Ischemia-induced neovascularization in tie2/lacZ mice. The ischemia model was studied in tie2/lacZ mice, in which β-galactosidase (blue staining) is expressed by all endothelial cells. (A) (B) Gross sections of the undersurface of mouse skin stained with X-gal are shown prior to and 14 days following ischemic surgery, respectively. Note the central zone of necrosis that could easily be demarcated from ischemic, but viable, tissue (arrow). (C) (D) (E) (F) (G) Histologic sections were stained for β-galactosidase (red) and demonstrated increasing microvessel density within ischemic regions at day 7 (blue indicates DAPI nuclei staining) (panels C-E). A subset of animals were injected with fluorescent lectin also (red) prior to humane killing to highlight functionally perfused vessels (panels F-H). As illustrated at day 14, neovessels formed in a direction along the gradient of ischemia toward the central portion of necrosis. Scale bars = 50 μm.