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Abstract

Membrane fusion is a process used by cells in a number of seemingly unrelated processes. In cells, it is regulated by a set of fusion proteins present on the opposing fusing membranes and, depending on environmental cues and system specifics, membrane fusion can transit through certain fusion intermediates that are occasionally shared by different fusion events. Due to the high complexity and dynamics, membrane fusion is usually studied using reconstituted membrane models and fusion assays. Using these systems and a combination of fluorescent probes, it is possible to assign changes in fluorescence to the fusion reaction and to detect intermediates. Here, we critically review the most commonly used membrane models and how they are used in resolving and quantifying fusion, comparing their main features and limitations. Depending on the model and assays, it is possible to quantify fusion efficiency under different conditions, extract mechanistic and kinetic parameters from fusion reactions, determine the role of accessory factors and the molecular parameters that regulate fusion.