After years of failed attempts, scientists have cloned the first canine. Cloning expert Woo Suk Hwang of Seoul National University in South Korea and his colleagues announce in tomorrow's issue of Nature the successful birth of two pups cloned from an Afghan hound named Tai. One of the pups died of pneumonia three weeks after birth, the team reports, but the second, named Snuppy because he was born at Seoul National University, is healthy and doing well.
The healthy pup is another coup for the lab that made the world's first stem cell lines derived from cloned human embryos (ScienceNow 19 May). Dogs have proved particularly difficult to clone, in part because their oocytes mature only after they are released from the ovary and are difficult to culture in the lab. To get around the problem, the Korean team waited for three days after ovulation to collect eggs from donor animals. They then removed the DNA from the oocytes and fused each one with a skin cell from Tai's ear. After a chemical shock, the fused cells began dividing to form an early embryo, which the team implanted into a surrogate mother.
The technique is far from efficient. Hwang and his colleagues implanted 1095 embryos into 123 surrogate mothers, but they only detected 3 pregnancies. One fetus miscarried, and the two live puppies were born by caesarean section after 60 days, which is full term for dogs. The puppy that died had been tube-fed, Hwang says, which might have caused the pneumonia. Its surrogate mother had been too weak to nurse after the caesarean section.
Hwang says Tai was chosen as a donor in part because of his "gentle and docile pedigree," but dog lovers hoping to copy their favorite mutt will have to wait a bit longer; the team is more interested in cloning dogs for research. A population of cloned dogs might help scientists find genes involved in hypertension, breast cancer, or heart defects, Hwang says, since dogs can suffer from those maladies. And he says the team is trying to develop embryonic stem (ES) cells from cloned canine embryos. That might allow dogs to serve as models for therapeutic cloning, in which genetically matched ES cells would be used to develop cells to replace those damaged by disease or injury.
Cloning researcher Philip Damiani of Genetic Savings and Clone, a California-based company that hopes to clone dogs, agrees that the animals are "a terrific scientific model for heart disease as well as lung and blood disorders." But cloning researcher Mark Westhusin of Texas A&M University in College Station, whose team has also tried to clone dogs, cautions that the birth of Snuppy doesn't mean dog cloning will soon be routine. Even with improved egg collection techniques, he says, the fact that scientists can't yet control dog reproductive cycles means that cloned puppies are likely to remain rare.