A simple active gel model for optogenetic control of cell migration

Cell motility is one of the hallmarks of life and often results from flow in the actin cytoskeleton that is driven by myosin II motors. The natural model to describe such flows is active gel theory, in which myosin II contractility enters as active stress. Advancements in synthetic biology and optogenetic tools have sparked renewed interest in predicting how these flows can be controlled. However, it is notoriously difficult to theoretically explain bistability of sessile and motile cells and study migration in current active gel models. Here we show that bistability emerges naturally in a one-dimensional active gel model if the myosin II motors are modeled as a supercritical van der Waals fluid, including volume exclusion and short-range attraction. We consider two optogenetically accessible protocols for migration control – localized contractility perturbations and global upregulation of contraction – and find that the local protocol permits full control. Global upregulation leads to irreversible motility initiation but does not allow for full control. Our results agree with recent optogenetic experiments on cell migration in microchannels and reconcile experimental observations of local versus global regulatory mechanisms.