Myelin plays an essential function in the behaviour of higher organisms by increasing the speed of axonal conduction. Indeed, myelin deficiency or damage can lead to serious motor and sensory dysfunction. In the central nervous system, myelin is produced by a specialized macroglial cell known as the oligodendrocyte. Although much is known about oligodendrocytes with respect to their role in myelin production, many details regarding their development and maintenance still remain unclear. These details may be of great importance for fully understanding the fundamental properties of oligodendrocytes and for devising strategies for treating myelin-related diseases. In this thesis, we report the development of a system using organotypic hippocampal slices, viral gene delivery methods, immunostaining techniques and confocal imaging that can be used to study the properties of oligodendrocytes and myelin. This system preserves many features of the intact brain and can be used to investigate cells of the oligodendrocyte lineage at different developmental stages. Individual oligodendrocytes were targeted using this system and we showed that they can be induced to express various proteins, such as proteolipid protein and neurofascin-155, that localized to specific compartments of oligodendrocytes. This system was then used to address the importance of glutamate receptor signalling on myelin. Studies were performed at the light microscopic level using agonists and antagonists of ionotropic glutamate receptors. Myelin showed progressive pathology over the course of hours following exposure to glutamate receptor agonists and, interestingly, glutamate signalling was not essential for myelin maintenance over a 48 hour period. This thesis work thus describes the use of a novel system that can help analyze both the cellular and molecular aspects of oligodendrocyte development and maintenance.

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For the past 45 years, QKI has been studied for its role in the processes of development and central nervous system myelination using the qkv mouse. The presence of a single KH domain and the recent identification of a high-affinity binding site in mRNAs, suggests that it can bind to and regulate mRNAs through processes such as stability, splicing and transport. As a member of the STAR RNA binding family of proteins the QKI isoforms may also be involved in cell signaling pathways. / QKI's involvement in all of these processes, lead us to examine both the protein partners and the mRNA targets of the QKI complex in order to identify potentially new pathways regulated by QKI. In doing so, we identified a novel direct protein-protein interaction with PABP and for the first time described the relocalization of QKI to cytoplasmic granules following oxidative stress. In addition, in vivo mRNA interaction studies were performed and allowed the identification of approximately 100 new mRNA targets in human glioblastoma cells. One of the targets identified was VEGF mRNA. / Another QKI target mRNA is MBP, a major protein component of the myelin sheath and the candidate auto-antigen in multiple sclerosis (MS). In vivo MBP is symmetrically dimethylated on a single arginine residue. To further establish the role of the methylation of MBP in myelination, a methyl-specific antibody and an adenovirus expressing a recombinant protein arginine methyltransferase 5 (PRMT5) was generated. We show that methylated MBP is found in areas of mature myelin and that overexpression of the PRTM5 blocked the differentiation of oligodendrocytes. / Taken together these datas implicate QKI for the first time in the process of human cancer angiogenesis and could explain the vascularization defects observed in some of the qkI mutant mice. In addition, arginine methylation of MBP may prove to have an important role in the process of myelination and in the pathogenesis of demyelination and the autoimmune reaction in diseases such as MS.

No description available.