Regional morphology and mucus composition in the urogenital papilla skin of the blackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809)

Blackbelly rosefish Helicolenus dactylopterus is a zygoparous fish whose males are equipped with the copulating organ named urogenital papilla (UP). This study deals with the morphology and the glycoconjugate pattern of the UP epidermis, which is the male tissue interacting with the female internal body during copulation. The carbohydrate content was studied by means of conventional and lectin histochemistry. The epidermis was shown to be a stratified cuboidal epithelium and to exhibit characteristic intraepithelial pits in the apical zone. The mucous cells are scattered in the epidermis. The epidermal cell layers and their thickness as well as the size of mucous cells varied along the UP. Conventional histochemistry showed that the mucous cells contained i) only neutral glycoproteins in the basal zone; ii) both neutral and acidic non-sulphated glycans as well as only acidic non-sulphated or sulphated glycoconjugates in the intermediate zone; iii) neutral and sulphated glycoconjugates in the apical zone. The mucous cells in the basal region expressed O-linked (mucin type) glycans terminating with αGalNAc, Galβ1,3GalNAc which could be α2,3-linked to sialic acid, and high mannose type N-linked glycans terminating with fucose, lactosamine, and sialic α2,6-linked to galactose/N-acetylgalactosamine; terminal Gal and terminal/internal GlcNAc were also found. The mucous cells in the intermediate zone lacked Galβ1,3GalNAc and showed less terminal α2,3-linked sialic acid, lactosamine, fucose, galactose, and internal N-acetylglucosamine residues. In the apical region, mucous cells only exhibited O-glycans terminating with GalNAc and N-acetylglucosamine. The demonstrated region-specific differences in the UP skin provide new insights into the reproductive biology of fishes with internal fertilization.