Heterogenous adhesion of follower cells affects tension profile and velocity of leader cells in primary keratocyte collective cell migration

Single cell studies demonstrate membrane tension to be a central regulator of lamellipodia-driven motility bringing in front-coherence. During collective cell migration, however, tension mapping or existence of intracellular tension-gradients and the effect of cell-cell interactions have remained unexplored. In this study of membrane fluctuations and fluctuation-tension of migrating primary keratocyte cell-sheets, we first show that some leader cells are followed by followers which remain de-adhered from the substrate while being attached to other cells and thus appear to be "taking a ride". A subtle yet significant enhanced long-timescale velocity in these leaders indicate increased directionality. Intriguingly, such leaders mostly have front-high tension gradients like single keratocytes, while followers and other leaders usually display front-low membrane tension gradients. The front-high tension gradient and higher membrane tension observed in these leaders, despite the high cell-to-cell variability in membrane tension demonstrate how leader-follower interactions and heterogenous adhesion profiles are key in collective cell migration.