Notch signaling acts downstream of Hey2 in arterial gene expression. Hey2 morphants failed to express the arterial genes efnb2a and notch1b in the DA angioblast cord (A,C,E,G black arrow). Heat-shock–induced ubiquitous activation of the Notch pathway rescued efnb2a (D) and notch1b (H) expression in the DA of hey2 morphants and caused ectopic induction of arterial gene expression in all embryos analyzed (B,D,F,H blue arrow). All views of embryos are lateral, with anterior left and dorsal up. Numbers of embryos with arterial gene expression in the DA are given as a fraction of the number of embryos analyzed. All morphants were injected with 4 ng of hey2 MO.