|
|
BY OUR PHARMA CORRESPONDENT
4 August, 2005: The South Korean researchers have successfully created the first-ever dog clone, reports Nature.
Deemed as the most difficult animal to be cloned, a male Afghan hound was born by cesarean section on April 24 to a yellow Labrador surrogate mother and turned 100 days old on (August 2), say the researchers' Seoul National University.
Scientists named him Snuppy (short for Seoul National University puppy).
The team worked for nearly three years, seven days a week, 365 days a year and used 1,095 eggs from 122 dogs before finally succeeding with the birth. The pregnancy lasted a normal 60 days and the newborn pup weighed 1 pound 3.4 ounces
Dogs have complicated reproductive biology, far more so than humans, that the methods that allowed cloning of sheep, mice, cows, goats, pigs, rabbits, cats, a mule, a horse and three rats, and creation of cloned human embryos for stem cells, simply do not work with them, scientists say.
A second cloned dog lived just 22 days before succumbing to aspiration pneumonia. A postmortem analysis showed no signs of "any congenital defect due to cloning," said Woo Suk Hwang, the leader of the Korean team. A third pregnancy resulted in a miscarriage.
Until now, somatic cell cloning in dogs has been hampered by limited success in maturing canine eggs in the lab, said Hwang. Such maturation is necessary because unlike those of other domestic animals, canine eggs aren't mature at ovulation. They're ovulated at prophase of the first meiotic division and undergo maturation in the distal part of the oviduct for at least 48 to 72 hours. The dog's opaque ova also make manipulation difficult.
So the researchers had to pinpoint when to pluck a mature egg from the oviduct, and needed surgery to retrieve it, instead of the kind of needle suctioning used in other animals.
The next step in cloning of any other animal is to replace the egg's genes with those of an adult and let the cloned embryo grow in the lab for several days.
But no one has been able to grow dog embryos in the lab. So the South Koreans quickly started the cloning. They removed the genetic material from the eggs and replaced it with skin cells from the ears of Afghan hounds. When the altered eggs were starting to develop into embryos, the researchers anesthetized a female dog, slipped the eggs into the animal's oviduct, and hoped the eggs would grow into early embryos, drift into the uterus, and survive. They found they had less than four hours after starting the process to get the eggs into the female dogs.
Ordinarily, researchers give hormones to female animals that are to serve as surrogate mothers, preparing them to become pregnant with a cloned embryo. Not so with dogs.
The team chose an Afghan hound because the dog was known to have a "gentle and docile pedigree," Hwang said. They also had access to a good collection of photos of the dog, which had unique fur color and appearance, when it was a puppy, he said, making it easier to distinguish whether the clone was identical. Microsatellite analysis of genomic DNA from the donor, the cloned dogs, and the surrogates confirmed that the clones were genetically identical to the donor.
However, experts believe that only few would be able to afford cloned dogs in the near future as it the entire procedure is estimated to more than $1 million.
BY OUR PHARMA CORRESPONDENT
|
