Rapid Treadmilling and Myosin Motors Synergistically Induce Formation of Ring-Like Actomyosin Architectures and Cortexes

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Semiflexible actin filaments crosslinked by myosins control cell motility and morphology via dynamic remodeling process - treadmilling. In less chemically dynamic reconstituted actomyosin networks, motor proteins induce global geometric contraction, creating cluster-like structures. However, filaments treadmill much faster in living cells and are often found to be abundant at the cell periphery, frequently forming ring-like structures or thin, contractile sub-plasma-membrane cortexes. To explore the interplay between treadmilling and myosin induced contractility, we used an advanced computational model MEDYAN, which couples stochastic reaction-diffusion scheme with polymer physics modeling. Our results indicate that the actomyosin network geometry is tightly regulated by filament treadmilling. In our simulation, non-treadmilling and slowly treadmilling actomyosin networks would geometrically collapse and form clusters. On the other hand, enhanced filament treadmilling generates ring-like structures that are dense and mechanically contractile with their stability regulated by myosin concentration. We found that rapid treadmilling towards boundary helps filaments escape from geometric collapse, while myosin prevents filaments from growing against the boundary by altering their orientation such that those filaments are rescued from destruction.