Traver and his colleagues, who included Julien Bertrand, a postdoctoral fellow in his laboratory, Neil Chi, an assistant professor of medicine at UCSD and Didier Stainier, a professor of biochemistry at UC San Franscisco, made their discoveries in zebrafish, a model laboratory organism for geneticists in which embryos are transparent, allowing the researchers to observe and track individual stem cells with a microscope.
A number of earlier studies using indirect observation had led to the idea that a particular region of the embryo surrounding the dorsal aorta, an early blood vessel, produced the first HSCs, but until now no one had been able to directly visualize the process in living animals.
"Indeed a number of conflicting studies had proposed different or earlier sites of origin, making the exact location where HSCs develop controversial," said Traver. "Using zebrafish embryos with fluorescently labeled tissues, we were able to demonstrate that HSCs arise directly from cells lining the floor of the dorsal aorta by imaging the process in living embryos."
The UCSD researchers also documented the stepwise formation of HSCs from "hemogenic" aortic endothelium and showed, by expressing a permanent fluorescent marker in these cells, that all adult blood and immune cell types derive from aortic endothelium of the early embryo.
"Our studies suggest that transition through a hemogenic endothelial intermediate is a requisite step for hematopoietic stem cell formation," said Traver. "Based upon the high degree of evolutionary similarity in the regulation of HSC formati
|Contact: Kim McDonald|
University of California - San Diego