Scientists have created "miracle mice" that can regenerate amputated limbs or damaged vital organs, making them able to recover from injuries that would kill or permanently disable normal animals.

The experimental animals are unique among mammals in their ability to regrow their heart, toes, joints and tail.

And when cells from the test mouse are injected into ordinary mice, they too acquire the ability to regenerate, the US-based researchers say.

Their discoveries raise the prospect that humans could one day be given the ability to regenerate lost or damaged organs, opening up a new era in medicine.

Details of the research will be presented next week at a scientific conference on ageing titled Strategies for Engineered Negligible Senescence, at Cambridge University in Britain.

The research leader, Ellen Heber-Katz, professor of immunology at the Wistar Institute, a US biomedical research centre, said the ability of the mice at her laboratory to regenerate organs appeared to be controlled by about a dozen genes.

Professor Heber-Katz says she is still researching the genes' exact functions, but it seems almost certain humans have comparable genes.

 "We have experimented with amputating or damaging several different organs, such as the heart, toes, tail and ears, and just watched them regrow," she said. "It is quite remarkable. The only organ that did not grow back was the brain.

 "When we injected fetal liver cells taken from those animals into ordinary mice, they too gained the power of regeneration.

We found this persisted even six months after the injection." Professor Heber-Katz made her discovery when she noticed the identification holes that scientists punch in the ears of experimental mice healed without any signs of scarring in the animals at her laboratory.

The self-healing mice, from a strain known as MRL, were then subjected to a series of surgical procedures. In one case the mice had their toes amputated -- but the digits grew back, complete with joints.

In another test some of the tail was cut off, and this also regenerated.

Then the researchers used a cryoprobe to freeze parts of the animals' hearts, and watched them grow back again.

A similar phenomenon was observed when the optic nerve was severed and the liver partially destroyed.

The researchers believe the same genes could confer greater longevity and are measuring their animals' survival rate.

However, the mice are only 18 months old, and the normal lifespan is two years so it is too early to reach firm conclusions.

Scientists have long known that less complex creatures have an impressive ability to regenerate.

Many fish and amphibians can regrow internal organs or even whole limbs.


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