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Less is more

作者:申屠撷    发布时间:2019-03-07 11:17:04    

By Andy Coghlan GIVE pigs a magic slug of DNA and they grow big enough to go to market earlier and on less food. And they’ll even churn out less manure. A farmer’s godsend? Perhaps, but given the current furore over agricultural biotechnology, the treatment is bound to be controversial. Robert Schwartz from Baylor College of Medicine in Houston and his colleagues treated three-week-old piglets with a package of DNA that boosted the production of natural pig growth hormone. Two months later, the piglets were almost 40 per cent heavier than untreated piglets. And it took 20 per cent less fodder to add each kilogram of weight to the treated pigs. “You get them ready for market two weeks earlier, and on 20 to 25 per cent less food,” says Schwartz. The key to this miraculous growth spurt is a souped-up version of GHRH. Normally produced by the hypothalamus in the brain, GHRH tells the pituitary gland to make pig growth hormone. Injecting either growth hormone or GHRH is impractical because they break down too quickly. “GHRH is degraded in 12 minutes in the pig,” says Schwartz. So his team has tinkered with the sequence of the pig GHRH gene to make it produce a hardier hormone. The researchers eventually hit upon a version that resists breakdown by pig enzymes, and binds five times as tightly as its natural counterpart to the molecular receptor in the pituitary that activates growth hormone production. The researchers packaged the gene inside a loop of bacterial DNA called a plasmid and linked it to a sequence of promoter DNA that would activate GHRH production only in muscle cells, but then drive the gene harder than its natural promoter. Finally, they delivered mild electric shocks to the piglets’ leg muscles as the plasmids were injected. “This puts little pores in the membrane of cells, and spreads the plasmid uniformly throughout the muscle,” says Schwartz. So 5000 times as many copies of the gene were introduced into the animals’ muscle cells, he says. Schwartz acknowledges that many safety tests will need to be done before European consumers are satisfied that pork from such pigs is free of hormone residues and safe to eat. “We’ll be testing animal safety and human safety,” he says. He says that the animals grew perfectly normally and showed no signs of distress. However, Ben Mepham, director of the Centre for Applied Bioethics at the University of Nottingham, fears that the treatment might cause dangerous immunological reactions in the animals. “There are a lot of things they haven’t looked at, and you need a whole battery of tests to assess the welfare of the animals,” he says. Schwartz is also working with Marta Fiorotto and her colleagues at the Children’s Nutrition Research Center, also at Baylor, to develop human applications of the technique. It might be possible to build up muscle in elderly and AIDS patients,

 

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