When the world's first cloned animal died in 2003 at the age of six, many suspected the cloning process put Dolly into an early grave. A new investigation of the cloned sheep's bones by scientists at the Universities of Glasgow and Nottingham suggests Dolly showed no signs of abnormal aging.
In 2004, researchers found that Dolly's telomers -- stretches of DNA at the end of our chromosomes which protect our genetic data like shoelace caps, allow cells to divide and hold some secrets to how we age and get cancer -- were shorter than they should have been. This has prompted suspicions that the process of cloning itself might reduce lifespan, or that the famous clone's painful osteoarthritis was the result of some inherent flaws with cloning.
Researchers gained access to the bones of Dolly, now housed at the National Museum of Scotland, but also those of her offspring Bonnie, as well as two other cloned sheep, Megan and Morag (two sheep cloned from non-adult cells who were prototypes for Dolly). All the bones were X-rayed for signs of arthritis. Megan and Bonnie died at the ripe old ages of 13 and nine, respectively, and showed some signs of arthritis, as is normal for their age. Morag died at age four due to the same lung virus that killed Dolly but did not show any signs of arthritis. Ultimately, the researchers concluded that arthritis is no more common among clones than ordinary sheep.
"We found that the prevalence and distribution of radiographic osteoarthritis were similar to that observed in naturally conceived sheep, and our healthy aged cloned sheep," said Sandra Corr, professor of small animal orthopaedic surgery at Glasgow University.
“As a result we conclude that the original concerns that cloning had caused early-onset osteoarthritis in Dolly were unfounded.”
Previously, Kevin Sinclair, a developmental biologist at the University of Nottingham and co-author of the new study, studied 13 cloned sheep -- including four derived from the same DNA strand as Dolly -- and concluded that there didn’t seem to be any evidence that indicates cloning has any long-term health risks. Dolly's 'four sisters' all lived to be at least eight years old, which is the approximate equivalent of 70 in human years, and all lived a healthy life. “They’re old ladies,” said Kevin Sinclair, a developmental biologist and lead author of the study of the 2016 study published in Nature Communications. “They’re very healthy for their age,” he added.
The Atlantic reports that since Dolly was cloned, a whole menagerie of other animals has been cloned as well: pigs, dogs, cats, monkeys etc. Studies that followed such clones found that their telomeres were shorter, normal or even longer. It all depended on the species and cloning technique.
That being said, this doesn't mean that cloning is 100% safe. Scientists are still learning and more research is needed to investigate the full scope of cloning. For instance, a team from South Korea has recloned the world's first cloned dog to investigate whether or not cloning shortens or affects lifespan in any way. So far, the nine-month-old pups are healthy and seem normal.