Molecular motors of the myosin family carry cargo proteins along filaments of actin bio-polymers. Inside cellular protrusions, such motors are often observed to concentrate at the growing tips of the filaments. However, they are also observed to form backward-moving “pulses”, that move towards the base of the protrusions due to the actin treadmilling process. This phenomenon presents an open challenge to theory, and we present two approaches that are based on the notion of a two-state motor, “on” or “off”: The first proposes a continuum model, whereby a strong non-linearity (cooperativity) in the interactions between motors gives rise to the pulses. The second approach is to use discrete models, of the Totally-Asymmetric-Exclusion-Process form, including an internal degree of freedom for the motors, as well as interactions.

Weizmann Institute, Israel