Aster Swarming by Collective Mechanics of Dyneins and Kinesins

TL;DR

This study uses a computational model to explore how microtubule asters and molecular motors interact within cells, revealing conditions that lead to spontaneous vortex-like rotation driven by motor dynamics and noise.

Contribution

It introduces a novel computational model demonstrating how motor interactions and noise induce collective aster rotation, a phenomenon not previously characterized.

Findings

Coordinated aster rotation emerges with sufficient cortical dynein and kinesin density.

MT dynamic instability acts as noise, breaking symmetry and enabling rotation.

Aster rotation depends on motor density thresholds and diffusion limitations.

Abstract

Microtubule (MT) radial arrays or asters establish the internal topology of a cell by interacting with organelles and molecular motors. We proceed to understand the general pattern forming potential of aster-motor systems using a computational model of multiple MT asters interacting with motors in a cellular confinement. In this model dynein motors are attached to the cell cortex and plus-ended motors resembling kinesin-5 diffuse in the cell interior. The introduction of 'noise' in the form of MT length fluctuations spontaneously results in the emergence of coordinated, achiral vortex-like rotation of asters. The coherence and persistence of rotation requires a threshold density of both cortical dyneins and coupling kinesins, while the onset of rotation if diffusion-limited with relation to cortical dynein mobility. The coordinated rotational motion arises due to the resolution of the 'tug-of-war' of the rotational component due to cortical motors by 'noise' in the form of MT dynamic instability, and such transient symmetry breaking is amplified by local coupling by kinesin-5 complexes. The lack of widespread aster rotation across cell types suggests biophysical mechanisms that suppress such intrinsic dynamics may have evolved. This model is analogous to more general models of locally coupled self-propelled particles (SPP) that spontaneously undergo collective transport in presence of 'noise' that have been invoked to explain swarming in birds and fish. However, the aster-motor system is distinct from SPP models with regard to particle density and 'noise' dependence, providing a set of experimentally testable predictions for a novel sub-cellular pattern forming system.