Fig. 7. Acute recruitment of zyxin on single SFs pulled with an AFM cantilever. (A) Position of the fibronectin-coated AFM cantilever, extracted from a transmission micrograph taken before traction, overlapped with a EGFP-zyxin-expressing Ptk-2 cell. In inset, schematic side view of the manipulation experiment with the AFM tip in orange, applied from the top and connecting to basal SFs through the membrane. Springs represent SF subunits. Traction applies to the neighboring cell's SFs and propagates to fluorescent SFs of interest through cell-cell junctions (white arrows). Two fibers are periodically pulled over a distance x (See supplementary material Movie 7). (B) Relaxed and pulled fibers during two different cycles. (C) Kymograph showing the full traction sequence over nine cycles. (D) Zyxin intensity increase over time (left, red) compared with a control fiber (green). x was manually measured from the kymograph. The total cell intensity was corrected for bleaching (see background in blue). The intensity of pulled and control SFs in -actinin-expressing cells (right, see supplementary material Movie 6), showing no correlation between the traction (top) and the intensity of the SFs. (E) Intensity profile of the seventh traction plotted before traction (dashed yellow, reported with offset in plain yellow because of overlap) and during the traction (red). Before traction, the typical sarcomeric labeling of zyxin is clearly visible from the intensity profile with, on average, 1 µm periodic ripples. After traction, the amplitude of the ripples increases in the front stretched part of the fiber, thereby showing a discrete and periodic recruitment of zyxin along the bundle. Scale bars: 5 µm (A-C) horizontal, 40 seconds vertical (C).