Fig. 3.

Global architecture of the F-actin cytoskeleton (CSK) regulates cell shape-dependent contractile force response. (A) Confocal immunofluorescence micrographs (top) showing the F-actin CSK structure in single HUVECs conformed to circular (left), square (middle) and rectangular (right) adhesive islands of an equal area (2,500 μm²). Cartoon representations (bottom) of global architectures of the F-actin CSK and their mechanical linkages to focal adhesions (FAs) were included, with force balance achieved between intracellular CSK tension and contractile forces transmitted through FAs against substrates. Scale bar, 20 μm. (B) Schematics of theoretical models of the F-actin CSK for single HUVECs conformed to circular (left), square (middle) and rectangular (right) adhesive islands. The dimensions shown were for the F-actin CSK at rest, i.e., when neither intracellular tension nor external stretch was applied. For contractile cells, force equilibrium between intracellular CSK tension T and reactive contractile force F can be established in pre-stressed and stretched configurations, respectively. See SI Text for description of theoretical modeling. (C&D) Comparisons between theoretical results (□) and experimental data (◆) for both total cellular (C) and subcellular (D) contractile forces from single HUVECs of different shapes under uniaxial stretch, as indicated. Parameter fitting was performed using experimental data from circular-shaped cells to determine the pre-strain, ε_pre, which was then used for calculations for cells with other shapes. For circular-shaped cells, n = 15; for each of other groups, n = 11.