Epithelial Monolayers Display Different Modes of Traction Stress Organization*

Monolayers of epithelial cells are characterized by both “classical” material properties as well as self-responsiveness and other properties defined by their non-equilibrium status, and as such pose interesting questions at the intersection of several disciplines. We have identified, in the case of wild type and zonula occludens (ZO) 1 and 2 dKD MDCK cells, at least two patterns of behavior in how monolayers distribute mechanical forces to their environment, i.e., traction stresses. In the first case, ZO dKD cells distribute stresses in analogy to an elastic contractile gel, results that agree with previous results from colonies of keratinocytes. The wild type cells, however, distribute stresses in contradiction to these results, notably in the movement of stress peaks over time. This underlines the need for a dynamic model of traction stresses; active matter provides natural candidates for such a model. A newly-developed active vertex model recapitulates the wild type behavior with a small set of tunable parameters. This, taken together with the experimental results, implies a spectrum of traction stress dynamics that could unify tissue-scale mechanics for several systems under one model.