Mice Cloned | The Canadian Encyclopedia


Mice Cloned

It was a humble setting for an epochal scientific breakthrough - a nondescript two-storey building tucked away on the sprawling University of Hawaii campus overlooking Honolulu's Waikiki district.

This article was originally published in Maclean's Magazine on August 3, 1998

Mice Cloned

It was a humble setting for an epochal scientific breakthrough - a nondescript two-storey building tucked away on the sprawling University of Hawaii campus overlooking Honolulu's Waikiki district. There, in a windowless laboratory run by biologist Ryuzo Yanagimachi, a post-doctoral student named Teruhiko Wakayama began working long hours last year on a pet project that gradually became a consuming passion for scientists in the lab. The work was crowned by success last October when the researchers cloned a healthy new-born female mouse that was an almost exact twin of its genetic mother. Soon, there were 10 infant mouse clones - all females. Extracting cells from the clones, the team repeated the process until they had produced a total of 50 cloned mice spanning three generations. At a news conference last week in New York City's Science Library, Yanagimachi's team described the feat, which settled beyond a shadow of a doubt the hotly debated issue of whether mammals could be cloned from adult cells. Back in Hawaii a few days later, the 69-year-old Yanagimachi confessed that it had been a gruelling effort. "It has been like climbing a mountain - it's very tiring," he admitted - then ticked off a list of future projects flowing from his team's achievement.

As well as constituting a quantum leap forward in the art of producing duplicates of adult mammals, the Honolulu mouse-cloning announcement appeared to vindicate last year's groundbreaking work in Scotland. In February, 1997, Dr. Ian Wilmut and fellow scientists at the Roslin Institute south of Edinburgh revealed that they had engineered the birth of the celebrated - and controversial - sheep Dolly. Now, says Jan Friedman, head of medical genetics at the University of British Columbia medical school in Vancouver, "The work in Hawaii puts to rest the debate over Dolly - it shows that the cloning of adult animal cells is something that certainly can be done."

More ominously, there was wide agreement among scientists that the Honolulu breakthrough, reported in the current issue of the British science journal Nature, shifted the unsettling notion of cloning humans from the world of science fiction into the realm of the possible. "The more we understand about cloning," says George Seidel, a cloning expert at Colorado State University in Fort Collins, "the closer we are to replicating humans. It is now clearly more imminent."

On a practical level, the successful experiments in Honolulu opened the way for a stepped-up effort by scientists to use cloning technology for the extraction of pharmaceuticals from the milk or blood of genetically altered animals. They could also spur research into the creation of animals with genes from more than one natural source, to be used to create tissues and even whole organs for transplantation into humans. As a step in that direction, PPL Therapeutics PLC, a firm set up in Roslin to develop the technologies pioneered by the creators of Dolly, and Honolulu's ProBio America, which works with Yanagimachi and his team, announced plans to collaborate on the development of a cloned pig with organs that could be transplanted into humans.

In theory, such organs as hearts, livers and kidneys from pigs should be suitable for transplantation into people because they are about the same size as those in humans. But in the past, attempted pig-to-human transplants have been defeated by organ rejection - a problem the two companies now may be able to overcome by cloning pigs that carry human genes.

The achievements of the Hawaiian-based scientists climaxed a spate of cloning experiments that began soon after Wilmut's team announced that it had produced Dolly from an adult sheep cell. It was an astonishing achievement: until then, the only way scientists had been able to clone mammals was by splitting fetal cells at an early stage of development. Dolly showed that mature cells could be used to create identical twins of adult animals. But some critics, led by Norton Zinder, a microbiologist at New York City's Rockefeller University, questioned whether Dolly was really made from an adult cell. Since the donor sheep was pregnant, scientists argued that Dolly might have come from a fetal cell after all.

As well, critics noted that despite a flurry of experiments by researchers around the world, none had been able to produce another clone from adult animal cells. (Scientists at a Japanese livestock research centre announced earlier in July that they had cloned two calves from adult cow cells, but they have not yet published their work in a peer-reviewed journal.)

Now the multiple clonings by Yanagimachi's team appear to go a long way towards dispelling doubts about Dolly. There was other convincing evidence in the same issue of Nature that published their report. In another article, scientists at the Roslin Institute and England's University of Leicester set out DNA profiles showing that Dolly was indeed a clone of the donor ewe.

The cloned mice and Dolly came into existence by significantly different routes. To create Dolly, the Roslin scientists took a cell from the udder of a six-year-old ewe and used a jolt of electricity to fuse it to an egg from another sheep, which they then implanted in the womb of a third female. Five months later, the mother ewe gave birth to Dolly - in effect, an identical twin of the original cell-donor sheep.

The technique devised by the University of Hawaii researchers was more sophisticated and reliable. They started by taking from a female mouse one of the cumulus cells that cluster around ovaries and are thought to nourish the eggs and steer their growth. Next, they extracted the genetic material from the cell and injected it into another female's egg from which all the DNA had been removed.

Finally, the scientists used a chemical trigger to make the re-engineered egg begin dividing and form an embryo - which they implanted in another female mouse's womb. Since the genetic material used came originally from a female, all of the cloned mice were females as well. Genetic testing showed that the successive mouse generations were definitely clones. In one experiment, the scientists used the natural color-coding of mice for extra proof, taking cumulus cells from coffee-colored animals, ovaries from black ones and using a white albino mouse as surrogate mother. As expected, the clones were coffee-colored.

Cloning techniques have clearly moved to another level of sophistication. But ethicists and scientists remain divided over whether the practice should ever be used on people. "I think most people would argue no," says Paul Young, a geneticist at Queen's University in Kingston, Ont. "And to do it now would be highly unethical because the success rate for the present technology is very low." Yanagimachi's team reported that fewer than three per cent of the implanted embryos survived. "You can't do that with humans," says Young, "because one of the faulty embryos might come to term and be born with horrible developmental problems."

Colorado's Seidel thinks that there could be circumstances in which it might be ethical to clone humans - in the case, say, of a woman whose only child dies after she has become unable to have more babies. Scientists someday might be able to use a cell from the dead child to create a cloned twin. But cloning humans, says Seidel, would "require huge resources - this is not something you could do in your garage. And probably society will say these resources could be put to better use."

In any case, adds Seidel, cloning humans or indeed other animal species may be more difficult than creating genetic replicas of mice or sheep. "It may turn out that something you can do with a cell from a 60-day-old mouse wouldn't work with a cell from a 30-year-old human." Yanagimachi has no patience with talk of cloning people. "If all the humans on the face of the earth were infertile," he told reporters, cloning human beings "may be justified. But until then we should stick to reproduction the way that Mother Nature did it for us." Yanagimachi told Maclean's that one of the next projects for his team would be determining whether there were cells that would be even more effective than cumulus cells for creating animal clones. Beyond that, he is anxious to explore cloning technology as a way of producing human tissues to be used in the treatment of cancer and other diseases - science in the service of humanity rather than the unknown perils of human cloning.

Maclean's August 3, 1998