Model of lamellipodium initiation during cell spreading

TL;DR

This paper presents a physics-inspired model explaining how actin filament reorganization initiates lamellipodium formation during cell spreading, highlighting a feedback loop involving membrane curvature and filament alignment.

Contribution

It introduces a novel biophysical model linking actin mechanics, membrane curvature, and filament orientation to lamellipodium initiation and cell spreading dynamics.

Findings

Identifies conditions for a full wetting transition leading to lamellipodium formation.

Reveals bi-stability between partial and full spreading, suggesting mechanisms for cell polarization.

Proposes a positive feedback loop driving cell spreading and migration.

Abstract

Cell spreading requires a major reorganisation of the actin cytoskeleton, from a cortical structure to a lamellipodium where filaments are mostly parallel to the substrate. We propose a model inspired by the physics of nematic liquid crystals and fluid membranes, in which the coupling between actin mechanics, filaments orientation, and the local curvature of the cell membrane naturally yields the collective reorientation of actin filaments at the highly curved edge of a spreading cell. Filament orientation increases the traction force exerted by the frictional flow of polymerising actin on the substrate, creating a positive feedback loop between edge curvature, filament alignment, and traction force that promotes cell spreading. We establish the condition under which this feedback leads to a full wetting transition, which we interpret as the initiation of a lamellipodium, and we uncover the existence of bi-stability between partial and full spreading which could trigger spontaneous cell polarization and lead to migration.