# Stress-shape misalignment in confluent cell layers

## TL;DR

This study shows that cells in a tissue layer can generate contractile forces that are not aligned with their shape, challenging previous assumptions about cell behavior.

## Contribution

The paper introduces a new model and experimental findings showing that contractile stress and cell shape can be misaligned in dynamic domains.

## Key findings

- Cells in monolayers form dynamic domains with misaligned contractile stresses and cell bodies.
- A continuum model successfully captures the spatial and temporal dynamics of these misaligned regions.
- The findings suggest that cell forces and shape are governed by more flexible physical rules than previously thought.

## Abstract

In tissue formation and repair, the epithelium undergoes complex patterns of motion driven by the active forces produced by each cell. Although the principles governing how the forces evolve in time are not yet clear, it is often assumed that the contractile stresses within the cell layer align with the axis defined by the body of each cell. Here, we simultaneously measured the orientations of the cell shape and the cell-generated contractile stresses, observing correlated, dynamic domains in which the stresses were systematically misaligned with the cell body. We developed a continuum model that decouples the orientations of contractile stress and cell body. The model recovered the spatial and temporal dynamics of the regions of misalignment in the experiments. These findings reveal that the cell controls its contractile forces independently from its shape, suggesting that the physical rules relating cell forces and cell shape are more flexible than previously thought.

When studying nematic ordering of cells in a monolayer, it is commonly assumed that the principal stress and cell shape axes are tightly coupled. Here, the authors measure cell shape and cell-generated contractile stresses and show that cells in monolayers form correlated, dynamic domains in which the stresses are systematically misaligned with the cell bodies.