Figure 3.
Myelination was early and enhanced in Plp-Akt-DD mice with no increase in oligodendrocyte cell number. A, Cerebrum samples from WT and Plp-Akt-DD9 littermates were immunostained for PLP/DM20 at P14, P21, and P30, and enhanced myelination was seen at all ages in Plp-Akt-DD9 compared with WT. Note increased premyelinating oligodendrocytes at P14 and increased myelinated areas at older ages. This image is representative of different experiments, in which between 3 and 10 pairs of animals were analyzed per age. Scale bars, 100 μm. B, Samples were analyzed for PLP and DM20 by Western blot, at P10, P14, P21, and P30. This is a representative image of blots of between three and five pairs of animals per age. PLP/DM20 expression was increased as early as P10, compared with WT. C, RNA was prepared from cerebrum samples at P10, P21, and P30, and quantified for PLP, MOG, and MBP by real-time PCR. Samples were quantified, relative to a standard RNA, GAPDH, and expressed relative to WT samples at P21, which were given an arbitrary value of 1.0. Thus, changes in WT RNA levels were analyzed over time, along with differences between WT and transgenic samples. n = 3. *p ≤ 0.05; **p < 0.005. D, To quantify the number of oligodendrocytes, the Plp-Akt-DD9 transgene was crossed into Plp-EGFP mice. Coronal sections were imaged for EGFP-expressing oligodendrocytes in cortical areas of WT/Plp-EGFP and Plp-Akt-DD9/Plp-EGFP littermates at P14, P21, and P30. Scale bars, 100 μm. E, The area of motor and cingulate cortex analyzed for quantifying oligodendrocytes in WT/Plp-EGFP and Plp-Akt-DD9/Plp-EGFP littermates is boxed [Franklin and Paxinos (2008), their Fig. 24, modified with permission]. It includes part of M1 (primary motor cortex), M2 (secondary motor cortex), Cg1 (cingulate cortex area 1), Cg2 (cingulate cortex area 2), and the associated subcortical white matter. F, Quantification of oligodendrocytes at P14, P21, and P30, in the area outlined in E, showed no difference in the number of oligodendrocytes between WT and Plp-Akt-DD9 mice at all ages studied. n = 3 per age per genotype. Error bars represent SEM.