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Scientists clone from frozen mice Scientists clone from frozen mice
(about 1 hour later)
Japanese scientists have managed to create clones from the bodies of mice which have been frozen for 16 years.Japanese scientists have managed to create clones from the bodies of mice which have been frozen for 16 years.
Cloning had so far only been achieved using live donor cells and transferring their DNA to recipient eggs. Cloning has largely been done using just live donor cells, transferring their DNA to recipient eggs.
Experts believed that using thawed frozen cells would not be possible because of ice damage to the DNA. Using thawed frozen cells runs the risk of ice damage to the DNA unless carefully handled.
The scientists in Kobe, Japan, said the technique raised the possibility of recreating extinct creatures such as mammoths from their frozen remains. The scientists in Kobe, Japan, said their technique raised the possibility of recreating extinct creatures, such as mammoth, from their frozen remains.
Many of the successful clones since Dolly the sheep was born in 1996 have been created by a method where the nucleus of a cell has been removed, placed in an empty egg and kick-started into replicating by chemicals or electricity.Many of the successful clones since Dolly the sheep was born in 1996 have been created by a method where the nucleus of a cell has been removed, placed in an empty egg and kick-started into replicating by chemicals or electricity.
It is not the only cloning technique, and Australian researchers reported cloning a pig in 2001 from cells that had been frozen for two years. The Adelaide-based team said its cloning method differed from the Dolly approach in important respects.
Frozen bodiesFrozen bodies
The Japanese research suggests it is not the case that frozen cells would be unusable because the formation of ice would be likely to damage the DNA they contained. The Japanese research was undertaken at Kobe's Centre for Developmental Biology and is reported in the journal Proceedings of the National Academy of Sciences (PNAS).
The scientists successfully created clones using the brain cells from mice that had been frozen at -20C. The work extends the time frozen material can be held before it is used to clone an animal.Pigs have been cloned using frozen material before now
The frozen bodies of mammoths have been found dating back 40,000 years. The scientists said they created their mice from the brain cells of rodents that had been kept in laboratory conditions at -20C.
However, the researchers warned that the lack of suitable species for recipient eggs and surrogate mothers were "major problems" for the technique to be used for extinct or endangered animals. Obviously, these are ideal conditions - far removed from the uncontrolled conditions of the Siberian steppe where mammoth remains dating back 40,000 years have emerged from the permafrost.
The work at Kobe's Centre for Developmental Biology was reported in the journal Proceedings of the National Academy of Sciences (PNAS). DNA previously removed from such animals has been found to be highly degraded.
And even if good material were available major obstacles would have to be overcome before such a technique could be used on extinct or even endangered animals - such as finding a suitable species to provide recipient eggs and surrogate mothers.
The donor genetic material came from animals stored at -20C for 16 years
Professor John Armitage is director of tissue banking at the Bristol Eye Hospital, UK.
He commented: "Mitochondrial and some nuclear DNA fragments have previously been isolated from mammoths frozen in permafrost, but the key question is whether sufficiently intact nuclei could be extracted from mammoth cells, which will have been frozen for at least 10,000 years at relatively high sub-zero temperatures.
Professor Armitage added: "-20°C, the temperature at which the mice used in these experiments were stored, is insufficient to stop physical and chemical reactions of biological significance - even food in a domestic freezer has a limited storage time based on changing texture and taste.
"To achieve long-term storage of viable cells, including embryos, requires far lower temperatures of at least -140°C in the presence of cryoprotectants."
It is conceivable the techniques being developed might have some application in future stem cell therapies in humans where a cloning process was used to generate particular tissues for transplantation.
Viable eggs, sperm and embryos are already retrieved from the frozen state for use in in vitro fertilisation (IVF).