It's been 20 years since the birth of Dolly the Sheep, the first mammal to be cloned from an adult. Because Dolly died prematurely, scientists have worried that cloning accelerates the ageing process. But a new analysis of 13 cloned sheep — including a batch of Dolly's genetic duplicates — shows that this isn't the case. Debbie, Denise, Dianna and Daisy are the "Nottingham Dollies" — cloned and doing just fine. (Image: University of Nottingham)
In a study published in Nature Communications, researchers from the University of Nottingham have shown that 13 cloned sheep, four of which were genetic duplicates of Dolly, have reached an advanced age in good health. It's the strongest evidence yet that large cloned animals age normally. This is an important result given that many animals are now being cloned on a regular basis — and that humans may eventually be produced with the technique.
Dolly, born on 5 July 1996, was produced by a cloning technique known as somatic-cell nuclear transfer. She lived her entire life at the Roslin Institute in Edinburgh, UK, but had to be euthanised after developing a progressive lung disease and severe arthritis. Most sheep live to be about 11 or 12, but Dolly lived just 6.5 years. Dolly's death prompted concern that cloned animals age more rapidly, or less healthily, than sheep born naturally.
To see if this is in fact the case, Nottingham researcher Kevin Sinclair and colleagues studied 13 cloned sheep between the ages of seven and nine (the equivalent of 60 to 70 human years). All 13 sheep were assessed for muscular and skeletal health, glucose tolerance, insulin sensitivity and blood pressure, and were administered metabolic and X-ray exams. Results showed that all the clones are healthy, except one sheep with mild osteoarthritis. Their health was compared to a group of naturally bred six-year-old sheep living in similar conditions.
Results of the tests showed that none of the cloned sheep exhibited signs of diabetes, hypertension, serious arthritis or abnormal blood pressure. Importantly, all of the sheep survived their first 6.5 years, surpassing Dolly's lifespan. It's worth pointing out that the researchers did not test for telomere length, a molecular marker linked to age-related diseases.
These results suggest that Dolly was a bit of an anomaly. And in fact, other sheep in Dolly's flock died of the same rare lung disease, a condition which may have been a consequence of being raised indoors. So it seems that environment, rather than genetics, may have ultimately been responsible for Dolly's premature demise. SCNT as a reproductive technique is still far from perfect, but this research strongly suggests that clones can live long and healthy lives.