Actin arcs/DSF play a role in flattening MEF cells. (A–C) MEF cells plated on 1,100-mm² micropatterned circles. Ventral (purple) and dorsal (blue-green) actin filaments are shown for a control cell (A) and cells treated with 5 µM blebbistatin (B) or 10 µm Y-27632 (C) for 2 h. Side views are x-z maximum projections from the yellow boxes. Arrows denote the transition between the flat portion of the cell (lamella) and the cell body. (D) Cell heights from five cells from the treatments in A–C. Arrows show the mean distance cell height rises above 2 µm (broken lines). (E) Quantification of the distance from the leading edge at which cells become higher than 2 µm (n = 12 cells per condition from three separate experiments). Error bars show standard deviation. *, P < 0.001. Bars, 10 µm.