Myosin turnover controls actomyosin contractile instability.

Area of Science:

• Cell biology
• Biophysics
• Cytoskeletal dynamics

Background:

• Actomyosin networks, driven by myosin II and actin filaments, are crucial for cell division and development.
• Actomyosin contractility is inherently unstable, prone to self-reinforcing variations that can disrupt cellular architecture.
• The complete progression of actomyosin instability in cells remains poorly understood.

Purpose of the Study:

• To observe the full course of actomyosin contractile instability in the absence of component turnover.
• To understand how cells manage the inherent instability of actomyosin networks.
• To identify mechanisms preventing catastrophic failure of actomyosin structures.

Main Methods:

• Observation of isolated cytokinetic contractile rings in cell ghosts.
• Molecularly explicit simulations of actomyosin dynamics.
• Analysis of myosin II aggregation, tension loss, and ring fracture.

Main Results:

• In cell ghosts without turnover, myosin II hierarchically aggregated, leading to increased separation and eventual ring fracture.
• Simulations reproduced hierarchical aggregation and identified actin filament length as critical for mechanical communication between aggregates.
• A stable, quiescent dead-end state with polarity-sorted actin asters was observed in simulations.

Conclusions:

• Myosin II turnover time is a critical regulator of actomyosin contractile instability in living cells.
• Sufficient turnover prevents catastrophic hierarchical aggregation and fracture, ensuring structural integrity.
• The findings provide insight into how cells maintain functional actomyosin structures despite inherent instabilities.