Histochemical analysis of glycoproteins in the secretory cells in the gill epithelium of a catfish, Rita rita (Siluriformes, Bagridae)

Mucosal affairs: glycosylation and expression changes of gill goblet cells and mucins in a fish-polyopisthocotylidan interaction

Introduction

Secreted mucins are highly O-glycosylated glycoproteins produced by goblet cells in mucosal epithelia. They constitute the protective viscous gel layer overlying the epithelia and are involved in pathogen recognition, adhesion and expulsion. The gill polyopisthocotylidan ectoparasite Sparicotyle chrysophrii, feeds on gilthead seabream (Sparus aurata) blood eliciting severe anemia.

Methods

Control unexposed and recipient (R) gill samples of gilthead seabream experimentally infected with S. chrysophrii were obtained at six consecutive times (0, 11, 20, 32, 41, and 61 days post-exposure (dpe)). In histological samples, goblet cell numbers and their intensity of lectin labelling was registered. Expression of nine mucin genes (muc2, muc2a, muc2b, muc5a/c, muc4, muc13, muc18, muc19, imuc) and three regulatory factors involved in goblet cell differentiation (hes1, elf3, agr2) was studied by qPCR. In addition, differential expression of glycosyltransferases and glycosidases was analyzed in silico from previously obtained RNAseq datasets of S. chrysophrii-infected gilthead seabream gills with two different infection intensities.

Results and Discussion

Increased goblet cell differentiation (up-regulated elf3 and agr2) leading to neutral goblet cell hyperplasia on gill lamellae of R fish gills was found from 32 dpe on, when adult parasite stages were first detected. At this time point, acute increased expression of both secreted (muc2a, muc2b, muc5a/c) and membrane-bound mucins (imuc, muc4, muc18) occurred in R gills. Mucins did not acidify during the course of infection, but their glycosylation pattern varied towards more complex glycoconjugates with sialylated, fucosylated and branched structures, according to lectin labelling and the shift of glycosyltransferase expression patterns. Gilthead seabream gill mucosal response against S. chrysophrii involved neutral mucus hypersecretion, which could contribute to worm expulsion and facilitate gas exchange to counterbalance parasite-induced hypoxia. Stress induced by the sparicotylosis condition seems to lead to changes in glycosylation characteristic of more structurally complex mucins.

Epidermal modifications in a hill stream catfish, Hara hara in relation to its natural habitat: A scanning electron microscope and histochemical investigation

In the present study, the epidermis of the hill stream fish Hara hara has been investigated employing scanning electron microscope, histology, histochemistry and immunofluorescence techniques. The epidermis is characteristically differentiated into plaques separated from each other by deep furrows. In plaques, the epidermis is keratinized. In contrast, in furrows, it is mucogenic. Surface epithelial cells in plaques get modified into characteristic spine-like unculi. At the distal ends of these unculi, we find tree-like branched dendritic structures. The keratinized epithelial cells in plaques together with unculi frequently exfoliate at the surface. The epidermis in furrows is equipped with secretory glandular cells, that is, mucous goblet cells, sacciform cells and club cells; and sensory structures, that is, the taste buds. These glandular cells are involved in the elaboration of different types of carbohydrate and protein moieties. Further, in the epidermis of both, plaques and furrows, melanophores are frequently interspersed between the epithelial cells. In the plaque epidermis, in addition to melanophores, melanin granules are observed in epithelial cells undergoing keratinization as well as in those sloughing at the surface. Sloughing of keratinized epithelial cells together with spine-like unculi at the surface of the plaques; the secretions of the glandular cells, the distribution of melanophore and the taste buds interspersed between the epithelial cells and the presence of melanin granules in the keratinized epithelial cells have been associated with different functional roles. These include hydrodynamic advantage, protection from mechanical stress, pathogens, UV radiation, localization of food accurately and so on in relation to the natural habitat of the fish.

Medicinal Plant Leaf Extract From Sage and Lemon Verbena Promotes Intestinal Immunity and Barrier Function in Gilthead Seabream (Sparus aurata)

The inclusion of a medicinal plant leaf extract (MPLE) from sage (Salvia officinalis) and lemon verbena (Lippia citriodora), rich in verbascoside and triterpenic compounds like ursolic acid, was evaluated in gilthead seabream (Sparus aurata) fed a low fishmeal-based diet (48% crude protein, 17% crude fat, 21.7 MJ kg-1, 7% fishmeal, 15% fish oil) for 92 days. In particular, the study focused on the effect of these phytogenic compounds on the gut condition by analyzing the transcriptomic profiling (microarray analysis) and histological structure of the intestinal mucosa, as well as the histochemical properties of mucins stored in goblet cells. A total number of 506 differentially expressed genes (285 up- and 221 down-regulated) were found when comparing the transcriptomic profiling of the intestine from fish fed the control and MPLE diets. The gut transcripteractome revealed an expression profile that favored biological mechanisms associated to the 1) immune system, particularly involving T cell activation and differentiation, 2) gut integrity (i.e., adherens and tight junctions) and cellular proliferation, and 3) cellular proteolytic pathways. The histological analysis showed that the MPLE dietary supplementation promoted an increase in the number of intestinal goblet cells and modified the composition of mucins' glycoproteins stored in goblet cells, with an increase in the staining intensity of neutral mucins, as well as in mucins rich in carboxylated and weakly sulfated glycoconjugates, particularly those rich in sialic acid residues. The integration of transcriptomic and histological results showed that the evaluated MPLE from sage and lemon verbena is responsible for the maintenance of intestinal health, supporting gut homeostasis and increasing the integrity of the intestinal epithelium, which suggests that this phytogenic may be considered as a promising sustainable functional additive for aquafeeds.

Epidermal Club Cells in Fishes: A Case for Ecoimmunological Analysis

Epidermal club cells (ECCs), along with mucus cells, are present in the skin of many fishes, particularly in the well-studied Ostariophysan family Cyprinidae. Most ECC-associated literature has focused on the potential role of ECCs as a component of chemical alarm cues released passively when a predator damages the skin of its prey, alerting nearby prey to the presence of an active predator. Because this warning system is maintained by receiver-side selection (senders are eaten), there is want of a mechanism to confer fitness benefits to the individual that invests in ECCs to explain their evolutionary origin and maintenance in this speciose group of fishes. In an attempt to understand the fitness benefits that accrue from investment in ECCs, we reviewed the phylogenetic distribution of ECCs and their histochemical properties. ECCs are found in various forms in all teleost superorders and in the chondrostei inferring either early or multiple independent origins over evolutionary time. We noted that ECCs respond to several environmental stressors/immunomodulators including parasites and pathogens, are suppressed by immunomodulators such as testosterone and cortisol, and their density covaries with food ration, demonstrating a dynamic metabolic cost to maintaining these cells. ECC density varies widely among and within fish populations, suggesting that ECCs may be a convenient tool with which to assay ecoimmunological tradeoffs between immune stress and foraging activity, reproductive state, and predator-prey interactions. Here, we review the case for ECC immune function, immune functions in fishes generally, and encourage future work describing the precise role of ECCs in the immune system and life history evolution in fishes.

Unveiling the effect of dietary essential oils supplementation in Sparus aurata gills and its efficiency against the infestation by Sparicotyle chrysophrii

A microencapsulated feed additive composed by garlic, carvacrol and thymol essential oils (EOs) was evaluated regarding its protective effect in gills parasitized by Sparicotyle chrysophrii in Sparus aurata. A nutritional trial (65 days) followed by a cohabitation challenge with parasitized fish (39 days) were performed. Transcriptomic analysis by microarrays of gills of fish fed the EOs diet showed an up-regulation of genes related to biogenesis, vesicular transport and exocytosis, leukocyte-mediated immunity, oxidation–reduction and overall metabolism processes. The functional network obtained indicates a tissue-specific pro-inflammatory immune response arbitrated by degranulating acidophilic granulocytes, sustained by antioxidant and anti-inflammatory responses. The histochemical study of gills also showed an increase of carboxylate glycoproteins containing sialic acid in mucous and epithelial cells of fish fed the EOs diet, suggesting a mucosal defence mechanism through the modulation of mucin secretions. The outcomes of the in vivo challenge supported the transcriptomic results obtained from the nutritional trial, where a significant reduction of 78% in the abundance of S. chrysophrii total parasitation and a decrease in the prevalence of most parasitic developmental stages evaluated were observed in fish fed the EOs diet. These results suggest that the microencapsulation of garlic, carvacrol and thymol EOs could be considered an effective natural dietary strategy with antiparasitic properties against the ectoparasite S. chrysophrii.

Mucosal responses of brown-marbled grouper Epinephelus fuscoguttatus (Forsskål, 1775) following intraperitoneal infection with Vibrio harveyi

Groupers are popular aquaculture species in South-East Asia, but their cultivation is affected by infectious disease outbreaks. Mucosa-associated lymphoid tissues provide a first-line defence against pathogens; however, few studies are available relating to cellular or proteomic responses of mucosal immunity in grouper. Skin, gill and intestine were sampled from brown-marbled grouper Epinephelus fuscoguttatus (Forsskål, 1775) at 4 and 96 hr post-infection (hpi) and 7 days post-infection (dpi) following intraperitoneal infection with Vibrio harveyi, and stained with haematoxylin/eosin and Alcian Blue/periodic acid-Schiff. Skin mucus was analysed by 2D-gel electrophoresis, and proteins modulated by the bacterial infection identified. In the infected fish, significant increases in sacciform cells in skin and increased levels of nucleoside diphosphate kinase in mucus were detected at 4 hpi. At 96 hpi, goblet cells containing acidic mucins significantly increased in the intestine, while those containing mixed mucins increased in skin and gills of infected fish. Proteasome subunit alpha type-I and extracellular Cu/Zn superoxide dismutase levels also increased in mucus. Rodlet and mast cells did not appear to respond to the infection. Mucosal tissues of grouper appeared actively involved in response to Vibrio infection. This information may help future research on improving grouper health, production and vaccine development.

Modifications in the gills of hill stream Moth catfish, Hara hara (Erethistidae, Siluriformes): A light and scanning electron microscope investigation

Present study reports significant modifications in surface ultrastructure, histological organization, and histochemical localization of glycoproteins (GPs) in the gills of a hill stream catfish, Hara hara. Punctate microridges on free surface of epithelial cells covering gill arches, gill rakers, gill filaments and secondary lamellae are considered to provide adaptive plasticity to gills in relation to the environment inhabited by fish. Short and stout gill rakers are considered to prevent food particles to pass in opercular chamber along with respiratory current that could damage delicate gill filaments. Mucous goblet cells show presence of different classes of glycoproteins. GPs with oxidizable vicinal diols are considered to control acidity of acidic GPs. GPs with carboxyl groups have been implicated with defensive mechanism against microorganisms. GPs with O-sulphate esters are associated to trap and to lubricate food particles for easy swallowing. Taste buds on gill arches and gill rakers function to select palatable food particles. Occurrence of taste buds on the gill filaments is regarded significant adaptation to analyse the chemical nature of water. This study could play a significant role to understand adjustment of gills in the hill stream fish.

In-depth proteomic analysis of Boleophthalmus pectinirostris skin mucus

Fish skin mucus serves as the first line of defence against pathogens and external stressors. The mudskipper Boleophthalmus pectinirostris inhabits intertidal mudflats containing abundant and diverse microbial populations; thus, the skin and mucus of B. pectinirostris are very important for immune defence. However, the molecules involved in the immune response and mucus secretion in the skin of this fish are poorly understood. To explore the proteomic profile of the skin mucus and understand the molecular mechanisms underlying B. pectinirostris adaption to amphibious environments, the microstructure of B. pectinirostris skin was analysed, and a series of histochemical procedures were employed for mucous glycoprotein localization and characterization. In addition, the antibacterial activity of B. pectinirostris skin mucus was studied, and the transcriptome of the skin and in-depth proteome of the mucus were determined. These studies revealed the hierarchical structure of B. pectinirostris skin and different types of glycoproteins (GPs) in the dermal bulge (DB) of the B. pectinirostris skin epidermis. The mucus has a broad antimicrobial spectrum and significant effects on the bacterial morphology. Furthermore, 93,914 unigenes were sequenced from B. pectinirostris skin tissue, and a total of 559 proteins were identified from B. pectinirostris skin mucus. SIGNIFICANCE.

Giemsa-based cytological assessment of area, shape and nucleus:cytoplasm ratio of goblet cells of rabbit bulbar conjunctiva

Goblet cells were visualized in impression cytology specimens from bulbar conjunctiva of the rabbit eye using Giemsa staining. Highly magnified images were used to generate outlines of the goblet cells and their characteristic eccentric nuclei. Using sets of 10 cells from 15 cytology specimens, I found that the longest dimension of the goblet cells averaged 16.7 ± 2.3 μm, the shortest dimension averaged 14.4 ± 1.8 μm and the nucleus averaged 6.3 ± 0.8 μm. The goblet cells were ellipsoid in shape and the longest:shortest cell dimension ratio averaged 1.169 ± 0.091. The goblet cell areas ranged from 108 to 338 μm² (average 193 ± 50 μm²). The area could be predicted reliably from the longest and shortest dimensions (r² = 0.903). The areas of goblet cell nuclei were 15-58 μm² (average 33 ± μm²) and the nucleus:cytoplasm area fraction was predictably greater in smaller goblet cells and less in the larger goblet cells (Spearman correlation = 0.817). The nuclei were estimated to occupy an average of 9.5% of the cell volume. The differences in size, shape and nucleus:cytoplasm ratio may reflect differences in goblet cell maturation.

Histopathological effects of silver and copper nanoparticles on the epidermis, gills, and liver of Siberian sturgeon

The influence of nanoparticles (NPs) on aquatic environments is still poorly documented. The aim of the study was to determine the effects of silver (AgNPs) and copper (CuNPs) nanoparticles on larval Siberian sturgeon (Acipenser baerii) after 21 days of exposure. Acute toxicity of AgNPs on Siberian sturgeon was investigated in a 96-h static renewal study and compared with the toxicity of CuNPs. The AgNPs and CuNPs 96 h mean lethal concentrations (96 h LC50) were 15.03 ± 2.91 and 1.41 ± 0.24 mg L(-1), respectively. Toxicity tests were done in triplicates for each concentration of AgNPs 0.1, 0.5, 1.5 mg L(-1) and CuNPs 0.01, 0.05, 0.15 mg L(-1). The control group was exposed in freshwater. The results indicate that AgNPs and CuNPs exposure negatively influenced survival; body length and mass; and morphology and physiology of the epidermis, gills, and liver of Siberian sturgeon larvae. Fish exposed to AgNPs and CuNPs showed similar pathological changes: irregular structure and pyknotic nuclei of epidermis, aplasia and/or fusion of lamellae, telangiectasis, epithelial necrosis and lifting of the gills, dilation of sinusoidal space, overfilled blood vessels, and pyknotic nuclei of the liver. Fish exposed to CuNPs only demonstrated hyaline degeneration in the gills epithelium and liver. The study shows that CuNPs were more toxic to Siberian sturgeon larvae than AgNPs.

Evaluation of waterborne exposure to heavy metals in innate immune defences present on skin mucus of gilthead seabream (Sparus aurata)

Aquatic animals are continuously exposed to chemical pollutants but the effects evoked in skin surfaces, which receive the most direct contact with them, are poorly investigated. Terminal carbohydrate composition and immunological components present in skin mucus of gilthead seabream (Sparus aurata L.) specimens exposed to waterborne sublethal dosages of heavy metals [arsenic (As2O3), cadmium (CdCl2) and mercury (CH3HgCl) at 5, 5 and 0.04 μM, respectively for 2, 10 and 30 days were analysed. Moreover, the presence of a fucose binding lectin (FBL) was evaluated by western blot and the protein profiles were by SDS-PAGE and HPLC. Results showed little effects of heavy metals in the presence of several terminal carbohydrates with few increments or decrements. Most of the enzyme activities related to immune responses were increased upon heavy metal exposure in the skin mucus including bactericidal activity. Methylmercury produced the most dramatic changes increasing all the activities. Moreover, the FBL was undetected in any of the control fish skin mucus but was evident in all the heavy metal exposed fish. In addition, As and Cd produced a clear change in the protein profile as evidenced by the lack of a protein band of around 12 kDa which is absent. These protein changes were more evident with the HPLC study showing the presence of different peaks and differences in intensity. The present results could be useful for better understanding the role and their behaviour of the mucosal immunity in skin as a key component of the innate immune system against pollutants.

Food deprivation causes rapid changes in the abundance and glucidic composition of the cutaneous mucous cells of Atlantic salmon Salmo salar L

Cutaneous mucus is the first physical and chemical barrier of fish. This slime layer is secreted by mucous cells located in the epidermis and is mainly composed of glycoproteins that have their origin in the diet. Therefore, food deprivation can potentially change the abundance and glucidic nature of skin mucous cells, thus changing the mucus properties. To test this hypothesis, we conducted an experiment with Atlantic salmon, Salmo salar L. Changes in the number and glucidic nature of epidermal mucus cells were analysed using standard techniques. The outcome of this study shows that food deprivation caused a rapid decrease in the density of epidermal mucous cells in Atlantic salmon. Lectin histochemistry revealed a change in the presence and stainability of some sugar residues in the mucous cells of unfed fish compared with fed fish. Given that the primary reason for mucus secretion in fish is for protection against infections, we speculate that the changes in the mucus properties caused by nutritional stress may affect their disease resistance. This fact is particularly important for fish that spend a period of time deprived of food, either as a part of their natural life cycle, or as part of farming practices.

Sex-response differences of immunological and histopathological biomarkers in gill of Prochilodus argenteus from a polluted river in southeast Brazil

The fish gill is in direct and standing contact with the immediate external environment and, therefore, is highly vulnerable to aquatic pollutants. In this study, Prochilodus argenteus were caught at two different points in São Francisco river. The first point is located near Três Marias dam, while the second is placed downstream the Abaeté river. Chemical approaches showed the presence of metals contamination in the first point. Thus, the main goal of this study was to investigate the possible toxic effects of these contaminants and the likely use of biomarkers on fish gills. Biometric data of length and weight of fish were obtained in order to calculate the condition factor as an organismal biomarker. The histological changes in gills and alterations in mucous and rodlet cells occurrence were detected microscopically and evaluated with quantitative analyses. Myeloperoxidase (MPO) and Eosinophil Peroxidase (EPO) were also assessed in fish gill. The analysis of the water and sediment samples revealed the presence of metals at the two points. As and Cd were detected at higher concentrations at point 1. The presence of lamellar cell hyperplasia, lamellar fusion, lamellar edema and inflammatory foci varied according to the point. Additionally, mucous and rodlet cells and MPO and EPO activities showed variability according to the environmental conditions. Furthermore, with exception of lamellar hyperplasia and eosinophil peroxidase activity, all others parameters showed sex-variation responses. At the first point, male fish showed a chronical inflammation in gills due to the lowest activity of MPO and EPO, as well as low occurrence of inflammatory foci and glycoprotein secretion by mucous cells, while female fish presented an opposite pattern of response to the same environmental conditions. Therefore, we suggest the use of such biomarkers in future monitoring of aquatic systems, taking into account the sex-variation responses.

Functional morphology of mucosal goblet cells based on spatial separation of orifice openings to the surface--application to the rabbit bulbar conjunctiva

The purpose of the study was to assess spatial separation of goblet cell orifices observed at the surface of the rabbit bulbar conjunctiva by scanning electron microscopy (SEM) specimens of the bulbar conjunctiva from 8 healthy pigmented rabbits were obtained using a special preparation technique by which the tissue was carefully stretched out during glutaraldehyde fixation. On high magnification prints of SEM images of the conjunctival surface, the locations of goblet cell openings (orifices) to the apical surface were marked and the centre-to-centre spacing between all such orifices measured. Across the regions of interest (ROI), with averaged dimensions of 322 μm × 230 μm (adjusted for tissue shrinkage), the averaged value for the distances between all orifices was 196 μm (range 141-241 μm), with the calculated density of orifices being 412 mm(-2). A sequential order-based analysis of the spatial separation between orifices indicated a predictable value of 6 μm, a separation that showed a nearly linear inter-dependence over distances of at least 200 μm. The openings of goblet cells to the surface of unstimulated bulbar conjunctiva have a organized spatial distribution that is consistent with there being an organized control of goblet cell secretion.

An Overview of the Immunological Defenses in Fish Skin

The vertebrate immune system is comprised of numerous distinct and interdependent components. Every component has its own inherent protective value, and the final combination of them is likely to be related to an animal’s immunological history and evolutionary development. Vertebrate immune system consists of both systemic and mucosal immune compartments, but it is the mucosal immune system which protects the body from the first encounter of pathogens. According to anatomical location, the mucosa-associated lymphoid tissue, in teleost fish is subdivided into gut-, skin-, and gill-associated lymphoid tissue and most available studies focus on gut. The purpose of this paper is to summarise the current knowledge of the immunological defences present in skin mucosa as a very important part of the fish immune system, serving as an anatomical and physiological barrier against external hazards. Interest in defence mechanism of fish arises from a need to develop health management tools to support a growing finfish aquaculture industry, while at the same time addressing questions concerning origins and evolution of immunity in vertebrates. Increased knowledge of fish mucosal immune system will facilitate the development of novel vaccination strategies in fish.

Histochemical analysis of glycoproteins in the gill epithelium of an Indian major carp, Cirrhinus mrigala

Glycoproteins were analyzed by a range of histochemical methods in the epithelium of gills of Cirrhinus mrigala, a valuable food fish of great economic importance cultured extensively in India. The gills consist of gill arches, gill rakers, gill filaments and secondary lamellae. Major components of the epithelium of gill arches and gill rakers are epithelial cells, mucous goblet cells, rodlet cells, lymphocytes, eosinophilic granular cells and taste buds. In contrast, in the gill filament epithelium, rodlet cells and taste buds, and in secondary lamellae epithelium, rodlet cells, lymphocytes, eosinophilic granular cells and taste buds are not discernible. The epithelial cells, the mucous goblet cells and the eosinophilic granular cells elaborate glycoproteins with oxidizable vicinal diols and glycoproteins with sialic acid residues without O-acyl substitution. In addition, glycoproteins with O-sulphate esters are secreted by the mucous goblet cells. The rodlet cells elaborate glycoproteins with oxidizable vicinal diols. Different types of glycoproteins elaborated on the epithelial surface of gills are discussed in relation to physiological significance of glycoprotein classes with special reference to their roles in lubrication, protection and inhibition of invasion and proliferation of pathogenic micro-organisms.

Monitoring stress in fish by applying image analysis to their skin mucous cells

Several authors have previously demonstrated that the number of the skin mucous cells of fish is affected by many stressors. In the present study, two experiments were conducted in order to examine the effects of two common environmental conditions on the morphology of skin of sea bass and particularly on the number and diameter of skin mucous cells. In the first experiment, two groups of sea bass (mean weight 155.6±10.3 g SD) were maintained in two different concentrations of nitrate, 100 and 700 ppm respectively, for 48 h, while a third group was used as control. In the second experiment, sea bass (initial mean weight 78.9±3.1 g SD) were divided into four groups and each group was maintained in a different level of oxygen for 9 weeks. The oxygen concentration in each group was: 3.6±0.2 ppm, 4.7±0.2 ppm, 6.2±0.2 ppm and 8.2±0.2 ppm. In both experiments the effects of the two environmental factors on the morphology of the fish skin were examined histologically and a software containing a visual basic script macro, allowing quantification of the skin mucous cells, was used to analyze the skin tissue sections. Concerning the overall morphology of the skin and the diameter of the skin mucous cells, no differences were noted in both experiments (P>0.05). It was demonstrated however, that fish maintained in the lowest oxygen level and fish maintained in the highest concentration of nitrate exhibited significantly increased number of mucous cells per skin area (mm²). There is evidence that the enumeration of the skin mucous cells of fish can be used to monitor stress in fish.

Scanning electron microscopy of the operculum of Garra lamta (Hamilton) (Cyprinidae:Cypriniformes), an Indian hill stream fish

The surface architecture of the epidermis on the outer surface of the operculum (OE) and the epithelium on the inner surface of the operculum (EISO) of Garra lamta was examined by scanning electron microscopy. The surface appeared smooth on the OE and wavy on the EISO. A wavy epithelium is considered to facilitate an increase in its stretchability, during the expansion of the branchial chamber. The OE and the EISO were covered by a mosaic pavement of epithelial cells with characteristic patterns of microridges and microbridges. Interspersed between the epithelial cells were mucous goblet cell pores, which were not significantly different in number in the OE and the EISO. Nevertheless, their surface area in the EISO was significantly higher than in the OE. This could be an adaptation to secrete higher amounts of mucus on the EISO for keeping the branchial chamber lining clean, avoiding clogging, the increased slipperiness reducing friction from water flow and increased efficiency in protecting against microbial attachments. Rounded bulges on the OE and the EISO were associated with mucous goblet cells. The absence of the taste buds in the EISO, in contrast to the OE, suggests that their function in the branchial chamber may not be of much significance in this fish. Breeding tubercles on the OE are believed to facilitate better contact between the male and female during breeding.

Histochemical analysis of glycoconjugates in the skin of a catfish (arius tenuispinis, day)

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.