| A History of Cloning Achievements | |||||||||||||||||||||||||||||||||||||||||
| by Tom W. Miller | |||||||||||||||||||||||||||||||||||||||||
| 1952: Robert Briggs and Thomas King clone northern leopard frogs | |||||||||||||||||||||||||||||||||||||||||
| Using nuclear transfer, Briggs and King created tadpoles from undifferentiated, embryonic cells. Their attempts to produce successful specimens from differentiated cells failed, prompting them to conclude that it was impossible to create a clone from adult cells. | |||||||||||||||||||||||||||||||||||||||||
| 1962: John Gurdon claims to have cloned adult frogs | |||||||||||||||||||||||||||||||||||||||||
| Using the nuclei from the adult intestinal walls of South African frogs, Gurdon claimed to have produced frog clones, which would disprove the previous conclusion of Briggs and King. Some scientists questioned the result. Small amounts of undifferentiated sex cells were mixed in with intestinal cells, and the clones may have resulted from these undifferentiated cells. Gurdon's experiment, however, kept the debate alive over whether differentiated cells had the potential to produce complete organisms. | |||||||||||||||||||||||||||||||||||||||||
| 1984: Steen Willadsen clones a sheep from embryo cells | |||||||||||||||||||||||||||||||||||||||||
| Willadsen refined the technique of nuclear transfer to create the first genuine example of a mammalian clone. Previous scientists had used fertilized eggs, but Willadsen found that unfertilized eggs were more receptive to a transferred nucleus. Willadsen also used electric current to fuse the embryo cell with the egg. Other scientists used Willadsen's technique to produce clones from cattle, pig, goat and rat embryos. | |||||||||||||||||||||||||||||||||||||||||
| 1986: Steen Willadsen clones a cow from differentiated cells | |||||||||||||||||||||||||||||||||||||||||
| Willadsen used week-old embryo cells to clone a cow. Unlike the younger cells he had used to clone a sheep, these cells had begun to develop into more specialized tissues. Willadsen showed that even a differentiated cell did not lose its totipotency-its capacity to give rise to a complete organism. | |||||||||||||||||||||||||||||||||||||||||
| 1995: Ian Wilmut and Kevin Campbell clone sheep from differentiated cells | |||||||||||||||||||||||||||||||||||||||||
| Wilmut and Campbell refined Willadsen's technique to produce two sheep-Megan and Morag-from differentiated embryo cells. Campbell, en expert on cell cycles, thought that nuclear transfer would be more likely to succeed if done before the chromosomes of the donor cell started to divide. The easiest way to ensure this, Campbell reasoned, was to deprive the cell of growth factor and induce a quiescent state known as G0. The team's success showed that attention to the cell cycle was crucial to the cloning process. | |||||||||||||||||||||||||||||||||||||||||
| 1996: Ian Wilmut and Keith Campbell clone a sheep from an adult cell | |||||||||||||||||||||||||||||||||||||||||
| Campbell had an epiphany after the birth of Megan and Morag. Maybe the G0 state was not merely a convenient way to synchronize cell cycles, but crucial to the reprogramming of a cell. To test this hypothesis, the team decided to attempt something previously thought impossible-cloning from an adult cell. Working with a mammary cell from a six-year-old ewe, Wilmut and Campbell repeated the process used to create Megan and Morag. On July 5, 1996, Dolly was born. | |||||||||||||||||||||||||||||||||||||||||
| 1997: Ian Wilmut and Keith Campbell clone a sheep using genetically altered cells | |||||||||||||||||||||||||||||||||||||||||
| Wilmut had begun his cloning experiments hoping to find a more direct way to produce transgenic animals-animals fitted with a human gene that would enable them to make valuable human proteins in their milk. In July 1997, with the birth of Polly-fitted with a gene for human factor IX-Wilmut accomplished his original goal and showed how cloning technology could be applied to make a useful product. | |||||||||||||||||||||||||||||||||||||||||
| 1998: Teruhiko Wakayama and his team at the University of Hawaii announce the cloning of mice from adult cells | |||||||||||||||||||||||||||||||||||||||||
| Wakayama, along with Ryuzo Yaganimachi and Toni Perry, built on the Dolly technique to create fifty cloned mice from adult cells. The "Honolulu Technique" differs from the process used to create Dolly in several important respects. First, Wakayama chose cells that are often naturally in the G0 state and so did not have to be forced into quiescence. Then, instead of fusing the entire donor cell with the enucleated egg, Wakayama inserted only the nucleus. He left the new cell alone for six hours, giving it extra time to accept the nucleus. Rather than using an electric pulse to jumpstart growth, Wakayama placed the cell in a chemical culture. The process proved more efficient at producing clones than did Wilmut's technique. Wakayama's team then created clones of the clones, and allowed the mice to reproduce. | |||||||||||||||||||||||||||||||||||||||||
| 1998: Yoko Kato and his team at Kinki University produce eight cloned calves from one adult cow | |||||||||||||||||||||||||||||||||||||||||
| Using a technique similar to that one that produced Dolly, Kato's team created eight genetically identical calves from a single adult cow. Like Wakayama, Kato found that certain adult cells proved more efficient than others at producing viable clones. Kato hoped that his success would boost Japan's beef and dairy industries. | |||||||||||||||||||||||||||||||||||||||||
| 2000: Five pigs cloned from adult cells | |||||||||||||||||||||||||||||||||||||||||
| Scientists at PPL Therapeutics-the company responsible for producing Dolly-announce that five cloned pigs were born in March. This success opened the door to produce genetically modified pigs suitable for xenotransplantation-the transplanting of animal organs into human beings. The piglets show yet another possible way that cloning technology could become practical and profitable. | |||||||||||||||||||||||||||||||||||||||||
| 2000: The first goat is cloned from adult cells | |||||||||||||||||||||||||||||||||||||||||
| A team of Chinese scientists cloned a goat, named Yuanyuan, from the ear cell of an adult goat. The animal died thirty-six hours after birth. Scientists still struggled to produce healthy clones. | |||||||||||||||||||||||||||||||||||||||||
| 2002: A cat is cloned from adult cells | |||||||||||||||||||||||||||||||||||||||||
| A team at Texas A & M University announced that they had cloned a cat, named Copycat, or CC for short, from adult cells. The success sparked new entrepreneurial possibilities as well as an ethical debate over pet cloning. | |||||||||||||||||||||||||||||||||||||||||
| 2003: The first deer is cloned from adult cells | |||||||||||||||||||||||||||||||||||||||||
| Researchers at Texas A & M University announced that they had cloned a white-tailed deer, named Dewey, from adult cells. | |||||||||||||||||||||||||||||||||||||||||
| 2003: The first horse is cloned from adult cells | |||||||||||||||||||||||||||||||||||||||||
| A team led by Cesare Galli of the Laboratory of Reproductive Technologies in Cremona, Italy, clones the first horse from adult cells. The foal, named Prometea, is also the first clone of any species to be carried to term by its twin mother. | |||||||||||||||||||||||||||||||||||||||||
| Sources | |||||||||||||||||||||||||||||||||||||||||
| Books | |||||||||||||||||||||||||||||||||||||||||
| Ian Wilmut, Keith Campbell, and Colin Tudge, The Second Creation: Dolly and the Age of Biological Control (Farrar, Straus and Giroux: New York, 2000). | |||||||||||||||||||||||||||||||||||||||||
| Websites | |||||||||||||||||||||||||||||||||||||||||
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Bbc.co.uk Cnn.com Faseb.org/opa/cloning/timeline Findarticles.com Library.thinkquest.org Genome News Network |
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