Light-regulated collective contractility in a multicellular choanoflagellate

In contrast to plants and fungi, animals can deform their bodies by the collective activity of contractile cells. Collective contractility underlies processes such as gastrulation and muscle-based motility. Brunet et al. report that a close relative of animals, a choanoflagellate they name Choanoeca flexa, forms cup-shaped colonies that undergo collective contractility, leading to a rapid change in colony morphology (see the Perspective by Tomancak). C. flexa colonies are each composed of a monolayer of polarized cells. In response to sudden darkness, a light-sensing protein triggers coordinated, polarized contraction of C. flexa cells, which results in colony inversion. The cellular mechanisms underlying this process are conserved between C. flexa and animals, indicating that their last common ancestor was also capable of polarized cell contraction.