  Migration of animal cells is based on the interplay between actin
polymerization at the front, adhesion along the cell-substrate interface, and
actomyosin contractility at the back. Active gel theory has been used before to
demonstrate that actomyosin contractility is sufficient for polarization and
self-sustained cell migration in the absence of external cues, but did not
consider the dynamics of adhesion. Likewise, migration models based on the
mechanosensitive dynamics of adhesion receptors usually do not include the
global dynamics of intracellular flow. Here we show that both aspects can be
combined in a minimal active gel model for one-dimensional cell migration with
dynamic adhesion. This model demonstrates that load sharing between the
adhesion receptors leads to symmetry breaking, with stronger adhesion at the
front, and that bistability of migration arises for intermediate adhesiveness.
Local variations in adhesiveness are sufficient to switch between sessile and
motile states, in qualitative agreement with experiments.
