Fig. 2. Somite contribution to aortic endothelium remodeling and vascularization of the body wall. (A,B) E2.5 chick host, 1 day post-grafting. QH1 immunohistochemistry DAB stained cross-sections. (A) Caudal region of the grafted embryo. The roof of the right aortic rudiment is colonized with QH1⁺ cells (arrowheads). QH1⁺ cells around the neural tube organize into the perineural plexus. No QH1⁺ signal is visible lateral to the somite. (B) Medial level of the graft. The roof of the aorta (Ao) is entirely of quail origin on the grafted side. QH1⁺ cells have also colonized the ipsilateral chick host body wall where they give rise to the vascularization of the neural tube, mesonephros (Me), lateral plate (LP) and cardinal vein (CV). Scale bar: 150 µm. (C) E4 chick host, 2 days post-grafting. QH1 immunofluorescence (green) overlaid with Nomarski's interferential contrast. QH1⁺ cells form a conspicuous plexus around the neural tube. The lateral plate contains numerous QH1⁺ vessels. The QH1 aortic domain has extended ventrally to the hematopoietic clusters. Scale bar: 150 µm. (Inset) A prominent QH1^- hematopoietic cluster of host (chick) origin is underlined by QH1⁺ ECs (arrow). Some QH1⁺ cells are integrated in the vascular endothelium (arrowhead). Scale bar: 30 µm. D, dermomyotome; Sc, sclerotome.