Filament turnover tunes both force generation and dissipation to control long-range flows in a model actomyosin...

Area of Science:

• Cell Biology
• Biophysics
• Computational Modeling

Background:

• Actomyosin-based cortical flow is crucial for cellular morphogenesis.
• This flow arises from actin filaments and myosin motors, balanced by network resistance.
• Local network remodeling is essential for sustained flow, but its precise role is unclear.

Purpose of the Study:

• To investigate how local remodeling, specifically filament turnover and cross-link dynamics, influences stress production and dissipation in actomyosin networks.
• To understand how these remodeling processes collectively shape long-range cortical flow.
• To identify different regimes of steady-state flow based on network remodeling parameters.

Main Methods:

• Development of a computational model for a cross-linked actin-myosin network.
• Incorporation of key elements: asymmetric filament compliance, heterogeneous motor activity, reversible cross-links, and filament turnover.
• Systematic analysis of how cross-link dynamics and filament turnover individually and collectively affect network stress and flow.

Main Results:

• Filament turnover is necessary for maintaining active stress and steady-state flow against resistance.
• Steady-state stress shows a non-monotonic dependence on filament lifetime, peaking at τm.
• Effective viscosity increases with filament lifetime up to τc, then depends primarily on cross-link dynamics.
• Multiple flow regimes emerge based on the interplay between stress and viscosity dependencies.
• Flow speed becomes insensitive to filament turnover when lifetimes are short, simplifying dependence on motor and cross-link dynamics.

Conclusions:

• The model provides a framework for understanding how cells regulate cortical flow through local network remodeling.
• Filament turnover and cross-link dynamics are critical, tunable parameters controlling cell shape and movement.
• Specific regimes of flow behavior are predicted based on the balance of remodeling processes.