A Star Is Cloned
Apr. 02, 2000
Researchers at the Oregon Regional Primate Research Center are heralding the arrival of Tetra, the first cloned primate. The birth of the apparently healthy female rhesus monkey is viewed by the animal research community as a move toward a potentially invaluable tool for studying human diseases. "In order to move discoveries from the laboratory bench to a patient's bedside, we need to have genetically identical models in which life-saving cures can be perfected," stated Professor Gerald Schatten, head of the research team. "It is a huge leap from a mouse to a patient. The monkeys could fill that scientific gap." But not all scientists are embracing such technological "advancements." "In essence, they're going to mass produce animal models that are invalid and irrelevant to begin with," said John E. McArdle, Ph.D., director of the Alternatives Research and Development Foundation.
Tetra was created by dividing an eight-celled embryo into quadruplets, and then implanting the four identical embryos into two surrogate mothers. Although the method has been used to successfully clone cattle and mice, it had yet to be performed with a primate. "The birth of Tetra...proves that this approach can result in live offspring," the research team reported in the January issue of Science. Schatten called the process "artificial twinning," saying that it mimics what can happen naturally when a single egg splits into multiple embryos.
Yet Tetra's birth appears to be anything but natural. The scientists split 107 embryos into two or four parts, resulting in 368 embryos. Out of 13 implant attempts, only four pregnancies resulted, from which the only live offspring was Tetra. Currently four other monkeys are expected to give birth to more clones in May.
The embryo-splitting method reportedly results in genetically purer animals than the technique used in 1996 to clone the famed sheep, Dolly. Unlike Tetra, Dolly was "conceived" from an adult ewe's DNA, which was inserted into another sheep's egg after the original nucleus was removed. The "host" egg was then implanted into a surrogate mother. Animals cloned by "nuclear transfer" are found to contain genetic material from both the adult animal whose DNA was used and the one who supplied the egg, which means the resulting animal is actually not a 100 percent clone.
Meanwhile, scientists in Japan and the United States working together announced in January that six calves had been cloned from the skin cells of a bull's ear. Days later, researchers in Japan also reported that they had succeeded in cloning a cloned bull, the world's first second-generation clone of a large mammal. The skin cell method seems to indicate a significant step forward in the ability to create identical genetically engineered herds, with implications for both the meat and drug industries. "Cloning will inevitably be used to increase the commercial value of livestock," commented Mario Capecchi, a researcher at the University of Hawaii . "Domestic animals, as well as plants, are being examined for their potential to produce pharmaceuticals." The procedure is also being looked at as a possible way to rebuild populations of endangered species. But as McArdle explained, how it would work is unclear, given that genetic diversity, not homogeneity, is what's needed for healthy populations. "There's more involved than numbers alone."
Yet, ironically, John D. Strandberg, D.V.M., director of comparative medicine at the National Centers of Research Resources, believes that relying on clones such as Tetra may actually reduce the number of animals used in tests if the subjects all respond the same way. But using fewer genetically identical animals is still a flawed approach, said McArdle. "The results may be statistically valid, but bear no resemblance to the real world."