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(image: National Museums Scotland) |
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On the tenth anniversary of her death, we remember Dolly, the first animal cloned from an adult cell. A lone sheep, she paved the way to advances in biotechnology and shed light on the nature of being “She’s been born and she has a white face and furry legs.” Thus read the text of a fax that went out to a village in the Scottish Highlands on 5 July 1996, announcing the birth of the lamb Dolly, the first animal to be cloned from an adult mammalian cell. The surrogate ewe that bore Dolly was a Scottish Blackface. The lamb’s white face was testament to the donor cell from which she had been cloned. The fax was sent to Karen Mycock, one of the team at the Roslin Institute, near Edinburgh, whose collective effort led to the birth of the lamb. Ian Wilmut, the leader of the team, has sometimes whimsically been called the father of Dolly. But it was in fact Mycock who physically made the embryo that went on to become the sheep. She did this by what is called somatic cell nuclear transfer: one starts with an egg from which the DNA, the genetic material, has been sucked out and then fuses it with another cell, which provides the DNA that directs the growth of the animal. Sperm are not involved. The donor cell that made Dolly came from the mammary gland of an adult sheep, giving her not only her DNA but also her name: a tribute to the well-endowed American country singer, Dolly Parton. Dolly was not the first cloned animal, nor even the first cloned mammal. Before her came lambs and calves cloned from embryonic donor cells, first as part of the work of Danish scientist Steen Willadsen and later by other laboratories. And mammalian cloning in turn rested on the slippery shoulders of amphibians – frogs and toads – shown to be clonable already in the mid 20th century, but again only with embryonic or larval cells as donors. Dolly was the first animal to be cloned from an adult cell. About 15 species of animal – dogs, cats, rabbits, cows, mice, pigs and monkeys among them – have by now been successfully cloned. The process is fiddly and inefficient and clones have a higher likelihood of developmental problems. But to the extent that one can tell, clones are often quite normal. The cloning of animals could have many potential uses, ranging from the exotic (interspecies clones to save endangered species) to the quixotic (attempting to resurrect dead pets). More realistically, cloning can help make genetically altered animals in species where it is otherwise difficult or impossible to do so. At the Roslin Institute, for instance, Dolly was followed some years later by Polly, a cloned sheep that produced a blood-clotting factor in her milk for the treatment of haemophilia. To use cloning in this way, the DNA of the donor cell must be altered before fusing it with the recipient egg. But the idea that cells of the body can be reprogrammed simply by exposure to the contents of the powerful egg has a conceptual reach beyond biotechnology. All multicellular animals, whether sheep or frogs or humans, begin as a single fertilised egg. Eventually the animal’s body consists of millions of cells, all of them originating from that fertilised egg and many of them with very different properties: some cells make up the beating heart; others the electrical brain; still others the blood or the mammary gland. Can this process be reversed? Is the DNA of an adult cell able to go back to the very beginning of life, to a state where it can behave like a fertilised egg and direct the making of a whole creature? This was the question to which Dolly, slightly overweight, unusually sociable for a sheep, but mostly normal, fertile and healthy, answered yes. |
Words Natalie de Souza |
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