生物谷報道：最新的Nature Biotechnology報道采用轉基因技術，讓奶牛產生蛋白質含量更高的牛奶,，這篇報道為今后高等生物的轉基因食品研究開創(chuàng)了先河,。

Protein-rich milk from cloned, genetically modified cows could cut cheese-making costs. Dairy manufacturers would need less milk to make cheddar firm and ice cream creamy.

Two years old and living in New Zealand, the clones produce about 13 percent more milk protein than normal cows. They carry extra copies of the genes for two types of the protein casein, key for cheese and yoghurt manufacture1.

"The proteins are important. They allow milk to have a high protein content, but to remain watery," says study leader Götz Laible of New Zealand biotech company AgResearch. His team must now find out whether the increase improves milk's calcium content or its ability to coagulate before they seek approval to sell the clones to dairy farmers.

Most scientists believe that milk from cloned cows is no different to normal milk. But they are less certain about the safety of milk from genetically modified cows.

It depends on which gene has been added to the cow's DNA, says animal reproduction specialist Will Eyestone of Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg. For instance, some cows are altered to produce pharmaceutical products. A drug could pose a health risk if it seeps into the milk.

Laible's cows might be less worrisome - they don't produce foreign proteins, just more of natural ones. "You're upping the nutrient value," says Roberts. "This is unlikely to be a problem." But further testing will have to confirm the milk's safety, he adds.

"A lot of cloned milk is being poured down the drain," says Michael Roberts, an animal biotechnologist at the University of Missouri-Columbia. Food products from transgenic and cloned animals, and their progeny, are not legally available in many parts of the world.

The US Food and Drug Administration has yet to issue its guidelines on the matter. Until then, companies producing cloned cows have volunteered not to sell their milk.

Laible created the high-output cows by inserting casein genes into the DNA of a cell taken from the 60-day old fetus of a female dairy cow. The researchers then transferred the nucleus into unfertilized cow eggs. Of the 126 modified embryos, 11 cows survived until after weaning.

 
References
Brophy, B. et al. Cloned transgenic cattle produce milk with higher levels of ß-casein and k-casein. Nature Biotechnology, published online, doi:10.1038/nbt783 (2003). |Article|