Japanese scientists have created healthy cloned mice from animals that have been dead and frozen for 16 years. The research opens the possibility of cloning extinct species, such as woolly mammoths.

Previously, clones had only been created from living donor cells. Scientists thought that the freezing process would damage DNA and the cells, but the new study found that DNA in brain cells was largely intact. In order to replicate the feat with frozen tissue from extinct animals, researchers would need to find a cell with intact DNA, as well as a donor egg and surrogate mother of a suitable living species.

According to an article from National Geographic,

For their cloning process, [Teruhiko] Wakayama and his colleagues drew dead brain and blood cells from the frozen mice. The researchers injected the nuclei from the dead cells directly into unfertilized mice eggs, creating embryos.

It's not known, however, whether nuclei from cells frozen for extended periods of time can be reprogrammed to develop into cloned animals.

So instead of transferring each embryo into a mouse's oviduct (the tube by which eggs leave an ovary), the researchers extracted the inner cell mass from each embryo and generated lines of embryonic stem cells. The researchers created 46 such lines, from which they were able to produce 13 mouse pups.

Embryonic stem cells are pluripotent--capable of becoming many other types of cells.

"These cells are the same as fertilized embryonic stem cells," Wakayama explained.

The scientists then transferred the nuclei from these cells into mouse eggs to produce healthy mouse pups. His findings appear today in the journal Proceedings of the National Academy of Science.

Since this cloning method does not require intact cells from the animal being cloned--cells of frozen animals usually deteriorate--the researchers believe that their technique could now allow them to work on the frozen remains of extinct mammals.

If you really love your dog and have about $150,000 to spare, you can now order a clone from Korean biotechnology company RNL Bio. Geneticists revealed earlier today that they have created the first dogs cloned for commercial purposes: five puppies created with DNA from Booger the pit bull terrier. (Dogs have previously been cloned for scientific and government purposes.)

According to the Guardian,

"The five clones cost Bernann McKinney, a Californian-based farmer, £25,000 ($50,000) and were well worth it, she said at a press conference in the South Korean capital, Seoul, where the announcement was made.

". . . When Booger got cancer, McKinney had skin cells taken from the dog and preserved in the hope that science would come to her aid. Scientists at Seoul National University used the cells to create embryos, which where [sic] then implanted into two surrogate mother dogs. The puppies were born on July 28."

RNL Bio, which produced seven clones of Toppie, a drug-sniffing dog, in 2006, and four clones of a cancer-sniffing dog from Japan named Marine in 2007, says that it is also interested in cloning camels for customers in the Middle East.