Hierarchical self-organization of cytoskeletal active networks

Abstract

The structural reorganization of the actin cytoskeleton is facilitated through the action of motor proteins that crosslink the actin filaments and transport them relative to each other. Here, we present a combined experimental-computational study that probes the dynamic evolution of mixtures of actin filaments and clusters of myosin motors. While on small spatial and temporal scales the system behaves in a very noisy manner, on larger scales it evolves into several well distinct patterns such as bundles, asters and networks. These patterns are characterized by junctions with high connectivity, whose formation is possible due to the organization of the motors in 'oligoclusters' (intermediate-size aggregates). The simulations reveal that the self-organization process proceeds through a series of hierarchical steps, starting from local microscopic moves and ranging up to the macroscopic large scales where the steady-state structures are formed. Our results shed light on the mechanisms involved in processes such as cytokinesis and cellular contractility, where myosin motors organized in clusters operate cooperatively to induce the structural organization of cytoskeletal networks.

Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals

“…Actin-myosin systems often exhibit negative isotropic pressure, commonly referred to as contractility (in contrast to the dipolar contractile stress described here.) Multiple microscopic mechanisms have been proposed as important to actin-myosin contractility, including nonzero motor size, crosslink tether elasticity, spatially-varying motor motion, and filament buckling 5,7,15,26,46,47,49,50 . However, the motor- and crosslink-modulated alterations in steric interactions we describe could also occur for actin filaments and may complement effects of buckling in actomyosin gels.…”

Active gel physics

“…This observation is in qualitative agreement with theoretical expectations 53 . Finally, collections of actin filaments interacting with myosin motors near a glass surface show a beautiful complex phase space with moving structures, characteristic of selfpropelling objects 84,85 .…”

Actively Stressed Marginal Networks

“…On a larger scale, collective motor activity allows the cell to contract the surrounding extracellular matrix, consisting also of biopolymer networks. Experiments show that such active contractility dramatically affects network elasticity, both in reconstituted intracellular F-actin networks with myosin motors [2][3][4][5] and in extracellular matrices with contractile cells [6]. The dynamics and elasticity of active biopolymer networks have been studied theoretically using long-wavelength hydrodynamic approaches as well as affine models [7][8][9].…”