Versatile skin. A stem cell isolated from skin (left) can form a spherical colony of cells (middle), which can give rise to neuronlike cells (right, green).

Skin Cells to Stem Cells

Skin grafts save the lives of patients with severe burns every day. If a new study pans out, skin might some day be used to repair internal organs as well. In the September issue of Nature Cell Biology, a team reports that cells from the skin of mice seem to have the ability to become other cell types in the lab, including neuronlike cells, muscle cells, and fat cells.

Until recently, most scientists believed that adult cells had already made certain irreversible decisions about what type of tissue they would be: Skin stem could make skin, for instance, but not liver or brain cells. But some preliminary studies have suggested that this may not be true.

Encouraged by those studies, neuroscientist Freda Miller of McGill University in Montreal started a "wild project" in her lab--an effort to find an easily accessible source of cells that could become neural cells. Skin would be "a dream source," Miller says: It's easily accessible, and there would be no danger of the immune system rejecting cell transplants derived from a patient's own skin.

The team took skin samples from juvenile mice and grew them in culture flasks. Many of the cells died, but a few formed sphere-shaped conglomerations that resemble the so-called neurospheres formed by neural stem cells. After 3 to 4 weeks, the team had purified populations of spheres that regenerate themselves from single cells. Exposed to various culture conditions, the cells could be prompted to express several proteins typical of neural cells in a range of developmental stages. Under different conditions, a few cells produced proteins normally made by smooth muscle cells, and other conditions prompted the formation of apparent fat cells. The team has also isolated similar cells from human skin, although they have not characterized them as thoroughly.

The neuronlike cells "really look like neurons," says cell biologist Derek van der Kooy of the University of Toronto. Most adult stem cells haven't proliferated very well in culture, but Miller and her team report that the skin stem cell cultures have grown for at least a year in the laboratory without losing their ability to differentiate. Van der Kooy cautions, however, that the team may have isolated so-called transformed cells, which have lost some of the normal genetic brakes on growth and could form tumors.

The work was done with support from a Montreal-based company called Aegera, founded by Miller and co-author David Kaplan of McGill. Aegera holds the patent on the isolation technique and has granted Boston-based biotech firm Curis an exclusive worldwide license to the cells. However, Kaplan says researchers are free to use the technique to isolate their own version of the cells for research purposes.

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