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The emergence of the first adult hematopoietic stem cells (HSCs) during mammalian ontogeny has been under intense investigation. It is as yet unresolved whether these first HSCs are derived from intraembryonic hemangioblasts, hemogenic endothelial cells, or other progenitors. Thus, to examine the spatial generation of functional HSCs within the mouse embryo, we used the well-known HSC marker, Sca-1, and a transgenic approach with an Ly-6A (Sca-1) GFP marker gene. Our results show that this transgene marker is expressed in all functional HSCs in the midgestation aorta. Immunohistology of aorta-gonads-mesonephros (AGM) regions show that GFP(+) cells are specifically localized to the endothelial layer lining the wall of the dorsal aorta but not to the mesenchyme, strongly suggesting that HSC activity arises within a few cells within the endothelium of the major vasculature.

Original publication




Journal article



Publication Date





673 - 683


Animals, Antigens, Ly, Aorta, Biomarkers, Cell Lineage, Embryo, Mammalian, Endothelium, Vascular, Gestational Age, Gonads, Green Fluorescent Proteins, Hematopoietic Stem Cell Transplantation, Hematopoietic Stem Cells, Kidney, Kinetics, Luminescent Proteins, Lymphocytes, Membrane Proteins, Mesoderm, Mice, Mice, Inbred C57BL, Mice, Inbred CBA, Mice, Transgenic, Umbilical Arteries