Hydrodynamics of shape-driven rigidity transitions in motile tissues

TL;DR

This paper introduces a hydrodynamic model linking cell shape, tissue stiffness, and motility, revealing how tissue behavior can be controlled between homogeneous and patterned states through a tunable parameter.

Contribution

It develops a novel coupled model of cell shape and motility, connecting tissue stiffness to pattern formation in biological tissues.

Findings

Tissue behavior can be tuned between homogeneous and patterned states.

A composite 'morphotaxis' parameter controls pattern formation.

The control parameter depends on cell movement direction and polarization sources or sinks.

Abstract

In biological tissues, it is now well-understood that mechanical cues are a powerful mechanism for pattern regulation. While much work has focused on interactions between cells and external substrates, recent experiments suggest that cell polarization and motility might be governed by the internal shear stiffness of nearby tissue, deemed "plithotaxis". Meanwhile, other work has demonstrated that there is a direct relationship between cell shapes and tissue shear modulus in confluent tissues. Joining these two ideas, we develop a hydrodynamic model that couples cell shape, and therefore tissue stiffness, to cell motility and polarization. Using linear stability analysis and numerical simulations, we find that tissue behavior can be tuned between largely homogeneous states and patterned states such as asters, controlled by a composite "morphotaxis" parameter that encapsulates the nature of the coupling between shape and polarization. The control parameter is in principle experimentally accessible, and depends both on whether a cell tends to move in the direction of lower or higher shear modulus, and whether sinks or sources of polarization tend to fluidize the system.