INDUCTION OF OLIGODENDROCYTE PROGENITORS IN THE TRUNK NEURAL-TUBE BY VENTRALIZING SIGNALS - EFFECTS OF NOTOCHORD AND FLOOR PLATE GRAFTS, AND OF SONIC HEDGEHOG

Recent evidence indicates that oligodendrocytes originate initially fr om the ventral neural tube. We have documented in chick embryos the ef fect of early ventralization of the dorsal neural tube on oligodendroc yte differentiation. Notochord or floor plate grafted at stage 10 in d orsal position induced the development of oligodendrocyte precursors i n the dorsal spinal cord. In vitro, oligodendrocytes differentiated fr om medial but not intermediate neural plate explants, suggesting that the ventral restriction of oligodendrogenesis is established early. Fu rthermore, quail fibroblasts overexpressing the ventralizing signal So nic Hedgehog induced oligodendrocyte differentiation in both the inter mediate neural plate and the E4 dorsal spinal cord. These results stro ngly suggest that the emergence of the oligodendrocyte lineage is rela ted to the establishment of the dorso-ventral polarity of the neural t ube.