Figure 3.

Schematic representation of crawling dynamics in a simulated cell. The actin field in lattice sites occupied by lamellipodium, represented in green, favors lamellipodium lattice sites overwriting medium lattice sites, increasing the volume of the lamellipodium compartment and extending the compartment to the left (1). The volume constraint on the lamellipodium compartment then favors cytoplasm lattice sites overwriting lamellipodium lattice sites, decreasing lamellipodium compartment volume and increasing cytoplasm compartment volume (2). Finally, the volume constraint on the cytoplasm compartment favors medium lattice sites overwriting cytoplasm compartment lattice sites. Together, these three steps create a polarization axis and polarized force generation that causes a net migration of the cell in the direction of the lamellipodium compartment (to the left in the figure). To see this figure in color, go online.