Cloning breakthrough: Dolly the sheep has sister clones and they’re healthy

On the topic of famous farm animals, a few come to mind: Babe the pig, Old Yeller, Mr. Ed, and the cast of Charlotte’s Web. Many of us grew up with these fictional characters and hold them near and dear to our heart, but what about real, living farm animals? The first that comes to my mind is Dolly the sheep.

Back in 1996, scientists made a major breakthrough when they cloned a sheep which they named after the famous singer and actress Dolly Parton. This famous sheep was born in a test tube – a product of a scientific process called somatic cell nuclear transfer (SCNT). It involves transferring the nucleus (which contains a cell’s genetic material) from an adult cell – a mammary gland cell in the case of Dolly – into an unfertilized egg cell that has had its own nucleus removed. Much like jumping a car, scientists use an electric shock to trigger the egg cell to divide and develop into an embryo that has the exact genetic makeup as the original organism it was derived from.

Are cloned animals healthy?

SCNT is a very inefficient process with a high failure rate during embryonic and fetal development. Dolly was a huge achievement for scientists as she was the first mammal to be successfully cloned using SCNT. Unfortunately, even though Dolly lived to the age of six and a half years, she wasn’t the healthiest of sheep. She suffered from a severe form of arthritis and tumors in her lungs and was eventually put down to relieve her from pain. Scientists hypothesized that the lung cancer was likely caused by a common virus that infects sheep, but they questioned whether some of Dolly’s other symptoms were caused by accelerated aging resulting from the cloning process.

Whether cloned animals are physically healthy and age normally are questions that have spurred much debate amongst scientists since Dolly’s inception. Further experiments have shown that cloned mammals that survive past their infancy are typically healthy, but some experiments in mice showed that cloned mice tended to be more obese, have diabetic symptoms, and live shorter lives. Concerns about the safety of cloning prompted many countries to ban reproductive cloning in mammals until more was known about the process.

Good news for Dolly’s sisters

Dolly’s 20th anniversary since her birth was earlier this year, and in celebration, many journals and news outlets wrote about the progress of SCNT and cloning over the past two decades. This week, a new study added an exciting new chapter to these recent stories about Dolly.

Published in Nature Communications, scientists from the University of Nottingham in Britain reported that cloned sheep are healthy and live normal lives. They studied 13 cloned sheep, four of which were Dolly’s sisters cloned from the same mammary gland cell line as Dolly. These sheep were between 7-9 years of age which is near the end of a healthy sheep’s average lifespan of 10 years.

Cloned sheep, sisters to the famous Dolly the Sheep. (University of Nottingham)

Cloned sheep, sisters to the famous Dolly the Sheep. (University of Nottingham)

The scientists wanted to know whether cloning had any negative impact on the health and lifespan of these sheep. Lead author on the study, Dr. Kevin Sinclair, explained to the Washington Post:

“When we did the study, these clones were already 2½ years older than Dolly was when she died. And they appeared to be perfectly healthy, but we wanted to see if they might be harboring subtle defects.”

They conducted studies that assessed symptoms typically caused by aging in both humans and sheep. These included tests for blood pressure, insulin sensitivity, arthritis, and heart disease. They also conducted MRI scans and X-rays to look at the integrity of their bones, joints, and muscles.

On the whole, the sheep were healthy and their tests yielded normal results. A few of the cloned sheep had early signs of arthritis, but their conditions were similar to normal non-cloned sheep of the same age. The scientists concluded that there were no obvious signs of premature aging in this group of cloned sheep and that the cloning process did not have negative effects on the health and lifespan of these animals.

“It was quite obvious that the concerns of Dolly just didn’t relate,” Sinclair said. “So you can’t extend beyond the Dolly experience and say this premature aging applies to all clones.”

Cloning breakthrough but questions remain about safety

This study, which many scientists are considering as a “breakthrough in cloning”, has received a lot of attention in the media from major news outlets like the New York Times, Washington Post, Statnews, and NPR.

The New York Times piece does a great job of discussing how the advancements in cloning could have positive impacts on reproductive technology, the farming industry (raising cloned farm animals as a food source), therapeutic development, and saving endangered species. But the article also balances this optimism with caution over the safety and ethics behind reproductive cloning. They posed the cloning safety question to Dr. Sinclair, the lead author on the study, whose response was positive but referenced the remaining issue of cloning being an inefficient process:

“If they [cloned sheep] could speak, they would say ‘yes; it’s perfectly safe. They’re perfectly healthy, and they’re old ladies now, and for them, their whole process worked perfectly. But there are others who struggled to adapt after birth.”

The STATNews piece also made a good point that further scientific studies on the cloned sheep need to be done to test for molecular signs of aging such as shortened telomeres, before the scientists can truly claim that these sheep are living normal healthy lives. The cloned sheep probably will live for another year at which point the scientists said they will conduct further experiments to look for other signs of aging at the cellular level.

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