(A–D) Analysis of venous ISVs in fli1a:GFP larvae at 4 dpf. (A) Control uninjected larva at 4 dpf, with the thoracic duct (TD) located below the dorsal aorta (DA). Embryos injected with photomorph solution and never photoactivated develop normal TD and vasculature (B), while injected embryos UV photoactivated at 24 hpf (C), develop normal vasculature compared to control embryos, while the thoracic duct is absent (asterisks) at 4 dpf. Note that the venous derived intersegmental vessels are present in both control and Etv2-inhibited larvae (arrowheads). (D) Quantification of percent of ISVs with venous connection at 4 dpf in control uninjected larvae (54.5±1.2%, n=13) compared to never photoactivated (55.1±1.2%, n=11, p=0.74, two tailed Student’s t-test) and 24 hpf photoactivated (52.9±1.2%, n=12, p=0.34, two tailed Student’s t-test) larvae, indicates no significant difference between groups. Mean±SEM is shown. Individual data points are shown in Fig. S4A. This experiment has been replicated 3 times.