Fig. 2. Spatial relationships between paxillin, actin, phosphotyrosine (PY), zyxin and ß₃-integrin in FA and FX. Endothelial cells migrating into an in-vitro `wound' were fixed and stained. (A) In a cell labeled for paxillin and actin we can distinguish a region that was protruding at the time of fixation (marked by a solid line oval) next to a region that was retracting (marked by a broken line circle). At the base of the protruding lamellipodium a rim of small FX can be seen surrounded by actin meshwork. At the edge of the retracting region large elongated FA extend towards the cell center, connected to stress fibers. (B) Leading edge movements were monitored by time-lapse microscopy prior to fixation and correlated with the pattern of protein distribution. For example here, a cell stained for PY and zyxin is shown along with frames from its corresponding phase-contrast movie. Retracting regions (marked by arrows) contain zyxin-positive FA, while protruding regions (marked by arrowheads) are lined by zyxin-negative FX. (C) A cell expressing GFP-ß₃-integrin was labeled for PY. Co-localization of the two labels is nearly complete both in FX (marked by the solid line oval) and in FA (marked by broken line circle) near the leading edge. In more central regions of the cell (not relevant for this work) ₅ß₁-integrins replace _vß₃-integrins. Scale bar: phase-contrast images, 10 µm; others, 5 µm.

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