Supplementary Figure 2: The peripheral actin cable is under tension and interacts directly with the substrate.

(A) Image sequence following the severing of the actin-GFP cable by photoablation (scale bar 10μm). The white arrow indicates the initial ablation. The solid triangles denote the extremities of the retracting cable (see also Supplementary Movie 1). Note that small structures next to the cable retract as well (empty triangle), demonstrating that this is a tension driven relaxation. Representative images. More than 20 replicates. (B) Distance between the two extremities of the cable as a function of time. The cyan line is the average of the different independent measurements (black curves), yielding a characteristic time of 37 ± 7 s (SD) after a fit by an exponential function. The orange area is the standard deviation over 20 experiments. (C) When cut by photoablation (top panel, arrow), not only the forces at the cut relax but also the neighboring pillars situated under the cable. t = 0 is the time of ablation. Top panel = actin-GFP and pillars bottom panel = local forces (colours give the intensity and arrows the direction). The white triangles denote the high forces at pillars next to the cut. Note that the relaxation at longer times involves more pillars at a distance from the physical cut which demonstrates the direct interaction of the tensile actin cable with the substrate. Representative image. 20 replicates.