Updated publication reference for PubMed record(s): 30446640. Sprouting angiogenesis is a highly dynamic process which relies on the continuous interchange of endothelial cell relative position within the vascular sprout, a process mediated by cell rearrangements. Here we take advantage of a previous identified role of p110a/PI3K regulating endothelial cell motility to address how cell rearrangement and interaction regulate vessel growth. By using advanced fluorescent zebrafish models and a tamoxifen-inducible endothelial-specific gene targeting in the postnatal mouse retina, we demonstrate that inactivation of the p110a isoform of PI3K in endothelial cells is a good model to study cell shuffling in the growing vasculature. We identify that a failure of endothelial cells to rearrange results in cell elongation and inability to stabilize new contacts upon anastomosis. Instead of rearrange, blockade of p110 signaling drive these cells to grow in a three dimension fashion by sending multiple protrusions which lack lumen and fail to stabilize upon anastomosis. Through a combination of in vivo and in vitro approaches together with a global phosphoproteomic screen, we discover that p110a signaling stimulates cell rearrangements by suppressing actomyosin contractility in a myosin light chain phosphatase (MLCP) dependent manner. Together, our findings highlight the importance of cell rearrangement orchestrating several steps within the angiogenic program and uncover a critical role of the p110a/MLCP axis to suppress actomyosin contractility.