Epithelial Cell Shapes Emerge from Motion in Confluent Monolayers

Epithelial cells are among the most mechanically intriguing cells in the body. They perform many important functions in different organs and tissues and as a result they are adaptable to a wide range of mechanical stimuli and environments. When epithelial cells are cultured in experiments, they form confluent monolayers where they actively push and pull on their neighbors as they move. These dynamic forces strongly affect the shapes of epithelial cells. Previous studies have assumed that each cell has its own preferred shape parameter , defined by the ratio of the squared perimeter of the cell to its area in 2D, and that the cell must reach a threshold shape parameter to move in a confluent monolayer. We show here that cell shape parameters are not elastically pinned to a preferred value, but instead the cell shapes are viscoelastic and change in response to local forces that each cell experiences. We compare the distributions of cell shape parameters from experiments of mobile cell monolayers from 4 different epithelial cell lines and find that they possess similar distributions. We also show that the time-averaged shape parameter distribution of individual cells within the monolayers is the same as the spatially-averaged shape parameter distribution of the entire monolayer.