Actin kinetics shapes cortical network structure and mechanics.

Area of Science:

• Cell Biology
• Biophysics
• Cytoskeleton Dynamics

Background:

• The actin cortex dictates animal cell mechanics and responds to stimuli via actin filament turnover.
• Two main actin nucleators, Arp2/3 complex and formin Diaph1, generate most cortical actin.
• Understanding their interplay and filament length distribution is key to cell mechanics.

Purpose of the Study:

• To investigate the kinetics and interplay of Arp2/3 complex and formin Diaph1 in living cells.
• To determine the length distribution of actin filaments nucleated by these two key proteins.
• To elucidate the contribution of different actin filament populations to cellular mechanics.

Main Methods:

• Utilized single-molecule fluorescence imaging in living cells.
• Employed stochastic simulations to analyze actin assembly rates.
• Performed mechanical measurements to assess cortical elasticity.

Main Results:

• Formin-nucleated actin filaments are approximately 10 times longer than Arp2/3-nucleated filaments.
• Despite representing <10% of filaments, formin-generated filaments significantly impact cortical elasticity.
• Actin nucleator activity influences filament length distribution and cellular mechanical properties.

Conclusions:

• Formin and Arp2/3 complex exhibit distinct roles in actin nucleation and filament formation.
• Filament length heterogeneity is critical for regulating cell mechanics.
• Cells may tune nucleator activity to adapt their mechanical properties.