Dolly the sheep was the very first mammal to be successfully cloned from an adult cell, and came into the world on the 5th of July 1996. The scientific brains who made her were Keith Campbell, Ian Wilmut and colleagues at the Roslin Institute in Edinburgh, Scotland. When her birth was announced seven months later the world was stunned. Her premature death in 2003 created just as many headlines.
Dolly attracted millions of column inches throughout her life and led to long running debates about the ethics of cloning, which became louder with news of her death. Sheep can live to twice her age and she suffered from a type of lung disease usually seen in much older animals.
To some critics this was all too predictable as cloning is a relatively new and difficult technology to get right. In fact Dolly was the end result of more than 250 attempts at cloning a sheep.
Dolly’s birth stunned the scientific community for two main reasons. The first was that she existed at all. The creation of a viable clone of a complex mammal was unexpected.
To create Dolly, scientists took an adult mammary cell from the udder of another sheep (she was called Dolly after the singer Dolly Parton, something to do with mammary cells!) They stripped away all the cellular machinery to leave the nucleus containing DNA and all the genetic material needed to create life. Then they introduced this into an oocyte (an unfertilised egg) that had had its nucleus removed. The process is known as somatic cell transfer and fertilisation was kick-started with a jolt of electricity. When the hybrid cell began to divide and develop into a blastocyst it was implanted into a surrogate mother.
The second incredible fact about the technology was that it showed that an adult differentiated cell, that is a mature cell that has reached the end of its developmental stages, could in effect be wiped back to its original state. So the mammary cell reverted back to its embryonic stage. The fascinating part about this is that a blank cell has the potential to grow into any other cell and could therefore be used to mend ageing tissues and organs.
For most of her life Dolly had excellent health and became a mum in her own right , when she was bred with a Welsh Mountain Ram. The first lamb, called Bonny, was born in 1998. A year later she gave birth to a set of twins and then another year later she had triplets.
Dolly started suffering from ill health in 2002 when she was diagnosed with a form of arthritis. Then she developed a progressive lung disease and a decision was made to have her put down. The cause of the arthritis was never discovered and there’s still widespread debate about whether Dolly died prematurely as the result of being a clone.
Dolly was an important animal to science and leaves a lasting legacy. The technology used to create her showed us that our cells are much more plastic and changeable than previously thought. It holds out hope for the process of therapeutic cloning where new healthy cells can be created from differentiated cells that have been wound back to their embryonic state. It’s also telling us much more about the body’s own repair mechanisms and could offer a way for science to intervene if a body is not doing a good enough job of repairing itself. Since Dolly, there have been many more cloned animals and the technology continues to improve.