Endothelial cells of the DA transdifferentiate to form Runx1-positive blood progenitors. Embryos bred from a Tg(runx1P2:EGFP) and Tg (kdrl:nls-mCherry) cross were imaged by time-lapse confocal microscopy from 22 to 35 hpf, which captured the development of endothelial cells within a segment of the trunk DA (supplemental Video 1). Panels display frames every 30 minutes from 24.5 to 30 hpf. Colored dots were superimposed to track red to yellow transition of individual cells. At 24.5 hpf, all the nuclei of endothelial cells that line the DA only expressed mCherry. By 30 hpf, several red cells of the DA also expressed EGFP in the ventral aspect of the DA and appear yellow. More rounded double-fluorescent cells are marked by asterisks. Scale bar represents 40 μm.