Hematopoietic stem cells (HSCs) give rise to all cells of the adult blood system, and understanding how these cells first arise during embryogenesis is important for developing regenerative medicine-based strategies for producing HSCs in vitro. Here, David Traver and colleagues demonstrate that Gata2b acts as an early regulator of zebrafish hematopoietic precursors (p. ). The zebrafish genome contains two Gata2 orthologues – gata2a and gata2b – and the researchers show that gata2b is expressed in a distinct subpopulation of endothelial cells within the dorsal aorta (DA), which gives rise to HSCs; gata2a in contrast is expressed throughout the DA. This expression of gata2b is Notch-dependent and occurs prior to the expression of runx1, which to date has served as an early marker of zebrafish HSCs. Using lineage tracing, the researchers further show that gata2b-expressing cells give rise to adult HSCs. Finally, knockdown studies indicate that gata2b is required for the formation of functional HSCs. In summary, this study reveals that Gata2b functions as an early marker and regulator of HSCs, prompting further studies into the role of Gata2 during HSC emergence.
