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Breakthrough in primate cloning
14/11/2007 15:42 - (SA)
Paris - Scientists said on Wednesday they had created the world's first cloned embryo from a monkey, in work that could spur cloning of human cells for use in medical research.
In work published online by the journal Nature, a US-led team said they had created cloned embryos from rhesus macaques using the same method that famously led to Dolly the Sheep and other genetically duplicated animals.
It is the first time that this technique has been successfully used to create cloned primate embryos.
The group generated two lines of embryonic stemcells from the embryos, according to the research headed by Shoukhrat Mitalipov of the Oregon Health and Science University in Beaverton, Oregon.
Dolly - the world's first cloned animal - was created in 1996 by using so-called somatic cell nuclear transfer (SCNT) in which the genetic core of an egg is removed and replaced with the nucleus of an adult cell.
The egg is then stimulated with chemicals or a jolt of electricity to prompt its division.
The list of other cloned creatures using SCNT includes mice, pigs, cats, cows and dogs.
Until now, though, there has been no cloned primate, as researchers encountered obstacles that caused cell development to be flawed.
Controversy
Work on primate cloning has stirred controversy in some quarters, with ethicists saying it could open the door to cloning human beings.
In an exceptional move, Nature said it was moving forward release of the paper because of "continuing speculation" about the research, following media reports at the weekend.
Researchers distinguish between "reproductive cloning", in which a putative cloned baby would be born and "therapeutic cloning", in which only cloned cells would be used for medical reasons and no baby would result.
Stemcells are immature cells that develop into the specific tissues of the body.
Embryonic stemcells have the highest capability of all, because they can differentiate into any tissue. Scientists hope to be able to coax these cells into one day becoming replacement tissue for organs that are damaged or diseased.
Transplanted cells from a donor, though, run the risk of being attacked as intruders by the patient's immune system. By creating stemcells that are cloned with the patient's own DNA, the risk of rejection would be skirted.
Claim validated
Mitalipov's team said they collected 304 eggs, also known as oocytes, from 14 female rhesus macaques.
The donor nucleus came from an adult male monkey housed at the Oregon National Primate Research Center.
Thirty-five blastocysts, or early-stage embryos, resulted from the SCNT operation. They in turn led to two lines of self-dividing embryonic stemcells - a success rate of 0.7% when compared to the number of eggs used.
"Our results represent successful nuclear reprogramming of adult somatic cells into pluripotent ES (embryonic stem) cells and demonstrate proof-of-concept for therapeutic cloning in primates," the paper said.
The claim that the stemcells were an exact DNA copy of the donor's genetic code was validated independently by a team led by David Cram of Monash University in Melbourne, Australia.
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