Sox18/Vegfd double loss-of-function causes arteriovenous fusion in zebrafish embryos. (A) Lateral views of gross morphology of zebrafish embryos at 48 hpf. (B-D) At 48 hpf, DA and PCV are formed in uninjected and single morpholino–injected control embryos (MO-sox18 ATG, MO-vegfd ATG) (i-iii). dKD embryos displayed DA and PCV fusion as shown on lateral view (Biv, white arrow) and transverse section (C,Div). Double morphants were rescued by injection of vegfd mRNA (v). Dashed lines in panel C indicate the magnified area in panel D. (E-F) Quantitative data show the number of embryos with arteriovenous and circulation defects upon MO injection. ***P < .001 by 1-way analysis of variance (ANOVA) test. No, notochord; NT, neural tube; Y, yolk. Scale bars represent 200 μm (A), 50 μm (B-C), and 20 μm (D).