For a molecule of RNA, the world is a dangerous place. Unlike DNA, which can persist for millions of years in its remarkably stable, double-stranded form, RNA isn’t built to last — not even within the cell that made it. Unless it’s protectively tethered to a larger molecule, RNA can degrade in minutes or less (opens a new tab). And outside a cell? Forget about it. Voracious, RNA-destroying enzymes are everywhere, secreted by all forms of life as a defense against viruses that spell out their genetic identity in RNA code.

There is one way RNA can survive outside a cell unscathed: in a tiny, protective bubble. For decades, researchers have noticed cells releasing these bubbles of cell membrane, called extracellular vesicles (EVs), packed with degraded RNA, proteins and other molecules. But these sacs were considered little more than trash bags that whisk broken-down molecular junk out of a cell during routine decluttering.

Then, in the early 2000s, experiments led by Hadi Valadi (opens a new tab), a molecular biologist at the University of Gothenburg, revealed that the RNA inside some EVs didn’t look like trash. The cocktail of RNA sequences was considerably different from those found inside the cell, and these sequences were intact and functional (opens a new tab). When Valadi’s team exposed human cells to EVs from mouse cells, they were shocked to observe the human cells take in the RNA messages and “read” them to create functional proteins they otherwise wouldn’t have been able to make.

Valadi concluded that cells were packaging strands of RNA into the vesicles specifically to communicate with one another. “If I have been outside and see that it’s raining,” he said, “I can tell you: If you go out, take an umbrella with you.” In a similar way, he suggested, a cell could warn its neighbors about exposure to a pathogen or noxious chemical before they encountered the danger themselves.