Cilia, tiny hair-like structures that propel mucus out of airways, have to agree on the direction of the fluid flow to get things moving. Researchers at the Salk Institute for Biological Studies discovered a novel two-step mechanism that ensures that all cilia beat in unison.
Their study, published in Nature, reveals that during early embryonic development, cilia point more or less in the general direction of the body's back end and start creating a weak flow. During the following refinement phase, all cilia get in line and trim their sails to the prevailing winds.
Two ciliated cells showing cilia (green) and basal bodies (red).