Cell spread area and traction forces determine myosin-II-based cortex thickness regulation

Area of Science:

• Cell biology
• Biophysics
• Cytoskeleton dynamics

Background:

• The actomyosin cortex underlies the plasma membrane, regulating cell shape and deformation.
• Cortex thickness is primarily attributed to actin dynamics, filament regulators, and myosin motors.
• Regulation by cell morphology and mechanical environment remains under-explored.

Purpose of the Study:

• Investigate how cell spread area and substrate stiffness influence actomyosin cortex regulation.
• Determine the role of myosin II and cofilin in cortex adaptation to mechanical cues.
• Elucidate the mechanosensing mechanisms governing cortex thickness.

Main Methods:

• Super- and high-resolution imaging of actin in Chinese Hamster Ovary (CHO) cells.
• Perturbation experiments involving myosin II deactivation and substrate stiffness reduction.
• Cell de-adhesion assays to induce spread area changes.
• Analysis of actin dynamics, myosin II activity, and cofilin levels.

Main Results:

• At high spread areas (>450 µm²), the cortex is thinner and sensitive to myosin II inhibition or reduced substrate stiffness.
• In less spread cells (<400 µm²), the cortex is less responsive due to altered myosin IIA dynamics.
• Cell de-adhesion leads to increased actin dynamics, fragmentation, and cortex thickening, correlated with reduced traction forces.
• Cortex thickness regulation by spread area is conserved during THP-1 monocyte differentiation.

Conclusions:

• Cell spread area is a key regulator of actomyosin cortex thickness.
• Traction-based mechanosensing by myosin II mediates the effect of spread area on cortex thickness.
• Actomyosin cortex adaptation is influenced by cell morphology and the mechanical microenvironment.