Sparse mesenchymal cell networks as a fluid under tension

The avian presomitic mesoderm (PSM) behaves as a fluid under tension, with organization that cannot be explained by simple Brownian-like cell motion.

• Why it matters: Sparse mesenchymal networks are widespread, but the physical rules behind their collective behavior are unclear due to stellate cells and large extracellular spaces.
• What they did: Using quantitative modeling plus experiments and simulations, the study identifies contact inhibition of locomotion (CIL)—active retraction and turning away on contact—as a mechanism, supported by observed cell turning and outward acceleration from spreading explants.
• The result: Continuum equations link cell-scale parameters to remodeling dynamics, implying CIL has a mechanical role in sustaining macroscopic tension while tissues flow, and defining a fluid-under-tension state relevant to developing embryonic tissues.

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