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Cloning from Frozen Cells
Researchers from Japan's Centre for Developmental Biology in Kobe have successfully cloned mice from dead cells. Up until now the reproductive cloning of animals such as Dolly the sheep and Ralph the rat has been achieved by using live donor cells. This is the first time that frozen dead cells have been used. It was previously thought that the use of frozen cells in reproductive cloning would result in failure because of the formation of ice crystals which would damage the delicate intracellular material. However, in this experiment, it did not prove to be the case.
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Reproductive Cloning Technology
To create the clones the Japanese researchers took dead brain cells from the frozen mice (the mice bodies had been kept at -20 degrees centigrade for 16 years) and extracted their nuclei which they then transplanted into mice egg cells. Embryos were created, but instead of implanting them straight away into surrogate mothers, the scientists waited until stem cells were developed and then extracted them from the embryos. This was because of an unknown factor; namely whether frozen nuclei would be able to be reprogrammed to develop into cloned animals.
During the next stage in this reproductive cloning technology scientists extracted nuclei from the embryonic stem cell lines and placed them into mouse egg cells before implanting them into surrogate mothers. It resulted in the birth of several healthy mice clones. The research was published in the Proceedings of the National Academy of Sciences.
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Could this be used on Extinct Animals?
Of course this work opens up the prospect of bringing back extinct species from the dead. For example 40,000 year old mammoths that have been found frozen in blocks of ice. The Japanese research has shown that live cells are not necessarily needed to create a healthy cloned animal, although the scientists say that a potential stumbling block would be the lack of suitable surrogate mothers. Nonetheless one of the major hurdles would appear to be overcome, namely that the freezing and thawing process did not damage the DNA in such a way as to make this kind of reproductive cloning impossible.
The research probably has a more immediate application than resurrecting part of our planet's history. It has shown that it would be possible to store tissues of animals that are facing extinction and to use that material to create new animals should a species become wiped out. This benefit is highlighted by the scientists in their paper. "....nuclear transfer techniques could be used to "resurrect" animals or maintain valuable genomic stocks from tissues frozen for prolonged periods of time without any cryopreservation."
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