Adhered MKs remodel matrix-bound FN. (A) confocal images showing streptavidin-FITC labeling of MKs having accumulated biotinylated FN at their periphery onto soft matrix and having remodeled into distinct fibrils onto stiff matrix at 5 hours; biotin-FN (green), F-actin (red); representative of at least 6 experiments; Scale bar, 10 μm. (B) Quantification of the proportion of MKs associated with peripheral FN assembly or distinct fibrils. Mean ± SEM, data are from 6 or 7 independent experiments. (C) Confocal images showing the localization of FN remodeling with that of Itgb3 (left) or Itgb1 (right); representative of at least 3 independent experiments. Scale bar, 10 μm. (D) FN internalization shown by streptavidin labeling of the substrate-bound biotinylated FN. Left, xz confocal images of MKs after 2 and 5 hours adhesion onto 1.5 and 90 kPa; (right) quantification of total fluorescence present inside MKs (arbitrary units) performed on maximal projections of image stacks above the substrate.