Functional analysis of a Gata2a endothelial enhancer reveals non-redundant roles for Gata2a and Gata2b in haemogenic endothelium programming and generation of haematopoietic stem cells

Haematopoietic stem cells (HSCs) maintain the vertebrate blood system throughout life. They arise during embryogenesis from the haemogenic endothelium (HE), located in the floor of the dorsal aorta. Our understanding of HE specification remains incomplete, but regulation of Gata2 is crucial for its programming. Here we investigate whether gata2a is required for HSC emergence in zebrafish. We found that the endothelial-specific intronic gata2a enhancer (i4 enhancer) is conserved throughout vertebrates and established a transgenic line driven by this enhancer to monitor the activity of gata2a in vivo. Homozygous deletion of the i4 enhancer (gata2aΔi4/Δi4) led to endothelial-specific loss of gata2a expression, including the HE. This correlated with a decrease in gata2b and runx1 in the HE of gata2aΔi4/Δi4 mutants, suggesting that Gata2a is an upstream regulator of the gata2b/runx1 axis that programmes the HE to become haematopoietic. Thus, endothelial Gata2a activity is required to programme the HE and generate HSCs.