Fig. 4. Comparison of ECM displacements with focal adhesion dynamics in living corneal fibroblasts on top of fibrillar collagen matrices. The red tracks show ECM displacements, whereas the white tracks show adhesion displacements (cross indicates initial position in the sequence). GFP-zyxin images are shown in green. The time (t) is relative to the start of time-lapse imaging. (A-D) The front of a cell moving in a northeast direction. Tracking of the adhesions confirmed our qualitative observation that the adhesions moved inward during cell extension (A-C, arrowheads), and that these movements generally correlated with the ECM deformation in front of the cell (D). See also movie 2 at jcs.biologist.org/supplemental. (E-H) A different cell moving in the northeast direction. Adhesions generally moved perpendicular to the local cell contour, i.e. in a centripetal direction (H), thereby pulling in the ECM in a radial pattern around the front of the cell. Note that as the ECM in front of the cell was pulled backward during extension, the cell body and adjacent ECM was pulled forward, resulting in ECM compression at the base of the lamellipodia. Cell body adhesions (arrows) also moved toward those at the tip (arrowheads), which is consistent with the cell body and ECM movement in this region. (I-L) A cell in which a slow retraction of the lamellipodium was observed. During retraction, adhesions at the front of the cell moved backward in unison (arrowhead) and generated significant ECM deformation. See also movie 3 at jcs.biologist.org/supplemental. At the same time, cell body adhesions moved forward (arrow), resulting in contractile-like shortening of the cell and ECM compression at the base of lamellipodia. See also movies 3 and 4 at jcs.biologist.org/supplemental.