Fig 2: Schematic diagram of the distribution of Sox10. In telogen, nucleus Sox10 was mainly distributed in the bulge and germ cell cap regions; at fully developed anagen, nucleus sox10 was showed in the ORS below sebaceous glands, especially the inner layer of ORS; during catagen, Sox10 was observed in the germ capsule and epithelial strand. Light blue cell with dark blue core described mainly nuclear staining of Sox10, and only light blue cell described mainly cytoplasmic staining of Sox10. ORS, outer root sheath; IRS, inner root sheath; HG, hair germ; TAC, transit-amplifying cell; ES, epithelial strand; DP, dermal papilla cells; SG, sebaceous glands.

Fig 3: Characterization of NCC stage(A) Expected phenotypes of properly differentiated NCCs. Brightfield images of NCCs were taken on the indicated days (top panel). Arrows show growth and progression of NCC “ridges”, which start to form on day 4. Expression of NCC markers. NCCs were fixed on the indicated days and stained for SOX10 (green), TFAP2A (red), and DAPI (blue). Images were taken at two different magnifications (middle and bottom panels).(B) Appropriate seeding density. H9 cells were seeded at a density of 200,000 cell/cm2 (day 0). The next day (day 1) brightfield images were taken to show the expected density (>80% confluency).(C) Expression of SOX10 mRNA by RT-qPCR. n=4 (biological replicates), one-way ANOVA followed by Dunnett’s multiple comparisons. Graph show mean ± S.D. *p < 0.05, ****p < 0.0001.(D) Expected phenotypes of improper NCC differentiation. Brightfield images were taken on day 12. Note small size of the NCC “ridges” (red arrows left and middle images) or the formation of a single large NCC cluster (red arrow, right image), which will cause a very low differentiation efficiency. Also, note the presence of large blister-like cells/aggregates (black arrows, left and right images), the identity of which we do not know at this point.

Fig 4: Prrc2a modulates oligodendroglia fate determination, proliferation, and differentiation in vitro. a Immunostainings of Pdgfra/Olig2 or GFAP in oligosphere-derived cells 14 days postBl04-CM treatment from mice with indicated genotypes. b Quantification of the percentage of Pdgfra+Olig2+ and GFAP+ cells from mice with indicated genotypes (one-way ANOVA followed Tukey test, **P < 0.01, n = 4 each group). c Gene expressions during neurosphere to oligosphere transformation in cells 14 days post B104-CM treatment. The gene expressions were normalized to those in wild-type neural stem cells (one-way ANOVA followed Tukey test, **P < 0.01, ***P < 0.001, n = 4 per group). d Immunostainings of Pdgfra and Sox10 in spinal cord from mice with indicated genotypes at E12.5 and E14.5. e The quantification of the number of OPCs (Pdgfra and Sox10 double positive) in spinal cord from mice with indicated genotypes at E12.5 and E14.5 (one-way ANOVA followed Tukey test, *P < 0.05, **P < 0.01, ***P < 0.001, n = 6 per group). f Immunostainings of Pdgfra/Olig2/BrdU in the cultured OPCs after incubation with BrdU (50 µg/ml) for 2 h. The bar graph (g) depicts the quantification of the percentage of BrdU+ Pdgfra+ Olig2+ cells (one-way ANOVA followed Tukey test, *P < 0.05, n = 4 per group). h BrdU (50 mg/kg) was intraperitoneally injected into P6 mice. 2 h later, the mice were sacrificed and the brain sections of corpus callosum were immunostained with anti-Pdgfra and anti-Ki67 (upper panel) or anti-BrdU (bottom panel) antibodies. Arrowheads indicate the proliferating OPCs (Pdgfra and Ki67/BrdU double-positive cells). iThe quantification of the number and percentage of proliferating OPCs from mice with indicated genotypes (one-way ANOVA followed Tukey test, *P < 0.05, ***P < 0.001, Pdgfra+Ki67+: n = 6 each group; Pdgfra+BrdU+: n = 7 each group; Proliferation OPCs Pdgfra+BrdU+/Pdgfra+: n = 7 each group). j Immunostainings of O4/Olig2 and Mbp/Olig2 in oligodendrocytes after 3 days of T3 treatment. The bar graph (k) depicts the quantification of the percentage of O4+ Olig2+ and Mbp+Olig2+ cells (one-way ANOVA followed Tukey test, **P < 0.01, ***P < 0.001, n = 4 per group). l Gene expressions of T3-induced differentiated oligodendrocytes from mice with indicated genotypes (one-way ANOVA followed Tukey test, ***P < 0.001, n = 4 per group)

Fig 5: Fto transgene triggers hypomyelination. a MeRIP-qPCR analysis of Olig2 RNA in m6A peak region in Fto transgenic (Tg) and wild-type (WT) mice at 4-weeks-old (two-tailed unpaired student’s t-test, ***P < 0.001, n = 4 per group). b Prrc2a RIP-qPCR analysis of Olig2 RNA in m6A peak region in Fto transgenic (Tg) and WT mice at 4 weeks old (two-tailed unpaired student’s t-test, **P < 0.01, n = 4 per group). c Cultured OPCs from WT and Fto transgenic mice were exposed to actinomycin D (1 µg/ml), then RNA was isolated at indicated time points. RT-qPCR was performed to assess the half-lives of Olig2 mRNA. The data were presented as means ± s.e.m. and the inserted numbers (T1/2 (WT) = 73.3 ± 1.1 min; T1/2(Tg) = 66.0 ± 0.6 min) show the calculated half-times from four independent experiments. d Volcano plot of RNA-seq data showing Fto-regulated genes from brain tissue samples of 4-week-old Fto transgenic vs. control mice. e Parts of GO terms of the biological process categories enriched in DEGs from Fto transgene vs. control samples. f Relative gene expression in hippocampus from 4-week-old Fto Tg and control mice (two-tailed unpaired student’s t-test, *P < 0.05, **P < 0.01, ***P < 0.001, n = 4 per group). g Immunostainings of Pdgfra (P7), CC1/Olig2, or Sox10 (P28) in corpus callosum from mice with indicated genotypes. The quantification of Pdgfra+, CC1+ Olig2+, and Sox10+ cells were shown in (h) (two-tailed unpaired student’s t-test, **P < 0.01, ***P < 0.001, Pdgfra+: n = 6 each group; CC1+ Olig2+ cells: n = 5 per group, Sox10+ cells: n = 5 per group). i T2-weighted MRI of 4-week-old mice with indicated genotypes. j Black-gold staining of brain sections from 4-, 8-, and 32-week-old Fto Tg and control mice. k The quantification of corpus callosum width at the midline from 4-, 8-, and 32-week-old Fto Tg and control mice (two-tailed unpaired student’s t-test, *P < 0.05, **P < 0.01, 4w: n = 5 per group, 8w: n = 6 per group, 32w: n = 6 per group). l TEM analysis of the myelin fibers in the corpus callosum from mice with indicated genotypes and ages. The white arrowheads indicated the naked axons. m The percentage of myelinated axons in the corpus callosum from 4-, 8-, and 32-week-old mice with indicated genotypes (two-tailed unpaired student’s t-test, ***P < 0.001, 4w: n = 5 per group, 8w: n = 6 per group, 32w: n = 6 per group)