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

Biochim Biophys Acta Mol Cell Res. 2019 Dec;1866(12):118516. doi: 10.1016/j.bbamcr.2019.07.011. Epub 2019 Jul 23.


Actomyosin network under the plasma membrane of cells forms a cortical layer that regulates cellular deformations during different processes. What regulates the cortex? Characterized by its thickness, it is believed to be regulated by actin dynamics, filament-length regulators and myosin motor proteins. However, its regulation by cellular morphology (e.g. cell spread area) or mechanical microenvironment (e.g. substrate stiffness) has remained largely unexplored. In this study, super- and high-resolution imaging of actin in CHO cells demonstrates that at high spread areas (>450 μm2), the cortex is thinner, better separated as layers, and sensitive to deactivation of myosin II motors or reduction of substrate stiffness (and traction forces). In less spread cells (<400 μm2) such perturbations do not elicit a response. Myosin IIA's mechanosensing is limited here due to its lowered actin-bound fraction and higher turnover rate. Cofilin, in line with its competitive inhibitory role, is found to be overexpressed in these cells. To establish the causal relation, we initiate a spread area drop by de-adhesion and find enhanced actin dynamics and fragmentation along with oscillations and increase in thickness. This is more correlated to the reduction of traction forces than the endocytosis-based reduction in cell volume. Cortex thickness control by spread area is also found be true during differentiation of THP-1 monocytes to macrophages. Thus, we propose that spread area regulates cortex and its thickness by traction-based mechanosensing of myosin II.

Keywords: Actin cortex; Cell spread area; Cortex thickness; Myosin II; Super-resolution imaging; Traction forces.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bridged Bicyclo Compounds, Heterocyclic / pharmacology
  • CHO Cells
  • Cell Adhesion / drug effects
  • Cell Differentiation / drug effects
  • Cells, Cultured
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism*
  • Cricetulus
  • Cytochalasin D / pharmacology
  • Humans
  • Myosin Type II / antagonists & inhibitors
  • Myosin Type II / metabolism*
  • THP-1 Cells
  • Thiazolidines / pharmacology


  • Bridged Bicyclo Compounds, Heterocyclic
  • Thiazolidines
  • Cytochalasin D
  • Myosin Type II
  • latrunculin B