Fig. 2.

Loss of microglial Mertk is associated with pathological myelin and reduced myelin gene expression. A Representative TEM images of myelinated axons in the corpus callosum of Mertk WT and cKO from P28, young adult (8–12 weeks) and aged (12 months) mice. B The density of myelinated axons was similar between WT and Mertk cKO mice at all time-points (two-way ANOVA; P > 0.05). Plots of myelin thickness versus axon calibre for P28 (C), adult (D) and aged (E) mice. A moderate shift towards thicker myelin was observed in adult (linear regression; P = 0.013) and aged (linear regression; P = 0.0004) mice was observed. F Representative high power TEM images of a myelinated axon in Mertk WT and cKO mice, demonstrating split lamellae in the latter. G Numbers of myelinated axons with at least one split lamellae are significantly increased in Mertk cKO mice (Fisher's exact test; P = 0.0016). The expression of the genes encoding MBP (H) and CNPase (I) is significantly reduced at P7 in the corpus callosum of Mertk cKO mice compared with WT, although this normalises by P15 (Student's t-test). Data represent mean ± SD with n = 3–5 biological replicates per genotype. For myelin thickness, all myelinated axons in a minimum of 6 non-overlapping images were measured. Data represent mean ± SD