Long-term dynamics of stress fibers in COS-7 cells expressing NMIIB only or NMIIA and NMIIB together. (A) COS-7 cells expressing GFP-NMIIB (cyan) and mCherry-NMIIA (red). (Left) First frame of the video. (Right) Kymographs along the arrow in the left panel showing two channels separately and as a merged image. Bar, 10 µm. Kymograph showing the distance bar (horizontal), 5 µm, and time bar (vertical), 2 h. (B and C) COS-7 cell expressing GFP-NMIIB only shows very slow stress fiber dynamics. (B) First (left) and last (middle) frames of the time-lapse sequence are overlaid at right. Stress fibers that appear white are largely unchanged after 10 h. Bar, 10 µm. (C) Time frames showing dynamics of individual stress fibers marked by numbered boxes in B. (1 and 2) Assembly of new stress fibers from faint tangential arcs. (3) Stable stress fiber. (4) Contracting stress fiber. Bar, 5 µm.