Scientists in New Zealand said yesterday they had cloned the lone surviving member of a rare breed of cow, marking the third reported cloning of an adult mammal this summer and the first of a rare or endangered species.
The announcement was made less than a month after researchers in Hawaii announced they had cloned dozens of mice, and follows a June report that Japanese researchers had cloned a cow, the first cloning of an adult mammal since Dolly the sheep was born two years ago.
Although the cow cloning experiments have not yet been published in a scientific journal, experts said the spate of apparent successes indicates that scientists are overcoming the once daunting technical roadblocks to cloning. The process uses a single cell from an adult animal to make an entirely new, genetically identical animal.
Researchers have been eager to apply the new science of cloning to cattle. Cows produce large amounts of milk, and one of the primary goals of cloning is to produce herds of identical, genetically engineered animals that produce human medicines in their milk.
But the New Zealand feat also provides the first solid evidence that cloning may have an important role to play in the preservation of rare or endangered species. The cow that was cloned was the last of a herd that had lived in isolation on Enderby Island, a barren, sub-antarctic piece of the Auckland Islands.
It's not yet clear whether that breed harbors genes with any particular economic value, but the work serves as "proof of principle" that cloning has the potential to bring some endangered species back from the brink, said David Wells, the scientist who led the effort at the Ruakura Research Center in Hamilton, near Auckland.
"The least that people should be doing is preserving viable cells from rare and endangered species and freezing them in liquid nitrogen so later we may be able to reintroduce those animals into the population," Wells said. "It's like an insurance policy."
A population of clones alone might be biologically unstable because they would lack genetic diversity, but there are ways around that problem, Wells said. In the case of the Enderby Island cattle, for example, sperm were retrieved from the last 10 bulls before they died. If enough females can be cloned from the last remaining cow, then each of them can be inseminated with a different bull's semen to create the beginnings of a newly diverse herd.
"This is a great example of how you can save a species with cloning," said Lee Silver, a professor of genetics at Princeton University. At the same time, Silver said, it adds to a growing pool of evidence that it's possible -- and in Silver's view inevitable -- that humans too will someday be cloned.
"In six years you'll be calling me to ask me what I think about the first human clone," Silver predicted.
The story of how a cow named Lady came to be cloned starts in the mid-1800s, when about 100 head of cattle were dropped on rocky and windy Enderby Island in a short-lived effort to establish a ranch.
The cattle keepers left almost immediately, discouraged by the harsh conditions. But somehow the cattle survived without the usual benefits of shelter, antibiotics or nutritional supplements.
Food was scarce, said Peter Rattray, assistant general manager of the government-funded Ruakura center. "They modified their diet to live very much on seaweed."
During the next 100 years and about 20 generations, through intense inbreeding and severe environmental pressures, the black and white cattle became specialized to suit their extreme environment. Those that survived had long bodies and short, strong legs.
But while the cattle did well, they increasingly disrupted the island's natural ecological balance. To restore that balance, the New Zealand government ordered the herd destroyed in 1992. Only Lady, then 7 years old, was saved and brought back to the New Zealand mainland along with the semen from 10 killed bulls.
After six years of unsuccessful efforts to make her pregnant with the sperm, Lady was transferred to the Hamilton research station. There her only son was created -- by in vitro fertilization, but scientists decided that with Lady's advancing age cloning was the best bet for saving the breed.
That effort got underway last year with assistance from the New Zealand Rare Breeds Conservation Society, which seeks to maintain genetic diversity in domestic animals. Wells and his colleagues took from Lady's ovaries several so-called granulosa cells, a kind of cell that nourishes egg cells in the ovaries, very much like the cumulus cells that Hawaiian researchers used to clone mice. Separately, they retrieved unfertilized egg cells from cows of different breeds, and removed the genetic material from the eggs.
The scientists used electrical shocks to fuse individual granulosa cells containing Lady's DNA with individual egg cells containing no DNA. In several instances the resulting fused cell began dividing and developing into an embryo. Each embryo was implanted into the uterus of a surrogate Angus cow.
On July 31, the first of those was born by Caesarean section and named Elsie, a phonetic play on L.C., for "Lady's Clone." Although Elsie has slightly different markings than does Lady, DNA fingerprinting tests proved that the two are genetically identical. Additional Lady clones are expected to be born soon, Wells said.
Keith Campbell, the Scottish researcher who with Ian Wilmut cloned Dolly, said current efforts to save rare species generally involve retrieving fresh semen or freezing embryos, which are technically difficult endeavors. He said cloning, which is starting to appear simpler, may help preserve some of the many rare breeds of cattle now becoming extinct in Africa and other regions.
"Some of these may be resistant to disease, or may make more milk or better meat or need less water," Campbell said. "But we don't know yet, and they are disappearing." CAPTION: Lady, until recently the end of the line of cattle that adapted to harsh living on Enderby Island in the Aucklands.