Fig. 2: VAMP2/3-mediated exocytosis occurs preferentially in myelin sheaths.

a Top: diagram depicting oligodendrocyte differentiation in culture; bottom: transfection of oligodendrocyte precursors with pHluorin-tagged VAMP2 or VAMP3 to visualize exocytosis. Created with BioRender.com. b Representative image of a pre-myelinating oligodendrocyte expressing VAMP2-pHluorin. Montage shows an exocytotic event over time, and the corresponding plot of intensity vs. time shows the characteristic fluorescent increase and decay (fitted by the green dotted line). c Frequency of VAMP2- or VAMP3-pHluorin events localized to the soma or to the processes/sheets in cultured rat oligodendrocyte precursors (gray), pre-myelinating (yellow), or mature oligodendrocytes (magenta). Each pair of points connected by a line shows events for one cell. See Supplementary Table 1 for average event frequencies ± SEM. Statistical significance was determined using the mean of each biologically independent replicate (n = 3) by an ordinary one-way ANOVA with Tukey correction for multiple comparisons. Source data are provided in the Source Data file. d Top: representative images of oligodendrocyte-lineage cells expressing VAMP2-pHluorin in the larval zebrafish spinal cord. Bottom: examples of VAMP2 exocytotic events within oligodendrocyte processes and sheaths. e Frequency of VAMP2- or VAMP3-pHluorin events in oligodendrocytes of the zebrafish spinal cord localized to the soma or to the processes/sheaths in precursors/pre-myelinating (yellow), early myelinating (pale pink), or mature oligodendrocytes (magenta). Each pair of points connected by a line shows events for one cell (typically from one fish). See Supplementary Table 2 for average event frequencies ± SEM. Statistical significance was determined by an ordinary one-way ANOVA with Tukey correction for multiple comparisons. f Spatial frequency of VAMP2 and VAMP3 exocytotic events within myelin sheaths, where the paranode is defined as 3 μm from the sheath edge⁶⁸. The measured frequencies at paranodes (mean ± SEM) were (50 ± 22.4)% for VAMP2 and (24.9 ± 12.7)% for VAMP3, each with n = 25 sheaths from five experiments. See Supplementary Table 3.