Healthy mice cloned from bodies frozen for 16 years

HEALTHY mice have been cloned for the first time from bodies kept in a deep freeze for 16 years.

The breakthrough increases the possibility of “resurrecting” extinct animals such as mammoths from their frozen remains.

Until now, Dolly the Sheep-style cloning has only been achieved using live donor cells, from which DNA is transferred to recipient eggs.

Cloning from thawed frozen cells was thought to be difficult, if not impossible, because their DNA would be damaged by ice crystals.

This presented a major obstacle to hopes of raising mammoths and other extinct animals preserved in ice from the dead.

A team of Japanese scientists has overcome the problem by producing clones from mice frozen at -20C for up to 16 years.

After thawing out the dead mice, the researchers collected nuclei from cells in their brain tissue. These were injected into empty eggs whose own DNA had been removed, to generate cloned embryos.

Stem cells taken from the embryos were then used in a second round of cloning. Their genetic material was inserted into de-nucleated eggs, to produce embryos that grew into four mouse clones. A further nine “chimeric” mouse clones were created by mixing the cells of embryos.

The research was reported yesterday in the journal Proceedings of the National Academy of Sciences.

The scientists, led by Dr Teruhiko Wakayama, from the Centre for Developmental Biology in Kobe, Japan, wrote: “We have demonstrated here that healthy cloned mice and chimeric clonal mice could be obtained by nuclear transfer using donor nuclei from cells obtained from bodies frozen without cryoprotectants for up to 16 years.”

The scientists said 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.”