Dog Cloning Could Lead to Insights Into Human Disease
But the benefits will take time to realize, experts predict
FRIDAY, Aug. 5, 2005 (HealthDay News) -- The announcement this week that South Korean researchers have created the world's first cloned dog is being hailed as a scientific marvel, but one without immediate medical benefits -- for dogs or humans.
And although the canine genome is far more complex than any other animal cloned to date, it doesn't bring the world closer to the ethically and emotionally charged possibility of cloning a human, experts said.
Yet the breakthrough could give scientists better insights and tools to study and possibly treat human diseases, the experts said.
"The dog is a very good model," said Alexander Travis, an assistant professor of reproductive biology at Cornell University College of Veterinary Medicine's Baker Institute for Animal Health. "The dog genome has just been sequenced, so we now have a lot of good genetic information. It's a lot more similar to a person than a mouse is and there are three or four hundred diseases that dogs get that have homologues in humans."
"This is a great accomplishment technically," Travis added. "Of all species of common veterinary interest, the dog is by far the least understood in terms of assisted reproductive technology."
Said Dr. Louis "Skip" Elsas, director of the John T. MacDonald Center for Medical Genetics at the University of Miami: "It [cloning a dog] was a mountain that had to be climbed because the reproductive physiology of the female dog is so complicated."
Snuppy -- for "Seoul National University puppy" -- was born April 24 to a surrogate mother, a yellow Labrador retriever. The puppy is genetically identical to an adult male Afghan hound, with which he is frequently photographed.
While the cloning barriers for sheep, mice, cows, goats, pigs, rabbits, cats, mules, horses and rats have already been broken, the dog hurdle had been higher and harder to jump.
"It has to do with the fact that the female ovulates the egg at a much earlier stage than any other mammal, at the very earliest stages of the egg," Travis explained.
Unlike in other animals, the eggs ovulated by dogs are immature. Because it was impossible to take an immature egg and mature it in a laboratory, the South Korean researchers had to retrieve the mature eggs from the oviduct, a procedure that required surgery instead of the needle suctioning that is sufficient in other animals, The New York Times reported.
Other timing issues were also problematic.
"Dogs breed only a couple of seasons a year, and it's very difficult to get a large number of good oocytes (eggs)," explained Robert Foote, professor emeritus of animal physiology at Cornell University.
The South Koreans discovered that a sudden increase in levels of the hormone progesterone indicated when a dog was ovulating, and when it was time to harvest eggs.
Yet it still required a Herculean effort.
Led by Woo Suk Hwang, the South Korean team started with 1,095 oocytes and ended up with one live hound -- another pregnancy ended in miscarriage and one puppy was born alive but died within a few weeks.
The success rate was low, but it does provide a new model to do certain kinds of experiments on stem cell therapeutics that you can't do in people, Travis said.
The idea would be to make a cloned embryo -- not an actual dog -- and then make embryonic stem cells from that embryo. Researchers could derive different tissues from those embryonic stem cells and use them to treat the original dog from which the clone was derived, and possibly other dogs as well.
And to really maximize the benefits of the dog cloning to help human disease, there would also need to be development of canine embryonic stem cells to better understand human disease and potential treatments.
According to The New York Times, dogs have already played a noble role in combating human disease. Insulin was first discovered in man's best friend and the first open-heart surgery was performed in dogs. Dogs are also frequently used to test new drugs.
But will this bring us any closer to the scientific breakthrough feared by so many: the cloning of a human?
Experts think not.
"They (the South Korean scientists) have overcome a major technical issue in dogs but I don't think they're any closer to the idea of being able to clone humans," Elsas said.
In fact, the procedure the South Korean scientists used was essentially the same as that used to clone other species.
"They just used the basic procedure that has gradually been successful in other species," Foote said. "Yes, it's a new species so it's interesting. But, as far as I can tell, we haven't learned anything new about how to clone animals."
The South Korean scientists used a procedure that involved transferring genetic material from the retrieved eggs and replacing it with skin cells from the ears of Afghan hounds, the Times reported. When embryos formed, they were inserted into a female dog's oviduct.
But the milestone has raised other ethical eyebrows.
"There were so many embryos and dogs that they had to use for this, and the immediate application to any critical public health problem that can be solved with cloned dogs rather than with dogs that are from normal reproductive systems or other kinds of animals is really questionable," said Celia Fisher, director of the Fordham University Center for Ethics Education, in New York City. "Why should science simply be doing things because it's a challenge to get it done?"
Added Foote: "I worry that this will encourage more wealthy dog owners to waste a lot of money trying to clone their pets rather than trying to invest in solid stem cell research."
Travis added this caveat.
"I would caution people not to expect this to change practical veterinary treatment of their dogs in the next few years. And it most certainly should not be viewed by people as 'I'm going to clone my dog so I'll have another exactly like him when he dies,' " he said.
The Oak Ridge National Laboratory has more on cloning.