Ets1 functions partially redundantly with Etv2 to promote embryonic vasculogenesis and angiogenesis in zebrafish

ETS transcription factors play an important role in the specification and differentiation of endothelial cells during vascular development. Despite previous studies, the role of the founding member of the ETS family, Ets1, in vascular development in vivo is only partially understood. Here, we generated a zebrafish ets1 mutant by TALEN genome editing and tested functional redundancy between Ets1 and a related ETS factor Etv2/Etsrp/ER71. While zebrafish ets1^-/- mutants have a normal functional vascular system, etv2^-/-;ets1^-/embryos had more severe angiogenic defects and lower expression levels of kdr and kdrl, the two zebrafish homologs of the mammalian Vascular Endothelial Growth Factor Receptor 2 VEGFR2/Flk1, than etv2^-/-embryos. Expression of constitutively active Mitogen-Activated Protein Kinase1 (MAP2K1) within endothelial cells partially rescued this angiogenic defect. Interestingly, ets1^-/- embryos displayed extensive apoptosis within the trunk vasculature despite exhibiting normal vascular patterning. Loss of Ets1 combined with a partial knockdown of Etv2 function resulted in a decrease in endothelial cell numbers in the axial vasculature, which argues for a role of Ets1 in promoting vasculogenesis. We also demonstrate that although both Ets1 and Etv2 can induce ectopic vascular marker expression in zebrafish embryos, Ets1 activity is dependent on MAPK-mediated phosphorylation of its Thr30 and Ser33 residues, while Etv2 activity is not. Together, our results identify a novel function of Ets1 in regulating endothelial cell survival during vasculogenesis in vivo. Based on these findings, we propose a revised model of how Ets1 and Etv2 play unique and partially redundant roles to promote vascular development.