Biological macromolecules such as proteins and nucleic acids undergo phase separation to form biomolecular condensates, achieving precise compartmentalization within cells and spatial-temporal regulation of various biological functions. Unlike membrane-bound organelles, biomolecular condensates lack a biological membrane but instead rely on complex multivalent interactions among molecules to dynamically separate them from the surrounding environment. These condensates exhibit both relative stability and intricate structural features rich in dynamic changes. They possess unique physical properties akin to liquids, such as fluidity, fusion, and fission capabilities. The introduction of phase separation has provided a novel and insightful perspective for deeply understanding the molecular mechanisms in biology. Recent studies have uncovered the vital biological roles played by biomolecular phase separation. Phase separation can be classified into three groupls based on their occurance in different cellular contexts: universally present phase separation, environmentally induced phase separation, and cell-type-specific phase seapration. Universally present phase separation encompasses fundamental cellular processes including chromatin organization, gene expression regulation, RNA processing and maturation, and protein translation control. Enviromentally induced phase separation plays a crucial role in cell’s response to external stimuli, demonstrating its importance in maintaining cellular homeostasis and adaptability in response to changing physiological conditions. Additionally, cell-type-specific phase separation contribute significantly in mediating cell-cell connections and modulating synaptic structures and functions. This review traces the research advancements of research in this field, from the early investigations into membraneless organelles to the more recent developments in phase separation. It begins with the early research history of membrane-less organelles prior to the advent of phase separation theory, aiming to trace the research trajectory before the introduction of phase separation theory. Then it delves into the molecular mechanism of phase separation, particularly those mediated by tandem repeat domains and intrinsically disordered regions, with emphasis on the correlation between their physicochemical properties and the functional roles of condensates. Subsequently, the focuses shifts to the diverse biological functions of biomolecular phase separation, emphasizing their functional diversity and specificity in diverse cellular environments. Finally, the review concludes by identifying pressing questions within the field of biomolecular phase separation and outlining promising avenues for future research. These include further analysis of membraneless organelles compositions, the exploration of fundamental theories governing phase separation, the elucidation of the relationships between condensates and cellular functions, the depiction of the intricate internal structure of membraneless organelles and the interactions between them, and the development of novel technologies to further our understanding of this fascinating and complex biological phenomenon. Additionally, research should focus on the investigation of links between phase separation and disease as well as therapeutic approaches targeting phase separation mechanisms. As research progresses, the continued investigation of membraneless organelles is poised to advance our knowledge of cellular biology and inspire new therapeutic strategies. © 2024 Chinese Academy of Sciences. All rights reserved.
