Filament capping and nucleation in actin-based motility

Propulsion by actin polymerization is versatilely used in cell motility. Here, we investigate a model of the semi-flexible region of an actin gel close to a propelled object describing the force generation, the dynamics of the propagation velocity, filament attachment to and detachment from the obstacle surface and dynamics of the number of filaments, which result from filament nucleation and capping. The model equations are derived as moment equations of the length distributions. We find a variety of dynamic regimes. The filament number may respond very sensitively to small changes of the attachment rate.