Development and migration of oligodendrocyte in the optic nerve

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The oligodendrocytes in the optic nerve are believed to originate in the forebrain (or diencephalon) and to disparse by migration during development. However, the site of oritin and mode of migration of the optic nerve oligodendrocyte remains unclear. In the present study, the chick embryos were used to study this issue. The monoclonal antibody O4, a marker for immature oligodendrocyte, immunohistochemically labeled cells in the floor of the third ventricle just dorsal to the optic chasm at 4th day of incubation (E4). The O4-positive (O4+) cells increased to form cell focus in the midline of the ventricular zone at 135. These O4-i-cells started to enter the optic chiasm and nerve at E6, and then disparse from the chiasmal end to the retinal end by E9. The labeled cells at these stages showed unipolar shape with a growth cone at the tip of the processes. The O4+cells also appeared in the retina close to the optic fissure at 1310. Isolated explant culture demosntrated that the oligodendrocyte precursors appeared at 136 in the chiasmal end of the optic nerve, at 137 in the retinal end and E10 in the retina, which was idential to the results from O4immunohistochemistry in situ. Intraventricular injections of DiI at E6 resulted in the O4+/DiI+ cells in the optic nerve at 138, and in the retina at E10. The present results clearly showed that the optic nerve oligodendrocytes originated in the floor of the third ventricle and then migrate along the optic nerve. Especially, DiI injection study provided a direct evidence for the ventricular origin and migration of 04-i-cells.