Summary
Phase separation is a popular idea to explain how cells organize their contents, but researchers have recently raised doubts about how often it occurs in cells and how important it is for them. Phase separation occurs when proteins or other molecules condense into liquid droplets that resemble the globules of oil that form in salad dressing. Some scientists have proposed that the process is commonplace in cells and produces and maintains organelles that lack a membrane, such as the nucleolus, Cajal bodies, and stress granules. Evidence also suggests faulty phase separation promotes illnesses such as cancer and some neurological diseases. But a recent review took the field to task for relying on qualitative rather than quantitative evidence, overinterpreting imaging studies, relying on equivocal techniques to demonstrate phase separation, and other failings.