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.

Unlocking the brain’s secrets: scientists find over 100 unique mutations in brain cells

Your brain is made up of approximately 100 billion neurons. These are the cells that process information and pass along electrical and chemical signals to their other neuron buddies throughout the body to coordinate thoughts, movement, and many other functions. It’s no small task to create the intricate neuronal network that is the backbone of the central nervous system. If any of these neurons or a group of neurons acquire genetic mutations that alter their function, a lot can go wrong.

The genetic makeup of neurons is particularly interesting because it appears that each neuron has its own unique genome. That means 100 billion different genomes in a single cell type in the brain. Scientists suggest that this “individuality” could explain why monozygotic, or identical, twins have different personalities and susceptibilities to neurological disorders or mental illnesses and why humans develop brain diseases or cancer over time.

To understand what a genome of a cell looks like, you need to sequence its genetic material, or the DNA, that’s housed in a cell’s nucleus. Sequencing the genome of an individual cell is hard to do accurately with our current technology, so scientists have developed clever alternatives to get a front-row view into the workings of neuronal genomes.

Cloning mouse neurons reveals 100+ unique genetic mutations

One such method was published recently in the journal Neuron by a CIRM-funded team from The Scripps Research Institute (TSRI). Led by senior author and Associate Professor at TSRI, Kristen Baldwin, the team took on the challenge of cloning individual mouse neurons to unlock the secrets of neuronal genomes. (For those who aren’t familiar with the term, cloning is a process that produces new cells or organisms that harbor identical genetic information from the originating cell.)

What they found from their cloning experiment was surprising: each neuron they sequenced had an average of more than 100 unique genetic mutations, and these mutations tended to appear in genes that were heavily used by neurons, something that is uncommon in cell types of other organs that tend to protect their frequently used genes. Their findings could help unravel the mystery behind some of the causes for diseases like Alzheimer’s and autism.

In a TSRI news release, Kristen Baldwin explained:

Kristen Baldwin

Kristen Baldwin

“Neuronal genomes have remained a mystery for a long time. The findings in this study and the extensive validation of genome sequencing-based mutation discovery that this method permits, open the door to additional studies of brain mutations in aging and disease, which may help us understand or treat cognitive decline in aging, neurodegeneration and neurodevelopmental diseases such as autism.”

Making mice with neuronal genomes

To clone individual neurons, the team took the nucleus of a single neuron and transplanted it into a mouse egg cell that lacked its own nucleus. The egg developed and matured all while copying and passing on the genetic information of the original mouse neuron. The team generated cloned embryonic stem cell lines from these eggs and were able to expand the stem cell lines to generate millions of stem cells that contained the same genetic material.

TSRI Research Assistant Alberto Rodriguez uses a tiny straw-like micropipette to pick up red fluorescent neurons and transfer their genomes into an egg.

TSRI scientists extract the nuclei of neurons and transfer their genomes into an egg. (Image courtesy of TSRI)

They made several different cloned stem cell lines representing different neuronal genomes and sequenced these lines to identify unique genetic mutations. They also were able to generate cloned stem cell lines from the neurons of older mice, and thus were able to track the accumulation of genetic mutations over time. Even more impressive, they made living mice that contained the cloned genomes of individual neurons in all of their cells, proving that neuronal genomes are compatible with development.

The team did report that not all neurons could be developed into cloned stem cell lines for reasons that they couldn’t fully explain, but they decided to focus on studying the cloned stem cell lines that were successful.

What does this mean for humans?

Baldwin explained that what was most surprising about their study was “that every neuron we looked at was unique – carrying more than 100 DNA changes or mutations that were not present in other cells.”

The next steps for their research are to explore why this diversity among neuronal genomes exists and how this could contribute to neurological disease in humans.

Co-first authors Jennifer Hazen and Gregory Faust.

Co-first authors Jennifer Hazen and Gregory Faust.

Co-first author Jennifer Hazen explains, “We need to know more about mutations in the brain and how they might impact cell function.”

Also mentioned in the news release, the team plans “to study neuronal genomes of very old mice and those with neurological diseases. They hope this work will lead to new insights and therapeutic strategies for treating brain aging and neurologic diseases caused by neuronal mutations.”


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