Hif-1α controls chemotaxis in a Cxcr4-dependent manner. Chemotaxis toward a localized source of SDF-1, which is located to the right of each panel, for each treatment as indicated at the top of the figure. (A–C) Time 0. (D–I) 3 h after culture. (A–I) Fluorescent (A–F) and bright-field (G–I) images. (J–L) Tracks of leader migrating cells. Chemotactic cells should move toward the right side of the panel, where SDF-1 is higher. (M and N) Angles of migration for individual cells. (O) Chemotaxis index for leader cells. (P) Persistence. (Q) Leader cells (green) are more efficiently attracted than trailing cells (red). (R) Chemotaxis of leader (green) and trailing (orange) cells under the indicated conditions. Bars represent the standard deviation from three independent experiments, with a minimal of 60 cells analyzed for each treatment. ***, P < 0.005. Ctrl, control.