Molecular Model of the Contractile Ring

We present a model for the actin contractile ring of adherent animal cells. The model suggests that the actin concentration within the ring and consequently the power that the ring exerts both increase during contraction. We demonstrate the crucial role of actin polymerization and depolymerization throughout cytokinesis, and the dominance of viscous dissipation in the dynamics. The physical origin of two phases in cytokinesis dynamics (“biphasic cytokinesis”) follows from a limitation on the actin density. The model is consistent with a wide range of measurements of the midzone of dividing animal cells.

💡 Research Summary

The paper presents a quantitative physical model of the actin contractile ring that drives cytokinesis in adherent animal cells. Traditional descriptions treat the ring as a static structure with a fixed tension and constant actin density, but live‑cell imaging shows that both the actin concentration within the ring and the ring’s thickness increase as the cell divides. To capture these dynamics, the authors formulate a set of coupled differential equations that describe (1) actin polymerization and depolymerization, (2) the mechanical balance between ring tension and viscous resistance, and (3) a saturation limit on actin density.

Polymerization is modeled as a rate proportional to the concentration of free G‑actin in the cytoplasm (k_on·