Scientists say that they have taken a step closer to recreating extinct animals like the mammoth, after successfully cloning living mice from donor animals that had been frozen.

A team of Japanese scientists produced the clones after thawing mice that had been frozen at minus 20C for up to 16 years.

Clones had been created previously only from live donor cells; cloning from frozen cells has been seen as difficult because DNA can be damaged by ice crystals.

A team at the Centre for Developmental Biology, at the RIKEN research institute in Kobe, collected the nucleii from brain cells of the frozen animals.

These were then injected into empty eggs whose own DNA had been removed, to generate the cloned embryos. Stem cells taken from the embryos were then used in a second round of cloning.

Four mouse clones were originally created, and a further nine "chimeric" clones were created by mixing the cells of different embryos.

The scientists, who publish their findings in Proceedings of the National Academy of Sciences today, write: "Thus, nuclear transfer techniques could be used to ‘resurrect’ animals or maintain valuable genomic stocks from tissues frozen for prolonged periods without any cryopreservation."

The project was led by Teruhiko Wakayama, whose group said that the discovery increases the possibility that extinct animals, such as mammoths could, perhaps, be resurrected. "Cloning animals by nuclear transfer provides an opportunity to preserve endangered mammalian species," they wrote.

The scientists wrote that the cloned mice did not show abnormalities and were healthy when they reached adulthood, although other attempts failed.

Although the team found that some of the cells taken from the frozen mice had been damaged — potentially affecting the DNA inside — they were most successful in taking cells from the brain.

The scientists said that other sources of frozen nuclei, such as white blood cells, might be as useful for cloning as brain tissue.

They added: "This would increase the chances of finding tissues in good condition. At present, the lack of suitable species for recipient oocytes [eggs] and for surrogate mothers is one of the major problems that needs to be solved for the method to be applied in extinct or endangered animals."

Malcolm Alison, Professor of Stem Cell Biology at St Bartholomew’s Hospital in London and the London School of Medicine and Dentistry, told the Daily Mail: "While 16 years is not a long time for cells to be frozen — IVF clinics often have viable sperm frozen for longer periods — there are no scientific reasons why extinct animals like mammoths could not be similarly generated."

As a caveat to reports that they might be able to resurrect extinct creatures, the Japanese team added: "However, it has been suggested that the ‘resurrection’ of frozen extinct species [such as the woolly mammoth] is impracticable, as no live cells are available, and the genomic material that remains is inevitably degraded."

It is 12 years since British scientists created Dolly the Sheep, the first mammal to be cloned from an adult cell. A number of other animals have since been cloned, including pigs, cattle, mice and dogs.

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