Dima

It's a good thing nobody has thrown Dima away during any spring cleaning.


Nov 03, 2008
By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - Japanese scientists have cloned mice whose bodies
were frozen for as long 16 years, and said on  Monday it may be possible to
use the technique to resurrect mammoths and other extinct species.


Mouse cloning expert Teruhiko Wakayama and colleagues at the Center for
Developmental Biology, at Japan's RIKEN  research institute in Yokohama,
managed to clone the mice even though their cells had burst.

"Thus, nuclear transfer techniques could be used to 'resurrect' animals or
maintain valuable genomic stocks from  tissues frozen for prolonged periods
without any cryopreservation," they wrote in the Proceedings of the National
Academy of Sciences.

Wakayama's team used the classic nuclear transfer technique to make their
mouse clones. This involves taking the  nucleus out of an egg cell and
replacing it with the nucleus of an ordinary cell from the animal to be
cloned.

When done with the right chemical or electric trigger, this starts the egg
dividing as if it had been fertilized by a  sperm.

"Cloning animals by nuclear transfer provides an opportunity to preserve
endangered mammalian species," they wrote.



"However, it has been suggested that the 'resurrection' of frozen extinct
species (such as the woolly mammoth) is  impracticable, as no live cells are
available, and the genomic material that remains is inevitably degraded,"
they  said.

DIGGING INTO FREEZERS

Wakayama's team dug out some mice that had been kept frozen for years and
whose cells were indisputably damaged.  Freezing causes cells to burst and
can damage the DNA inside. Chemicals called cryoprotectants can prevent this
but  they must be used before the cells are frozen.

They tried using cells from several places and discovered that the brains
worked best.

This is a bit of a mystery, as no one has yet cloned any living mouse from a
brain cell.

Many animals have been cloned, starting with sheep, and including pigs,
cattle, mice and dogs. Livestock breeders want  to use cloning to start
elite herds of desirable animals, and doctors want to use cloning technology
in human  medicine.

Mammoths may be the extinct animals that scientists would be most likely to
try to clone, as many of the animals have  been found preserved in ice.

In July 2007 Russian scientists discovered the body of a baby mammoth frozen
in the Arctic Yamalo-Nenetsk region for  as long as 40,000 years.

"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," Wakayama's team wrote.

"It remains to be shown whether nuclei can be collected from whole bodies
frozen without cryoprotectants and whether they will be viable for use in
generating offspring following nuclear transfer."

Courtesy of Barb