Japanese scientists have managed to create clones from the bodies of mice which have been frozen for 16 years. The scientists said they created their mice from the brain cells of rodents that had been kept in laboratory conditions at -20C.

They used a modified version of a cloning technique in which the nucleus of a mouse cell from dead tissue that has been frozen and then thawed - is injected into a mouse egg that has had its nucleus removed. The resulting embryo was then used to create embryonic stem cells, capable of generating every cell type in the body, and the nuclei of these cells were injected into other eggs to produce clones.

Teruhiko Wakayama, the head of the research, speculates that freezing and thawing the tissue somehow makes it easier to "reprogram" the brain cell

nucleus. Also, brain tissue high in sugars can protect cells when they freeze. This may explain why the DNA remained undamaged, says Wakayama.

Globally, there are several cloning programs that aim to increase the size of rapidly-dwindling populations of endangered species. These programs depend on the animal cells undergoing specialized chemical procedures before being frozen so that they come to life when thawed.

Despite the excitement surrounding the technique, more research will be needed before it can be used on endangered species.

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