Vascular lumen formation proceeds independently of circulation in <i>Xenopus</i>.

<p>(<b>A-B</b>). In situ hybridization with endothelial-specific <i>Erg</i> followed by sectioning was performed to determine the time course of vascular lumen formation of the dorsal aorta (DA) and posterior cardinal veins (PCV) in <i>Xenopus</i>. (<b>A</b>). Endothelial cells are coalesced together at the correct positions of the DA and PCVs in late tailbud stage (stage 33/34) control embryos. (<b>B</b>). Lumenized DA and PCVs become apparent by early tadpole stage (stage 35/36) in control embryos. 3–4 embryos from each condition/stage were assessed from at least three independent injection batches at the same position along the anterior-posterior axis of the embryo. (<b>C-D</b>). In situ hybridization with <i>Erg</i> followed by sectioning. (<b>C</b>). Transverse section of an early tadpole stage (stage 35/36) wildtype embryo depicting lumenized DA and PCVs. (<b>D</b>). Following the removal of the anterior and heart of early tailbud embryos, explants were cultured until early tadpole stage (stage 35/36) and processed as indicated above. PCV and DA lumens readily form in the absence of a functioning heart or circulatory system. 3–4 embryos from each condition were assessed from two independent experiments. Top image of each panel was taken at 20x magnification. Black boxes correspond to enlarged images of each vessel displayed below. Scale bars represent 20 μm.