As with any celebrity, the world's most famous sheep has to deal with her share of paparazzi that keep a close eye on her ups and downs. On Friday, reports emerged that Dolly, the first mammal to be cloned, has arthritis--a possible sign that she may be aging faster than normal. But researchers caution not to make too much of the diagnosis.
Scientists clone an animal by taking an egg cell, removing its genetic material, and replacing it with the nucleus of a cell from the animal they wish to clone--in Dolly's case, a mammary cell from a 6-year-old sheep. Researchers think this process may not completely reprogram the adult donor's DNA to resemble that of a fresh embryo; if that's true, cloned animals might age faster than normal animals, in essence starting out at the age of the donor.
In 1998, 2 years after creating Dolly, cloning researcher Ian Wilmut and colleagues at the Roslin Institute in Edinburgh reported that the ends of her chromosomes were shorter than they should be for a newborn sheep, a possible indication that the chromosomes retained the age of Dolly's adult progenitor (Science, 28 April 2000, p. 586). But other researchers have not found this effect in cloned cattle.
Now, Dolly's arthritis, which has struck her left hip and knee, may be another sign that she is aging rapidly--but then, it may not be. Arthritis isn't alarming in a sheep Dolly's age, according to her veterinarian, Tom King, although it usually occurs in the elbow. In a press statement, Wilmut points out that there's no way to tell whether Dolly's arthritis is a result of her clone status and says that her debility should remind researchers to keep an eye out for health problems in cloned animals as they age.
Robert Lanza, a researcher at Advanced Cell Technology in Worcester, Massachusetts, says Dolly's earlier obesity could have brought on her current condition. More important, he warns that the health of one sheep, however famous, doesn't mean much. Most of the 335 cattle, sheep, pig, goat, and mice clones to date are relatively healthy, he says. "What concerns me is these anecdotal reports: 'Dolly has arthritis, this other animal dropped dead,'" Lanza says. "We can't be doing science that way."
The Roslin Institute