Differential expression of lactoseries carbohydrate epitopes HNK-1, CD15, and NALA by olfactory receptor neurons in the developing chick.

The formation of the nasal lining with its sensory and its nonsensitive respiratory epithelium requires a spatially ordered pattern of cellular differentiation. Aiming at identifying cell recognition molecules that may be involved in cellular differentiation steps, we applied a panel of antibodies to terminal carbohydrate sequences of the lactoseries on the developing chick olfactory epithelium. This approach is based on the idea that these terminal sugar residues may be involved in certain steps of maturation. Restricted expression of three epitopes NALA, HNK-1, and CD15 was observed in olfactory receptor neurons. The first immature olfactory receptor neurons were observed by day 3 of incubation, expressing the HNK-1 epitope, whereas a total epithelial staining was observed for NALA. By day 9 of incubation high numbers of HNK-1 positive immature olfactory receptor neurons were observed. At the same time mature olfactory receptor neurons showed immunoreactivity for CD15, whereas NALA was still expressed throughout the whole epithelial cell population. However, there was a pronounced staining in the population of mature olfactory receptor neurons. Around hatching only CD15 was detectable in (mature) olfactory receptor neurons, whereas HNK-1 and NALA immunoreactivity have switched to glandular and sustentacular cells respectively. The differentiation-dependent expression patterns of these three cell surface molecules suggest them as suitable markers to explore mechanisms that determine embryonic olfactory receptor neurogenesis.