In a Furry First, A Dog Is Cloned In South Korea

Scientists have cloned mice, cows, sheep, goats, rabbits, cats and a few other mammals since Dolly the sheep -- the first cloned mammal -- was born in 1996. But dog cloning has proved a formidable challenge, largely because of inefficiencies that result from the dog's quirky reproductive physiology, Westhusin said.

"It's an incredible logistical nightmare," he said. "You must have access to hundreds and hundreds of dogs. We were never able to handle that many dogs at one time."

Cloning starts with the creation of an embryo in a laboratory dish. Scientists take a cell from the animal to be duplicated -- typically a skin cell -- and fuse it to an egg cell whose own DNA has been removed. Fluids in the egg "reprogram" the skin cell's genes, prompting that most ordinary cell to grow into an embryo.

In the new study, a team led by Woo Suk Hwang of Seoul National University fused individual cells from an adult hound's ear to eggs painstakingly obtained from fertile female dogs.

This required a staggering amount of work because, in contrast to women, dogs cannot be prompted to produce ripe eggs with hormone injections. Instead, the researchers had to monitor the dogs daily for signs of natural egg ripening -- estrus, or "heat," which occurs about twice a year. Then they measured the dogs' blood hormone levels daily.

Within hours after a blood test confirmed that a batch of ripe eggs had been released from a dog's ovaries, Korean veterinarians anesthetized the dog, surgically exposed her reproductive tract and flushed the barely visible eggs into laboratory dishes.

Then began the exquisitely delicate task of extracting the DNA from those eggs. Many eggs are inadvertently destroyed in this process, but Hwang's team is world-renowned for its manual dexterity under the microscope -- a skill Hwang has credited to the Korean tradition of eating food with difficult-to-master steel chopsticks.

Of about 1,400 embryos created by fusing those eggs to skin cells with an electrical shock, 1,095 were deemed healthy enough to be transferred to the reproductive tracts of surrogate mother dogs -- each of which also had to be in heat, to support the growth of those embryos into fetuses. That required more surgeries, with five to 12 embryos transferred to each of 123 surrogates.

The breed of the egg donors and the surrogate mothers varied and were irrelevant because they did not contribute any DNA to the clones.

As is typical for cloned embryos, very few survived their time in the womb, perhaps because of abnormalities induced by the process. Follow-up sonograms later indicated thatthree of the 123 surrogate mothers were pregnant. One miscarried, and the other two delivered puppies after full-term pregnancies. One newborn died from pneumonia after 22 days, a common but still inexplicable fate for young cloned mammals. The survivor is Snuppy, for "Seoul National University puppy."

The work drew congratulations from Genetic Savings & Clone, a Sausalito, Calif.-based company that offers cat-cloning services and hopes to clone dogs soon.

The American Anti-Vivisection Society, which recently failed to force the Food and Drug Administration to regulate pet cloning, renewed its call for limits. "Using 123 dogs to obtain one cloned puppy is absurd," said Crystal Miller-Spiegel, the group's senior policy analyst.

Jorge A. Piedrahita, a professor of genomics at North Carolina State University's College of Veterinary Medicine in Raleigh, said people hoping to get their old pets back through cloning are likely to be disappointed.

In studies he conducted, pigs that were clones of each other were no more alike than were conventional pigs with regard to food preferences, sleep habits or levels of aggressiveness. "What was most fascinating is how important the environment is -- that it really overrides the genetic similarities," Piedrahita said.

Ian Wilmut of the University of Edinburgh in Scotland, who led the effort to clone Dolly, said in an e-mail that the success in dogs should motivate legislators to enact bans on the creation of cloned babies.

"Successful cloning of an increasing number of species confirms the general impression that it would be possible to clone any mammalian species, including humans, given an optimized method," Wilmut wrote.