Crlr knockdown results in vascular defects. Vascular morphology in tg(fli1:EGFP)^y1 embryos injected with std-MO (control in panels A,C,E,F,I, and K) or crlr-MO1 (morphant in panels B,D,G,H,J, and L). Morphologic appearance of control (A) and crlr morphant (B) embryos at 28 hpf (head and trunk regions are highlighted by black and red boxes, respectively). Differential interference contrast images of the trunk region (lateral view) of live zebrafish embryos injected with std-MO (C) or crlr-MO1 (D), the lumen of DA and PCV are indicated by red and white bars, respectively; note the abnormal size of DA and the presence of cells with endothelial morphology (red arrow) in proximity to the notochord in crlr morphant (D). Confocal laser microscopy showing details of the head (E,G) and trunk (F,H) regions (lateral view) in std-MO– and crlr-MO1–injected tg(fli1:EGFP)^y1 embryos (DA [red bar], PVC [white bar]; white arrow points to poorly developed ISVs in crlr morphant). Crlr knockdown causes also an interruption of the vascular tube at the bifurcation of the DA. Dorsal view of the lateral dorsal aortae (red arrows) and of cardinal vein branches (white arroweads) in control (I) and crlr-MO1–injected (L) tg(fli1:EGFP)^y1 embryos; lumens of the lateral dorsal aortae and cardinal vein branches are indicated by red and white bars, respectively. Note the poor lumenization and formation of lateral aortae branches in crlr morphant compared with the posterior cardinal vein. Microangiography performed at 50 hpf shows that blood circulation is confined to the head and heart regions (white arrow) in crlr morphants (L) when compared with control embryos (K). White arrowhead in panel L points to the interruption of the blood flow at the level of bifurcation of the DA.