Disassembly of actin networks by filament severing

The disassembly of actin networks by filament severing is studied by simulation of a model in which the actin filaments are crosslinked in a periodic network and begin to sever as soon as they are created at the cell membrane. The actin network is defined as the set of all sites which have a connecting path leading to the membrane. An extension of this model including annealing effects, corresponding to restoration of links between nodes, is studied as well. The simulations show that in the presence of only severing, the network density drops abruptly at a critical distance from the network, which is inversely proportional to the severing rate. This result is explained by a mean-field theory based on a layer-by-layer approach in which the average size of an in-layer connected cluster is used to calculate the probability of a given site having a connected path to the membrane, via the next layer in. Inclusion of annealing effects leads to a broadening of the attached portion of the network. At a critical value of the annealing rate, the network density develops a component that does not decay away from the membrane.