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Fig. 6 Overexpression of dll4 reduces sprouting from the PCV. (A,B) Injection of mRNA encoding full-length Dll4 into TG(flt1:YFP)hu4624 zebrafish embryos leads to a reduction in the number of venous sprouts in injected (B) as compared with uninjected control (A) embryos at 52 hpf. ISAs that connect directly to the dorsal aorta (red bar) are indicated by yellow arrows. Venous spouts (yellow brackets) can be readily identified by the absence of TG(flt1:YFP)hu4624 expression in the ventral component of an intersegmental vessel. Venous sprouts connect directly to the posterior cardinal vein (blue bar) from which they derive during secondary sprouting. (C) Quantification of the number of venous sprouts (y-axis) on one side of the embryo across 12 segments anterior to the cloaca (n=23 embryos scored for both dll4 MO-injected and uninjected controls). dll4 MO-injected embryos show a significant decrease in the number of intersegmental venous sprouts (P<0.001, Mann-Whitney rank sum test).