First reported complete akt loss-of-function zebrafish Free

During vascular system development, Notch and vascular endothelial growth factor (VEGF) signalling are important for the differentiation of the aorta and vein. Both Notch and VEGF signalling involve the protein kinase Akt; however, studying its role is difficult because the loss of Akt is embryonic lethal in mice. Now, Joey Ghersi, Stefania Nicoli and colleagues delete all four zebrafish Akt genes (akt1, akt2, akt3a and akt3b) using CRISPR/Cas9 to create an akt^Δ/Δ mutant line. Unlike in mice, akt^Δ/Δ zebrafish exhibit surprisingly few defects during early development; however, most akt^Δ/Δ larvae die within 11 days post-fertilisation. Using time-lapse imaging of transgenic reporters and single-cell sequencing, the authors reveal that, although Akt-signalling is dispensable for embryogenesis, there is a specific requirement for Notch-dependent development of aorta. In akt^Δ/Δ mutants, aorta development is delayed and morphologically disrupted (e.g. reduced lumen diameter), with reduced expression of artery-specific markers, such as efnb2a and vegfc. These phenotypes could be rescued by a constitutively active Akt or by activation of the Notch pathway in endothelial cells, indicating that Akt acts through the Notch pathway. Together, these results describe the role of Akt kinases in arterial development in the first reported vertebrate knockout model.