DDR1-expressing cells form linear invadosomes. (A) A549 (left) and MDA-MB-231 cells (right) were cultured on FITC-gelatin for 24 h. F-actin (red), cortactin (green), and degradation area (black) are shown. (B) A549 cells were seeded for 4 h on collagen I. (B, top) Colocalization of cortactin (green) and F-actin (red) at linear invadosomes. (B, bottom) Confocal images of linear invadosomes (cortactin, green) along collagen I fibrils (gray). (C) The same process was applied on MDA-MB-231 cells. (C, top) Colocalization of Tks5 (green) and F-actin (red) at linear invadosomes. (C, bottom) Confocal images of linear invadosomes (Tks5, green) along collagen I fibrils (gray and red in merge panel). Correlation coefficient of colocalization (collagen I/cortactin r = 0.15; collagen I/Tks5 r = 0.28; actin/cortactin r = 0.30; actin/Tks5 r = 0.23; n = 10). (D) Quantification of the percentage of A549 and MDA-MB-231 cells exhibiting invadopodia on gelatin versus linear invadosomes on collagen I. Values are expressed as the mean ± SEM of three independent experiments. ***, P < 0.001 as compared with plating on gelatin. Bars: (A) 5 µm; (B and C, top left) 10 µm; (B, enlarged panel on the top right) 3 µm; (B, bottom; and C, top right and bottom) 2 µm.