Twenty years ago, the famous Dolly the sheep, the first large mammal successfully cloned from an adult cell, was born. Now, at the University of Nottingham, four of her cloned offspring (twin sisters?) are providing science with a better understanding of the cloning process and showing that clones can live to a healthy old age.

Dolly the sheep was born at Edinburgh University in 1996, but instead of having parents, she was created using a single adult mammary cell from a ewe in a process called somatic-cell nuclear transfer (SCNT). It was hailed as a major advance in biological science, but it wasn't a complete success. SCNT turned out to be very inefficient and Dolly seemed to age prematurely until she had to be put down at the age of six due to progressive lung disease and advanced arthritis. The question was, was Dolly's condition a coincidence or a result of the cloning process?

"Despite technological advances in recent years, efficiency of SCNT remains low but there are several groups across the world working on this problem at present and there is reason to be optimistic that there will be significant improvements in future," says Professor Kevin Sinclair in the School of Biosciences at Nottingham. "These improvements will stem from a better understanding of the underlying biology related to the earliest stages of mammalian development. In turn this could lead to the realistic prospect of using SCNT to generate stem cells for therapeutic purposes in humans as well as generating transgenic animals that are healthy, fertile, and productive. However, if these biotechnologies are going to be used in future we need to continue to test their safety."

Part of the answer may come from Sinclair's study of a new generation of Dollies. Sinclair is a colleague of Professor Keith Campbell, who was part of the team that cloned Dolly and he inherited a flock of four cloned sheep created by Campbell, which he left to the university after his death in 2012. By studying them and nine other cloned sheep, Sinclair's team is learning more about how clones age and how to make SCNT more efficient.

Now nine years old (that's 70 in human years), the four Dollies, called Debbie, Denise, Dianna, and Daisy, were produced from the same cell line as the original Dolly and are genetically identical to her. By studying them and the other cloned sheep, Sinclair says it was possible to make the first detailed study of the longevity and health of SCNT clones.

Last year, the Nottingham clones were subjected to a battery of tests of age-related diseases, such as obesity, hypertension, and osteoarthritis. Under anesthetic, they were given X-rays and MRI scans, radio-telemetric assessments of heart rate and blood pressure, and a full musculoskeletal examination, as well as tests for glucose tolerance and insulin sensitivity. The results were then compared to a control group of naturally-bred six-year-old sheep.

"Healthy aging of SCNT clones has never been properly investigated, says Sinclair. "There have been no detailed studies of their health. One of the concerns in the early days was that cloned offspring were aging prematurely and Dolly was diagnosed with osteoarthritis at the age of around five, so clearly this was a relevant area to investigate. 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."

According to the team, none of the sheep showed indications of diabetes, high blood pressure, or clinical degenerative-joint disease. Only Debbie showed signs of moderate osteoarthritis, but did not require treatment. The upshot is that cloned animals can live long and healthy lives.

Sinclair says that because SCNT involves the use of the same techniques used in fertility treatments, more work is needed on the long-term effects of cloning.

"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," says Sinclair. "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."

The research was published in Nature Communications.

The video below discusses the Nottingham study.

University of Nottingham