Anillin propels myosin-independent constriction of actin rings

Abstract

Constriction of the actin cytokinetic ring is an essential step of cell division. In a generally accepted view, the constriction is driven by relative sliding of actin filaments propelled by myosin motors. However, in multiple organisms, the ring constriction is myosin independent. How actin rings constrict in the absence of motor activity remains unclear. Here, we demonstrate that actin contractility can be propelled by anillin, a diffusible non-motor actin crosslinker, localising to the cytokinetic ring. We in vitro observed the formation and constriction of rings comprising multiple actin filaments bundled by anillin. Rings constricted due to anillin-generated forces maximising the overlap lengths between the filaments. Actin disassembly promoted constriction. We propose that actin crosslinkers, generating forces complementary to molecular motors, contribute to the contractility of diverse actin structures, including the cytokinetic ring.