Instabilities on the leading front of collectively migrating tissue

Instabilities are often observed on the leading front of a collectively migrating cellular sheet both in vivo and in vitro. Instead of moving forward uniformly, the leading front often destabilizes into multicellular fingering-like structures. To decipher the mechanical origin of the instabilities, we develop a continuous model based on the Toner-Tu equations for active fluids, in which the collectively moving cells are modeled as a system of self-propelled particles. We perform different perturbations on the front edge and analyze the linear stability. We show the instabilities are due to some kinds of perturbations, for example, leader cells. Finally, we show our simulation of figuring-like protrusions with the guidance of leader cells.