Mechanisms of cell motion in confined geometries

We present a simple mechanism of cell motility in a confined geometry, inspired by recent motility assays in microfabricated channels. This mechanism relies mainly on the coupling of actin polymerisation at the cell membrane to geometric confinement. We first show analytically using a minimal model of polymerising viscoelastic gel confined in a narrow channel that spontaneous motion occurs due to polymerisation alone. Interestingly, this mechanism does not require specific adhesion with the channel walls, and yields velocities potentially larger than the polymerisation velocity of the gel. We then study the effect of the contractile activity of myosin motors, and show that whilst it is not necessary to induce motion, it quantitatively increases the velocity of motion in the polymerisation mechanism we describe. Our model qualitatively accounts for recent experiments which show that cells without specific adhesion proteins are motile only in confined environments while they are unable to move on a flat surface. It also constitutes a first step in the study of cell migration in more complex confined geometries such as living tissues.