Dolly the sheep was born at the Roslin Institute in Midlothian, seven miles south of Edinburgh, on 5 July 1996. She was not announced to the world until February 1997, when the paper describing her creation was published in Nature. The delay was partly procedural – the research needed to be published before it could be publicly discussed – and partly, it has been suggested, to allow the scientists and their institution to prepare for the reaction.
The reaction was considerable. Dolly was the first mammal to be cloned from an adult somatic cell – a differentiated cell taken from the mammary gland of a six-year-old Finn Dorset sheep. Previous cloning experiments had used embryonic cells, where the dedifferentiation problem was less acute. The Roslin team’s achievement was to demonstrate that an adult cell’s nucleus could be reprogrammed to produce a complete organism. This had been considered theoretically possible but practically unachievable.
Ian Wilmut and the Science
Ian Wilmut was the lead scientist on the project, though the technique of somatic cell nuclear transfer was developed primarily by Keith Campbell, his colleague at Roslin. The two men had a relationship that became contentious after Dolly’s announcement: Campbell maintained that his contribution to the core scientific innovation was underacknowledged in the public presentation. Wilmut subsequently acknowledged that Campbell was responsible for more of the key scientific work than the initial reporting had suggested.
The process that produced Dolly involved taking cells from the mammary gland of the adult sheep, starving them of nutrients to induce a quiescent state, then fusing the nucleus of one of these cells with an enucleated egg cell using an electric pulse. The fused cell was then implanted in a surrogate ewe. 277 attempts were made. One produced Dolly.
What It Meant
The scientific significance of Dolly was that it demonstrated nuclear reprogramming as a practical reality. If an adult cell’s nucleus could be made to behave as an embryonic nucleus, the implications for understanding cellular differentiation were profound. It opened lines of research that led directly to Shinya Yamanaka’s development of induced pluripotent stem cells in 2006, for which he won the Nobel Prize in 2012. Wilmut has described Yamanaka’s work as the more important achievement, capable of delivering the therapeutic benefits without the ethical complications of embryo use.
The immediate popular response to Dolly was largely about human cloning – the assumption that if a sheep could be cloned, human cloning was both imminent and inevitable. Wilmut was clear from the outset that he considered human reproductive cloning ethically unacceptable and was not pursuing it. Regulatory frameworks in Britain and internationally were updated to prohibit human reproductive cloning in the years following Dolly’s announcement.
Dolly’s Life and Death
Dolly lived at the Roslin Institute until her death in February 2003, aged six and a half. She developed a progressive lung disease – Jaagsiekte sheep retrovirus – that is common in sheep kept indoors, and was euthanised when it became clear the disease was advanced. She had given birth to six lambs during her life, demonstrating that a cloned animal could reproduce normally.
There was extensive discussion about whether her relatively early death was related to her cloning – whether she was, in some sense, born old because her genetic material came from a six-year-old. Her telomeres were shorter than expected for a sheep her age, consistent with this hypothesis. The research community has not reached consensus on whether her specific health problems were a consequence of the cloning process or coincidental.
Dolly’s taxidermied body is in the National Museum of Scotland on Chambers Street in Edinburgh, on permanent display in the science and technology galleries. She looks, to the average visitor, like a sheep.
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