Turnover versus treadmilling in actin network assembly and remodeling

Area of Science:

• Cellular Biology
• Biophysics
• Cytoskeletal Dynamics

Background:

• Actin networks are dynamic cytoskeletal structures essential for cellular functions.
• Fluorescence Recovery After Photobleaching (FRAP) estimates actin monomer turnover rates.
• Filament treadmilling and de novo nucleation are proposed mechanisms for actin turnover.

Purpose of the Study:

• To investigate the relative contributions of filament treadmilling and de novo nucleation to actin network turnover.
• To analyze actin turnover dynamics in models with Arp2/3, formin, and capping protein.

Main Methods:

• Utilized a 3D stochastic reaction-diffusion model, MEDYAN.
• Simulated actin networks at experimentally relevant scales.
• Analyzed turnover kinetics influenced by key actin-binding proteins.

Main Results:

• Filament treadmilling of older filaments is the predominant mechanism for actin network turnover.
• Demonstrated instances where rapid turnover does not correlate with fast treadmilling, particularly in Arp2/3 networks.
• Highlighted the distinction between actin turnover and treadmilling rates.

Conclusions:

• Actin network turnover is most commonly driven by filament treadmilling.
• The assumption that turnover and treadmilling are interchangeable is not always valid.
• Dendritic Arp2/3 networks can exhibit rapid turnover with slow treadmilling.