Cloning of Dolly the Sheep, 1996
Dolly the Sheep, the first animal to be cloned from an adult somatic cell, was born at Roslin Institute, Edinburgh University, on 5 July 1996.
Previous Breakthroughs
Dolly was created by a team headed by Sir Ian Wilmut (1944- ) and Keith Campbell (1954-2012) that was researching the application of transgenic technology to farm animals. Dolly was cloned using the technique of Somatic Cell Nuclear Transfer, where the nucleus from a body cell is transferred into an unfertilized oocyte (developing egg cell) that has had its cell nucleus removed. This hybrid cell is then stimulated to divide by electric shock, and the resulting blastocyst is implanted into a surrogate mother. The technique had been successfully used since the 1980s to clone cattle and sheep from cells taken from early embryos. The Roslin Institute team’s first major breakthrough came in 1995, when they employed Somatic Cell Nuclear Transfer to create Megan and Morag, live lambs cloned from embryo derived cells that had been cultured in vitro for several weeks. These were the first live mammals to have been created from differentiated somatic cells, opening up new possibilities for introducing genetic modifications into farm animals.
Birth of Dolly
With Dolly, the Roslin Institute team overturned the widely-held assumption that cell differentiation was irreversible. She was created from a cell taken from the mammary gland of a six-year-old Finn-Dorset ewe. This showed that genes in the nucleus of a mature differentiated somatic cell are capable of reverting to an embryonic state, creating a cell that can develop into any part of an animal.
Dolly was the only live lamb to emerge from 277 attempts. Nevertheless, unlike many cloned animals, she suffered no neonatal problems at birth, and was standing unaided within minutes. She was named in honour of the famously voluptuous country singer Dolly Parton. Her birth was publicly announced in the journal Nature on 27 February 1997, sparking worldwide interest and controversy. Dolly was successfully bred with a Welsh Mountain ram and produced a total of six lambs. She lived until 14 February 2003, when a progressive lung disease and severe arthritis caused her to be euthanized. The Roslin Institute team has stated that these are common diseases of sheep, particularly when kept indoors, and that there is no reason to link her relatively early death with her being a clone.
After Dolly
Dolly proved that cells could be reprogrammed to function as different cell types, providing a major impetus for stem cell research, and holding out the promise of using stems cell therapies in human medicine.
Since the Roslin Institute's breakthrough, many other animals have been cloned from adult cells, including cats, rabbits, horses, donkeys, pigs, goats and cattle. The Roslin team's own next step was to create mammals which were cloned from an adult somatic cell but were also transgenic. In creating ewes Polly and Molly in 1997, they used cells into which a new gene had been inserted, so that the cloned animals produced a therapeutic protein in their blood.
External Links
Sources
- Roslin Institute, 'Dolly the Sheep' [[1], accessed 3 September 2014]