Oligodendrogenesis is not affected in MyD88-deficient mice. (A) The numbers of oligodendrocytes and OPCs in the corpus callosum (CC) of P7 Myd88^−/− and WT mice were similar. The nuclei of OPCs were identified by the expression of both transcription factors NKX-2.2 and OLIG2. (B) The cell density of OPCs in the CC was similar. (C) The cell density of oligodendrocyte-lineage cells in the CC was similar. (D) The proportion of OPCs among oligodendrocyte-lineage cells was similar, suggesting normal OPC proliferation in the developing brain of MyD88-deficient mice. n = 4 or 6 animals. (E–G) Electron micrographs of mouse spinal cord cross sections of 7–8-wk-old WT and Myd88^−/− mice. The number of myelinated axons was determined in two or three 1,600-µm² areas per animal. Myelin thickness was determined by g-ratio analysis in 225 µm² per animal. n = 4 animals. Data are mean ± 95% CI (error bars) in B, C, and D or SEM in F and G. Scale bar: 100 µm in A; 2 µm in E.