Traction dynamics in collective cell migration

Recent theoretical models have emphasized cell motility force as a key driver of collective cell migration. In experiments, the equivalent to the motility force is traction applied by each cell to the substrate, which can be measured by traction force microscopy. Previous experiments have measured tractions in groups of cells but have not tracked tractions applied by individual cells. As a result, there is a lack of information on single-cell tractions over time, which makes it difficult to bridge the gap between single cell and collective cell dynamics. Here, we designed experiments to follow cells in a Lagrangian frame of reference, tracking each cell using fluorescent imaging of its nucleus. To investigate the evolution of traction of each cell over time, we built a Voronoi tessellation based on the centroids of cell nuclei and mapped tractions obtained from traction force microscopy onto each cell’s Voronoi-based polygon. The resulting data can be used to compute different metrics of traction dynamics of each cell such as the persistence of both direction and magnitude of traction. This new approach helps to investigate theoretical predictions of cell motility force on collective cell migration, thus bridging the gap between single cell and collective cell dynamics.