When the birth of Dolly the sheep was announced in 1996 it caused a worldwide sensation. She was the first mammal to be cloned and, as such, caused celebrants of science to marvel at what could be achieved when we put our minds to it, and for the nay sayers to do their usual handwringing act about ‘playing God’.
As Dolly got older it became clear that not all was well with her. She appeared to be ageing faster than you might expect for a sheep of her age. She was quite arthritic and her telomeres were shorter than in similarly aged sheep. Telomeres are the tips of the chromosomes, sort of like those little plasticky bits that you get at the ends of your shoelaces. They protect chromosomes from damage but, as an organism ages, they become shorter and their protective effect is diminished. Shortened telomeres are now recognised as one of the many signs of ageing.
Dolly’s short telomeres and advanced arthritis led many to speculate that although she was physically young she was genetically old, as old as the sheep that she had been cloned from. Dolly, and other non-cloned sheep in her herd, died at the age of 6 from a virus unrelated to her genetics.
For several years it wasn’t possible for us to speculate further as to how Dolly’s status as a clone affected her life. It is extremely expensive to clone mammals as, to this day, it is not an especially easy feat to achieve. However, a recent open access paper in Nature Communications has shed some light on the matter. They conducted thorough health checks on 13 cloned sheep aged between 7 and 9 years, the equivalent of late middle age in humans. Four of the sheep; named Daisy, Debbie, Denise and Diana; are sisters of Dolly having been cloned from the same sample of mammary gland tissue.
Techniques had moved on in the decade since Dolly and her sisters had undergone a technique to genetically ‘reset’ them before they were conceived. Telomeric data is, unfortunately, not yet available for this new cadre of clones which is rather a shame because I think this is an important part of the question. Certainly, as a geneticist, I’m very interested to have that data.
What they were able to do is measure their blood glucose levels, insulin sensitivity, blood pressure and take x-ray and MRI imaging of the knee and hip joints to look for signs of arthritis. Pleasingly, they could find no evidence to suggest the 13 sheep were ageing any faster than would be expected.
So does this mean newer cloning techniques have resolved the problems that Dolly suffered from? Not necessarily. Many in the genetic community believe that Dolly’s problems weren’t really there in the first place. Sure, she had arthritis; but with an n of 1 there’s no way of knowing if it was caused by her cloning or if she was just plain unlucky. I recently found out that I have a weirdly arthritic spine for someone in their early 30s but I’m not a clone. As far as I’m aware…
We’ll never know what caused Dolly’s bad joints, but we do know that the sheep clones alive today are doing well, including her sisters taken from the very same sample a decade later. That bodes well for the future of cloning, not just of whole organisms, but also for individual organs for replacing damaged ones.