Fig. 4. Tek expression during ex vivo angiogenesis. (A) Tissue fragments isolated from Tek GFP mice were embedded in 3D collagen gels and neovessel formation was assessed by phase-contrast (left panel) and fluorescence microscopy (right panel). The GFP signal was restricted to the stalk region of the growing neovessel (white arrows) whereas the endothelial tip cells were GFP-negative (yellow arrows). (B) Higher magnification of yellow boxed areas from upper two panels. Bar, 0.1 mm.