CD63-pHluorin fusion events are derived from MVBs. (a) Left three panels: live imaging of fusion events (indicated by white arrows) over a time course of 12 s onto one cell before the event (left), at the start of the event (middle), and right before fixation of the cell (3). Right: inset showing a magnification of the localized sudden increase in fluorescence at the PM (highlighted by a dashed line square) right before fixation. (b) Left: correlation of light microscopy signal of a fusion event observed by live imaging with EM pictures of the first section of the cell facing the coverslip (low magnification). Right: correlation of light microscopy signal with the first slice of the electron tomographic reconstruction of the first section of the cell facing the coverslip. The orange circle indicates the error range (167 nm) of the correlation performed by eC-CLEM. (c) 3D model of the electron tomographic reconstruction. The ER is depicted in light violet. Dense compartments are depicted in brown. The structure of interest is depicted in red and orange. (d) Bottom side view of the 3D model of the compartment of interest in its surroundings. The white arrow indicates the opening of the MVB where ILVs are released. (e) 3D model showing the MVB isolated from its environment. ILVs secreted through the opening of the MVB are depicted in white. (f) Top view of the secretory profile of the MVB that correlates with the fluorescence burst of the CD63-pHluorin fusion event.