized beating of cilia and flagella.