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Review
. 2019 Jun 20:88:661-689.
doi: 10.1146/annurev-biochem-062917-012530. Epub 2019 Jan 16.

Molecular Mechanism of Cytokinesis

Thomas D Pollard  1   2   3 , Ben O'Shaughnessy  4
Affiliations
Review

Molecular Mechanism of Cytokinesis

Thomas D Pollard et al. Annu Rev Biochem. .

Abstract

Division of amoebas, fungi, and animal cells into two daughter cells at the end of the cell cycle depends on a common set of ancient proteins, principally actin filaments and myosin-II motors. Anillin, formins, IQGAPs, and many other proteins regulate the assembly of the actin filaments into a contractile ring positioned between the daughter nuclei by different mechanisms in fungi and animal cells. Interactions of myosin-II with actin filaments produce force to assemble and then constrict the contractile ring to form a cleavage furrow. Contractile rings disassemble as they constrict. In some cases, knowledge about the numbers of participating proteins and their biochemical mechanisms has made it possible to formulate molecularly explicit mathematical models that reproduce the observed physical events during cytokinesis by computer simulations.

Keywords: actin; contractile ring; cytokinesis; mathematical models; myosin.

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Figures

Figure 1
Figure 1
Illustrations comparing the steps in cytokinesis by animals, budding yeast, and fission yeast. Figure modified from Reference . Abbreviations: CPC, chromosomal passenger complex; Rho-GEF, Rho GTPase guanine nucleotide exchange factor.
Figure 2
Figure 2
Biochemical mechanisms that position the cleavage furrow in animal cells. Abbreviations: Arp2/3, actin-related protein 2 and 3; Cdk1, cyclin-dependent kinase 1; CPC, chromosomal passenger complex; GEF, guanine nucleotide exchange factor; Rac, small GTPase; Rho, small GTPase; ROCK, Rho-kinase.
Figure 3
Figure 3
Mechanisms of contractile ring formation. (a) Astral microtubules concentrate the centralspindlin complex, Rho-GEF Ect-2, and CPC at the equator and send a negative signal to the poles. (b Pom1 kinase and other signals from the poles exclude type I nodes from the poles during interphase. (c) Cdc42 GTPase establishes a bud site next to the bud scar from previous division during interphase. Figure modified from Reference . Abbreviations: Cdc42, small GTPase; CPC, chromosome passenger complex; GEF, guanine nucleotide exchange factor; Pom1, a fission yeast kinase; Rho, small GTPase.
Figure 4
Figure 4
Radial and transverse anchoring in constricting contractile rings in fission yeast. (a) Nodes anchor myosin-II Myo2 and the formin dimer Cdc12p to the plasma membrane. The formin anchors the actin filament barbed end (B) to the node (i). Stepping of Myo2 toward the barbed end produces tension, if lateral anchors produce a drag force (black arrow) opposing the myosin forces (red arrows). Myo2 also anchors curved actin filaments radially, producing inward Laplace forces (blue arrows). The ring tension is the sum of the tensions of all filaments passing through a cross section of the ring (blue, iii). Anchoring the pointed end of the actin filament (P) would generate compression rather than tension (ii). (b) A contractile ring segment detaches from the membrane and shortens in a permeabilized fission yeast protoplast (right). At the anchored-unanchored interface, barbed-end–anchored actin filaments point into and reel in the tensionless unanchored segment at approximately the load-free velocity of myosin-II (left). Orange bipolar filaments represent unanchored myosin-II. (c) Myosin-II Myp2 may be unanchored in the fission yeast ring. An unanchored cluster of Myp2 (green) is depicted exerting tensile force after migrating to a location with equal numbers of actin filament orientations to the right (green) and left (red). (d) model of detachment of contractile ring segments in cells with the myo2-E1 mutation where Myo2 binds actin filaments weakly. Straight bundles of actin filaments (gray) and Myp2 (green) detach from the plasma membrane, leaving Myo2 (red) behind on the membrane.
Figure 5
Figure 5
Two mechanisms for regulated disassembly of constricting contractile rings. (a) In model A, the ring consists of many similar or identical contractile units and shortens by controlled dissociation of proteins from each unit without compromising global structure. Memory of the initial structure is maintained throughout constriction. (b) In model B, the ring is continuously rebuilt as it constricts and as incoming components self-assemble and replace dissociated components more rapidly than constriction. The memory time is the turnover time. Both models preserve the organization of the ring and its ability to generate tension.
Figure 6
Figure 6
The relationship between ring tension and constriction rate. (a) By Laplace’s law, a contractile ring of radius R with tension T exerts an inward radial force T/R per ring length, tending to constrict the ring. The constriction rate is set by a balance of this force with opposing osmotic, elastic, and viscous cytoplasmic forces, tensile and viscous cortical forces in animal cells, and force associated with the septum in organisms with cell walls. (b) Fission yeast grows cell wall material termed the septum inward behind the contractile ring as it constricts. Confocal fluorescence micrographs of the division plane of a fission yeast cell expressing β-glucan synthase GFP-Bgs1 (labeling septum) and myosin-II light chain Rlc1-tdTomato (labeling the contractile ring). (c) In fission yeast, ring tension is too small to deform the septum mechanically, so the constriction rate is presumably set by the rate the septum is grown by Bgs1 and other glucan synthases in the membrane. The activity of Bgs1 may be mechanosensitive, with faster septum synthesis where curvature and the inward force from ring tension are high (green arrows). This mechanism would suppress rough features and ensure the septum is almost circular.
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