Glycoconjugate histochemistry of mucous glands in the skin of metamorphosing Bufo viridis

Mucins are the major glycoprotein secretions of mucous glands and display important functions in amphibian skin such as regulation of water homeostasis and mechanical and chemical protection. In the present study, we evaluated the glycoconjugate contents of developing mucous glands on dorsal regions of metamorphosing Bufo viridis (Amphibia: Anura) tadpoles using an alcian blue-PAS panel and lectin histochemistry. All the conical cells of mucous glands showed weak positivity for alcian blue in 0.025 M MgCl2 at pH 5.7 but only a few cells were positive for 0.3 M MgCl2 at the same pH. In addition, all the conical cells of mucous glands were negative for alcian blue at pH 2.5. In lectin histochemistry, conical cells reacted strongly with Galanthus nivalis agglutinin (GNA), Datura stramonium agglutinin (DSA) and peanut agglutinin (PNA), weakly with Maackia amurensis leucoagglutinin (MAL). These results suggest that they express predominantly mannose, galactose and partially alpha(2-->3)-linked sialic acid containing glycoconjugates. We concluded that dorsal mucous glands of metamorphosing Bufo viridis tadpoles contain at least two different conical cell types and glycoconjugate heterogeneity of mucous glands may be related with different functions of mucins.