Keynote
Theoretical Models for Traffic Jams of Molecular Motors along Actin-Filled Cellular Protrusions

Molecular motors of the myosin family transport cargo molecules along actin fibers. Within cellular protrusions, which extend outwards from the cell, the actin filaments form a bundle that is polarized: the growing ends are at the tip of the protrusion while the actin depolymerizes at the base. On top of this treadmilling actin bundle there are myosin motors that walk, mostly to the tips, carrying molecules that are essential to maintain the bundle structure and the tip polymerization. Motors therefore accumulate at the tips, but are also observed to undergo pulse-like accumulations that are carried back towards the base. These observed "traffic jams" of motors remain an open puzzle, and we`ll describe several theoretical attempts to explain them. The models presented are either continuum, where motors are described by a local density, or discrete, where exclusion prevents motors occupying the same position. The theoretical models explain some experimental features and provide possible mechanism that can drive the observed dynamics, as well as make predictions for future studies.