Effects of Ang1 on retinal vascular development. (a–g) P4 retinal vasculature stained with Tie2 (a and e) or with PECAM-1 (b–d, f, and g). Normally, Tie2 is expressed in all retinal vessels (a). Intraocular injections of Tie2-Fc (c) and Ang1* (d) displayed clear contrasts in effects on vascular remodeling, especially in generation of trunk vessels. In the APB5-treated mice, Tie2 is still expressed in all retinal vessels even in the absence of MCs (e). Disorganized vascular architecture induced by systemic APB5 treatment (f) was ameliorated to a great extent by intraocular injections of Ang1* (g). (h) Scanning electron microscopy demonstrating complete absence of MCs in the retina treated with APB5 + Ang1*. (i–m) Quantitative analysis of the radius (i), density (j), arterial diameter (k), venous diameter (l), and capillary diameter (m) of retinal vasculature at P4. Data (mean ± SD) are expressed as percentages relative to the normal retina. *P < 0.05 versus normal (Student t test).