Researchers in the United States and Japan claim to have created cow embryos that cannot produce the protein responsible for bovine spongiform encephalopathy (BSE), according to a Nature News Service report. Without it, the animals should be immune to mad cow disease.
A "handful" of the BSE-free cows will be born early next year, the researchers say. The calves will be tested with a small dose of mad cow protein to see whether they are truly resistant to the disease.
The BSE-causing protein, called a prion, is present in both healthy and diseased cattle; it is only when it twists out of shape that it causes problems. When normal prion protein comes into contact with the disease-causing version it can flip into the malignant form, causing rogue prions to spread through the brain. This leads to coordination problems, behavioural changes and death.
The US and Japanese researchers aimed to bypass this problem by creating genetically engineered cows that do not produce prions at all. This means that they should be safe from small doses of diseased prions, explains James Robl, president of biotechnology firm Hematech in Sioux Falls, South Dakota, and one of the leaders of the team.
The researchers began by identifying a target sequence within the gene that encodes prion protein. They created an artificial DNA segment that inserts itself into this sequence and stops the gene functioning. This artificial DNA was injected into cow cells.
Having checked that the DNA had inserted itself into the correct place, the researchers created cloned embryos by fusing these cells with egg cells that had had their nuclei removed. Finally, they implanted the embryos into surrogate mothers.
The cows will be used for research into the possibility of engineering cattle to produce human antibodies for medical applications. Their BSE-free status will alleviate health fears over the human consumption of cow products, says Robl. BSE is related to the fatal human brain condition Creutzfeldt-Jakob disease.
But the technology seems unlikely to end up on our dinner plates, as many consumers refuse to eat genetically modified food and are opposed to animal cloning. "I think there's no question that we can make a mad-cow-free line," says Robl. "But is there a market for it? If there is we'll do it."