Cloning From the Frozen Dead

Nov. 4, 2008 — -- Scientists in Japan say they have successfully cloned a mouse from a body that had been frozen for 16 years, theoretically opening the door to a range of possibilities from preserving endangered animals, to resurrecting extinct animals to cloning Ted Williams.

The authors of the study made no bones about what they believe the implications of their work could be.

"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," wrote the authors in the Monday edition of the Proceedings of the National Academy of Sciences.

But the researchers say they got around the dead tissue issue by adapting new fertilization techniques for damaged sperm into a cloning technique for damaged frozen tissue. The authors of the study concluded these "techniques could be used to 'resurrect' animals or maintain valuable genomic stocks from tissues frozen for prolonged periods without any cryopreservation."

Other cloning scientists say cloning a wooly mammoth may not be so easy, but that cloning frozen dead tissue without the work of cryopreservation could have useful applications.

Sperm-Inspired Work

The term "cryonics" often summons images of baseball legend Ted Williams, who was controversially frozen at the Alcor Life Extension Foundation in Scottsdale, Ariz., by his children in hopes of reviving him with future scientific advances.

Yet, much more cryonic work is done to clone prized livestock than to preserve loved ones. Cloning typically requires intact cells, so breeders turn to cryonics to preserve their prized animals.

To circumvent cryonic cloning, which must use high-tech equipment and protective chemicals, the researchers looked to past experiments with dried sperm.

"It's not surprising that it worked," said Randall Prather, a professor of animal sciences at the University of Missouri at Columbia.

"It has been shown that you can take sperm and desiccate [dry] them and leave them out on the table, then rehydrate them and inject those into eggs and get a viable embryo," said Prather, who works with cloning pigs.

If sperm dries up and dies, the sperm cell's membrane cannot fuse with an egg to fertilize it. But researchers have shown they can still fertilize an egg by extracting the sperm's DNA and surgically inserting it into the egg, Prather said.

Cloning Animals

When cloning an animal, researchers often mimic fertilization, but instead of using a sperm and an egg, scientists fuse a live adult animal cell with an egg that has had its DNA surgically removed.

"But they weren't able to find live cells from these frozen mice," said Kenneth White, head of the Animal, Diary and Veterinary Sciences Department at Utah State University in Logan.

So, the researchers in Japan borrowed the techniques used to fertilize eggs with damaged sperm to clone healthy eggs with DNA from damaged and frozen mice cells.

"And voila, they were able to generate embryos from that," White said.

White said he was impressed with the capabilities of cloning from frozen tissue.

"Remember that those [mice] were frozen for 16 years, those cells still don't look too bad," he said.

"There are tissue samples of animals out there that may have direct application for this new technology," said Dirk Vanderwall, associate professor in the Department of Animal Veterinary Science at the University of Idaho in Moscow.

He suggested, the "frozen zoo" of tissue samples of endangered animals at the San Diego Zoo in California.

But White and other scientists caution that it would be much more difficult to clone extinct animals.

Jurassic Park, or Ice Age Park, Relived?

"If you're just running around and found some frozen extinct animal, you're still going to have to have a suitable womb, and a suitable egg," White said.

For example, White said scientists do not know whether an elephant could provide a suitable replacement womb, or a suitable replacement egg for a woolly mammoth.

"I'm certainly not going to say it can't be done, but there are incredible hurdles," Prather said.

Current cloning techniques with live animal cells only work 1 percent of the time, he said, so to clone an extinct animal like a woolly mammoth, researchers might need hundreds of donor elephant eggs and surrogate parents.

Prather predicts even more challenges.

"We know what a gestation period is for an elephant; we don't know what it is for a woolly mammoth. We know what to feed an elephant; we don't know what to feed a woolly mammoth," he said.