NEW YORK (CNN) July 26th -- Researchers in Honolulu have done what many scientists thought impossible -- successfully cloning multiple generations of adult mice using a new micro-injection technique.
The announcement was made at a news conference, referring to research published in the July 23 issue of the journal Nature. According to the international team of scientists at the University of Hawaii, this is the first time the new technique has been used to successfully clone the mice. "This is an important breakthrough because it's the first time that mice have been cloned from adult cells or indeed any cells," said researcher Tony Perry. "I think it may be true to say it's the first report of cloning clones of any vertebrate species." The new technique, previously described as impossible by scientists, has significant advantages. Previous cloning techniques, such as the one used to produce the sheep "Dolly," involved fusion of one cell to another and had an extremely low success rate. The researchers said their technique has a higher success rate, about three percent!
The Importance of Mice
The cloning of mice is extremely important because of their rapid reproductive cycle, the scientists said. At last count, they have cloned five generations -- and have made clones of the clones - with all mice healthy and reproductive. The researchers said the technology can be applied to cloning other mammals such as pigs and sheep. The cloned animals could be used in genetic and embryonic studies, which researchers say could help advance their understanding of cellular and molecular activities involved in aging and diseases such as cancer, AIDS, diabetes and multiple sclerosis.
Researchers said the discovery is not about cloning humans, but rather they hope the new technology can be used to help fight diseases and perhaps produce organs for human transplantation from genetically altered animals.
Selected excerpts from "Cloned Mice Provide Company for Dolly" by Elizabeth Pennishi, Science, Vol. 281, pp. 495-497 (July 24, 1998).
Dr. Teruhiko Wakayama of the John A. Burns School of Medicine at the University of Hawaii, Honolulu, said that experiments so far have yielded more than 50 cloned mice! Their method uses a very fine needle to take up the donor cell nucleus, which is very gently and quickly injected into a waiting enucleated egg. "The team is very careful to make sure as much of the donor cytoplasm is gone as possible. That cytoplasm could contain factors that might thwart proper development." Wakayama first lets the cells sit for up to six hours to give the egg cell time to prepare the donated DNA, so that its developmental genes can be expressed again. Then the Honolulu team triggers development of the eggs by putting them into a culture medium containing strontium, which stimulates the release of calcium from the eggs' internal stores- the same signal that tells fertilized eggs that it's time to begin the process of mitosis. For some not yet explained reason, cumulus cells have worked best for the Honolulu team so far.
Cloning researchers can now move on to other challenges, such as trying to improve their success rates, currently only a few percent at most, but a lot better than the days of Dolly. This effort should be helped by the ability to study cloning in mice, which have shorter life cycles (two years) and require much less care and space than, say, sheep or cows. With improvements in technique, nuclear transfer is "going to be a very reliable and robust method," said Ian Wilmut of Scotland. Then the veterinarians who specialize in animal husbandry can work with bigger, commercially-interesting animals after the bugs have been worked out of the method.
A more detailed discussion can be found at the Scientific American Website, p. 28 (October 1998).