The humanFLT1regulatory element directs vascular expression and modulates angiogenesis pathwaysin vitroandin vivo

There is growing evidence that mutations in non-codingcis-regulatory elements (CREs) disrupt proper development. However, little is known about human CREs that are crucial for cardiovascular development. To address this, we bioinformatically identified cardiovascular CREs based on the occupancy of the CRE by the homeodomain protein NKX2-5 and cardiac chromatin histone modifications. This search defined a highly conserved CRE within theFLT1locus termedenFLT1. We show that the humanenFLT1is an enhancer capable of driving reporter transgene expressionin vivothroughout the developing cardiovascular system of medaka. Deletion of the humanenFLT1enhancer (ΔenFLT1) triggered molecular perturbations in extracellular matrix organisation and blood vessel morphogenesisin vitroin endothelial cells derived from human embryonic stem cells and vascular defectsin vivoin medaka. These findings highlight the crucial role of the humanFLT1enhancer and its function as a regulator and buffer of transcriptional regulation in cardiovascular development.