Endothelial Ca 2+ oscillations reflect VEGFR signaling-regulated angiogenic capacity in vivo

Sprouting angiogenesis is a well-coordinated process controlled by multiple extracellular inputs, including vascular endothelial growth factor (VEGF). However, little is known about when and how individual endothelial cell (EC) responds to angiogenic inputs in vivo. Here, we visualized endothelial Ca(2+) dynamics in zebrafish and found that intracellular Ca(2+) oscillations occurred in ECs exhibiting angiogenic behavior. Ca(2+) oscillations depended upon VEGF receptor-2 (Vegfr2) and Vegfr3 in ECs budding from the dorsal aorta (DA) and posterior cardinal vein, respectively. Thus, visualizing Ca(2+) oscillations allowed us to monitor EC responses to angiogenic cues. Vegfr-dependent Ca(2+) oscillations occurred in migrating tip cells as well as stalk cells budding from the DA. We investigated how Dll4/Notch signaling regulates endothelial Ca(2+) oscillations and found that it was required for the selection of single stalk cell as well as tip cell. Thus, we captured spatio-temporal Ca(2+) dynamics during sprouting angiogenesis, as a result of cellular responses to angiogenic inputs.