Tag: miRNA

Natural RNA, Transgenic DNA, and What They Actually Mean for Our Food

By Veronique Greenwood | January 13, 2012 2:33 pm

rice

Earlier this week, food columnist Ari LeVaux set off a storm of media reaction with a piece with this premise: tiny plant RNAs, recently discovered to survive digestion and alter host gene expression, are a major reason why genetically modified foods should be considered dangerous. For anyone familiar with the paper he referred to, or with molecular biology in general, the article was full of conflation and sloppy logic, and even as it became the most-emailed story on TheAtlantic.com, where it was published, biology bloggers and science writers were pointing out its significant flaws. To his credit, LeVaux revised the article to fix many (though not all) of the errors concerning genetics; the new version appeared yesterday at AlterNet and today replaced his original piece at The Atlantic.

So what did LeVaux get so wrong, and, once all of the wheat was sorted from the chaff, was there anything to what he was trying to say?

At the heart of the fracas is LeVaux’s claim that a class of molecules called miRNA is a reason to fear GMOs specifically, more than any other food plant or animal. miRNA, which is short for microRNA, is a class of molecules that perform various tasks in plants and animals. They were first discovered about twenty years ago, in nematode worms, and they regulate gene expression by binding the messenger RNA involved in translating a gene into a protein. The messenger RNA carries the “message” of the DNA’s sequence to a group of enzymes that translate it into the amino acid sequence of a protein. But if a miRNA binds to a messenger RNA, the message is destroyed, and the protein is never made. Thus, miRNA can be a powerful tool for preventing the expression of genes. In fact, that is what’s made it such an important lab tool in recent years: it allows researchers to knock down the expression of genes without physically removing them from an organism’s genome.

In the paper that LeVaux pegged his article on, Nanjing University researchers found that miRNAs usually seen in rice were circulating in the blood of humans, and that mice fed rice had the miRNA in their blood as well. That particular miRNA, in its native context, regulates plant development. When the researchers added it to human cells, it appeared to bind to the messenger RNA of a gene involved in removing cholesterol from the blood. Previous papers had found that plants have plenty of miRNA floating around in them [pdf] (as does just about everything we eat, since plants and animals make them by the thousands), but having them show up whole and unmolested in blood, apparently after digestion, was a new and very intriguing discovery.

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