Double dog: researchers produce first cloned canine.
Scientists have had continuing success in recent years with cloning a variety of mammals, including cats, horses, and rats (SN: 3/23/02, p. 189; 8/9/03, p. 83; 10/11/03, p. 237). However, cloning dogs had proved particularly tricky.
According to Mark Westhusin, whose team at Texas A&M University in College Station produced the first cloned cat in 2002, dogs are "a logistical nightmare in terms of dealing with this species' reproductive physiology" Unlike most other mammals, a dog releases eggs during ovulation that aren't fully mature. These eggs must spend several days ripening inside the mother before they're capable of growing into an embryo.
Researchers typically clone an animal by harvesting eggs soon after ovulation and then stimulating the egg with electricity or chemicals to make it divide in a petri dish. Implanting embryos made of many cells increases the chances of a successful pregnancy. Because scientists have been unable to keep canine eggs alive for long outside the body, this technique hadn't worked for dogs.
Using a slightly different procedure, Woo-Suk Hwang of Seoul National University and his colleagues collected eggs from dogs about 72 hours after ovulation. That delay gave the eggs some time to mature. The scientists then removed each harvested egg's nucleus and replaced it with the nucleus from a skin cell taken from the ear of the Afghan hound.
After prompting the eggs to divide by bathing them with a chemical, the researchers implanted 1,095 eggs into 123 surrogate mothers. Between removal and implantation, the eggs spent just 4 hours outside a dog's body.
Only three of the surrogates became pregnant, each with only one puppy. One miscarried. Another gave birth to a pup that died from pneumonia 22 days after it was born. Only Snuppy survived, and he appears to be healthy. Hwang's team details its success in the August 4 Nature.
"The good news here is that it affirms dogs can be cloned," says Phil Damiani of Sausalito, Calif.-based Genetic Savings and Clone, which focuses on cloning people's pets. Damiani says that his company is now working toward a more efficient procedure that requires fewer canine eggs and surrogates.
Jaime Modiano of the University of Colorado Health Sciences Center in Denver, who studies differences between dog breeds in their cancer risk, cautions that cloned dogs may not exactly replicate their genetic double's appearance or share its behavioral traits. Environmental differences, such as diet and life experiences, have an important influence, he explains.
"No two animals are alike. [By cloning pets,] in some ways, we devalue the individual," Modiano adds.
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|Date:||Aug 6, 2005|
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