![image: [ A likely tail: the mice experimented on regrew their tails ]](/olmedia/55000/images/_56799_mice300.jpg)
Professor Ellen Herber-Katz made the breakthrough after cutting off a part of a laboratory mouse's tail.
The tail grew back, although the experiment did not work so well if any more than half an inch was amputated.
She announced the accidental discovery at the annual meeting of the American Association for the Advancement of Science in Philadelphia.
The professor acknowledged that it may be a long time before humans can grow a new hand or leg.
But in the future it might become possible to switch off specific genes in humans who have lost limbs, so that the limbs regrow.
Surprise discovery
Professor Herber-Katz was studying multiple sclerosis at the Wistar Institute in Philadelphia when she made the discovery.
She was using specially bred mice which lacked a component of their immune system.
The mice had their ears pierced to identify them. But three weeks later, there was no sign of the holes.
Thinking they must have made a mistake, the scientists pierced the mouse ears again. But again they healed and did so in a way that left no trace or scar.
On closer investigation it became clear that this was not simply wound-healing but regeneration.
Soft tissue, cartilage and skin all grew back in the right place, in the same way that they do in amphibians such newts which can regrow severed limbs.
Professor Herber-Katz believes the specially bred mice lack specific genes that normally prevent regeneration in mammals.
She said that there seems to have been an evolutionary trade-off in mammals like normal mice and humans. Their bodies defend against tumours, but the same process may prevent the ability to regenerate limbs.
In the future Professor Herber-Katz hopes to find out how stimulate regeneration without causing tumour growth.
Genetic tests have pointed to seven possible genes, one of which might also be involved in embryonic wound healing.
Doctors already know that unborn babies in early development can be operated on in the womb and no scars will show when they are born.
The American Association for the Advancement of Science
AAAS Conference Homepage
The Wistar Institute
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