Lateral plate mesoderm contributes to hemogenic endothelial beds, including the VA and its hematopoietic derivatives. (A) The HoxB6 Cre mouse line was crossed to a R26R LacZ Cre reporter mouse to lineage-trace LPM. All previously reported hemogenic endothelial beds, including the AGM at E11 (top panel), yolk sac (middle panel), and placenta (bottom panel) (both at E10.5), were faithfully labeled (β-galactosidase in blue) from labeled LPM. The associated HCs were also labeled, except for the yolk sac where labeled (arrow) and unlabeled (arrowhead) HCs are seen. (B) The VA-derived hematopoietic clusters (HC, arrows) and all the surrounding endothelium and mesoderm are traced from the LPM at E10.5. (C) The adult bone marrow (BM) in the HoxB6-Cre mouse is fully labeled, indicating an LPM origin (histologic LacZ section on left). FACS analyses using a EYFP reporter (graph on right) demonstrates that EYFP⁺ cells constitute 98% of CD45⁺ BM cells and that the majority of all hematopoietic lineages are also EYFP⁺ and thus have an LPM origin. Graphical results are shown as the mean (n = 3) ± SEM (A-C) Scale bars as labeled.