Clones of Dolly the sheep are ageing just fine

Twenty years ago, Dolly the sheep was born. The first mammal to be successfully cloned from an adult may have kickstarted a whole new chapter in cloning (and dystopian literature), but it also didn’t live very long. Ill health and a premature death at the age of six-and-a-half raised concerns about the sustainability of clones.

Now a study into a second batch of cloned sheep, including a number of direct duplicates of Dolly, has shown this isn’t the case. In a study published in the journal Nature, researchers from the University of Nottingham have concluded that cloning via somatic-cell nuclear transfer (SCNT) – the process that created Dolly – “has no obvious detrimental long-term health effects”.

The cohort of 13 cloned sheep, including the four “Nottingham Dollies” (Debbie, Denise, Dianna and Daisy), underwent extensive muscular and skeletal investigations, with X-ray and metabolic tests assessing glucose tolerance, insulin sensitivity, and blood pressure. Compared to a group of naturally bred six-year-old sheep, they were all judged to be healthy, except for one that had developed mild osteoarthritis.  

Crucially, all of the tested clones have surpassed Dolly’s lifespan of 6.5 years. Before she was euthanised, Dolly had developed progressive lung disease and severe arthritis, and this raised concerns that the health of cloned animals could never match one born naturally. It now seems that Dolly’s condition was something of an outlier, and may have been a symptom of being raised indoors rather than any issues with the cloning process.

“One of the concerns in the early days was that cloned offspring were ageing prematurely, and Dolly was diagnosed with osteoarthritis at the age of around five, so clearly this was a relevant area to investigate,” commented Nottingham researcher Kevin Sinclair.

“We found that our clones, considering their age, were at the time of our research healthy. This shows that there are cells that can undergo complete reprogramming and be completely normal. So whether you’re aiming for stem cells, or whether you’re aiming for cloned offspring, there is a target you can aim for, and that target is normality.”

Somatic-cell nuclear transfer (SCNT) involves transferring an adult cell nucleus to an unfertilised donor egg, whose nucleus has been removed. As well as creating healthy animal clones, Sinclair said that improvements in SCNT could lead to lead to the prospect of generating stem cells for therapeutic purposes in humans.

(Images: University of Nottingham)