Carbohydrates of the otolith organ in the rainbow trout Oncorhynchus mykiss detected by lectins

Abstract

A lectin-binding assay was applied to the rainbow trout, Oncorhynchus mykiss, sacculus in order to identify specific sugars in the otolith organ. The binding of biotinylated lectins to the sagitta, otolith membrane and saccular epithelial cells was detected by histochemistry, and their binding to the EDTA-soluble fraction of the otolith matrix and saccular endolymph was detected by dot-blot analysis. N-Acetylglucosamine (GlcNAc) and mannose (Man) were identified in the otolith matrix with both techniques. These data indicate that glycoproteins in the otolith matrix have N-glycosidically linked sugar chains. In the otolith membrane, GlcNAc and Man were identified in the subcupular meshwork, whereas only Man was identified in the gelatinous layer. This is in line with the hypothesis that a part of the subcupular meshwork is incorporated into the otolith as an organic matrix. The saccular epithelial cells reacted with at least one of the lectins which bound to the otolith matrix. The endolymph had the same reactivity with lectins as the otolith matrix. Thus, we suggest that otolith-matrix carbohydrates are produced in the saccular epithelial cells, secreted into the endolymph, and deposited onto the otolith.