- WASHINGTON (AP) -- Japanese researchers report they have cloned eight, genetically
identical calves from cells removed from a single cow.
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- In a study to be published this week
in the journal Science, researchers from three Japanese institutions report
the calves were cloned with techniques similar to those used to clone the
famed Scottish sheep known as Dolly.
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- The Japanese said they transferred the
nuclei from cells removed from a single adult animal into cow eggs from
which the nuclei had been removed.
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- The eggs and the transferred cell nuclei
fused and grew into blastocysts, an early embryonic stage that resembles
a ball of cells.
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- Ten blastocysts were placed into five
unrelated cows, all of which became pregnant. Eight calves were born from
the 10 blastocysts but four of the eight animals died shortly after birth
from what the researchers called "environmental factors."
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- Each of the surviving calves is a genetic
duplicate of the cow from which the cells were removed, the researchers.
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- Cloning cows in this manner, the scientists
said, gives an important economic benefit because it could, in effect,
duplicate cows that are "proven to be ideal milk and meat producers."
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- Japanese researchers reported last month
they cloned at least 15 calves using the Dolly technique. Japan imports
much of its beef and agricultural researchers have been aggressively studying
cloning techniques as a way of improving meat and milk production.
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- Dolly was the first mammal in history
to be cloned from an adult cell. Researchers announced last year the Finn
Dorset sheep was cloned using the nucleus taken from a cell that had been
removed from the udder of an adult sheep.
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- U.S. researchers have since cloned calves
using cells taken from unborn cows. Laboratory mice also have been cloned
using the Dolly technique.
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- In the new Japanese work, the researchers
used two different types of cells removed from the reproductive tract of
a single Japanese beef cow.
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- Both types of cells carried the same
genetic pattern as the donor adult cow and all of the cloned calves retained
this same pattern, proving they were true clones, the researchers said.
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- However, the Japanese researchers said
they have achieved a higher degree of efficiency than earlier Scottish
and U.S. researchers. They said 23 per cent of one type of cell, the oviductal,
developed into advanced embryos, while 49 per cent of another type
of cell, the cumulus, were successful.
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- Dolly's creators had hundreds of failures
and some U.S. researchers reported a success rate of only about 12 per
cent.
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