By making mice grow furrier coats, researchers have discovered that an enzyme known to serve as a last-ditch defense against cancer also activates adult stem cells, which the body uses to repair its tissues.

The insight could lead to new treatments for certain diseases, possibly even promoting hair growth in animals other than mice.



The research, reported by Steven E. Artandi and colleagues at Stanford University in Nature today, shows that adult stem cells can be activated by an enzyme called telomerase.



The finding is surprising because telomerase is well known in a quite different context, protecting against tumors by limiting the number of times a cell can divide. The new findings put the enzyme astride two major biological pathways, one that promotes the growth of new cells for maintaining tissues and the other that prevents the excessive growth that leads to tumors.



The finding is “very interesting and very tantalizing,” said Carol Greider, a telomerase expert at the Johns Hopkins University, who was not involved in the research.



Dr. Artandi chose to study the effects of telomerase on mouse fur not to develop a Rogaine for rodents, but because mice have an easily accessible stem cell system built into their skin. Each hair follicle has attached to it a small bulb full of stem cells. When the stem cells are activated, the follicle grows a new hair shaft.



Dr. Artandi’s team genetically engineered a strain of mice in which the telomerase gene could be turned on with a drug. When the mice were given this drug, the stem cells in their hair follicles proliferated, and the mice grew extra furry coats.



The usual role of telomerase is to maintain the telomeres, special lengths of DNA that cap each end of the chromosomes. But it performs this service only for egg and sperm cells and to some extent for stem cells.



The telomerase gene is switched off almost entirely in normal cells. So each time a normal cell divides, its telomeres become shorter, and after they dwindle to a certain length, the cell is forced into senescence and cannot divide again.



For several years, there have been hints that the telomerase protein performs some role other than just maintaining telomeres. Dr. Artandi said he had decided to look for that role in stem cells, because the gene that makes the enzyme is active in these cells.



To avoid confusion with the telomere-lengthening role of telomerase, he engineered the mice to lack the additional biochemical machinery needed to maintain telomeres. Thus when the mice were fed the telomerase-activating drug, the telomerase must have activated the stem cells in some way that did not involve their telomeres.



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