Circulating RNAs carry messages for plants and invertebrates. Do they do the same for us?
For decades, researchers have been finding DNA and its sister, RNA, circulating in the body, outside the safe interior of cells where these molecules do their essential work of storing and translating the code of life. The reasons for these molecular voyages have remained mysterious, but in recent years evidence has accrued that this extracellular RNA may have a different job, at least in some organisms.
RNA, best known to basic biology students for its role in translating genes into proteins, has turned out to be a surprisingly versatile and cosmopolitan molecule. Plants, roundworms, flatworms and insects use RNA to carry signals through their tissues, and perhaps further. Inspired by laboratory studies hinting that RNA may play a role in interactions between organisms, and even different species, Eric Miska, a molecular geneticist at the University of Cambridge, coined the term “social RNA”to describe the molecule’s apparent role in communication both inside and outside organisms.
Plants and the pests seeking to infect them can deploy RNA against one another. In a paper published in Science in October, researchers describe how a fungus — one responsible for both destroying crops with gray mold and producing the noble rot that flavors dessert wines — protects itself by using its own small RNA molecules to hijack the plants’ RNA defense machinery, silencing genes that would normally fight fungal infections. Discoveries like this point to a role for RNA in the arms race between plants and parasites, one of the potential instances of social RNA, Miska said. “I think it’s quite exciting, but it is early days,” Miska said. “A lot of things need to be discovered yet.”
While RNA’s role in signaling in plants and invertebrates is not fully understood, that role is clearly established. This is not the case for RNA in mammals, including humans. In these species, scientists know these molecules are traveling outside cells, but it is not yet clear whether or not they are a form of communication.
RNA has been found in a panoply of human body fluids: blood, urine, tears, cerebrospinal fluid, breast milk, amniotic fluid, seminal fluid and others. Moreover, scientists have discovered that small bits of circulating RNA can reflect particular conditions, such as the presence of a cancerous tumor or pregnancy-related disorders. “It’s like opening up a Pandora’s box,” said Xandra Breakefield, a neurogeneticist at Massachusetts General Hospital, of the discovery of circulating RNA. “We didn’t realize all these things were out there.”
Via Dr. Stefan Gruenwald