Dolly the sheep clones have aged well, say scientists

Nottingham's cloning success not usual, though

Dolly sheep. Photo courtesy  University of Nottingham
Actual Dolly the Sheep clones. Similar, no? Photo credit: The University of Nottingham

Scientists working on a long-term study of the world’s first cloned animal, Dolly the sheep, have reported that cloned sheep age normally in a paper published today in Nature Communications.

Dolly’s life started in the laboratory. Scientists replaced the nucleus of an egg cell with a nucleus taken from a somatic cell to preserve Dolly’s DNA. The egg cell was zapped with an electric current to trigger cell division and then implanted into a surrogate mother, a process known as somatic-nuclear cell transfer (SNCT).

The birth of Dolly in 1996 made headlines and captured people’s attention as it provided evidence that a living creature could be completely cloned.

Now, twenty years after Dolly’s birth, a team of scientists led by the University of Nottingham have declared that cloned sheep age healthily after conducting the first long-term study into the health of cloned sheep.

The scientists performed cardiovascular and metabolic assessments, blood pressure measurements and musculoskeletal scans on 13 cloned sheep and compared the results to uncloned control sheep.

Results show that all cloned sheep are healthy with no signs of metabolic diseases and have normal blood pressure readings. One sheep had moderate osteoarthritis - a joint disease that also affected Dolly and raised concerns of premature ageing.

The cloned sheep were between seven to nine years old - approximately equivalent to 60 to 70 in human years, according to the University of Nottingham. Kevin Sinclair, lead author of the paper and professor of developmental biology at the University of Nottingham said the sheep were healthy considering their age.

Four of the cloned sheep at the University of Nottingham are genomic copies of Dolly and have been affectionately named Debbie, Denise, Dianna and Daisy. The other clones came from fibroplasts – cells that came from other fetuses.

Nottingham’s Dollies have just reached their ninth birthdays and are younger than the control sheep.

Although there is a difference in age and breed between the cloned sheep and the control sheep, the scientists said this was the strongest evidence that cloned animals age normally.

Not all SNCT procedures have been successful. Previous experiments have failed to clone healthy calves, lambs and mice. Despite technological advances, the efficiency of SNCT remains low, the paper said.

“It is well established that prior to conception and in the early stages of pregnancy during natural or assisted reproduction subtle chemical changes can affect the human genome leading to development and late-onset chronic diseases. Given that SCNT requires the use of assisted reproductive procedures it is important to establish if similar diseases or disorders exist in apparently healthy aged cloned offspring,” said Sinclair.

They did not report whether or not the sheep were happy or had friends like normal sheep. ®




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