Arterial specification in ptc1;ptc2 mutants is dependent on Notch signaling. (A) Tg(fli1a:EGFP)y1/+;ptc1;ptc2 embryos exhibit blood vessel formation (B, yellow arrowhead; n = 15 of 230), even after Su(H) morpholino injection (B yellow arrowhead; n = 5 of 95). (C) Normal DA ephrinb2a expression in uninjected non–double mutant embryos (C red arrowhead; n = 157 of 167). (D) Loss of ephrinb2a in DA of non–double mutant Su(H) morphants (red arrowhead; n = 159 of 180). (E) Increased (red arrowhead), ectopic (green arrowhead) ephrinb2a expression in uninjected ptc1;ptc2 embryos (n = 10 of 167). (F) Loss of ephrinb2a in DA of ptc1;ptc2 Su(H) morphants (n = 16 of 180).