Molecular basis of cytokinesis in fission yeast

Abstract

Cell division by cytokinesis in animals and fungi depends on a contractile ring of actin filaments and the motor protein myosin‐II. Fluorescence microscopy of live fission yeast cells reveals that they assemble a cytokinetic contractile ring by condensation of a broad band of membrane‐associated nodes. The position of the nucleus determines the initial location of the zone with these nodes by releasing the anillin‐like protein Mid1p, which recruits to nodes myosin‐II followed by other proteins including formin Cdc12p. Actin filaments nucleated by Cdc12p form a network between the nodes and myosin‐II pulls the nodes together into a ring. Our analysis of node motions and numerical simulations show that a simple, unassisted search, capture, pull, and release mechanism can account for contractile ring assembly. A key element in the mechanism is that the connections between actin filaments from one node and myosins in another node are transient, so that myosins produce force on a captured actin filament for only about 20 seconds before being released.