Figure 4. ERK2 is important for the translation of MBP but is dispensable for its transcription during remyelination. Immunostaining with antibodies against PLP (A), MBP (B), and MOG (C) demonstrates a selective deficit in MBP expression in the lesion area of corpus callosum from Erk2 CKO mice at 7 dpl compared with control littermates. D, Colabeling with antibodies against OLIG2 and MBP along the lesion edge shows appropriate localization of MBP to the OL processes in both control and Erk2 CKO mice. E, Quantification confirms a significant decrease in the percentage of the lesion area containing MBP immunopositivity in the Erk2 CKO mice, while no significant differences between control (n = 4) and mutant (n = 3) mice were found for PLP or MOG. F, Immunostaining demonstrates similar numbers of CC1+ OLs in lesioned corpus callosum from control and Erk2 CKO mice suggesting that OPC differentiation is unaffected. G, In situ hybridization shows comparable levels of Mbp mRNA from control and Erk2 CKO mice at 7 dpl. H, Quantification demonstrates no significant difference in the percentage of the lesion area containing Mbp mRNA between Erk2 CKO (n = 3) and controls (n = 3). I, High-resolution imaging of in situ hybridization for Mbp with cresyl violet counterstaining shows proper Mbp mRNA localization in Erk2 CKO mice. J, Quantitative RT-PCR confirms comparable levels of Mbp, Plp, Mrf, and Olig1 mRNA in microdissected lesions from Erk2 CKO and control littermates. K, Representative graph showing absorbance at 260 nm from fractions collected following sucrose density fractionation. Boxed areas show the fractions combined to generate the five samples used for RT-PCR. L, Semiquantitative RT-PCR demonstrates that a significantly lower percentage of the total Mbp mRNA was present in sample 5 from Erk2 CKO mice compared with control littermates, while a significantly higher percentage of the total Mbp was present in samples 1 and 2. Dashed lines highlight the lesioned area of the corpus callosum. Values are expressed as ±SEM, *p ≤ 0.05, **p ≤ 0.01. Scale bars: D, 50 μm, I, 20 μm, A–C, F, G, 100 μm.