London, November 4 : Japanese researchers have successfully cloned healthy mice from cells derived from dead mice, which had been frozen for 16 years.
Teruhiko Wakayama, of the RIKEN Center for Developmental Biology in Kobe, says that the breakthrough has raised the possibility of cloning endangered species from old carcasses.
He says that this advancement even indicates that researchers may someday be able to resurrect extinct animals frozen in permafrost, such as the woolly mammoth.
"It would be very difficult, but our work suggests that it is no longer science fiction," New Scientist magazine quoted him as saying.
For their experiment, Wakayama and his colleagues used a modified version of a cloning technique wherein the nucleus of a cell from dead tissue that has been frozen and then thawed was injected into the egg of a mouse, which had had its nucleus removed.
The researchers then used the resulting embryo to create embryonic stem cells, capable of generating every cell type in the body. They injected the nuclei of such cells into other eggs to produce clones.
Wakayama said that his team got surprised to find that it was easiest to create clones from brain tissue, as clones have never been created from living brain cells.
He believes that freezing and thawing the tissue somehow makes it easier to "reprogram" the brain cell nucleus. Since brain tissue is high in sugars, according to the researcher, it can protect cells when they freeze.
The researcher said that it might be the reason why the DNA used for the study remained undamaged.
Though some research teams have cloned mice from previously frozen dead cells, Wakayama claims that his team is the first to clone the animals from lumps of tissue frozen without the use of chemicals, a reason why their process may protect the cells from damage.
Experts, however, believe that more research will be needed before it can be used on endangered species.
"For instance, we don't know how long we can keep bodies of different species frozen and still get viable DNA. It may depend on size and species," said Martha Gomez of the Audubon Nature Institute in New Orleans, Louisiana.
An article describing Wakayama's work has been published in the journal Proceedings of the National Academy of Sciences.