# Mechanical interplay between cell shape and actin cytoskeleton organization

## TL;DR

This study explores how the organization of the actin cytoskeleton influences cell shape and vice versa, using a combined analytical, simulation, and experimental approach to reveal a feedback mechanism governed by a dimensionless anchoring number.

## Contribution

The paper introduces a novel model linking actin cytoskeleton organization with cell shape, incorporating a feedback mechanism controlled by the anchoring number, validated by experiments.

## Key findings

- Cell edge shape approximated by elliptical arcs in aligned cytoskeletons
- Eccentricity of cell shape reflects internal stress anisotropy
- Model accurately predicts cell shape and cytoskeleton structure

## Abstract

We investigate the mechanical interplay between the spatial organization of the actin cytoskeleton and the shape of animal cells adhering on micropillar arrays. Using a combination of analytical work, computer simulations and in vitro experiments, we demonstrate that the orientation of the stress fibers strongly influences the geometry of the cell edge. In the presence of a uniformly aligned cytoskeleton, the cell edge can be well approximated by elliptical arcs, whose eccentricity reflects the degree of anisotropy of the cell's internal stresses. Upon modeling the actin cytoskeleton as a nematic liquid crystal, we further show that the geometry of the cell edge feeds back on the organization of the stress fibers by altering the length scale at which these are confined. This feedback mechanism is controlled by a dimensionless number, the anchoring number, representing the relative weight of surface-anchoring and bulk-aligning torques. Our model allows to predict both cellular shape and the internal structure of the actin cytoskeleton and is in good quantitative agreement with experiments on fibroblastoid (GD$\beta$1,GD$\beta$3) and epithelioid (GE$\beta$1, GE$\beta$3) cells.