VWF is required for VSMC coverage in developmental angiogenesis. (A) Representative images of retinas undergoing early postnatal retinal developmental angiogenesis at 3 different time points: P3, P5, and P7. Retinas were immunostained with CD31 (red) to label the endothelium and αSMA to label VSMCs (green). (B) VWF KO mice have significantly less VSMC coverage compared with age-matched controls, measured along each artery as a percentage of the outgrowth of the vascular plexus (dotted lines). Arterial coverage is reduced 37% at P3, 21% at P5, and 17% at P7. Values represent means ± SEM. C57BL/6 (n = 12 [P3], n = 23 [P5], n = 19 [P7]), VWF KO (n = 14 [P3], n = 25 [P5], n = 14 [P7]), where n is the number of retinas analyzed. P = 9.3 × 10⁻⁴ (P3), P = 1.7 × 10⁻⁹ (P5), P = 7.3 × 10⁻³ (P7). Scale bars: 150 μm (P3), 300 μm (P5), and 600 μm (P7).