Summary
Phase separation is a popular idea to explain how cells organize their content, but researchers have recently raised doubts about how often it occurs in cells and how important it is to them. Phase separation occurs when proteins or other molecules condense into liquid droplets that resemble the bulbs that form in salad dressing. Some scientists have suggested that the process is commonplace in cells and produces and maintains organelles that do not have a membrane, such as the nucleolus, Cajal bodies, and stress beads. Evidence also suggests that faulty phase separation promotes diseases such as cancer and some neurological diseases. But in a recent review, the field has been put to the point of relying on qualitative rather than quantitative evidence, over-interpreting imaging studies, relying on ambiguous techniques to demonstrate phase separation, and other failures.