Fig. 2: Oligodendrocyte calcium signaling is required for normal sheath length and myelin morphology.
From: Oligodendrocyte calcium signaling promotes actin-dependent myelin sheath extension
a Transmission electron microscopy (TEM) of WT (left micrograph) or OL-CalEx (right three micrographs) of P60 mouse optic nerve cross sections, highlighting examples of outfoldings that reach extreme lengths. Scale bar, 1 μm. b Quantification of percentages of myelin sheaths with observed outfoldings at P21 and P60 timepoints in a. Average ± SEM; P21, N = 4 WT and N = 4 OL-CalEx; P60, WT N = 5, OL-CalEx N = 4. Statistical significance determined by unpaired, two-tailed Student’s t test; *p = 0.01, **p = 0.0045. c Quantification of percentages of myelin sheaths with observed outfoldings greater than 2x the diameter of the axon (which we refer to as long outfoldings) at P21 and P60 timepoints. Average ± SEM; P21, N = 4; P60, WT N = 5, OL-CalEx N = 5. Statistical significance determined by unpaired, two-tailed Student’s t test; **p = 0.0044, ***p = 0.0001. Note in b, c that the actual percentage of sheaths with outfoldings somewhere along their length is much higher than these numbers, which only visualize a small fraction of each sheath (see “Methods” section). d 3-dimensional reconstruction of two proximal myelin outfoldings (top, blue; bottom, purple) and their respective axons (orange) from serial sectioning scanning electron microscopy (3DSEM) of P21 OL-CalEx optic nerve. e Example (left) colorized and (right) raw scanning EM z planes through 3D reconstructions of both outfoldings. Dotted lines in d correspond to four numbered example z-planes through each outfolding. f Quantification of total myelin area from P60 TEM in Fig. 1e. Average ± SEM, WT N = 5, OL-CalEx N = 4; n.s., not significant. g Epifluorescence microscopy of P21 WT and OL-CalEx mouse whole-mount spinal cords with AAV- mediated sparse labeling of oligodendrocytes (myelin basic promoter driven EGFP). Scale bar, 100 μm. h Quantification of myelin sheath (internode) length from spinal cords in g. Average ± SEM, N = 7. Statistical significance determined by unpaired, two-tailed Student’s t test; **p = 0.0016.
