(A–E) Quantification of CNS pathology as summarized in main Figure 1A. Electron micrographs of optic nerves were evaluated for the indicated pathologies. Note that myelin outfoldings are common to all three mutants. n=4 mice per genotype; age P75; one-way ANOVA with Bonferroni’s multiple comparisons test comparing to WT. p-values are as follows: (A) WT vs. Cnpnull p=0.002, WT vs. Magnull p=0.02, WT vs. Plp1null p=0.002; (B) WT vs. Cnpnull p=0.11, WT vs. Magnull p=0.02, WT vs. Plp1null p<0.001; (C) WT vs. Cnpnullp<0.001, WT vs. Magnull p<0.001, WT vs. Plp1null p=0.56; (D) WT vs. Cnpnull p<0.001, WT vs. Magnull p>0.999, WT vs. Plp1null p=0.37; (E) WT vs. Cnpnull p=0.22, WT vs. Magnull p>0.999, WT vs. Plp1null p=0.0012. (F) Diminishment of myelin septins in models of myelin-related pathology according to label-free proteomics. Myelin was purified from the brains of the indicated mutants and littermate controls, and analyzed by quantitative mass spectrometry. Given is the abundance in myelin of SEPT2, SEPT4, SEPT7, SEPT8 relative to their respective littermate controls. Note that the abundance in myelin of SEPT4, SEPT7, and SEPT8, was significantly reduced in all analyzed mutants. The diminishment in myelin of SEPT2 was significant in Cnpnulland Plp1nullmice and at the border of significance in Magnullmice. See Figure 1—source data 1 for the entire dataset. n=3 mice per genotype; age P75; unpaired two-tailed t-test; p-values are as follows: SEPT2: p=0.012 (Cnpnull), p=0.0614 (Magnull), p=0.013 (Plp1null); SEPT4: p<0.001 (Cnpnull), p=0.002 (Magnull), p<0.001 (Plp1null); SEPT7: p<0.001 (Cnpnull), p=0.0114 (Magnull), p=0.009 (Plp1null); SEPT8: p=0.007 (Cnpnull) p=0.011 (Magnull) p=0.011 (Plp1null). (G–I) Immunoblotting validates the diminished abundance of septins (SEPT2, SEPT4, SEPT7, SEPT8) in CNS myelin of all three models. Genotypes and equal loading were controlled by immunoblotting. Blots are representative of 3 animals per genotype. (J–M) Abundance of septin-mRNAs in models of myelin-related pathology. The abundance of the indicated mRNAs in a myelin-rich white matter tract (corpus callosum) of the indicated models was determined by qRT-PCR. The abundance of Sept2, Sept7, and Sept8 mRNA was unaltered in all models (J, L, M). The abundance of Sept4 was moderately reduced in Cnpnull and Magnull corpus callosi (K). Corpus callosi of n=4 animals per genotype were analyzed. One-way ANOVA with Bonferroni’s multiple comparison test comparing to WT. (J) WT vs. Cnpnull p=0.0767, WT vs. Magnull p=0.3661, WT vs. Plp1null p> 0.9999; (K) WT vs. Cnpnull p=0.006, WT vs. Magnull p=0.0014, WT vs. Plp1null p=0.175; (L) WT vs. Cnpnull p=0.45, WT vs. Magnull, p>0.999, WT vs. Plp1null p=0.085; (M) WT vs. Cnpnull p>0.999, WT vs. Magnull p>0.999, WT vs. Plp1null p=0.14.