Stress-shape misalignment in confluent cell layers

TL;DR

This paper explores the complex relationship between cell shape and contractile forces in confluent cell layers, revealing significant misalignments and proposing a new continuum model that decouples force orientation from cell shape.

Contribution

It introduces a continuum model that decouples active force orientation from cell shape, challenging existing active nematic models of cell motility.

Findings

Discovery of up to 90° misalignment between cell shape and force directions.

Identification of dynamic, correlated domains with misaligned orientations.

Development of a continuum model decoupling force and shape orientations.

Abstract

This study investigates the relationship between cell shape and cell-generated stresses in confluent cell layers. Using simultaneous measurements of cell shape orientation and cell-generated contractile forces in MDCK and LP-9 colonies, we report the emergence of correlated, dynamic domains in which misalignment between the directors defined by cell shape and by contractile forces reaches up to 90$^o$, effectively creating extensile domains in a monolayer of contractile cells. To understand this misalignment, we develop a continuum model that decouples the orientation of cell-generated active forces from the orientation of the cell shapes. This challenges the prevailing understanding that cells throughout a tissue create either contractile or extensile forces, and the validity of the usual active nematic models of cell motility where active forces are strictly slaved to cell shape orientation.