FIGURE 4.

Immunofluorescence staining of FN^f/f and FN^−/− fibroblasts on contracted collagen gels. Control (FN^f/f) fibroblasts spread extensively on native collagen, whereas FN-null (FN^−/−) cells appeared roundish and tended to form clusters. In the presence of exogenous FN, FN^−/− fibroblasts increasingly spread as seen on the phase contrast images (top panels; scale bar 100 μm). The assembly of a FN network (green) and α₅ integrin in focal adhesions (green) by FN^−/− cells in the presence of exogenous FN could also be observed (middle panels; F-actin in red). Mature myofibroblasts were present amongst FN^f/f fibroblasts; these were characterized by a well-organized alpha-smooth muscle actin (αSM-actin) positive cytoskeleton (bottom panels; Texas Red staining). A fraction of FN^−/− fibroblasts showed higher αSM-actin expression in the presence of exogenous FN (bottom panels; scale bar 50 μm).