Intra-bundle contractions enable extensile properties of active actin networks

Area of Science:

• Cell Biology
• Biophysics
• Actin Cytoskeleton Dynamics

Background:

• The cellular cortex, a dynamic actomyosin network, is crucial for cell mechanics and shape.
• Actin-binding proteins and motor proteins like myosin regulate cortex organization and contractility.
• Understanding cortex self-organization requires minimal reconstituted systems.

Purpose of the Study:

• To investigate the role of myosin-mediated contractility and actin monomer turnover in cortex self-organization.
• To elucidate the mechanism by which myosin reorganizes actin networks.
• To determine if reconstituted systems can generate cellular structures.

Main Methods:

• Reconstitution of a minimal actomyosin cortex adhered to a model cell membrane.
• Utilizing the motor protein myosin to induce contractility and high actin monomer turnover.
• Observing network reorganization, filament dynamics, and cluster formation.

Main Results:

• Myosin-driven extensile intra-bundle contractions reorganized the actin network.
• Network stress led to filament nicking and repair via monomer incorporation, altering growth.
• This mechanism broke network symmetry, generating extensile clusters similar to cellular structures.

Conclusions:

• Myosin activity can drive self-organization in minimal actomyosin networks.
• A novel mechanism involving filament nicking and repair contributes to cortex dynamics.
• Reconstituted systems can recapitulate complex cellular structures like extensile clusters.