Hong Kong scientists are one step closer to understanding how the regenerative power of stem cells is activated, after discovering a molecule that facilitates the proliferation of muscle stem cells, known to build new muscle tissues when damaged. The research was carried out by Professor Wu Zhenguo and his colleagues at the division of life science at the University of Science and Technology. They've been trying to unravel the mystery of the working mechanisms of Pax7, a protein that is present in the nucleus of skeletal muscle stem cells. Their findings were published in the latest issue of Cell Stem Cell , a leading bioscience journal. "We know if we can successfully unravel the function of Pax7, it will be very useful in understanding how muscle stem cells work," Wu said. Pax7 was first discovered in 1993 but its importance in muscle stem cells was not revealed until 2000, when a group of Canadian scientists found that newborn mice which had Pax7 removed would be largely devoid of muscle stem cells and die within two weeks, showing that the protein is essential for muscle stem cells in young mice. But it had been unclear how exactly Pax7 worked. Professor Wu's team identified a new molecule that helps explain the mechanism by which Pax7 functions. The protein, which they named Pax3/7BP, works like a bridge, connecting Pax7 with a particular complex of histone-modifying enzymes. After the molecules are connected thanks to the protein, multiple Pax7 target genes are activated, resulting in the proliferation of muscle stem cells and the growth of muscle tissues in young mice. Like other tissue stem cells, muscle stem cells are capable of regenerating new muscles in damaged muscle tissues. Although scientists are still years away from developing practical therapies for human beings, Wu is confident that the new finding could lead to more effective stem cell treatments for various forms of muscular dystrophy, including Duchenne muscular dystrophy, a genetic disease that mostly affects boys. Those born with the disease often struggle to stand, and many die before the age of 20. Understanding how muscle stem cells function is also the key to understanding how stem cells wear out in older people. In aged animals, including humans, both the number of muscle stem cells and their potential to proliferate decrease. Restoring the number and function of muscle stem cells in old people should strengthen their muscles and greatly improve their quality of life. While hard work and time are essential, Wu believes a lot of scientific discoveries also require a lucky element. "The excitement we get when we make a new discovery and get it published in a top journal is beyond description," the professor adds.