Actin arc contraction is coupled to DSFs. (A) α-Actinin–mApple speckles in a U2OS cell before and 3 min after 50 µM blebbistatin. Line 1 (arcs) and line 2 (DSF) were drawn parallel to the direction of speckle translocation. (B) Kymographs show the actin arc and an adjacent DSF flow before and after blebbistatin. (C) Actin arc and DSF translocation rates showing similar speeds before and after blebbistatin treatment (n = 3 experiments). *, P < 0.001. (D) Counterbalance model shows the arrangement of an actin arc (blue), DSF (black), and focal adhesion (gray) when a new actin arc is formed (top) and after the arc moves away from the edge (bottom). As the actin arc moves away from the edge it pulls on the dorsal side of the DSF. Because the DSF is attached to the focal adhesion, the force from actin arcs causes the DSF to bend downward and the edge of the cell to flatten. (E) 3D traction force map showing upward forces (green arrows) and downward forces (red arrows) exerted by a single U2OS cell spread out on a 2D gel (3 kPa). (F) High-magnification view of the edge of another U2OS cell with accompanying traction map. The white arrow denotes lamellipodium and yellow arrowheads denote the beginning of DSF. Bars: (A and E) 10 µm; (F) 5 µm.