Effects of genetic and pharmacologic inhibition of Dll4/Notch on capillary remodeling during retinal vascular development. (A-C) Reduced blood vessel pruning in conditional Dll4^+/− mice. Retinal vasculature at P10 in Dll4^+/+;Rosa26-CreERT2^+/− (A) and Dll4^+/COIN;Rosa26-CreERT2^+/− (B) mice treated for 72 hours with tamoxifen; GS lectin staining. (C) Quantification of total blood vessel length in the central retina (per 100 × microscopic field); percentages indicate changes in total vessel length compared with WT (Dll4^+/+;Rosa26-CreERT2^+/−) control mice. (D-F) Reduced blood vessel pruning in Dll4-Fc-treated mice. Retinal vasculature in P10 mouse pups treated systemically with Fc control protein (D) or Dll4-Fc (E) for 48 hours; GS lectin staining. (F) Quantification of total blood vessel length in the central retina (per 20× microscopic field); percentages indicate increase in total vessel length. (G-I) Reduced blood vessel regression in Dll4-Fc-treated mice. Retinal vasculature in P9 mouse pups treated systemically with Fc control protein (G) or Dll4-Fc (H) for 24 hours; double labeling with PECAM (green) and collagen IV (Col IV) antibody (red) staining. (I) Quantification of the number of regressed capillary segments (empty Col IV-positive tubes; per 400× microscopic field); percentages indicate decrease in the number of regressed capillary segments. (J-L) Reduced blood vessel occlusion in Dll4-Fc-treated mice. Double labeling with GS lectin staining (green) and ConA lectin perfusion staining (red). (L) Quantification of the number of occluded capillary segments (nonperfused capillaries; per 400× microscopic field); percentages indicate decrease in the number of occluded capillary segments. Original magnifications: A-B,D-F, ×40; J-K, ×200; G-H, ×400.