The Big Question: Will scientists ever be able to resurrect long-extinct animals by cloning?
Wednesday 05 November 2008
Why are we asking this now?
Scientists in Japan have refined a cloning technique that has enabled researchers to clone apparently healthy mice from the frozen corpse of a mouse that had been kept in a freezer for 16 years at a temperature of -20C. They employed the same techniques that scientists used to create Dolly the sheep, but added an extra stage where they effectively repeated part of the cloning process, which enabled them to successfully produce cloned offspring. The scientists believe the study shows that it might be possible in the future to use the same techniques to clone creatures from the frozen tissue of animals found buried in permafrost regions, for example, the frozen corpses of mammoths.
Who carried out this work and why?
The team was led by Teruhiko Wakayama of the Riken Centre for Developmental Biology in Kobe, Japan. He was interested in adapting the Dolly method of cloning, which involves taking the nucleus of a cell and inserting it into an unfertilised egg cell that has had its own nucleus removed. After a jolt of electricitythe unfertilised egg develops into an early embryo, just as if it had beenfertilised by a sperm cell.
This was how Dolly herself wascreated. However, unlike Dolly, the resulting mouse embryos in the Japanese study were not inserted into surrogate mothers but broken apart to retrieve individual embryonic stem cells. These stem cells were then inserted into another batch of unfertilised egg cells and, after yet another jolt or two of electricity, the result was the creation of early, cloned embryos. Only at this stage were the embryos implanted into surrogate mothers, which then gave birth to the clones of the original frozen mouse that had died 16 years previously.
Is this the first time that scientists have produced clones from dead animals?
No. In fact Dolly herself was cloned from a sheep that had died long before. Dolly was born in 1996. In Dolly's case, scientists had taken tissue from the udder of Dolly's clone and carefully frozen it using special chemicals called "cryopreservatives". These prevent the formation of damaging ice crystals inside the cells. Dolly was therefore the clone of a frozen animal that had died many years before she was born. Indeed, when one national newspaper learnt that Dolly was the clone of a dead animal, it famously asked the question: "Can we now raise the dead?" on its front page.
Can we now raise the dead?
It depends what you mean. Dolly was the clone of a dead animal, and scientifically it means that the dead animal's entire genome was "resurrected" once more in the body of another individual. But if this were ever to happen to a human being, few people would consider that the deceased person had been raised from the dead as a result of having a living clone. It's no more true than saying that when a person dies, he or she has been "raised from the dead" if they happen to have an identical twin who is still alive. However, what concerns some people is whether these sorts of scientific developments will lead to individuals storing their bodies, or parts of them, in order for that their cells might be cloned in the future – if or when it is scientifically and legally possible to do so.
So will it be possible to resurrect extinct animals?
This is what Wakayama and hiscolleagues tentatively propose in their research paper published in the Proceedings of the National Academy of Sciences. They pointout that all clones so far produced from dead animals have been created from quick-frozen tissue that has been meticulously kept at very cold temperatures without thawing, using cryopreservation. This does not happen in real life.
As the scientists say: "In dead specimens frozen in natural conditions such as permafrost tundra, the cells of tissue will presumably bind strongly to each other and freeze gradually after death due to the large body size. It remains to be shown whether nuclei can be collected from the whole bodies frozen withoutcryoprotectants, and whether they will be viable for use in generating offspring following nuclear transfer. This is an important question with potential application in the cloning of extinct animals frozen in permafrost, or specimens collected opportunistically from endangered species in the field without access to sophisticated laboratory facilities."
Has anyone tried to "resurrect" extinct animals?
Scientists have tried with some success to extract DNA from various extinct mammals, such as mammoths and the Tasmanian tiger, but cloning poses a whole set of different and more intractable problems. The first concerns the difficulty of extracting cells with perfectly preserved DNA, since it degrades over time. Corpses frozen in permafrost for several thousand years are likely to have suffered repeated thawing and freezing that will damage both the cells and their DNA.
Another problem is trying to find suitable non-extinct animals to act as surrogate egg donors and mothers. For the mammoth, the African elephant might be the best choice, although there may be important biological differences that pose insuperable barriers. One problem has to do with mitochondrial DNA, which is passed on down the maternal line through the egg cell. An elephant's mitochondria may simply not work in a mammoth clone.
Could cloning be used to protect living species from extinction?
Some scientists are suggesting this as a last-ditch measure to safeguard threatened animals that are difficult to breed in captivity. However, cloning is never going to be the panacea to the threat of extinction. The biggest problems faced by large endangered animals are habitat loss, human encroachment on their territories, hunting and climate change. Cloning animals on the verge of extinction could help a species to hang on in zoos and parks, but it does little to generate the genetic diversity that is so important for the long-term survival of species. It also does nothing to address the root causes of extinction.
Will this latest cloning development ever be used on people?
One can never say never in science. But it is illegal in Britain to clone babies and this technique will, if applied in full on human tissue, result in the birth of cloned individuals. Unless there is a change in the law, it is therefore unlikely that anyone will ever attempt to clone babies from dead people – in this country at least. Cloning from the grave, as one newspaper put it yesterday, is still a very long way from reality for all sorts of ethical, legal and scientific reasons.
What further research is necessary in this area?
Quite a lot. For a start, showing that it is possible to produce clones from a corpse stored in a laboratory freezer kept at a constant temperature is not the same as being able to clone from a dead body kept in a precarious state of preservation. It is an important step forward, but it will be many years before it can have a practical use.
Should we rely on cloning to protect endangered species?
* It offers hope for species that cannot be bred in captivity with conventional reproductive methods.
* It means that we can preserve the unique combination of genes found in some animals.
* Cloning would make extinction obsolete because animal genomes could be preserved in perpetuity.
* Cloning does nothing to address the underlying problems faced by endangered animals.
* Cloning bypasses sexual reproduction, which generates critical individual differences within a species.
* Cloning is no solution to extinction but it could be used to justify inaction towards endangered species.
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