N-CAM, polysialic acid and chick tail bud development.

We have previously shown that the binding of the lectin wheat germ agglutinin (WGA) to developing tail buds results in a range of caudal axial defects, which were most likely due to the affinity of the lectin for sialic acid residues. In the present study, we examined the distribution and role of a sialic acid-containing glycoprotein, N-CAM, in chick tail bud development. In the early tail bud, anti N-CAM, staining was found in the medullary cord. However, there was no uptake of an antibody specific to N-CAM containing moderate to long chains of polysialic acid (5A5 monoclonal antibody). At later stages, while N-CAM localized throughout the neural tube, staining with the 5A5 antibody was restricted to the floor plate. Sub-blastodermal injection of the anti N-CAM antibody beneath the tail bud region of HH stages 13-14 embryos produced caudal axial malformations. These malformations included the presence of accessory segments of neural tube and/or notochord, and fusion between the neural tube and underlying segment of notochord. Our results suggest that N-CAM is present during the development of the secondary neuraxis from the tail bud, although the highly sialylated form of this molecule could not be visualized until relatively late stages. N-CAM probably plays a role in the normal course of tail bud development, since perturbation of the molecule with an antibody resulted in malformations. Since these malformations were similar to those we have previously reported when we treated similarly staged chick embryos with WGA, there is a possibility that the sialic acid residues recognized and bound by the lectin are those associated with the N-CAM molecule.