ptc1;ptc2 mutants exhibit ectopic arterial differentiation at the expense of venous differentiation, resulting in conversion of the PCV into a second artery. Lateral views of the trunk region are shown, oriented anterior to left, posterior right. (A) kdrl exhibited arterial preference in wild-type embryos (red arrowheads) but was present ectopically in the PCV in ptc1;ptc2 embryos (B blue arrowheads). (C) ephrinb2a was restricted to the DA in wild-type embryos (red arrowhead) but present ectopically in the PCV in ptc1;ptc2 embryos (D blue arrowheads). (E) aplnra and (G) flt4 expression was restricted to the PCV in wild-type embryos (blue arrowheads) and down-regulated in ptc1;ptc2 embryos (F,H blue arrowheads). (I) runx1 was restricted to the DA in wild-type embryos (white arrowhead), down-regulated in the DA of ptc1;ptc2 embryos (J white arrowhead), and ectopically expressed in the PCV of ptc1;ptc2 embryos (J black arrowheads). (K) Increased trunk vegfa expression was present in ptc1;ptc2 embryos (L green arrowhead) compared with wild-type (K green arrowhead).