A type of cell found naturally in the body holds hope of treatments for muscle diseases such as muscular dystrophy, say UK scientists.
Satellite cells repair muscle
It has long been suspected but never proved that satellite cells which coat muscles can make new muscle.
The Medical Research Council and experts at University College London have now shown this is the case, at least in mice.
Similar repair cells may be present in other tissues, they told Cell journal.
Stem cells are at an early stage of development and have the ability to become almost any tissue type in the body.
Professor Terence Partridge and colleagues took between five and 25 mouse satellite cells and transplanted or grafted them into some muscle tissue in the lab.
They then measured the amount of new muscle and satellite cells produced.
Each grafted satellite cell produced new muscle.
Some of the grafted satellite cells also replicated more of themselves, expanding greatly in number by at least 10 times.
These new satellite cells were robust, being able to sustain vigorous regeneration over at least two subsequent rounds of muscle damage in the lab.
The researchers said this not only proves that these cells are responsible for muscle repair but also suggests that they share the same renewing properties of stem cells.
Type of stem cell
Professor Partridge said: "We have established that the satellite cell in muscle is a sort of stem cell.
"This is the first evidence of such a thing in a solid stable adult tissue and suggests that this type of system may exist in other stable tissues.
"If we can work out what controls these satellite cells and what goes wrong in the various conditions in which they seem not to keep up our muscle size and strength, then we can devise rational ways of modifying the system to our advantage."
His colleague, Dr Jennifer Morgan from Imperial College London, said the next step was to see if the same was true in humans.
"It will take some time because there are very difficult problems to be solved. The technique is complicated," she said.
Professor Kate Bushby from the Institute of Human Genetics at the University of Newcastle said: "This work is significant because this shows there are cells that have the potential to promote regeneration of muscle.
"This is a step forward which, if shown to be applicable to humans, might point a way to investigate new therapies."