Today, Nature published a paper describing the generation of haematopoietic stem cells from aortic endothelium. During embryonic development, haematopoietic stem cells arise during four disctinct stages, the last of which involves the dorsal aorta. Previously, it was not known exactly what this involvement entailed. The paper, by Bertrand et al, shows that aortic haemogenic endothelium directly converts into baby haematopoietic stem cells, which eventually grow up to found the entire adult haematopoietic system. To do this, Bertrand et al conducted confocal time-lapse imaging in zebrafish embryos (on cmyb:eGFP; kdrl:memCherry double transgenic animals, to label the baby haematopoietic stem cells and the aortic endothelium, respectively). Excitingly, the authors include videos of this process as supplemental figures, which can, and should, be viewed, here (remember, green=stem cells, red=endothelium).
Their results, showing that haematopoietic stem cell generation requires a transition through a haemogenic endothelial intermediate is expected to help in researcher induce haematopoietic stem cell formation from pluripotent precursors, which previously has not been possible.