Scientists have developed
mice which can regrow lost limbs or organs (or, in fact, everything other than brains).
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.
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.
Not only that, but cells from the mutant mice, injected into ordinary mice, confer the regenerative ability, and it is believed that it may confer greater longevity. The genes in question are believed to exist in humans as well.