Membrane Merger Dynamics in Exocytosis and Endocytosis

Exocytosis releases vesicular cargo to the extracellular space and adds membrane to the cell surface, whereas endocytosis retrieves membrane and internalizes extracellular material; together, they maintain membrane homeostasis and enable rapid intercellular signaling. Super-resolution imaging has revealed that these processes are far richer than the classical "kiss-and-run vs. full-collapse" or flat-to-round schemes. Exocytosis now encompasses at least seven fusion modes with reversible pores, vesicle shrinking or enlargement, and compound or sequential compound fusion, while endocytosis proceeds mainly via modular flat→Λ→Ω→O transitions and rapid closure of preformed Ω-profiles. These dynamic transformations are orchestrated by Soluble N-ethylmaleimide-sensitive factor Attachment protein REceptors, Ca²⁺/synaptotagmin, dynamin, clathrin, and the actomyosin cortex, and their dysregulation underlies neurological, metabolic, and oncogenic disorders.