Figure 7. Spontaneous Ca2+ transients in OPCs progressively decline as they differentiate into myelinating oligodendrocytes.

a, Representative images showing diverse Ca²⁺ dynamics within different OPCs. Cyan arrowhead indicates PDGFRα⁺ perivascular fibroblasts, which were used as landmarks to register images across different time points. The OPC highlighted in green persisted throughout the recording. The OPC highlighted in red became undetectable at Day 19, while a nearby OPC (cyan) extended its processes (yellow arrowhead) to the space now left unoccupied by the absent OPC. A similar phenomenon was also seen with the neighboring OPC highlighted in green on Day 29 (yellow arrowhead). b, Heatmaps showing the Ca²⁺ activity of the OPC highlighted in green on Day 1, 19 and 29. c, Heatmaps showing the Ca²⁺ activity of the OPC highlighted in red on Day 1, 13, 15, 17 and 19. The red arrowhead indicates the position of the cell body of the disappearing OPC (red) on Day 17. d, Quantification of the OPC Ca²⁺ event frequency, amplitude, and duration over time (n = 9 cells from 6 mice). e, Schematic illustration of the dual longitudinal imaging experiment using both 2P to detect Ca²⁺ changes and SCoRe imaging to detect changes in myelin (see Methods). f, An example of an OPC (blue) with declining activity, and the local myelin pattern surrounding its cell body on the day the OPC became undetectable (Day 0, green), and 16 days after the disappearance (Day 16, magenta). Yellow arrowheads indicate the new myelin found 16 days after the disappearance of the OPC. g, Quantification of f. n = 18 cells (7 stable and 11 declining) from 4 mice.