Mapping human haematopoietic stem cells from haemogenic endothelium to birth.

The ontogeny of human haematopoietic stem cells (HSCs) is poorly defined owing to the inability to identify HSCs as they emerge and mature at different haematopoietic sites. Here we created a single-cell transcriptome map of human haematopoietic tissues from the first trimester to birth and found that the HSC signature RUNX1HOXA9MLLT3MECOMHLFSPINK2 distinguishes HSCs from progenitors throughout gestation. In addition to the aorta-gonad-mesonephros region, nascent HSCs populated the placenta and yolk sac before colonizing the liver at 6 weeks.