From Flow to Form: Emergence of the Cytokinetic Ring via Active Cortical Dynamics

TL;DR

This study uses 3D simulations to show how cortical flows and nematic order lead to the spontaneous emergence of a cytokinetic ring and associated cell shape changes during division.

Contribution

It reveals that flow patterns and ring formation can arise from initial nematic alignment bias, not just filament chirality, highlighting a memory effect in cortical dynamics.

Findings

Nematic actomyosin ring spontaneously emerges at the cell equator.

Different cortical flow patterns, including counter-rotating flows, can develop.

Initial nematic alignment bias influences flow patterns and ring formation.

Abstract

During cell division active flows occur in the cortex, a thin layer of gel like network of acto myosin filaments, beneath the cell surface. The cortical flow and the associated stresses bring about change in the cell shape, in particular a sharp invagination at the mid cell. Using 3D phase field simulation of an active deformable shell, which captures coupled dynamics of cortical velocity and nematic order, we show how a nematic like actomyosin ring spontaneously emerge at the equator and drive sharp invagination. We further demonstrate how different cortical flow patterns, including counter rotating flows emerge near the division furrow. We show that these flow patterns, often attributed to intrinsic chirality of actomyosin filaments can instead arise from bias in the initial nematic alignment, revealing a memory effect in the system. By analyzing a simpler model of activity gradient driven compressive flow on a flat interface we decipher the main ingredients for surface instability leading to invagination and counter moving flows.