Soft Listeria: actin-based propulsion of liquid drops

TL;DR

This paper models the actin-driven propulsion of liquid drops, revealing how elastic stresses and polymerization dynamics influence shape and motion, with quantitative agreement between theory and experiments.

Contribution

It introduces a theoretical framework for the shape and motion of actin-propelled drops, incorporating elasticity and stress-dependent polymerization velocity.

Findings

Drop shapes are deformed by elastic stresses from actin polymerization.

The model predicts zero net propulsive force without surface tension or pressure gradients.

Quantitative parameters of actin polymerization are derived from experimental data.

Abstract

We study the motion of oil drops propelled by actin polymerization in cell extracts. Drops deform and acquire a pear-like shape under the action of the elastic stresses exerted by the actin comet. We solve this free boundary problem and calculate the drop shape taking into account the elasticity of the actin gel and the variation of the polymerization velocity with normal stress. The pressure balance on the liquid drop imposes a zero propulsive force if gradients in surface tension or internal pressure are not taken into account. Quantitative parameters of actin polymerization are obtained by fitting theory to experiment.