Morphological changes and regulation mechanisms of oligodendrocyte migration and myelination

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Migration and proliferation of oligodendrocyte precursor cells (OPCs) were examined with lineage marker antibodies O4 and O1.(1) OPCs in the metencephalon (brainstem and cerebellum) undergo gradual dispersal from the medial brainstem, the lateral part and finally to the cerebellar anlage. To verify the migration of OPCs, plasmid encoding EGFP gene was transfected to the metencephalon ventricular cells on E4 or E5, and appearance and dispersal of O4-positive/EGFP-positive cells were examined sequentially. Transfection of the plasmid to the medial ventricular layer resulted in appearance of O4-positive/EGFP-positive cells in the brainstem and also in the cerebellum. This result indicates that OPCs arise in the medial brainstem ventricular layer and that at least some fractions of OPCs may migrate to the cerebellar anlage from the brainstem.(2) Proliferation of OPCs was examined by double-labeling of OPCs with bromodeoxyuridine (BrdU) and with O4 or O1. Approximately 20 % of O4-positive ventricular cells incorporated BrdU, while 40-50 % of O4-positive cells was labeled in the parenchyma right after their appearance in these regions. Labeling indices gradually decreased as embryo developed. Finally, less than 5 % of mature oligodendrocytes were labeled with BrdU. Oligodendrocyte lineage cells may generate their cohorts most actively in the parenchyma just after they leave from the ventricular layer.(3) Molecules regulating the OPC migration were examined with neutralizing antibodies against cell surface recognition molecules. Hybridomas secreting antibody was injected into the third ventricle of the E5 chick embryo and O4-positive cell distribution in the optic nerve was examined at E8. When the embryos were received injection of the hybridoma generating the antibody against N-cadherin, O4-positive cell number decreased to 50 % as compared to the control embryos. N-cadherin may be involved in the OPC migration in the optic nerve.