Abstract 16812: ETV2- Rhoj Cascade Regulates Endothelial Progenitor Cell Migration During Embryogenesis

Background: Endothelial progenitors migrate early during embryogenesis to form the primary vascular plexus. ETV2, an Ets-transcription factor, governs the specification of the earliest hemato-endothelial progenitors during embryogenesis. The regulatory mechanisms that govern their migration are undefined. In the present study, we describe a novel role for ETV2 in cell migration and provide evidence for an ETV2 -Rhoj network as a mechanism responsible for this process. Approach and Results: We analyzed our RNAseq datasets, which revealed robust enrichment of migratory/motility pathways following overexpression of ETV2 during mesodermal differentiation. We then analyzed ETV2 ChIPseq and ATACseq datasets, which showed enrichment of ChIPseq peaks with increased chromatin accessibility in migratory genes following overexpression of ETV2. Additionally, scratch and sprouting assays showed that overexpression of ETV2 enhanced cell migration in mouse embryonic stem cells (ESCs), embryoid bodies (EBs) and mouse embryonic fibroblasts (MEFs). Knockout of Etv2 led to migratory defects of Etv2-EYFP + angioblasts to their pre-defined regions of developing embryos relative to wildtype controls at embryonic day (E) 8.5, supporting its role during migration. Mechanistically, we showed that ETV2 binds to the promoter region of Rhoj serving as an upstream regulator of cell migration. Single cell RNAseq analysis of Etv2-EYFP + sorted cells revealed co-expression of Etv2 and Rhoj in endothelial progenitors at E7.75 and E8.25. Overexpression of ETV2 led to a robust increase in Rhoj in both EBs and MEFs, whereas, its expression was abolished in the Etv2 knockout EBs. Finally, shRNA-mediated knockdown of Rhoj resulted in migratory defects which were rescued by overexpression of ETV2. Conclusions: These results define an ETV2 -Rhoj cascade, which is important for the regulation of endothelial progenitor cell migration during embryogenesis.