Emigration of neuroepithelial cells from the hindbrain neural tube in the chick embryo

It is generally believed that after the emigration of neural crest, the neuroepithelial cells of the neural tube are committed to differentiate only as neurons and supporting cells of the central nervous system. Neural crest cells arise from the dorsal portion of the developing neural tube and contribute to the formation of the peripheral nervous system and a variety of non-neural structures. In contrast to this view we have recently shown, by focal application of the vital dye Dil in duck embryos, that an additional population of cells emigrates from the neural tube. By using an entirely different technique we confirm and extend these observations in the chick embryo. Replication-deficient retroviral vector LZ12 containing the gene LacZ was utilized to label the neural tube cells. The viral concentrate was microinjected into the lumen of the rostral hind-brain neural tube, considerably after the completion of emigration of neural crest cells. The labeled cells were monitored in whole mounts and histological sections. Initially, the labeled cells were restricted to the neuroepithelium of the hindbrain neural tube. Subsequently, they were seen in the neural tube and in the ganglion of the fifth cranial nerve (trigeminal ganglion). Later, they migrated beyond the trigeminal ganglion, i.e., into the mesenchyme of the first pharyngeal arch. Immunostaining with the neural crest cell marker, HNK-1, indicated that the emigrated neuroepithelial cells were HNK-1 negative. It is concluded that in the chick embryo some neuroepithelial cells emigrate at the site of attachment of the trigeminal nerve, migrate into the ganglion and then into the mesenchyme of the first arch. This cell population differs antigenically from the neural crest cells.