Phenotypic analysis of mice deficient in the major myelin protein MOBP, and evidence for a novel Mobp isoform

Myelin-associated oligodendrocytic basic protein (MOBP) is a recently identified major component of central nervous system (CNS) myelin. We previously reported a detailed characterization of the genomic region encompassing the Mobp gene, elucidating the complex series of transcript splicing responsible for the generation of its diverse family of protein isoforms. These basic, positively charged polypeptides display spatial and temporal expression patterns consistent with a potential role in the compaction and maintenance of the myelin sheath. MOBP isoforms have also been localized to the nucleus and the microtubular network of oligodendrocytes; transcript corresponding to one isoform is present during embryonic development. Recent reports have identified a role for this protein family in the pathogenesis of multiple sclerosis, but a clear function for the wild-type protein has remained unclear. We report a detailed analysis of a targeted mutation of Mobp, which results in the deletion of the translational start site and most of the coding sequence of MOBP, and the deletion of the entire coding sequence corresponding to a novel, putative MOBP isoform. Our analyses clearly demonstrate that MOBP-deficient mice develop normally, generate intact compact CNS myelin, and demonstrate no obvious clinical phenotype. Furthermore, in contrast with another recent study, we find that Mobp null mice demonstrate no significant influence on the axonal diameter of myelinated axons. Although MOBP is not essential for myelination, it appears that its absence is not simply compensated for by increased expression of the "classic" myelin basic protein (MBP).