Figure 6: Conceptual model of F-actin dynamics in leading edge protrusion during interstitial migration.

In confined environments, leading edge protrusion results from the interaction between the adherent and the free F-actin networks. Nucleation of the adherent network (green) is directed perpendicular to the channel walls and its thickness increases from front to rear creating a constriction that compresses the free F-actin network (red). This constriction prevents rearward movement of the free F-actin network enabling new polymerization under the front membrane to create forward protrusion. Compression of the free network by the adherent network creates an outward pressure on the channel walls (arrows) as well as a protrusive force at the free membrane.