Hydrodynamic interactions of filaments polymerizing against obstacles

Area of Science:

• Cellular mechanics and biophysics
• Cytoskeletal dynamics
• Hydrodynamic interactions

Background:

• Cytoskeletal filaments drive essential cellular functions like motility and cell division through polymerization and depolymerization forces.
• These forces create cytoplasmic flows and couple filament dynamics via long-range hydrodynamic interactions (HIs), which have been largely overlooked.
• Understanding HIs is crucial for a complete picture of cytoskeletal mechanics.

Purpose of the Study:

• To investigate the relationship between polymerization forces, resulting cytoplasmic flows, and hydrodynamic interactions (HIs).
• To model a system of a filament polymerizing against an obstacle within an array of parallel filaments.
• To analyze the impact of different filament mechanical scenarios and buckling on polymerization forces and HIs.

Main Methods:

• Utilized three-dimensional discrete simulations to model filament polymerization dynamics.
• Simulated a model system with a single filament polymerizing against an obstacle, embedded in an array of parallel filaments.
• Investigated three mechanical scenarios for filaments in the array: constant polymerization velocity, fixed in space, and freely suspended.

Main Results:

• Each mechanical scenario (polymerizing, fixed, suspended) generated unique cytoplasmic flows, polymerization forces, and velocities.
• Filament buckling was studied, revealing its effect on polymerization forces and velocities.
• Hydrodynamic interactions were shown to influence the onset of the buckling transition and lead to the bundling of buckled filaments.

Conclusions:

• Cytoplasmic flows and polymerization forces are distinct for different filament mechanical states, highlighting the importance of mechanical context.
• Hydrodynamic interactions play a significant role in modulating cytoskeletal filament behavior, including buckling and self-organization into bundles.
• This study underscores the necessity of incorporating HIs into models of cytoskeletal dynamics for accurate predictions of cellular processes.