US scientists Victor Ambros and Gary Ruvkun won the Nobel Prize in Medicine on Monday for their discovery of microRNA and its role in how genes are regulated, solving a decades-old mystery, the Nobel Assembly at Sweden’s Karolinska Institute said.If gene regulation goes awry, it can lead to serious diseases such as cancer, diabetes, or autoimmune illnesses.“Their groundbreaking discovery revealed a completely new principle of gene regulation that turned out to be essential for multicellular organisms, including humans,” the jury said.Ruvkun said he was shocked to win the prestigious prize.“It’s quite a sea change,” the 72-year-old professor at Harvard Medical School told AFP after receiving the news in a call from the prize committee in the early hours of Monday.The Nobel committee failed to reach Ambros by telephone to give him the news. He heard it instead from a reporter who called.“Wow, that’s incredible! I didn’t know that,” the 70-year-old professor at the University of Massachusetts medical school said, adding: “Good. Wonderful.”Collaborating but working separately, Ruvkun and Ambros conducted research on a 1mm roundworm, C. elegans, to determine why cell mutations occurred and when.They discovered microRNA, a new class of tiny RNA molecules that play a crucial role in gene regulation, which in turn allows each cell to select only relevant instructions.Their findings were published in two articles in 1993. – AFP