Fig. 5

Arterial blood flow activates Notch signaling in ISVs. Panels (a–d) show lateral images of zebrafish embryos with anterior side facing left. ECs express lifeact-mCherry. Notch signaling is reported by the expression of destabilized GFP (d2GFP) under the control of 12xCSL Notch responsive elements. Red arrows point to arterial ISVs. Orange arrows indicate the direction of blood flow. White arrowheads highlight ISVs without blood flow. Scale bars are 25 μm. The numbers are averages ± SEM. P < 0.001. a Stills from Supplementary Movie 9. White arrowheads highlight ISVs without blood flow. Insets a’ and a” show expression of lifeactCherry (grey). Green arrows in the insets point to a venous sprout that did not anastomose with an arterial ISV. b Stills from Supplementary Movie 11. Green arrows point to venous sprouts. The sprout on the right detached from an ISV expressing d2GFP before a functional connection with the PCV was formed, as indicated by the extent of lumen formation (black arrow). c Green arrows highlight an ISV with above-the-average expression of d2GFP prior to initiation of blood flow. d Expression of Notch signaling reporter in embryos with reduced blood flow (60 hpf). e Quantification of the effect of a reduction in blood flow on d2GFP expression in arterial ISVs (60 hpf; n = 10 embryos per condition; 4–6 ISVs per embryo)