Actomyosin Contraction Induces In-Bulk Motility of Cells and Droplets

Abstract

Cell crawling on two-dimensional surfaces is a relatively well-understood phenomenon that is based on actin polymerization at a cell's front edge and anchoring on a substrate, allowing the cell to pull itself forward. However, some cells, such as cancer cells invading a three-dimensional matrigel, can also swim in the bulk, where surface adhesion is impossible. Although there is strong evidence that the self-organized engine that drives cells forward in the bulk involves myosin, the specific propulsion mechanism remains largely unclear. Here, we propose a minimal model for in-bulk self-motility of a droplet containing an isotropic and compressible contractile gel, representing a cell extract containing a disordered actomyosin network. In our model, contraction mediates a feedback loop between myosin-induced flow and advection-induced myosin accumulation, which leads to clustering and locally enhanced flow. The symmetry of such flow is then spontaneously broken through actomyosin-membrane interactions, leading to self-organized droplet motility relative to the underlying solvent. Depending on the balance between contraction, diffusion, detachment rate of myosin, and effective surface tension, this motion can be either straight or circular. Our simulations and analytical results shed new light on in-bulk myosin-driven cell motility in living cells and provide a framework to design a novel type of synthetic active matter droplet potentially resembling the motility mechanism of biological cells.

Self-organization in amoeboid motility

“…As the cortex of a model spherical cell polarizes, with actomyosin enriched at one pole and flows directed between poles, the cortical tension becomes inhomogeneous. As a result, Laplace's law tells us that shape change occurs, the surface curvature varies with position, and the cell is no longer spherical Bun et al (2014);; Wu et al (2018); Le Goff et al (2020). This, then, raises the question of whether the deformation of the cortical layer feeds back in any way on the cortical flow, and if so, is the mechanism of migration altered.…”

The Influence of Nucleus Mechanics in Modelling Adhesion-independent Cell Migration in Structured and Confined Environments

“… 2019 ; Le Goff et al. 2020 ), demonstrating that motility can still occur and making the models non-specific to the adhesion properties of the cell with its environment. However, since most of these models are interested in determining the minimal ingredient for the onset of cell motion, they are solved in a 1D setting (Farutin et al.…”

“… 2019 ; Le Goff et al. 2020 ), the presence of the nucleus as a limiting factor for cell migration and the effect of confinement are not taken into account.…”