Arterial specification occurs independently of VEGF signaling in ptc1;ptc2;plcg1 triple mutants. (A-E) Tg(fli1a:EGFP)y1/+;ptc1;ptc2 embryos formed 2 separate vessels, both with sprouting capacity (B), whereas Tg(fli1a:EGFP)y1/+;plcg1^t26480 embryos formed a single vessel without ISV sprouts and lacking arterial gene expression (data not shown; C). Two separate vessels were present in triple mutant embryos (D, zoomed view of panel E), but no ISVs formed. kdrl (F-G) and ephrinb2a (H-I) expression indicated that the DA remained duplicated in the triple mutants, albeit with fewer cells.