Creating a whole new organism from a single cell has been more the stuff of science fiction than of science. Not anymore. Scientists have cloned a lamb using a cell nucleus taken from an adult ewe's udder, according to a report scheduled to appear later this week in Nature. The breakthrough has generated a fierce backlash from ethicists and others who fear the prospect of human cloning.
Embryologist Ian Wilmut and his colleagues from Scotland's Roslin Institute first grew the udder cells in laboratory dishes, then put nuclei from those cells into ova whose DNA had been removed. They found that in the egg, the transferred genome reverted to embryonic patterns of gene expression, prompting the egg to begin dividing. The viable embryo was then placed in the womb of the ewe that had produced the egg.
Wilmut's team first used this technique a year ago, producing lambs with nuclei transplanted from very early embryos. In their latest work, the group reports how cells taken from sheep at any point in their lives will do the job. In addition to the lamb from a 6-year-old ewe's mammary tissue, four offspring were produced with nuclei from 9-day-old embryos and three from the skin cells of 26-day-old fetuses.
Others have made new organisms, primarily amphibians and mice, using embryonic nuclei, but failed when they used cells from adults. "Now we have convincing evidence that it's doable," says embryo researcher Colin Stewart of the National Cancer Institute-Frederick Cancer Research and Development Center in Frederick, Maryland.
It had been thought that in mature somatic cells, some genes necessary for development were permanently turned off, even lost. Thus the group's success was a "big surprise," says Wilmut. "The mechanisms which regulate gene expression are more labile than might have been imagined." Eventually, says Wilmut, he hopes to use nuclear transplantation to create sheep, or cattle, with specific genes added to their genomes.
Theoretically, people too could be cloned: Just imagine how much someone would pay for a basketball team fielding five versions of Michael Jordan. Wilmut told ScienceNOW that his group is ethically opposed to human cloning. "We have no idea whether it will work [in people]," he adds. Activists, however, are taking steps to thwart that possibility. For instance, biotech critic Jeremy Rifkin of the Foundation for Economic Trends announced yesterday that his group, along with some religious leaders and nongovernmental organizations, "is determined to mount a global effort in opposition to human cloning and will seek legislation to outlaw this technology in every nation." Several countries--including Germany and the United Kingdom--have laws on the books forbidding human cloning, but the United States is not among them.