Young bulls were genetically engineered to be prion-free.
By Elizabeth Weise, USA TODAY
Scientists at a South Dakota biotech company have genetically engineered cattle that appear to be resistant to mad cow disease, a paper published in the Monday issue of the journal Nature Biotechnology reports.
Although similar genetic engineering had been done in mice, this is the first time it has been accomplished in cattle.
The team of scientists first genetically engineered a cell line in which the gene that produces the infectious protein that cause mad cow disease — prions — was disabled. They then used those cells to clone 12 bulls on the theory that the genetic engineering will prevent them from making the protein that, when "misfolded," causes prion diseases such as mad cow.
Those 12 bulls are now two years old and so far appear to be perfectly normal, says James Robl,. president of Hematech Inc.. in Sioux Falls, S.D., a biotech firm owned by the pharmaceutical division of Japanese brewing giant Kirin..
Although misfolded prions are not alive in the conventional sense, they can cause other proteins they come in contact with to misfold as well, creating the holes in the brain that characterize bovine spongiform encephalopathy (BSE, or spongy brain disease) in cattle and variant Creutzfeldt-Jakob. disease in humans and other mammals.
When scientists took brain cells from the resistant cattle and mixed them with prions in a test tube, the cattle brain cells did not misfold. Brain cells from normal cattle did. "That's a pretty good indication that they will not be able to contract the disease, nor would they be able to pass the disease on," Robl says.
Researchers have now injected mad cow-infected brain cells into the brains of some of the resistant cattle to see whether they develop mad cow disease.
"In one and a half years we'll have an answer," because prion diseases are so slow to develop, says Jürgen Richt,. a co-author on the paper and veterinary microbiologist at the National Animal Disease Center in Ames, Iowa.
The bulls appear to be developmentally and reproductively normal and should be able to breed true, creating a line of mad cow-resistant cattle, says Robl. Because they are still adolescents, they have not yet been bred, but their semen appears to be normal.
Because the animals are only two years old it's not certain if they might begin to show signs of difference as they live out their natural lifespan, which in cattle is about 15 years, says Richt.
In general the animals are no different from regular cattle, he says.
"They're more friendly than the other because they have been bottle fed and they had a lot of human interaction when they were calves. But they do seem more nervous." However that could simply be that the original bull they were cloned had a nervous disposition, he says.
Some scientists have argued that because the gene for creating prion proteins is so common in mammals and hasn't mutated, it must have some critical function that researchers don't yet know about.
Whether it's that the gene actually isn't important, or if there are redundant systems within the genome that take over when it's gone isn't known, Richt says.
At least for now the cattle are not meant for human consumption, says Robl. Instead, if they prove incapable of getting mad cow disease, they could be used to produce products important to industry, such as blood serum used in making pharmaceuticals and collagen for cosmetics. Because of concerns about mad cow disease, many companies have been scrambling to find cost-effective replacements for these, often with little success.
George Seidel, a expert on cattle reproduction technologies at Colorado State University in Ft. Collins, CO, calls the research "elegant" but with mad cow disease so rare in North America, he says it's more a niche market.
"There are much easier ways to deal with mad cow than to make transgenic cattle," he says.
source:
http://www.usatoday.com/tech/science/2007-01-01-
genetic-cattle_x.htm?POE=TECISVA
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