a, Dorsal vascular plexus (anti-CD31/anti-Nrp1) in flat-mounted hindbrain roofs (E9.5). Asterisks and boxed areas (right panels) show sprouts quantified in (b). b,c, Quantification of sprouts (b) and dorsal anastomoses (c). d, Dorsal aortae (anti-CD31) from control and dKOEC E9.5 embryos, arrow heads show ectopic sprouts. e,f, Quantification of proliferation (phospho H3-positive ECs) in the dorsal vascular plexus. g, Position of the Golgi apparatus (anti-GM130) in tip cells. h, Filopodia (anti-Nrp1) in endothelium (anti-CD31). Boxed region in g-h are magnified in right panels. Abbreviations: tc, tip cell. Quantifications are averages from several embryos (b,c: n ≥ 21; e: n ≥ 11). Scale bars: 200 μm (a, left panels), 20 μm (a, boxed area; g, left panels); 150 μm (d,f,h, left panels); 4 μm (g, boxed area) and 50 μm (h, boxed area). See also Figure S2 and S3.