Interplay between Rac1/RhoA and actin waves in giant epithelial cells: Experiment and theory.

Area of Science:

• Cell Biology
• Biophysics
• Biochemistry

Background:

• The acto-myosin cytoskeleton drives cellular shape changes.
• Actin assembly and myosin interactions, regulated by Rho GTPases (Rac1, RhoA), govern cytoskeletal organization.

Purpose of the Study:

• To uncover principles governing cytoskeletal organization.
• To analyze actin patterns and their evolution in enlarged cells using live microscopy and theory.

Main Methods:

• Live microscopy of actin patterns in enlarged cells (Madin-Darby Canine Kidney epithelial cells and REF52 fibroblasts).
• Theoretical analysis using a polar reaction-diffusion system for actin and Rac.
• Characterization of acto-myosin stress fibers and propagating waves.

Main Results:

• Observed stationary acto-myosin stress fibers correlated with homogeneous Rac1 and RhoA activity.
• Identified propagating waves (≈1μm/min) associated with actin, Rac1, and RhoA density variations.
• Demonstrated that myosin activity and RhoA activation can suppress or break waves, while wave collision leads to annihilation.

Conclusions:

• The coupling between acto-myosin and Rho GTPases generates diverse cytoskeletal structures and dynamics.
• Wave propagation dynamics are captured by reaction-diffusion models.
• Findings highlight mechanisms of cellular organization and shape regulation.