When Phillip Zamore finished his postdoctoral fellowship, he had a plan: he would spend his career using fly genetics to answer questions in biochemistry. But the results of a single experiment derailed those plans and propelled his research in a new direction.
"One afternoon in 1999 my whole life changed," says Zamore, now at the University of Massachusetts Medical School. "In that one moment, I used up my entire allotment of scientific serendipity."
It began with a friendly argument in a journal club. He and fellow postdoc Tom Tuschl (now an HHMI investigator at the Rockefeller University) had been reading about a type of gene regulation just discovered in flatworms and disagreed about how to re-create the phenomenon in a test tube. "As I listened to Tom, I became convinced that he wasn't proposing the right experimental approach and I told him that," Zamore says. "Tom turned it back on me and said, 'Well, how would you do it?'"
The dispute had been provoked by a report that double-stranded RNA could shut off genes with matching sequences, a finding that later earned HHMI Investigator Craig Mello, also at the University of Massachusetts, and Andrew Fire of Stanford University the 2006 Nobel Prize in Physiology or Medicine. RNA is most often thought of as a cellular messenger that relays information from genes to the machinery that produces proteins. But it was becoming increasingly apparent that RNA was much more versatile and had the ability to silence genes, a property called RNA interference (RNAi).
Zamore suggested that Tuschl use components from fly cells to find out whether double-stranded RNA molecules could silence a gene in a test tube the way they did in worms. The two decided to test the idea in their Whitehead Institute lab and, surprisingly, it worked. "At that moment, we knew everything we had planned to do in our labs as faculty members was never going to happen," Zamore says. "Once you can [re-create an activity outside the cell], it ceases to be an abstraction."
Researchers immediately recognized the power of RNAi as a research tool. It was quickly put to use silencing genes one by one to determine the function of the proteins they produced. Today, researchers are also investigating the therapeutic power of RNAi, testing its ability to block the action of genes that have gone awry in diseases such as macular degeneration, hepatitis, and cancer.
Zamore and Tuschl went on to show how short segments of RNA act as guides during the RNAi process, ensuring that the appropriate gene is silenced. Since then, Zamore has devoted his research to understanding how RNA silences genes.
Now Zamore is comparing how RNAi works in flies and humans. His team has found that small RNAs—both the small interfering RNAs (siRNAs) that trigger RNAi and another class of small RNAs called microRNAs—contain many layers of information that guide the gene-silencing process. The RNA sequence on the molecule specifies not only which gene will be silenced but also how that silencing will occur. Understanding exactly how the RNA code spells out these instructions has changed the way scientists use RNAi.
Zamore's team also discovered that microRNAs and siRNA are produced by the same enzyme. After that, Zamore said that he and other scientists studying RNAi were convinced that all small RNAs found in the cell were produced when the enzyme Dicer chopped larger RNA into smaller pieces. Then they found that a newly discovered class of small RNAs—called piwi-interacting RNAs (piRNAs) because they associate with Piwi proteins—proved that dogma wrong. Piwi proteins are important in reproductive cells like eggs and sperm.
"We don't know where they come from but we know Dicer isn't involved," Zamore said of work in his lab. "We don't understand them at all. It's perfect: any piece of information you get about them is worth having because it converts to knowledge."
Zamore says this pattern of supposed scientific understanding being overturned by a new, dogma-changing discovery highlights the challenge of training students. They need to be both extremely knowledgeable and suspicious of "fact." "One of the great pleasures we have as scientists is discovering that what we think we know is wrong," Zamore says.
After working on basic science, he also finds pleasure working out problems that benefit people. Zamore is actively engaged in exploring RNAi as a potential treatment for Huntington's disease, a fatal illness caused by one defective gene. Zamore is targeting siRNAs to turn off the defective gene in mouse models of Huntington's disease. He began the work after a physician colleague asked for his help in developing a treatment that shuts down the Huntington's gene. "I'm interested in the practical applications of these scientific discoveries, and I'm now at that age where I see people I care about beginning to decline, so I want to cure disease," Zamore says.