The mechanism of dynamic steady states in lamellipodia
Fig 4
Intermediate F-actin severing activity is necessary to maintain a dynamic steady state.
(A, B) Snapshots of the branched networks taken at ~150 s with a lower (0 s-1) or higher (10-25 s-1) value of severing rate constant (k0,sev) relative to that of the reference condition, 10-45 s-1. In the absence of severing, a bundle structure was formed by the initial accumulation of F-actins. Due to the delayed disassembly of the bundle, motors remained trapped within the bundle until ~60 s and could not induce further network contraction. Once the bundle was finally disassembled by depolymerization, motors were unable to find F-actins to bind, leading to disconnection between the network and the motors. With fast severing activity, the filaments were immediately disassembled before motors could induce contraction, and the network eventually lost connection to the motors. (C, D) Kymographs of actin density as a function of y position and time with different k0,sev. (E) Heterogeneity of the network quantified as a coefficient of variation in actin density in the y direction. (F) Retrograde flow speed for different k0,sev. With intermediate values of k0,sev, network was more homogeneous, and the flow was faster with smaller fluctuations.