Spontaneous polarization in an interfacial growth model for actin filament networks with a rigorous mechano-chemical coupling

TL;DR

This paper introduces a continuum theory for actin filament network growth under stress, revealing a spontaneous polarization mechanism and morphological instability that align with experimental observations, advancing understanding of cell motility.

Contribution

It provides a novel mechano-chemical coupling framework for actin growth, bridging mesoscale and continuum models, and predicts spontaneous polarization phenomena.

Findings

Predicts morphological instability on rigid spheres

Shows contact mechanics influence instability existence

Derives scaling laws for growth dynamics

Abstract

Many processes in eukaryotic cells, including cell motility, rely on the growth of branched actin networks from surfaces. Despite its central role the mechano-chemical coupling mechanisms which guide the growth process are poorly understood, and a general continuum description combining growth and mechanics is lacking. We develop a theory that bridges the gap between mesoscale and continuum limit and propose a general framework providing the evolution law of actin networks growing under stress. This formulation opens an area for the systematic study of actin dynamics in arbitrary geometries. Our framework predicts a morphological instability of actin growth on a rigid sphere, leading to a spontaneous polarization of the network with a mode selection corresponding to a comet, as reported experimentally. We show that the mechanics of the contact between the network and the surface plays a crucial role, in that it determines directly the existence of the instability. We extract scaling laws relating growth dynamics and network properties offering basic perspectives for new experiments on growing actin networks.