Expression and immunohistochemical localization of heparan sulphate proteoglycan N-syndecan in the migratory pathway from the rat olfactory placode.

N-syndecan, a membrane-bound heparan sulphate proteoglycan, is abundantly present in the developing nervous system and thought to play important roles in the neurite outgrowth. In the present study, we examined the distribution of N-syndecan in the migratory route from the rat olfactory placode using immunohistochemistry and in situ hybridization. At embryonic day 15, both heparan sulphate and N-syndecan immunoreactivities were localized in and around the migrating cell clusters, which contained luteinizing hormone-releasing hormone (LHRH) and calbindin D-28k. Immunoreactivity for other glycosaminoglycan chains, such as chondroitin and keratan sulphate, and core proteins of the chondroitin sulphate proteoglycan, neurocan and phosphacan, were barely detected in the migratory pathway from the olfactory placode. By in situ hybridization histochemistry, N-syndecan mRNA was localized in virtually all of migrating neurons as well as in cells of the olfactory epithelium and the vomeronasal organ. N-syndecan immunoreactivity surrounded cells migrating along the vomeronasal nerves that were immunoreactive for neural cell adhesion molecules, NCAM, L1 and TAG-1. Considering that NCAM is implicated in the migratory process of LHRH neurons and specifically binds to heparan sulphate, it is likely that a heterophilic interaction between NCAM and N-syndecan participates in the neuronal migration from the rat olfactory placode.