Cells of the DA expressing both Runx1/EGFP and Kdrl/mCherry migrate to the DA/CV subaortic region, thymus, and kidney. (A) Confocal images of a segment of the trunk of a larvae 3 days postfertilization (dpf) showing the AGM region. (Top panel) A 6-somite span of the subaortic space flanked by the DA and CV. (Bottom 3 panels) High-resolution images of double-positive cells (not from the top panel) occupying the subaortic space. Yellow cells with rounded morphology expressing both Runx1/EGFP and Kdrl/mCherry were seen intimately associated with the floor of the DA (arrows), within the subaortic space, or close to the CV (arrowheads). EGFP expression was also observed within elongated endothelial cells of the DA, distinct from the round presumptive HSCs. Some mCherry-positive cells within the region were part of intersegmental vessels. (B) Photoactivatable rhodamine-dextran uncaged in Runx1/EGFP-expressing cells of the AGM region in 48-hpf embryos was traced to the thymus at 5 dpf. (C) Photoactivatable CMNB-fluorescein uncaged in double-fluorescent (Runx1/EGFP, Kdrl/mCherry) AGM cells at 48 hpf was detected in the thymus () and kidney (↑) at 5 dpf by fluorescein antibody staining. No antibody staining was observed in control embryos injected with caged fluorescein (n = 10).