A longstanding mystery in biology is how the millions of molecules bumping around in a cell “find” one another and organize into functional structures. So it was a big surprise in 2008 when participants in the Marine Biological Laboratory physiology course realized that simple phase separations—like oil separating from water—may be one important way to create order inside a cell.
While not without controversy, this idea has taken cell biology by storm. In the past decade, scientists have watched protein and RNA molecules condensing into droplets, or membrane-free condensates, in many kinds of cells, from bacterial to human. They have also noted that the same proteins that form liquid droplets in healthy cells can “solidify” in the context of disease, such as neurodegenerative disorders. But what makes certain molecules come together in the same droplet, while others are excluded, has been unexplained.
This week in Science, a team shows for the first time that RNA molecules recognize one another to condense into the same droplet due to specific 3-D shapes that the molecules assume. The study’s senior author, Amy S. Gladfelter of the University of North Carolina, Chapel Hill began this work at the MBL as part of the HHMI/HCIA Summer Institute, a group of 70 scientists who explored this emerging paradigm of cellular organization over five summers of intense, synergistic research.