Spatiotemporal dynamics of actomyosin networks

Area of Science:

• Biophysics
• Cell Biology
• Materials Science

Background:

• Actin filaments and myosin motors are fundamental to cellular mechanics.
• Understanding their collective behavior is crucial for cell motility and muscle contraction.

Purpose of the Study:

• Investigate the collective behavior and emergent order of actin filaments gliding on myosin motors.
• Determine factors influencing filament alignment and domain formation.

Main Methods:

• Visualizing rhodamine-phalloidin-labeled actin filaments gliding on heavy meromyosin (HMM)-coated surfaces.
• Analyzing filament collisions, bending, and shape using microscopy.
• Varying HMM surface density and actin filament concentration.
• Employing correlation analysis and simulations to study spatiotemporal alignment.

Main Results:

• Filament collisions result in alignment or crossover, with a 40° angle favoring alignment.
• Significant filament bending during collisions requires approximately 13 kBT of energy.
• Gliding speed and path persistence plateau at critical HMM densities.
• High actin concentrations lead to dramatic, common-direction alignment.
• Long-range alignment arises from incremental recruitment, not domain fusion.
• Global alignment peaks at optimal actin and myosin concentrations.

Conclusions:

• Mechanical interactions between actin filaments drive the generation of long-range order.
• Myosin motors can align short actin filaments into large, motile surface domains.
• Observed alignment patterns challenge predictions of a critical phase transition.