Localization of glycoconjugates recognized by the hnk-1 antibody in mouse and chick embryos during early neural development

The monoclonal antibody HNK-1 recognizes a carbohydrate epitope present on a host of glycoconjugates which include the glycoproteins neural cell adhesion molecules (N-CAM) myelin-associated glycoprotein and ependymins, and two glycolipids. Other antibodies, including NC-1, L2 and IgM paraproteins from neuropathy patients share similar binding specificity to the same or related sulfated glucuronyl-containing antigen (SGA), To further investigate its possible significance in early development, the distribution of SGA was studied in the head region of early developing chick (S13-S18) and mouse (E8.5-El 1.5) embryos by immunocytochemistry. A striking species difference was found in the apparent distribution of immunodetectable SGA. In chick, migrating neural crest cells and their related cell types were heavily stained by HNK-1; whereas no stain was detectable on mouse neural crest cells at comparable stages, except perhaps in a restricted area adjacent to the otic placode and immediately adjacent to the neural tube. Within the developing CNS, the distribution of SGA was similar in both species. It was first expressed on neuroepithelial cells prior to axonal outgrowth, and was distributed in a continuous zone along the entire lateral walls of the early neural tube. Little or no SGA was detectable along most of the floor and roof plates. SGA appeared during this same period in the lateral basal lamina and within the adjacent mesenchyme and nearby cells. SGA was particularly evident on neuroepithelial endfeet at this stage. Early developing longitudinal axons were subsequently found to grow in association with the endfeet of SGA-positive neuroepithelial cells. These findings, in conjunction with previous studies, suggest that SGA is associated as a marker, and perhaps functionally, with the organization of early neuronal settling and axonal growth patterns within the developing vertebrate CNS.