Scientists 'clone mice from deep freeze bodies'

By John von Radowitz, PA
Tuesday, 4 November 2008 


National Academy of Sciences/PA 

Undated handout photo issued by the National Academy of Sciences of a brown 
mouse that scientists have cloned from brain tissue extracted from a frozen 

Healthy mice have been cloned from bodies kept in deep freeze for 16 years, 
scientists are reporting. 

The breakthrough increases the possibility of "resurrecting" extinct animals 
such as mammoths from their frozen remains. 

Until now "Dolly the Sheep"-style cloning has mostly been achieved using live 
donor cells, from which DNA is transferred to recipient eggs. 

Cloning from thawed frozen cells was thought to be difficult, if not 
impossible, because their DNA would be damaged by ice crystals. 

This presented a major obstacle to hopes of raising mammoths and other extinct 
animals preserved in ice from the dead. 

A team of Japanese scientists says it has now overcome the problem by 
successfully producing mouse clones from mice frozen at minus 20C for up to 16 

After thawing out the dead mice, the researchers collected nuclei from cells in 
their brain tissue. 

These were injected into empty eggs whose own DNA had been removed, to generate 
cloned embryos. 

Stem cells taken from the embryos were then used in a second round of cloning. 
Their genetic material was inserted into denucleated eggs, to produce embryos 
that grew into four mouse clones. 

A further nine "chimeric" mouse clones were created by mixing the cells of 
different embryos. 

The research was reported today in the journal Proceedings of the National 
Academy of Sciences. 

The scientists, led by Dr Teruhiko Wakayama, from the Centre for Developmental 
Biology in Kobe, Japan, wrote: "We have demonstrated here that healthy cloned 
mice and chimeric clonal mice could be obtained by nuclear transfer using donor 
nuclei from cells obtained from bodies frozen without cryoprotectants for up to 
16 years." 

The scientists said other sources of frozen nuclei, such as white blood cells, 
might be as useful for cloning as brain tissue. 

They added: "This would increase the chances of finding tissues in good 
condition. At present, the lack of suitable species for recipient oocytes 
(eggs) and for surrogate mothers is one of the major problems that needs to be 
solved for the method to be applied in extinct or endangered animals. 

"However, the use of interspecies nuclear transfer techniques could solve this 
problem and provide a possibility of reconstituting the genomes of animals from 
samples frozen without access to sophisticated laboratory facilities." 


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