Morphology and Glycan Composition of the Mandibular Glands in the White-Eared Opossum (Didelphis albiventris)

The white-eared opossum, Didelphis albiventris, is an opportunistic and omnivorous marsupial, whose diet ranges from wild fruits to eggs and birds. Salivary glycoproteins play a key role in the protection of the oral cavity and the formation of the food bolus. Despite the importance of salivary glycoproteins, their detailed investigation in the white-eared is lacking. This study investigated the morphology and glycan composition of the mandibular salivary glands of the white-eared opossum for the first time. Histological and histochemical investigations were conducted on tissue fragments fixed with 4% PBS-buffered paraformaldehyde and embedded in Paraplast. The pattern of glycoproteins was investigated using traditional histochemical methods (PAS, Alcian Blue pH 2.5, and High-Iron Diamine staining) and lectin histochemistry. The glandular parenchyma consisted of acinar secretory units and a duct system characterized by abundant striated ducts. Secretory acini secrete neutral glycans and non-sulfated acid glycans. Mannosylated N-linked glycans terminating in α2,6-sialic acid and fucose are expressed in the secretory acini, containing intraluminal α2,3-sialylated O-linked glycans. The epithelial lining of the striated and interlobular ducts also shows O-linked glycans with terminal Galβ1, 3GalNAc, and αGalNAc residues. Finally, the epithelium and lumen of interlobular ducts are enriched with additional GalNAc-terminated O-linked glycans with the appearance of lactosaminated glycans and the disappearance of α2,3-sialylated glycans. These results suggest that the saliva produced by the mandibular gland of the white-eared opossum consists of a species-specific pattern of glycoproteins, to whose composition the ductal system also contributes. The observed glycan composition is probably related to the diet of the white-eared opossum and its adaptations to the environment and food availability. These results indicate that the mandibular salivary gland of the white-eared opossum Didelphis albiventris has specific histological and molecular characteristics compared to other marsupial species, suggesting that diet and habitat, but not the taxonomic group, influence the mandibular gland features.