They were cloned using cells from the same adult sheep as Dolly, who stunned the scientific community when she was born more than 20 years ago. The ground-breaking animal has always been deceased but genomic copies of the ewe are living on healthily.
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Besides the four Dolly clones, nine other cloned sheep from three different cell lines were included in the study, giving a total of 13 sheep between seven and nine years old (making them senior citizens in human years). Dolly’s knee arthritis, which developed when she was only 5 and raised concerns that cloning accelerated aging, was apparently an anomaly. Their good health is being hailed as a success for cloning as there’s “no evidence” of a “detrimental long-term” health effect in the miniature flock. “One of the concerns in the early days was that cloned offspring were ageing prematurely”, said Kevin Sinclair at the University of Nottingham.
“We can say with confidence that at least some embryos are able to successfully complete this whole process”. Part of what made Dolly’s successful birth so remarkable is that scientists were able to “reset” those differentiated cells back to undifferentiated cells so they could grow into an entirely new lamb.
In 1996, Sir Ian Wilmut, Keith Campbell, and colleagues at the University of Scotland’s Roslin Institute created Dolly by SCNT-transferring the nucleus of a female mammary gland cell to an unfertilized egg cell whose nucleus had been removed. Sinclair’s team also conducted magnetic resonance imaging (MRI) scans on the animals’ joints to look for signs of the osteoarthritis that afflicted Dolly. “We found that the majority of sheep were really very healthy considering their age”.
Some of the animals showed signs of mild or moderate osteoarthritis but none were lame or required treatment for the condition, researchers said.
“Following our detailed assessments of glucose tolerance, insulin sensitivity, blood pressure and musculoskeletal investigations, we found that our clones, considering their age, were at the time of our research healthy”. Because Dolly died prematurely, scientists have anxious that cloning accelerates the aging process. The ewe was put down after developing a progressive lung disease; as well as premature arthritis – something that prompted debate over whether it was caused by the cloning process.
“This shows cells can undergo complete reprogramming and it’s reassuring to know that cells can be perfectly normal”, Sinclair said. The study concludes that SCNT is safe for “long-lived species”. Rather, these latest findings in sheep suggest that “if we make stem cells derived by nuclear transfer, we should be capable to make any cell type of the adult body in a fairly normal way”, he said.
The findings open up possibilities for further cloning research.
Today, SCNT is primarily used to produce cloned animals for agriculture, or-in the case of human cells-to reprogram the cells into a pluripotent state. As they are nearing the end of their lives they will undergo more experiments before finally being examined on a cellular level.
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“We’re presented with a blank slate in a way”, researcher David Gardner said during a press conference in the United Kingdom on Monday.
