Histochemical Analysis of Glycoconjugates in the Skin of a Catfish (Arius Tenuispinis, Day)

Abstract

Summary A histochemical study using conventional carbohydrate histochemistry (periodic‐acid staining including diastase controls, alcian blue staining at pH 1 and 2.5) as well as using a battery of 14 fluorescein isothiocyanate (FITC)‐labelled lectins to identify glycoconjugates present in 10 different areas of the skin of a catfish (Arius tenuispinis) was carried out. The lectins used were: mannose‐binding lectins (Con A, LCA and PSA), galactose‐binding lectins (PNA, RCA), N‐acetylgalactosamine‐binding lectins (DBA, SBA, SJA and GSL I), N‐acetylglucosamine‐binding lectins (WGA and WGAs), fucose‐binding lectins (UEA) and lectins which bind to complex carbohydrate configurations (PHA E, PHA L). Conventional glycoconjugate staining (PAS staining, alcian blue at pH 1 and 2.5) showed that the mucous goblet cells contain a considerable amount of glycoconjugates in all locations of the skin, whereas the other unicellular gland type, the club cells, lacked these glycoconjugates. The glycoproteins found in goblet cells are neutral and therefore stain magenta when subjected to PAS staining. Alcian blue staining indicating acid glycoproteins was distinctly positive at pH 1, but gave only a comparable staining at pH 2.5. The mucus of the goblet cells therefore also contains acid glycoproteins rich in sulphate groups. Using FITC‐labelled lectins, the carbohydrate composition of the glycoproteins of goblet cells could be more fully characterized. A distinct staining of the mucus of goblet cells was found with the mannose‐binding lectins LCA and PSA; the galactosamine‐binding lectins DBA, SBA and GLS I; the glucosamine‐binding lectin WGA; and PHA E which stains glycoproteins with complex carbohydrate configurations. No reaction occurred with the fucose‐binding lectin UEA and the sialic acid‐specific lectin SNA. In addition, the galactose‐binding lectins PNA and RCA showed only a weak or completely negative staining of the mucus in the goblet cells. The specificity of the lectin staining could be proved by inhibiting binding of the lectins by competitive inhibition with the corresponding sugars. From these data, we can conclude that the mucus produced by the epidermal goblet cells of A. tenuispinis is rich in mannose, N‐acetylgalactosamine and N‐acetylglucosamine residues.

Morphology of the Epidermis of the Neotropical Catfish Pimelodella lateristriga (Lichtenstein, 1823) with Emphasis in Club Cells

“…Club cells are concentrated in the middle region of the epithelium, thus not reaching the surface. This location corroborates previous findings, for both marine and fresh water Siluriformes [4], [7], [31], [41].…”

“…However, the number of layers and thickness of the epithelium is quite varied across species. In general, there is a thick stratified epithelium, as in Siluriformes [4], [7], [11], [39], in Characiformes [2] and in non-Ostariophysi such as Aguiliformes [40]. P. lateristriga epithelium is formed only by one or two layers of club cells lined with small epidermal cells.…”

“…Club cells are distributed throughout the epidermal layer and possess cytoplasm filled with material to be secreted and one centered nucleus [1]–[4], [7], [9]–[11]. They are found in different fish groups associated with distinct functions [12].…”

An Overview of the Immunological Defenses in Fish Skin

“…This study has permitted to identify the glycoconjugates present in the skin of a catfish (A. tenuispinis), and the results confirm that mucous goblet cells contain a considerable amount of glycoconjugates in all locations of the skin, whereas the other unicellular gland types, the club cells, lacked these glycoconjugates. The mucus produced by the epidermal goblet cells of this species is rich in mannose, N-acetylgalactosamine, and Nacetylglucosamine residues [117].…”

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

“…Many of these lectins may be secreted directly into the mucus where they are held by binding to mucin glycoproteins and where they can provide protection and surveillance against foreign pathogens. 66,67 A rise in mucin secretion, therefore, may lead to a rise in the presence of certain mucus-bound lectins.…”