Pattern formation, localized and running pulsation on active spherical membranes

TL;DR

This paper investigates how active forces from the actin-myosin cortex induce pattern formation and pulsations on spherical membranes, providing insights relevant to cell behavior and artificial cell experiments.

Contribution

It introduces a coupled field model analyzing membrane instabilities driven by active forces, revealing conditions for pattern formation and pulsations on spherical membranes.

Findings

Membrane becomes unstable and forms patterns when activity exceeds surface tension and rigidity.

Localized and running pulsations occur as dynamic membrane behaviors.

Results are summarized in phase diagrams and field evolution simulations.

Abstract

Active force generation by actin-myosin cortex coupled to the cell membrane allows the cell to deform, respond to the environment, and mediate cell motility and division. Several membrane-bound activator proteins move along it and couple to the membrane curvature. Besides, they can act as nucleating sites for the growth of filamentous actin. Actin polymerization can generate a local outward push on the membrane. Inward pull from the contractile actomyosin cortex can propagate along the membrane via actin filaments. We use coupled evolution of fields to perform linear stability analysis and numerical calculations. As activity overcomes the stabilizing factors such as surface tension and bending rigidity, the spherical membrane shows instability towards pattern formation, localized pulsation, and running pulsation between poles. We present our results in terms of phase diagrams and evolutions of the coupled fields. They have relevance for living cells and can be verified in experiments on artificial cell-like constructs.