Myelination was analyzed by transversal section of sciatic nerves stained with PPD (A–L). All mutants overexpressing PMP22 showed lack of large caliber myelinated fibers, which are depicted in wildtype and MAG-deficient mice (A–C, white star). Small and medium size fibers of those animals manifested either a normal g-ratio (J, arrows) or were hypomyelinated (J, arrowheads). Overall, there was a significant reduction of myelinated fibers in the C22 mouse line (m) compared to wildtype littermates (*, p<0.0005). The deletion of MAG in the C22 background did not further decrease the total number of myelinated fibers (*, p<0.0005, M). Data are expressed as mean and s.e.m. of three animals at P40. Scale bars: (A–F) 100 μm; (G–L) 10 μm.