Endothelial Shc knockout causes defective angiogenesis in vivo. (A) Shc knockout in ECs results in decreased vascular density in the postnatal retina. Retinas from P5 mice were stained with isolectin-B4 Alexa Fluor 488 to visualize ECs. Vascular density was quantified by counting branch points per 100 square micrometers and percentage of vascular area (performed blind by 2 different people). Shcflox/flox, n = 17; Shcflox/flox;Tie2-Cre⁺, n = 15; and Shc wt/wt;;Tie2-Cre⁺, n = 9 mice. Scale bars indicate 100 μm. (B) Matrigel Plug assay in 4- to 6-week-old mice reveals a role for EC Shc in angiogenesis toward VEGF. Matrigel plugs containing 250 ng/mL of VEGF or vehicle alone were implanted into each mouse. After 7 days, plugs were H&E stained and microvessels per square millimeter were counted in serial sections through the plug. Values are means ± SEM (by Student t test). Shcflox/flox, n = 5 and Shcflox/flox;Tie2-Cre⁺, n = 6 mice.