Expression of neuronal markers in the secondary neurulation of chick embryos.

The goal of our study was to evaluate the expression patterns of neuronal antigens during the process of secondary neurulation.Chick embryos of Hamburger and Hamilton stages 16, 18, 20, 22, 24, 26, 30, 35, 40, and 45 were harvested, and tail sections were processed for neuronal antigen studies.The areas and periods showing positive reactions for each antigen are as follows: neuronal cell adhesion molecule (N-CAM): the secondary neural tube and notochord from stages 18 to 26 and the germinal and mantle layers from stages 30 to 45; synaptophysin: the caudal cell mass, secondary neural tube, and notochord from stages 22 to 26, the germinal and mantle layers from stages 30 to 45, and the marginal layer at the later stages of development; neurofilament-associated protein (3A10): the dorsal white matter, dorsal root ganglion, and scattered cells around the germinal layer from stages 35 to 45; and neuronal nuclear-specific protein (NeuN): the mantle layer at stage 35, which shows decreased reaction at stages 40 and 45; islet-1: no remarkable staining on the caudal cell mass or on the other neural structures at all stages. Our results indicate that neuronal markers of the secondary neurulation in chick embryos have their own chronological patterns of expression. At early stages of secondary neurulation, N-CAM and synaptophysin are thought to modulate the differentiation of structures derived from the caudal cell mass. At later stages, N-CAM, synaptophysin, 3A10, and NeuN seem to be involved in the maturation of the caudal spinal cord.