Regulation of endothelial cell chromatin availability and transcription factor activity during arterial-venous specification.

Arterial-venous specification of endothelial cells during vascular development requires coordination between intracellular signaling, cell cycle state and transcription factor activity. However, the intrinsic regulatory mechanisms that govern these processes are poorly understood. To investigate this, we assessed endothelial chromatin accessibility during vascular development. Murine postnatal day (P) 6 and P15 retinal endothelial cells were analyzed by single cell assay for transposase accessible chromatin sequencing, revealing heterogeneous chromatin accessibility across an arterial-venous continuum and in distinct cell cycle states. Enhancer regulatory network analysis predicted transcription factors with differential cell cycle and arterial-venous activity, and many with dual activator and repressor functions, including SOX17. We then validated SOX17 function in human endothelial cells, identifying that it inhibits proliferation and promotes arterial gene expression. Our findings suggest that dual roles of key endothelial transcription factors are regulated by chromatin accessibility in a cell cycle- and subtype-specific manner to control arterial-venous specification.