Integrin β3 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. Mice with deficient downstream αvβ3 signaling (DiYF) have less arterial VSMC coverage at each time point than age-matched wild-type (C57BL/6) controls. Retinas were immunostained with isolectin GS-IB₄ from Griffonia simplificonia (lectin, red) to label the endothelium and αSMA to label VSMCs (green). (B) VSMC coverage was measured along each artery as a percentage of the outgrowth of the vascular plexus (dotted lines). Arterial coverage is reduced by 30% at p3, 22% at p5, and 14% at P7. (C-D) Intravitreal injection of blocking Abs against integrin β3 (D) reduces arterial αSMA staining compared with control (C). (E) The β3 function-blocking Ab reduced arterial VSMC coverage by 74% (P = .01). Values represent means ± SEM. C57BL/6 (n = 12 [P3], n = 23 [P5], n = 19 [P7]), DiYF (n = 15 [P3], n = 23 [P5], n = 21 [P7]), isotype control-injected, n = 5; anti-β3 injected, n = 6, where n is the number of retinas analyzed. For the DiYF time course, P = 1.4 × 10⁻⁴ (P3), P = 7.5 × 10⁻⁹ (P5), P = 1.0 × 10⁻³ (P7). Scale bars: (A) 150 μm (P3), 300 μm (P5), 600 μm (P7); and (C-D) 50 μm.