Imaging Techniques for the Study of Protein Condensates and Filaments and Their Applications.

Protein condensates and filaments are both intracellular structures characterized by their ability to facilitate specific biological functions. Their formation is primarily driven by phase separation, which can be elucidated by fluorescence microscopy or electron microscopy. Here we summarize the main studies on protein condensates and filaments organized according to the techniques used, including fluorescence methods like localization screening, fluorescence co-localization spectroscopy, methods based on photobleaching, super-resolution imaging, and electron methods including negative-stain electron microscopy and cryo-EM. We also discuss correlative light/electron microscopy (CLEM), which integrates fluorescence microscopy and electron microscopy to provide complementary insights. Collectively, these methods offer temporal and spatial insights into investigating the phase separation of protein condensates and filaments, and promote the discovery of unexplored structures and their yet-to-be-characterized biological roles.