Fig. 5. The progression of PGC responsiveness to SDF-1a. (A) PGCs (green) do not respond to SDF-1a expressed by transplanted cells (red), from the time of their specification until 4.5 hpf. (B) At 5.5 hpf, the PGCs (green) migrate actively towards the SDF-1a expressing transplant (red) and remain in close proximity to it. Two PGCs migrating toward the SDF-1a source are marked with an asterisk and an arrowhead. (C) A control experiment shows that migrating PGCs (green) remain indifferent to transplanted cells (red) that do not express SDF-1a. The images were obtained from time-lapse movies generated for each experiment (see supplementary material Movies 12-14). Bars, 100 µm.