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Cloning 'resurrects' long-dead mice
(New Scientist Via Acquire Media NewsEdge) HEALTHY mice have been cloned from the dead brain cells of animals frozen 16 years ago. The stored mice had been chilled using no elaborate cryogenic techniques, so the hope is that populations of endangered species such as the Northern white rhino (pictured) could one day be boosted using cells extracted from carcasses simply tossed into freezers.
Teruhiko Wakayama of the RIKEN Center for Developmental Biology in Kobe, Japan, and colleagues modified a technique Wakayama pioneered in 1998, in which the nucleus of a mouse cell - in this case taken from thawed tissue - is injected into a mouse egg with its nucleus removed (Nature
, vol 394, p 369). The egg "reprograms" the nucleus so that it is capable of generating every cell type in the body.
The researchers then removed these nuclei and injected them into fresh eggs, also with their nuclei removed, for yet more reprogramming. The resulting embryos were then implanted into the wombs of female mice, which gave birth to healthy mouse clones (Proceedings of the National Academy of Sciences
, DOI: 10.1073/pnas.0806166105).
It was easiest to create clones from brain tissue - a surprise given that clones have never been created from living brain cells. One might expect freezing and thawing to destroy the nucleus, but Wakayama says the high sugar content of brain tissue may actually protect the nucleus.
Mice have been cloned from cells frozen without sophisticated cryogenics (Biology of Reproduction
, vol 79, p 588), but these are the first clones to come from lumps of tissue frozen without any pretreatment.
"Many zoos are not in a position to collect cells and freeze them, but they can put a dead animal in a plastic bag and throw it in the freezer," says Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts, which has cloned the endangered gaur. "With a kitchen freezer you could store the genetic diversity of every panda in existence."
There are programmes that aim to boost dwindling animal populations and maintain genetic diversity by cloning individuals that have failed to breed, but these cells go through specialised procedures before being frozen.
More questions need to be answered before Wakayama's technique can be used on endangered species, says Martha Gomez of the Audubon Nature Institute in New Orleans, such as how long different species can stay frozen and still yield viable DNA. "It may depend on the size and the species," she says.
Cloning should be used only when all other options have failed, says Paul Bartels of BioBankSA at the National Zoological Gardens of South Africa in Pretoria. Nevertheless, he will ask biologists to start freezing bodies of endangered species that have died.
Resurrecting long-extinct animals will be trickier. Woolly mammoth carcasses remain in the permafrost but would likely have frozen and thawed several times, causing more damage than one-off freezing. "It would be very difficult, but our work suggests that it is no longer science fiction," says Wakayama.
It is unlikely that people who have been cryogenically preserved after death will be cloned. Besides being unethical, dangerous and usually illegal, they signed up to be resuscitated one day, not cloned, Lanza notes.
Copyright ? 2008 Reed Business Information - UK. All Rights Reserved.
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