Extending and Contracting Cells

Physics 15, s21
Cell-substrate interactions explain a difference in behavior between individual cells and tissues on a surface.
A. Killeen/Imperial College London

Stretch an individual epithelial cell on a surface, and upon release, it will tend to contract back to its original shape. But some experiments have observed a fundamentally different behavior when such cells form tissues, which sometimes seem to prefer to extend—not contract—after stretching. Now, Andrew Killeen of Imperial College London and colleagues demonstrate with a model how this apparent change in behavior arises [1]. Their findings mean that some interpretations of past experiments may need to be updated, the researchers say.

Epithelial cells come in a variety of different shapes. Some epithelial tissues consist of elongated cells that tend to align like the rod-like molecules in a liquid crystal. However, such tissues contain sites where cells with one alignment butt against cells with another alignment. Previously, researchers studying these topological defects observed “extensile nematic behavior”: the cells moved as if they had a tendency to extend when stretched rather than to contract as individual cells on a substrate do.

To investigate how this apparent change in behavior arises, Killeen and colleagues hydrodynamically modeled a layer of cells on a surface, accounting specifically for cell-substrate interactions, such as the way cells propel themselves on a surface and the shear forces that act on cells when stretched. They found that fluctuations in cell-substrate forces could cause the defect regions to show extensile behavior even if the individual cells remained contractile; the cells only appeared to adopt extensile behavior within the cell layer. This finding means that researchers studying tissues on substrates may need to take cell-substrate interactions into account to get a complete picture of what is going on.

–Erika K. Carlson

Erika K. Carlson is a Corresponding Editor for Physics based in New York City.


  1. A. Killeen et al., “Polar fluctuations lead to extensile nematic behavior in confluent tissues,” Phys. Rev. Lett. 128, 078001 (2022).

Subject Areas

Biological PhysicsSoft Matter

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