Pulmonary vascular endothelial cell differentiation is not affected in Sox17Δ/Δ mouse lungs. Staining for GSL-IB4 (A–B), Pecam-1 (C–D), CD34 (E–F), and EphB4 (G–H) was performed on sections from E18.5 control (A, C, E, and G) and Sox17Δ/Δ (B, D, F, and H) lungs. No differences in staining for these endothelial cell markers were observed between control and Sox17Δ/Δ embryo lungs. (G–H) EphB4-positive veins and EphB4-negative arteries were enlarged in Sox17Δ/Δ mouse lungs. Insets show higher magnification of veins (A–D, G–H) or arteries (E–F). Scale bars, 100 μm. a, Artery; v, vein.