VEGFR2 was localized by fluorescent immunohistochemistry. Tissue sections were air-dried, then washed in PBS containing 0.2% Tween (PBST), blocked for one hour at room temperature with 5% goat serum, 1.5% BSA in PBST, and then incubated overnight at 4°C with a rabbit polyclonal antibody directed against murine VEGFR2 (5 μg/ml; a generous gift from Rolf Brekken, University of Texas Southwestern Medical Center, Dallas, TX) or in blocking buffer only as a negative control. Samples were washed in PBS, and a mixture containing goat anti-rabbit cy3 antibody (1:300; Jackson ImmunoResearch Laboratories, West Grove, PA) as well as 4′, 6-diamidino-2-phenylindole (DAPI; 1:100) was added for one hour at room temperature. Tissue sections were washed in PBS, slides were mounted, and images were taken with the Axioscope microscope (Axioscope Mot 2; Carl Zeiss Meditec, Inc., Dublin, CA).