'Miracle mouse' can grow back lost limbs

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August 28, 2005

'Miracle mouse' can grow back lost limbs

Leake, Science Editor

SCIENTISTS have created a " miracle mouse " that can regenerate

amputated limbs or badly damaged organs, making it able to recover

from injuries that would kill or permanently disable normal animals.

The experimental animal is unique among mammals in its ability to

regrow its heart, toes, joints and tail.

The researchers have also found that when cells from the test mouse

are injected into ordinary mice, they too acquire the ability to

regenerate.

The 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, Strategies for Engineered Negligible Senescence,

at Cambridge University. Ellen Heber-Katz, professor of immunology at

the Wistar Institute, an American biomedical research centre, says

that the ability of mice at her laboratory to regenerate appears to be

controlled by about a dozen genes.

She is still researching their exact functions, but it seems almost

certain that 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 foetal 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. "

Heber-Katz made her discovery when she noticed that the identification

holes that scientists punch in the ears of experimental mice healed

without any signs of scarring.

The self-healing mice, from a strain known as MRL, were then subjected

to a series of surgical procedures. In one the mice had their toes

amputated — but the digits grew back, complete with joints.

In another test some of the tail was cut off but also regenerated.

Then the researchers used a cryoprobe to freeze parts of the animals'

hearts, only to see these grow back again. A similar phenomenon was

observed when the optic nerve was severed and the liver partially

destroyed.

Heber-Katz will describe some of her findings at the Cambridge

conference and plans to publish her results in a research paper. " We

have found that the MRL mouse seems to have a higher rate of cell

division, " she said. " Its cells live and die faster and get replaced

faster. That seems to be linked to the ability to regenerate. "

The researchers suspect that the same genes could confer greater

longevity and are measuring the animals' survival rate. The mice are,

however, only 18 months old and the normal lifespan is two years so it

is too early to reach 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.

Humans can regenerate their liver provided at least a quarter remains

intact, as well as their blood and outer skin, but no other organs regrow.

This is probably because, although most mammalian cells start off with

the potential to develop into any cell type, they soon become very

specialised. This allows mammals to develop more complex brains and

bodies but deprives them of the power of regeneration.

By contrast, if a newt loses a limb then cells around the injury

revert back into so-called stem cells. These can develop into whatever

types of cell are needed, including bone, skin or nerves.