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Mean squared displacement as an identifier in classification of membrane fusion events

Multivesicular endosomes (MVEs) are intracellular membrane-bound compartments containing exosomes that are used to communicate with neighboring cells upon MVE fusion events with the plasma membrane. While regulation and kinetics of exosome release were not previously well characterized, the use of Total Internal Reflection Fluorescence (TIRF) microscopy and fluorescent probes allows for real-time imaging and tracking of single membrane fusion events. Fusion events were measured in A549 cells held at 23-37°C. Events were identified using an automated detection algorithm and the mean squared displacement (MSD) of events was calculated as a measurement of motion. Fusion events are shown to have a significantly lower MSD as opposed to diffusing vesicles across cells. These findings can be used in future research of MVE fusion events and advance knowledge on their classification and analysis.