Stem cells are a bit like wild cards in the body's deck: some can become almost any other tissue type. For this reason, scientists have hoped that these cells might eventually be used to rebuild tissues damaged by disease, trauma or age. Now researchers from New York and Yale Universities have discovered remarkably versatile stem cells in the bone marrow of adult mice. They describe their findings in this month's issue of Cell.

Until recently, scientists believed that the only truly versatile stem cells were those derived from early-stages embryos. But the scarcity of these cells¿along with numerous ethical issues¿has limited their use in humans. Stem cells derived from adults, on the other hand, were always considered too specialized, capable of giving rise to only a few tissue types.

Even adult bone marrow stem cells, however, can form bones and muscles, as recent studies have shown in human and mice. So to see just how versatile these cells could be, the researchers purified stem cells from the bone marrow of male mice, selecting those with the highest potential to multiply. Then they transplanted one of these cells each to female mice whose bone marrow had been previously destroyed by radiation. By using color dyes that make the Y chromosome (which only male cells possess) visible under special light, the researchers could see which cells in the females were then derived from the transplant and which were not.

Eleven months after the transplant, cells bearing the Y chromosome not only appeared in the bone marrow and blood of the females, but had also contributed to the regeneration of several other tissues, including the lungs, stomach, intestines, liver and skin. Surprisingly enough, bone marrow stem cells were able to form epithelial tissues, such as those in the skin or lungs, which have very different developmental origins. "It is astounding that there are cells in our bone marrow that can become so many different cell types," Diane Krause of the Yale Cancer Center says. These results could help researchers develop therapies for many different human diseases and injuries, but she cautions that this field is very much in its infancy, and much more work is needed on both embryonic and adult-derived stem cells to move ahead.

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