Multicellular traction alignment affects collective pack size during collective migration

During collective cell migration, cells coordinate their motion with their neighbors giving rise to collectively moving packs spanning multiple cell lengths. However, the physical mechanism controlling the collective pack size remains unclear. We hypothesized that one factor affecting pack size is coordination of propulsive traction between neighboring cells. To test this hypothesis, we used the self-propelled Voronoi model and experimental data on cell tractions and motion. We calibrated the model using a new experimental measurement of persistence time of propulsive traction and subsequently implemented an alignment of traction between each cell and its immediate neighbors. Comparison of spatial autocorrelation of cellular tractions and velocity between the experimental data and the model suggested the presence of coordinated traction between neighboring cells, thus confirming our hypothesis. The results give a new evidence for alignment of traction between neighboring cells, which is a physical mechanism by which cells coordinate motion with their neighbors.