Development

Budding Blood Cells

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Science  09 Jan 2009:
Vol. 323, Issue 5911, pp. 187
DOI: 10.1126/science.323.5911.187b

Arguably the best-understood stem cells are those that generate the body's blood cells—hematopoietic stem cells (HSCs). Although the place of origin, the aortic-gonado-mesonephric (AGM) columns, is known, the specific cell type responsible for their emergence is not. By labeling cell populations in vivo either with the adhesion molecule VE cadherin or the transcription factor myocardin, Zovein et al. were able to follow endothelial and mesenchymal progeny, respectively. Their data point to an endothelial origin of HSCs for subsequent long-term, multilineage adult hematopoiesis. Further, the HSC endothelial progeny could be monitored as they traveled first to the fetal liver and then to the bone marrow for subsequent expansion and multilineage differentiation. Besides the AGM region, the authors also identified the placental vasculature and yolk sac as endothelial sources of HSCs. Hence, the origin of hematopoietic stem cells is endothelium, which itself comes from a transient mesenchymal population of cells. — BAP

Cell Stem Cell 3, 625 (2008).

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