There seems to be an end to animal cloning in sight. Only monkeys are left to go.
A team led by Professor Hwang Woo-suk succeeded in cloning dogs for the first time in the world. Other than humans, monkeys have become the only animal left to be cloned.
Since the birth of the cloned sheep Dolly in 1996, scientists around the world have competed in cloning livestock useful to humans, pets, and laboratory animals. Until now, a total of 12 kinds of species including 11 kinds of mammals, and one kind of fish have been cloned.
Professor Lee Byeong-cheon of the team that experimented to clone dogs said, The cloned animals in the early stages of cloning include animals whose basic information such as mating season and ovulation period are acquired in abundance by people. Among the animals that are worth cloning but have yet to be cloned are dogs and monkeys that are useful as human disease models.
Professor Gerald Schatten at the University of Pittsburgh School of Medicine announced in October last year that he successfully planted 135 cloned embryos in the wombs of 25 female monkeys with the help of Professor Hwang, but failed to impregnate them.
Before the success of Professor Hwang, it was considered impossible to clone dogs as well as monkeys.
There Is No Test-Tube Dog-
Professor Lee explained the reason why it is difficult to clone dogs, saying, There exists a test-tube tiger, but there is no test tube dog.
Test-tube animals are born when an ovum and a sperm are fertilized and implanted in the womb of a surrogate mother. But no test-tube dog was born because it is difficult to acquire the ovum of dogs.
Most mammals produce mature ova from their ovaries during mating season. Therefore, by dissecting the ovary, researchers can acquire an ovum needed for cloning.
However, dogs ova derived from the ovary are immature. The cultivation condition to mature these ova in test tubes has yet to be discovered.
Study the Fallopian Tube to Overcome Hurdles-
Researchers paid attention to the fact that dog ova mature as they move through a 12 centimeter-long fallopian tube toward the womb. Two to three days after ovulation, ova fully mature somewhere in the fallopian tube.
Researchers collected ova with syringes attached with fine needle. However, it was difficult to find an intact fallopian tube because the ovary and surrounding areas of the fallopian tube are surrounded by tough tissue, like wrapping clothes. It was also difficult to find out where the ova completed its maturity in the fallopian tube.
Professor Lee said, To focus on the fallopian tube was the unique idea of our research team. After numerous trials, the chance to find a mature ova in the fallopian tube runs to 90 percent.
The team was careful to choose dogs whose somatic cells were used.
Only when the appearance of the new born puppy looks identical to the provider of the somatic cells can the puppy be confirmed as a cloned dog. Therefore, researchers used the ear cell of an Afghan hound whose distinct appearance sets it apart from other kinds of dogs. The research attempt succeeded.
Professor Kang Seong-keun of the team said, A genetic test found that the born puppy and the dog that provided the somatic cells were completely identical.
Dogs Used as Human Disease Model -
The team singled out the procurement of disease models as the most important meaning of the success. Cloned dogs will be made to fall ill with human diseases, and they will be treated with new medicine candidates. The condition of the dog with the diseases will be examined.
Professor Hwang said, The efficacy of medicines in normal dogs differs from dog to dog, since genes are different depending on individual dogs. But cloned dogs have the same genes, so 10 cloned dogs will do what 100 normal dogs can do.
He also added, This success will be useful to the applied research of stem cells. Stem cells from cloned embryos of dogs can be transplanted into dogs with diseases. Then, the therapeutic value and side effects of stem cells can be examined. In addition, stem cells from humans (patients) can be transplanted into dogs with the same diseases.
Professor Lee said, This achievement paved the way for cloning wolves of Korean origin on the verge of extinction and dogs with special duties such as detecting drugs.