Two competing orientation patterns explain experimentally observed anomalies in growing actin networks

Area of Science:

• Cell biology
• Biophysics
• Actin dynamics

Background:

• Cell migration relies on lamellipodium protrusion driven by branched actin networks.
• In vitro studies show conflicting force-velocity relations for these networks, including convex/concave shapes and history dependence.

Purpose of the Study:

• To develop a generic model explaining the anomalous force-velocity relations observed in actin networks.
• To investigate how actin filament branching and capping influence network stability and dynamics.

Main Methods:

• Modeling actin network branching as a reaction independent of filament number.
• Modeling capping as proportional to the existing filament number.
• Utilizing stochastic network simulations and deterministic rate equations.

Main Results:

• The model predicts two stable network states: +/- 35 degrees and +70/0/-70 degrees orientation patterns.
• Changes in network growth velocity trigger transitions between these states.
• The model reproduces hysteresis in actin network growth velocity under force, explaining convex and concave force-velocity relations.

Conclusions:

• A simple, generic model can reconcile conflicting experimental findings on actin network force-velocity relations.
• The model's predictions have significant implications for understanding the mechanics of cell migration.