Clone and never end
It's all over the media once again: Researchers have cloned living creatures again. But what are new experiments actually about? Dolly, Polly and Molly have found successors: now it's George and Charlie, two calves born on a farm in Texas, whose names are on everyone's lips. In part it is not so new, but what the University of Massachusetts in Amherst brought to the public. The researchers wanted to find a way to produce medicines cheaply and effectively. The approach of equipping a gene responsible for the production of desired proteins with a switch that activates it only in the mammary glands and transferring it to female livestock is promising. These transgenic animals then release the desired substance in their milk. Substances such as human antithrombin III (used to inhibit the formation of blood clots) and alpha-1 antitrypsin were obtained from milk in this way. A route that is not limited to lactating mammals has also been explored. In the January issue of Nature Biotechnology, a group of researchers from the US Department of Agriculture laboratory reports that they engineered mice by inserting a gene into the cells of their urinary bladder. After the cells were tagged with the gene for the production of human growth hormone (hGH), they secreted this hormone in the urine. There the protein can be separated more easily from accompanying proteins than in milk.
These approaches initially have nothing to do with the cloning process. Cloning only comes into play when it comes to the fact that many transgenic organisms are to be used for this type of drug production. It offers the possibility of avoiding certain "disadvantages" of sexual reproduction: On the one hand, large animals have a long generation period. On the other hand, the genetic information is mixed up. Here the production of genetically identical living beings offers a way out. The reproduction of animals with an extremely high breeding value or the preservation of genetic resources could be areas of application for cloning outside of basic research.
The first successes in cloning livestock were achieved using very young (embryonic) cell nuclei. In 1996, Sten M. Willadsen of the University of Cambridge managed to clone sheep by replacing embryonic cell nuclei. This was later also achieved using embryonic cells that had previously been propagated in culture. The advantage: very many copies of an embryo can be produced and it is possible to genetically manipulate the cells. A further step has been taken with Dolly: according to the scientists, mature (adult) cells were used in their cloning. A transgenic animal was then cloned with Polly. And what they did there with a sheep, the researchers at the University of Massachusetts and Advanced Cell Technology Inc. have now repeated with Charlie and George: These are male calves cloned from genetically modified adult cells. They are to form the basis for breeding a herd that is used to produce the protein albumin, a component of human blood.
The results of James Robl, a professor at Massachusetts University, and Steven Stice, associate of Advanced Cell Technology Inc., were presented on January 20 at a meeting of the International Embryo Transfer Society in Boston. At this meeting, other research groups also presented their current work in the field of cloning:
A research group from the University of Wisconsin-Madison transplanted the cell nuclei of various animal species such as sheep, pigs, rats and monkeys into enucleated egg cells from cows. After that, the cells were cultivated in the laboratory; they developed into embryos that were placed in cows as surrogate mothers. So far, however, the pregnancy has always ended in a miscarriage.
A Japanese working group is also trying to achieve successful cloning with differentiated instead of embryonic cells, but this time – as with George and Charlie – from cattle. So far, however, no statement can be made as to whether one of the cows that became pregnant in this way will actually give birth to a live calf.
See also Spectrum of Science 3/97, page 70:
"Human proteins from the milk of transgenic animals"
See also Spectrum of Science 4/97, page 18:
"The first cloning of an adult mammal"
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