Stem cell surprise for tissue re...( Baltimore MDScientists working at th...)

Baltimore, MDScientists working at the Carnegie Institution's Department of Embryology, with colleagues, have overturned previous research that identified critical genes for making muscle stem cells. It turns out that the genes that make muscle stem cells in the embryo are surprisingly not needed in adult muscle stem cells to regenerate muscles after injury. The finding challenges the current course of research into muscular dystrophy, muscle injury, and regenerative medicine, which uses stem cells for healing tissues, and it favours using age-matched stem cells for therapy. The study is published in the June 25 advance on-line edition of Nature.

Previous studies have shown that two genes Pax3 and Pax7, are essential for making the embryonic and neonatal muscle stem cells in the mouse. Lead researcher Christoph Lepper, a predoctoral fellow in Carnegie's Chen-Ming Fan's lab and a Johns Hopkins student, for the first time looked at these two genes in promoting stem cells at varying stages of muscle growth in live mice after birth.

As Christoph explained: "The paired-box genes, Pax3 and Pax7 are involved in the development of the skeletal muscles. It is well established that both genes are needed to produce muscle stem cells in the embryo. A previous student, Alice Chen, studied how these genes are turned on in embryonic muscle stem cells (also published in Nature). I thought that if they are so important in the embryo, they must be important for adult muscle stem cells. Using genetic tricks, I was able to suppress both genes in the adult muscle stem cells. I was totally surprised to find that the muscle stem cells are normal without them."

The researchers then looked at whether the same was true upon injury, after which the repair process requires muscle stem cells to make new muscles. For this, they injured the leg muscles between the knee and ankle. They were again surprised that these muscle stem cells, without the two key
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