Density-dependent flow generation in active cytoskeletal fluids

Area of Science:

• Cellular dynamics
• Biophysics
• Cytoskeletal organization

Background:

• The actomyosin cytoskeleton, composed of actin filaments and myosin motors, generates contractile forces crucial for cellular processes.
• The precise relationship between actomyosin density and the resulting ordered structures and force generation remains unclear.

Purpose of the Study:

• To investigate the density dependence of actomyosin cytoskeleton-driven flow generation.
• To understand the emergent dynamics and force-controlled structures arising from actomyosin networks.

Main Methods:

• Utilized cell-sized droplets containing purified actomyosin cytoskeleton and nucleation factors.
• Varied the concentration of actomyosin to observe effects on actin flow and tracer particle motion.
• Measured contraction-driven flow and analyzed oscillatory dynamics.

Main Results:

• Observed continuous actin flow towards the center at a critical actomyosin density.
• Discovered emergent oscillatory dynamics in actin flow, characterized by periodic stop-and-go motion of tracers.
• Found that tracer particle velocity decreases with actomyosin density in the oscillatory regime, exhibiting superdiffusive behavior.
• Demonstrated that alterations in myosin activity disrupt the regularity of oscillatory flow.

Conclusions:

• Actomyosin density-dependent flow generation is governed by the interplay between actin concentration and myosin motor force.
• Emergent oscillatory dynamics are a key feature of actomyosin networks at specific densities.
• This work provides insights into the self-organization principles of cytoskeletal systems.