cular niche" can self-renew adult hematopoietic stem cells for weeks, both in vitro and in vivo, by co-culturing them on a bed of endothelial cells. The researchers chose endothelial cells because they are in close contact with blood stem cells, and previous work from Dr. Rafii's lab had demonstrated that endothelial cells produce novel stem-cell-active growth factors. However, maintenance of the endothelial cells is cumbersome and if they are not "fed" specific substances, such as growth factors known as "angiogenic factors," they immediately die. To get around this problem, the researchers genetically engineered the endothelial cells to stay in a long-term survival state by inserting a recently discovered gene cloned from adenoviruses, which does not promote oncogenic transformation of the human cells. This earlier discovery, using a single gene to put endothelial cells into a long-lasting "suspended animation" state without harming their ability to produce blood vessels, was also discovered in Dr. Rafii's lab and published in the journal Proceedings of National Academy Sciences in 2008.
Endothelial Cells Could Generate Stem Cells and Their Differentiated Progeny
In this study, the researchers also discovered that endothelial cells not only could expand stem cells, but also instruct stem cells to generate mature differentiated progeny that could form immune cells, platelets, and red and white blood cells, all of which constitute functioning blood.
"We are the first group to demonstrate that endothelial cells elaborate a repertoire of stem-cell-active growth factors that not only stimulate stem cell expansion but also orchestrate differentiation of these stem cells into their mature progeny," says Dr. Jason Butler, a senior investigator at Weill Cornell Medical College and first author of the study. "For example, we have found that expression of specific stem-cell-active factors, namely Notch-ligands, by the endothelial cells liniPage: 1 2 3 4 5 6 Related biology news :1
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