Fig. 5. Primary network formation proceeds normally in embryos that have no blood circulation. (A-D) Lateral views of the mid-trunk of Tg(fli1:EGFP)^y1/Tg(fli1:EGFP)^y1, sih/sih or Tg(fli1:EGFP)^y1/Tg(fli1:EGFP)^y1 (E,F) embryos. (A) The primary vascular lattice appears normal at 1.5 dpf. (B) Secondary sprouts (arrows) are apparent by 2 dpf. Their appearance is also normal. (C) Secondary sprouts (arrows) contribute to the parachordal system by 2.5 dpf, as they do in wild-type embryos. (D) By 3.5 dpf primary segments display dorsal enlargement and ramification (arrows), but lack obvious vessel lumenization. (E) Control morpholino and (F) anti-Vegf morpholino injected transgenic at 1.5 dpf. Anti-Vegf morpholino-injected animals do not form the primary angiogenic network, although initial sprouting is sometimes observed (arrows in F). Images were collected by multiphoton confocal microscopy. Anterior is towards the left in all panels. Scale bar: 50 µm. 3-D reconstructions of these images are available at http://dir.nichd.nih. gov/lmg/uvo/ISV3_D.html