Born in 1996, Dolly the Sheep was a very special lamb and her birth sparked a media storm around the globe. Although several clones had been produced in the lab before, including frogs and cows, Dolly was the first mammal to be cloned from an adult cell.
This was a revolutionary scientific achievement as it demonstrated that the DNA from adult cells, despite having specialised as one cell, can be used to create an entire organism.
Animal cloning from an adult cell is much more challenging than from an embryonic cell. So when scientists working at the Roslin Institute in Scotland produced Dolly, the only lamb born from 277 attempts they made scientific history.
How was Dolly cloned?
To clone Dolly, scientists used an udder cell from a six-year-old Finn Dorset white sheep. They had to find a way to keep the udder cells alive but stop them growing, which they achieved by altering the growth medium (the ‘soup’ in which the cells were kept alive).
Then they injected the cell into an unfertilised egg cell which had had its nucleus removed, and made the cells fuse by using electrical pulses. The research team then fused the nucleus from the adult white sheep cell with the egg cell from the black-faced sheep and cultured it for six or seven days to see if it divided and developed normally. Finally, the resulting embryo was implanted into a surrogate mother, another Scottish Blackface ewe.
From 277 cell fusions, 29 early embryos developed and were implanted into 13 surrogate mothers. However, only one pregnancy miraculously went to full term, and the 6.6 kg Finn Dorset lamb 6LLS (aka Dolly) was born after 148 days.
What happened to Dolly?
Dolly lived a pampered existence at the Roslin Institute. She produced offspring in the normal way, proving that cloned animals can reproduce.
However, Dolly suffered from from arthritis in a hind leg joint and a virus-induced lung tumour that is common among sheep which are raised indoors. She was euthanised on 14 February 2003, aged six and a half.
Dolly’s chromosomes were also a little shorter than those of other sheep her age and her early ageing may reflect that she was raised from the nucleus of a 6-year old sheep.
The benefits of cloning sheep
Despite being a miraculous feat of nature, the development of cloning technology has led to new ways to produce medicines and is improving our understanding of development and genetics.
Researchers have managed to transfer human genes that produce useful proteins into sheep and cows, so that they can produce, for instance, alpha-1-antitrypsin to treat cystic fibrosis and other lung conditions. Cloning animals has also led to a potential new therapy to prevent mitochondrial diseases in humans being passed from mother to child like diseases like muscular dystrophy.
The treatment is currently not permitted for use in humans. However, the Human Fertilisation & Embryology Authority in the UK has reported that there is general support in the public for legalising the therapy and making it available to patients.
Since 1996, when Dolly was born, other sheep have been cloned from adult cells, as have cats, rabbits, horses and donkeys, pigs, goats and cattle. However, Dolly remains one of the most iconic clones in the world, meaning its only fitting to give her well deserved recognition on her special day.