Cortactin clustering at nascent focal adhesions in migrating cells. (A) Immunofluorescence staining of cortactin and FAK on the leading edge of migrating HT1080 cells. Bar, 20 μm. The HT1080 cell monolayer was scratched with a rubber policeman. After 2 hours, the cells were fixed and stained with anti-cortactin antibody, anti-FAK antibody and phalloidin. The arrow indicates the direction of cell migration. The big arrowheads indicate the edge of lamellipodia, and the small arrowheads indicate focal adhesions. The insert represents the enlarged area. The images of the anti-cortactin and anti-FAK labeling are merged. (B) The localization of GFP-tagged FAK at focal adhesions. Bar, 20 μm. COS7 cells were transiently transfected with the GFP-tagged FAK expression vector and cells were fixed and stained with anti-cortactin (Cttn) and anti-paxillin (Pax) antibodies. GFP-FAK, GFP fluorescence. M, merged picture.