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By SARAH SUE GOLDSMITH, LSU News Service
LSU's resident transgenic goat is Millie. Though she's a million-dollar goat, she doesn't look any different from the other goats she hangs out with. She is different, though, because her milk contains a therapeutic protein that could be extracted to make a drug for patients undergoing coronary bypass surgery. The drug works in conjunction with heparin, which prevents blood from clotting.
The protein, anti-thrombin III (AT III), is now in the third phase of human clinical trials. Pending FDA approval during the next 12 months, the product could be on the market in the next couple of years.
"The technology used to clone the three Genzyme goats is one of the first applications of the nuclear transfer (cloning) procedure to produce transgenic goats for the pharmaceutical industry, said Richard Denniston, a researcher with the LSU Agricultural Center. An article in the May issue of Nature Biotechnology will announce the breakthrough. Researchers at Tufts University School of Veterinary Medicine also participated in the research.
LSU researchers have for the past six years carried a collaborative research program with Genzyme, which may become the first company to have a transgenic product on the market. "The FDA is being very careful because there's no precedent," Denniston said. Transgenics is the process of taking DNA from one species and implanting it into the genetic structure of another.
"Genzyme takes the gene for anti-thrombin III. The DNA is like a computer code. Once researchers identify the code, they can punch it into a DNA sequencer. Four different molecular building blocks of the DNA material are put in a vial, and a gene is built synthetically. Then you can make millions of copies of that," he explained.
The AT III gene is attached to a promoter gene, usually the gene for casein, a milk protein, and then microinjected into the male pronucleus of the newly fertilized egg. During the first cell divisions, the gene may become attached to the genetic material of the embryo. If this happens, the new gene, or transgene, will be incorporated into every cell of the developing goat embryo. The embryo is cultured and then transfered to the goat surrogate mother, and researchers wait for normal fetal development. If a female is produced, she will produce milk with the AT III protein, which can be extracted from the milk for pharmaceutical use.
"When you breed the AT III female offspring, 50 percent of her offspring will have this gene. Now you've got an animal that is very valuable. How do you produce these animals as quickly as possible? Genzyme does the molecular work. We are trying to develop technologies to reproduce these transgenic animals as quickly as possible," Denniston said.
"The idea of cloning arose in the past two years. Cloning is desirable because it would increase the efficiency rate. When you insert the AT III protein into 1,000 fertilized eggs and transfer 100 embryos, you can expect one transgenic offspring. There's a 50 percent chance of its being female," he said.
Denniston explained that there are three possible sources of genetic material for cloning. One source is the adult animal; this is how Dolly the sheep was produced. "That's what really made big news, taking a cell from an adult animal," he said. "Another source is the 16-32 cell-stage embryo, which was first done about 15 years ago. A third source is a developing fetus. In each case, the donor cell containing all the genetic material is fused with an enucleated egg (an egg that has had its genetic material removed). The resulting cloned embryo is then transferred into a recipient female that carries the clone to term."
The transgenic goat clones born from the joint LSU/Genzyme project were produced by taking fibroblast cells from a 30-day female goat fetus. These cells were grown in an incubator in media containing the gene for AT III. The growing cells then underwent a procedure called electroporation, which allows the gene to cross the cell membrane and enter the host cell's nucleus.
The resulting transgenic fibroblast cells were then fused with an enucleated egg. These cloned embryos were then transferred into a recipient goat. The result was three genetically identical transgenic female goats that can produce the valuable AT III protein in their milk. Using the cloning process in conjunction with transgenics improves the overall efficiency of producing transgenic animals, Denniston said.
Not all pregnancies are successful, but 100 percent of the births will be females with the gene for AT III," Denniston said.
The agricultural applications of this technique are widespread. For example, researchers could insert a gene for bruccilosis resistance and clone a herd of bruccilosis-resistant cattle.
"What we are doing for Genzyme is to test procedures or techniques and develop in vitro fertilization. Six years ago, nobody was doing in vitro fertilizationin goats. They asked us to, and we did," he said.
"The Massachusetts farm has more than 1,500 goats under the watchful eye of the FDA. They produce the gene in a lab in Framingham. They get a 30-day fetus, culture fiborblast cells, insert the gene for AT III into fiborblast cells, do nuclear transfer, send embryos to us, and we transfer them into recipients."
"The market for AT III is $200 million. That amount of protein can be produced by fewer than 100 goats. Even with the cost being a half to $1 millon per animal, the potential earnings from the pharmaceutical product are enormous," the LSU researcher said. Genzyme has received a patent on the protein.
It is cheaper to produce transgenic goats than cows; the goat's gestation period is shorter (5 months to a cow's 9 months), and the protein is not required in huge quantities, Denniston said.
LSU's contract with Genzyme has brought LSU approximately $850,000 in research funds, and LSU's reproductive physiology laboratory will continue working with the nuclear transfer process as a tool for pharmaceuticals, agricultural applications and propagation of endangered species.
Source: This story has been adapted from a news release issued by Louisiana State
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