Scientists claim finding more efficient cloning method

US researchers said on Sunday they had found a more efficient way to clone mice, and said their experiment solved a basic question about cloning science8212;whether it truly is possible to clone animals from mature cells.

US researchers said on Sunday they had found a more efficient way to clone mice, and said their experiment solved a basic question about cloning science8212;whether it truly is possible to clone animals from mature cells.

Dolly the sheep made headlines around the world in 1997 because she was the first mammal to be cloned from an adult cell8212; a cell taken from a grown animal. Animals had been cloned using cells from foetuses and embryos, but not grown animals.

But some scientists argued that mature tissue is too old to be re-generated, and that Dolly and the hundreds of cloned cattle, pigs and other creatures that followed here were in fact created using stem cells or stem-like cells by accident.

These master cells of the body retain an ability to form various tissues, and they are not always easy to pick out from the cells around them.

Dr Jerry Yang of the University of Connecticut noted that cloning is still very difficult to do. Only about 2 or 3 out of 100 tries generally works.

8220;This was seen as circumstantial evidence that it was stem-like cells that succeeded in cloning,8221; Yang said in a telephone interview.

8220;The question is important because the success rate for reproductive cloning is still quite low.8221;

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Yang, Dr Tao Cheng, of the University of Pittsburgh, and colleagues cloned mice using fully differentiated, or mature, white blood cells called granulocytes.

Writing in the November issue of Nature Genetics, they said they used somatic cell nuclear transfer, in which the nucleus from a cell of the animal to be cloned is injected into an egg whose nucleus has been removed. This process works very poorly in mice and usually a two-step procedure is needed8212;first growing tiny embryos, then removing their embryonic stem cells to generate mouse pups.

Yang8217;s team tried cloning using the blood cells at various levels of development8212;from the stem cells stage through full maturity, called full differentiation.

8220;What was surprising8212;the efficiency went up as we got more differentiated cells,8221; Yang said. 8220;That was very, very surprising, very shocking to us.8221;

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Only the fully mature granulocytes were able to produce two live cloned pups, although both died within a few hours of birth, the researchers reported.

8220;Even we were surprised to find fully differentiated cells were more efficient for cloning, because granulocytes are not capable of dividing,8221; Cheng said in a statement.

8212;Maggie Fox