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. 2022 May 11;11:e77019. doi: 10.7554/eLife.77019

Figure 2. Comparison of the protein composition of human and mouse central nervous system (CNS) myelin.

(a) Silver-stained SDS-PAGE (0.9 μg protein load) of myelin purified from human normal-appearing white matter and C57Bl/6N mouse brains. Note that the band patterns are roughly comparable but not identical. Gel shows n = 3 biological replicates per species. (b) Venn diagram comparing 65 selected known myelin proteins identified by MSE and UDMSE in myelin purified from human white matter (blue) and C57Bl/6N mouse brains (orange) as recently established using the same methods (Jahn et al., 2020). Note that most known myelin proteins were identified in myelin of both species, while multiple myelin proteins were identified in myelin of only one species. (c, d) Scatter plots of the log2-transformed relative abundance of proteins identified in human myelin by MSE (c) or UDMSE (d) plotted against their relative abundance in mouse myelin as recently established using the same methods (Jahn et al., 2020). Correlation coefficients (r) were calculated for all proteins identified in human myelin (gray) or known myelin proteins (blue). Regression lines serve as navigational mean. (e) Heatmap comparing the relative abundance of known myelin proteins identified by MSE in human myelin with that in mouse myelin according to the same method (Jahn et al., 2020). Each horizontal line displays the fold change (FC) of a protein in five biological replicates (M1–M5) of human myelin compared to its average abundance in CNS myelin of mice plotted on a log2-color scale. Note that several proteins display higher abundance in human (blue) or mouse (orange) myelin, while others show approximately similar relative abundance (white). (f) Immunoblot analysis confirms comparatively higher abundance in human myelin of PMP2, CRYAB, CD9, and PADI2, approximately equal abundance of PLP, CNP, SEPTIN2, SEPTIN7, and SEPTIN8, and comparatively higher abundance in mouse myelin of TSPAN2, GPM6B, GJC3, ASPA, MOBP, IGSF8, SIRT2, CLDN11, CA2, MAG, and MOG, as implied by the MSE analysis. Note that immunoblot-based comparison of the relative abundance of MBP across species is not straightforward because MBP displays one dominant isoform (18.5 kDa) in human CNS myelin but three main isoforms (14.0, 17.0, and 18.5 kDa) in mouse CNS myelin due to species-dependent alternative splicing. Blots show n = 3 biological replicates per species. For immunohistochemistry detecting PMP2 in human optic nerve cross sections, see Figure 2—figure supplement 1.

Figure 2—source data 1. Labeled original immunoblots.

Figure 2.

Figure 2—figure supplement 1. Detection of PMP2 in human central nervous system (CNS) myelin by immunoblot and immunohistochemistry.

Figure 2—figure supplement 1.

(a) Immunoblot analysis of myelin purified from human normal-appearing white matter (CNS), C57Bl/6N mouse brains (CNS), and C57Bl/6N mouse sciatic nerves (peripheral nervous system [PNS]) using antibodies specific for PMP2. Blot shows two biological replicates per condition. Note that PMP2 was readily detected in human CNS myelin and mouse PNS myelin but not in mouse CNS myelin. SIRT2 was detected as a control. (b) Confocal micrograph of immunohistochemistry detecting PMP2 (green) and TUJ1 (magenta) in paraffin-embedded cross-sectioned optic nerves of a human subject. Note that PMP2 labels myelin sheaths (arrowheads), while TUJ1 labels neuron-specific beta-III tubulin, that is, axonal microtubules in this cross section. Nuclear staining (DAPI) is in blue. Shown is one biological replicate representative of three biological replicates. Scale bar, 20 µm.