Figure 6

Simulation illustration with small single surface structure with a fixed amount of actin and no limitation of filament orientation or severing (i. e., no cofilin). Magenta circles represent actin entities with other entities bound at both ends (i.e., in filament chains), light blue circles are actins at filement ends (i.e., occupied pointed end, free barbed end), Purple/dark blue circles: free actin, smaller red circles: integrins at start of filament, dark green and brown circles, free integrin on and outside of a surface structure. Surface structure boundaries marked by green dashed lines. Too little actin can lead to relatively short filaments (left), too little integrin and abundant actin to a few long filaments and many free actins that have no room to bind to a filament (right). Filament “growth” can also be impeded by the two-dimensional approach where filament crossing or bending is not allowed (center right; note also several free actins trapped in regions bound by different filament segments).