Simulations of Branching Actin Filament Networks at the Leading Edge of Moving Cells

Branched filamentous actin networks provide the driving force for lamellipodial protrusions in motile cells. Structural network changes occur due to filaments polymerizing, depolymerizing, capping, severing, and nucleating either as branches or de novo. The actin network in lamellipodia has been studied in prior mathematical and computational models; however, little is known about how network remodeling away from leading edge regulates its size and structural properties. We developed a 3D simulation of this network at the level of individual filaments, defining various processes as occurring with defined rate constants. Through changing of rates, effects on the network’s structure and size due to different parameters were observed. In particular, it was seen that increased severing leads to a faster drop off in actin concentration, resulting in a shorter lamellipodium. In addition, branching not limited to occurring near the leading edge extends the depth of the lamellipodium, by allowing away from leading edge nucleation of filaments. Orientation of branches dependent on the actin helix repeat, there is a distinct pattern in spacing between branches on the same mother filament when branching is restricted to a near 2D plane.