Histochemical studies on mucin-rich cells in the digestive tract of a teleost, the Buenos Aires tetra (Hyphessobrycon anisitsi)

Cellular evidence of mucus cell immunological and differentiation characteristics in allogeneic crucian carp intestinal lamina propria

The allogeneic crucian carp is an important fish farm animal with a very different digestive system structure from that of mammals. The lamina propria of the fish intestine is also considered to be an important site of intestinal immunity in fish, but functional histological studies of the lamina propria of the allogeneic crucian carp intestine are still lacking. In this study, Identification of the ubiquitous lamina propria mucus cells in the lamina propria of the intestine by hematoxylin-eosin staining, and determination of the mucocytic properties, class, and distribution of these cells in each intestinal segment by Alcian Blue-Periodic Acid-Schiff (AB-PAS) staining. The results show that type III mucus cells were abundant in the lamina propria of the foregut and midgut, while type II and type IV mucus cells predominate in the hindgut, possibly reflecting the distinct functions of these intestinal segments. Transmission electron microscopy dissected the differentiation of mucus cells in the lamina propria of the intestine at the ultrastructural level and investigated their morphology and distribution patterns in different intestinal segments, the findings revealed that lamina propria mucus cells perform rudimentary functions such as mucous secretion, phagocytosis, and degradation functions. Moreover, immunohistochemistry labeling with CD68 and LAMP1 revealed that numerous cells in the anterior, middle, and posterior intestines were positive for both proteins. Immunofluorescence double-labeling demonstrated that these cells highly co-expressed CD68 and LAMP1. Besides, the distribution and morphology of CD68+ and LAMP1+ cells were similar to those of AB-PAS positive cells and they accounted for the majority of parenchyma cells. Considering the above results, there were abundant cells with both mucous secretion and phagocytosis in the intestinal lamina propria of allogeneic crucian carp, which are a essential component of the intestinal immune process of allogeneic crucian carp.

Microscopic Characterization of the Mucous Cells and Their Mucin Secretions in the Alimentary Canal of the Blackmouth Catshark Galeus melastomus (Chondrichthyes: Elasmobranchii)

Sharks belong to the most primitive group of jawed vertebrates and have some special structural and functional features such as a cartilaginous skeleton, a spiral intestinal valve, and a rectal gland for osmoregulation. In January 2020, ten specimens of Galeus melastomus, the Blackmouth catshark, were collected from the Gulf of Asinara (North Sardinia, Italy) and the entire alimentary canal was studied using histochemical reactions to characterize the mucous cell types. In the alimentary canal of G. melastomus, mucous cells mainly secrete a mixture of acidic and neutral mucins. Of the acidic mucins, only the carboxylated type was present in mucous cells of the stomach, while the sulfated type predominated in the esophagus and the intestines. The use of lectins revealed a distribution of sugar residues in mucins related to cellular activities of the different regions of the catshark alimentary canal. The current study is the first report to characterize the intestinal mucous cells of G. melastomus and to provide quantitative data on their different populations in the alimentary canal.

Morphology, histology and histochemistry of the digestive tract of the Banded tilapia, Tilapia sparrmanii (Perciformes: Cichlidae)

This study described anatomical, histological and histochemical features of the mucosal layer of the digestive tract of Tilapia sparrmanii Smith, 1840, an omnivorous freshwater fish endemic to Southern Africa. This species exhibited a short thick oesophagus with long deep longitudinal folds (466.68 ± 16.91 µm), and a thick (173.50 ± 10.92 µm) muscular layer that allow the passage of large food items. The mucosa was lined with stratified secretory epithelium rich in goblet cells that secreted neutral and acid mucins. The stomach was a sac-like structure with simple tubular glands surrounded by connective tissue. The mucosa was lined with simple columnar epithelium and the lamina propria exhibited a well-developed layer of gastric glands that occupied the entire length of the cardio-fundic region. The stomach mucosa consisted of epithelial cells with intense neutral mucin secretion which protects against gastric juice. Neck cells of gastric glands synthesized neutral and acid mucins. The intestine was highly coiled and presented a complex pattern of transversal folds internally (villi). Villi length decreased progressively from the anterior to the posterior intestine (p < 0.0001). Tunica muscularis of the mid-intestine had the thinnest thickness among all parts of the intestine (p < 0.0001). Goblet cells whose numbers increased towards the rectum secreted both acid and neutral mucins. The results indicate structural similarities of T. sparrmaniiGIT with other tilapia species and will be useful for understanding the physiology of the digestive systems as well as functional components of the GIT.

Morpho-histochemical adaptations of the digestive tract in Gangetic mud-eel Ophichthys cuchia (Hamilton 1822) support utilization of mud-dwelling prey

Freshwater mud-eel, Ophichthys cuchia is nocturnal, carnivorous and economically important fish, yet its digestive physiology is unknown. We therefore studied the gastrointestinal (GI) tract of O. cuchia using morphological, osteological, histological and histochemical approach to understand how the structural adequacy of GI tract helps in acquisition of bottom and mud-dwelling prey and supports utilization of uncommon food resources. Morphologically the GI tract showed typical features of carnivorous fishes in the form of sub-terminal mouth, short muscular esophagus, expendable stomach, short intestine and rectum. Osteological investigation clearly showed that the specialized arrangement of teeth in the oral cavity and pharyngeal region helps in digging and manipulation of bottom and mud-dwelling prey. Longitudinal mucosal folds, stratified squamous epithelium with numerous goblet cells of esophagus protect mucosa from mechanical harm and also allow easy transit of prey into the stomach. Large-sized rugae of stomach are complemented with numerous gastric glands which together increase the transit time of carnivorous food stuff and ensure its complete digestion. The pylorus specifically allows only digested and finely ground food stuff into the intestine and thus avoids the intestinal blockage due to entry of undigested food. The enterocytes and goblet cells of intestine are absorptive and lubricative in their functions respectively. A significant increase in the number of goblet cells and thickness of muscularis from the intestine to the rectum was evident which facilitates the easier transit of food, protection for the epithelium from abrasion, and helps in defecation. Histochemistry revealed that the mucins are secreted throughout the GI tract and thus catalyze faster digestion of carnivorous food stuff, providing protection to mucosal membrane from abrasion, acts as a co-factor to support digestion, absorption of proteins, ions, fluids and helps in defecation. The outcome of this study clearly supports the notion that structural adaptations in the digestive tract of fishes can be effectively used as a blueprint to understand why and how particular fish species feed and use unique food. Additionally, the structural and functional adequacy of the digestive tract helps the fishes to acquire and utilize novel habitats and food resources. The results presented in this study will serve as a reference point for future studies, which focus primarily on understanding the evolution of carnivory in Synbranchids.

Mucosal Hallmarks in the Alimentary Canal of Northern Pike Esox lucius (Linnaeus)

Simple Summary

In vertebrates, mucous cells are one of the main cellular components of the gut mucosal system, which secrete different mucin types involved in several functions. Endocrine cells are scattered in the epithelium of the gut mucosa, and they produce and release regulatory molecules affecting food intake and nutrition. The goal of this study was to obtain data on quantitative distribution of mucous and endocrine cell types in the alimentary canal of the northern pike (Esox lucius), using histochemistry and immunofluorescence. In the stomach of pike, there is a high abundance of mixed mucins, with the acid component contributing to the lubrication of mucosae, where they are associated with the rapid passage of digesta through the intestine. Neutral mucins increase in the intestine aborally. The distribution of endocrine cells of the diffuse endocrine system shows the presence of somatostatin and catecholamine-secreting endocrine cells and the lack of gastrin-secreting endocrine cells. We show a close regulatory relation between endocrine and mucous cells of the gut mucosal system involved in the physiology of fish nutrition. Results confirmed the relationship between the carnivorous diet and the gut mucins distribution of northern pike; indeed, our data provide very important information to ichthyologists who study dietary behavior of species.

Abstract

On the basis of trophic behavior, fish are classified as herbivores, carnivores, omnivores, or detritivores. Epithelial mucous cells secrete mucin types specific to diet and digestive function. Mucus secretion is regulated mainly by molecular modulators produced by epithelial endocrine cells in response to luminal or tissue stimuli. These modulators are involved in control of food intake and digestive functions. Immunohistochemical and immunofluorescence studies were conducted on 10 adult northern pike (Esox lucius Linnaeus, 1758) from Lake Piediluco (Central Italy) to quantify distribution of sub-types of mucous and endocrine cells in alimentary mucosal epithelium. Neutral mucins predominated in the esophagus, and mixed and acidic mucins predominated in stomach and intestine. The gastric epithelium contained endocrine cells secreting somatostatin, tyrosine hydroxylase, and substance P. Mucous cells secreting neutral mucins increased in number from proximal to distal intestine, with endocrine cells containing substance P in the proximal intestine and those containing Leu-enkephalin throughout the intestine. Lectin histochemistry of gut sections revealed an abundance of N-acetyl-glucosamine and N-acetyl-galactosamine as carbohydrate residues on the mucin chain. The quantity and content of endocrine and mucous cells in the alimentary canal of E. lucius showed a direct relationship with its diet.

Histochemical distribution of four types of enzymes and mucous cells in the intestine of koi carp (Cyprinus carpio var. koi)

The main purpose of this study was to investigate the distribution of acid phosphatase (ACP), alkaline phosphatase (ALP), non-specific esterase (NSE), peroxidase (POD), and mucous cells in the intestine of the koi carp Cyprinus carpio var. koi. ACP activity was located in the striated border, enterocytes, and lamina propria of the anterior and middle intestines. The ACP activity in the anterior intestine was higher than that in the middle and posterior intestines. ALP existed in the striated border of enterocytes and lamina propria, serosa, muscular layer, and the junction between muscular layer and submucosa layer of the intestine. The ALP activity in the anterior intestine was higher than that in the middle and posterior intestines. NSE activity was localized in the cytoplasm of enterocytes in the whole intestine, and the middle intestine showed the lower NSE activity than the anterior and posterior intestines. POD activity was localized in the blood cells of the lamina propria and cytoplasm of enterocytes in all intestinal segments. The POD activity among the anterior, middle, and posterior intestines was non-significantly different. Alcian blue periodic acid-Schiff histochemical results revealed three types of mucous cells in the intestine. The total number of mucous cells and percentage of type I cells among the anterior, middle, and posterior intestines were non-significantly different. The percentage of the type II cells was the highest in the posterior intestine, while the lowest in the anterior intestine. The percentage of the type III cells was the highest in the anterior intestine, while the lowest in the posterior intestine.

Cytochemical features of the digestive tract mucosa of Hemisorubim platyrhynchos (Siluriformes: Pimelodidae)

Membranous organelles, acid glycoconjugates and lipids were characterized in the digestive tract mucosa of Hemisorubim platyrhynchos by cytochemistry techniques. Two types of mucous-secreting cells were observed in the digestive tract epithelium: goblet cells in the oesophagus and intestine and epithelial cells in the stomach. These cells had a Golgi apparatus more developed than the other cell types. The cytochemical analysis revealed that secretory granules are reactive to acid glycoconjugates, varying in reaction intensity according to the region of the digestive tract. Acid glycoconjugate reactions were also observed in oesophageal epithelial cell microridges and in enterocyte microvilli. In the digestive tract, acid glycoconjugates act to protect the epithelial surface, increasing mucous viscosity, which facilitates the passage of food, prevents the binding of parasites and facilitates their removal. Through lipid staining, a coated membrane was observed around each secretory granule of the oesophageal and intestinal goblet cells, while gastric epithelial cells granules were fully reactive. Oxynticopeptic cells of the gastric glands showed lipid droplets in the cytoplasm and also in the mitochondrial matrix, which act as an energy reserve for these cells that have a high energy demand. Enterocytes showed a well-developed smooth endoplasmic reticulum, especially in the apical region of the cell, being related to absorption and resynthesis of lipids.

Gross anatomy and histology of the alimentary system of Characidae (Teleostei: Ostariophysi: Characiformes) and potential phylogenetic information

A compared study of the morphology of the alimentary tract and liver of seven selected species corresponding to the main clades of the Characidae family is presented herein. Three new set of characters corresponding to 1) alimentary tract gross anatomy, 2) alimentary tract histology and 3) liver gross anatomy are evaluated as potential sources of data for future phylogenetic studies of the Characidae. Not considerable interspecific variation was observed at the histological level and therefore this source is not considered to be phylogenetically informative at the taxonomic level analyzed. In contrast, liver and alimentary tract gross anatomy presented important interspecific variation while a relatively homogenous intraspecific morphology was observed. Those characters are optimized in tree-topologies from previous phylogenetic analyses and their evolution and potential relationship with ecological traits are discussed.

Histological, histochemical and ultrastructural analysis reveals functional division of the oesophagogastric segment in freshwater tubenose goby Proterorhinus semilunaris Heckel, 1837

Histological and histochemical features of the oesophagogastric segment of the alimentary canal as well as ultrastructure of gastric gland cells of freshwater tubenose goby Proterorhinus semilunaris were examined. The studies revealed that despite the lack of anatomical distinction, the oesophagogastric segment is histologically divided into the oesophagus, oesogaster and stomach, which provides evidence for the functional compartmentation of this organ. The oesophagus was characterised by the presence of numerous goblet cells secreting mainly a mixture of neutral and acid mucopolysaccharides. In the stomach, the apical zone of the surface epithelial cells contained neutral mucopolysaccharides. Numerous proliferating cells were scattered throughout the surface epithelium. In the lamina propria of the stomach, a well-developed layer of gastric glands was observed. The glands were of the alveolar type and occupied nearly the entire length of the stomach except the pyloric region. The gastric gland cells were varied into light and dark; however, their ultrastructure was identical. All cells had numerous mitochondria and a well-developed tubulovesicular system typical for the oxynticopeptic cells, but pepsinogen granules were not present in the cytoplasm of these cells. These findings contribute new evidence to literature reports that not all gobiid fish are stomachless. Moreover, they suggest higher adaptation of the species to utilise protein-rich food compared to stomachless fish, and its ability to adjust the alimentary canal quickly to changing diet. How this may facilitate establishment of P. semilunaris in invaded environments remains an open question.

Histochemical and biometric study of the gastrointestinal system of Hyla orientalis (Bedriaga, 1890) (Anura, Hylidae)

This study was carried out to assess the localization of hyaluronic acid (HA) and the distribution of glycoproteins in the gastrointestinal system of adult Hyla orientalis. Histochemical analysis of the gastrointestinal system in H. orientalis showed that mucous content included glycogene and/or oxidable dioles [periodic acid/Schiff (PAS)+], neutral or acid-rich (PAS/AB pH 2.5+), sialic acid residues (KOH/PAS+) and acid sulphate [Aldehyde fuchsin (AF)+] glycoproteins. However the mucus content was not the same in stomach, small and large intestine. The mucus content of stomach included only glycogene and/or oxidable dioles and sialic acid residues. Besides these histochemical methods, the localization of HA was detected using biotinylated hyaluronic acid binding protein labeled with streptavidin-fluorescein isothiocyanate (FITC). In the extracellular matrix of the submucosa, the reaction for HA was evident. Since HA was located in submucosa beneath the epithelial layer of gastrointestinal system, it has a significant role in hydric balance, and essential to provide the gastrointestinal system integrity and functionality. According to biometric results, there were statistical differences between small and large intestine in terms of the amount of material stained positive with PAS/AB, PAS, KOH/PAS and AF/AB. Additionally, number of goblet cells in the small and large intestine was significantly different.

Goblet cell types in intestine of tiger barb and black tetra (Cyprinidae, Characidae: Teleostei)

Histochemical properties of goblet cells in intestine of a stomach-less teleost, tiger barb (Puntius tetrazona), and a stomach-containing teleost, black tetra (Gymnocorymbus ternetzi), are described and compared. The intestine goblet cells were mostly wide in both species, but in tiger barb, some of them were markedly thinner. In black tetra, all the intestine goblet cells displayed magenta colour after PAS, whereas in the tiger barb, only the thinner goblet cells displayed such affinity. The latter cell type was coloured strongly magenta when the tissue was treated with alcian blue (pH 2.5) followed by PAS, whereas the wide goblet cells in tiger barb and all goblet cells in black tetra displayed mainly a blue colour after such treatment. Further, the goblet cells in both species were coloured cleanly blue after high iron diamine followed by alcian blue (pH 2.5). The intestine goblet cells in both species displayed a moderate affinity to WGA and concanavalin A lectins and no affinity to DBA. Most of the goblet cells displayed no affinity to PNA, but some of them in the tiger barb displayed a moderate or strong affinity to this lectin. The affinity to WGA was somewhat strengthened after pre-treatment with neuraminidase. These results suggest that tiger barb contains two types or variants of intestinal goblet cells: high numbers of wide cells filled by acidic, non-sulphated mucin and some thinner cells filled by neutral mucin. The intestine goblet cells in black tetra were filled by variable amounts of neutral and acidic mucin, but the total number of such cells is much less than in tiger barb. The present lectin and neuraminidase results suggest that the intestinal mucins in both species contain significant amounts of N-acetylglucosamine, sialic acid and glucose/mannose, but seem to lack N-acetylgalactosamine. However, some of these cells in tiger barb contain moderate to large amounts of galactose. Together, these results suggest significant species-specific features of the intestine goblet cells and mucin types in tiger barb and black tetra. In conclusion, the present results suggest that the diet and feeding habits in stomach-less teleosts compared with stomach-containing teleosts, greatly influence the number of intestine goblet cells and type of mucin in these cells.

Seawater acclimation and inositol monophosphatase isoform expression in the European eel (Anguilla anguilla) and Nile tilapia (Orechromis niloticus)

Inositol monophosphatase (IMPA) is responsible for the synthesis of inositol, a polyol that can function as an intracellular osmolyte helping re-establish cell volume when exposed to hypertonic environments. Some epithelial tissues in euryhaline teleosts such as the eel and tilapia encounter considerable hyperosmotic challenge when fish move from freshwater (FW) to seawater (SW) environments; however, the roles played by organic osmolytes, such as inositol, have yet to be determined. Syntenic analysis has indicated that, as a result of whole genome- and tandem-duplication events, up to six IMPA isoforms can exist within teleost genomes. Four isoforms are homologs of the mammalian IMPA1 gene, and two isoforms are homologs of the mammalian IMPA2 gene. Although the tissue-dependent isoform expression profiles of the teleost isoforms appear to be species-specific, it was primarily mRNA for the IMPA1.1 isoform that was upregulated in epithelial tissues after fish were transferred to SW (up to 16-fold in eel and 90-fold in tilapia). Although up-regulation of IMPA1.1 expression was evident in many tissues in the eel, more substantial increases in IMPA1.1 expression were found in tilapia tissues, where SW acclimation resulted in up to 2,000-fold increases in protein expression, 16-fold increases in enzyme activity and 15-fold increases in tissue inositol contents. Immunohistochemical studies indicated that the tissue and cellular distribution of IMPA1.1 protein differed slightly between eels and tilapia; however, in both species the basal epithelial cell layers within the skin and fin, and the branchial epithelium and interstitial cells within the kidney, exhibited high levels of IMPA1.1 protein expression.

Immunohistochemical study of the digestive tract of Oligosarcus hepsetus

AIM: To describe the histology of the digestive tract and to investigate the occurrence of endocrine cells in Oligosarcus hepsetus (O. hepsetus).

METHODS: The digestive tract (DT) of O. hepsetus was divided into esophagus, two stomach regions (glandular and non-glandular) and two intestinal regions (anterior and posterior). These specimens were processed by routine histological techniques and stained with hematoxylin-eosin, Gomori’s trichrome, periodic acid Schiff (PAS) and Alcian blue (AB). An immunohistochemical method using avidin-biotin-peroxidase was employed.

RESULTS: The esophagus is lined with a non-keratinized stratified squamous epithelium that is reactive to PAS and AB. The stomach has a mucosa lined with a simple columnar epithelium with mucus-secreting cells that are reactive only to PAS. The intestine has a simple columnar epithelium with a brush border and goblet cells that are reactive to PAS and AB. Somatostatin, serotonin and cholecystokinin immunoreactive cells were identified throughout the DT.

CONCLUSION: This study revealed adaptations for the species’ diet and showed that the distribution and relative frequency of immunoreactive cells are similar to those of other fish.

Mucus cells in the digestive tract in prenatal platyfish larvae (Poeciliidae, Teleostei)

The appearance and histochemical properties of mucus cells in various parts of digestive tract in prenatal larvae of platyfish (Xiphophorus maculatus), a stomachless teleost, are described and compared. Such cells occurred regularly throughout the entire epithelial cell layer in mouth, pharynx, oesophagus and intestine in 6 mm long larvae i.e. approximately 1 week before delivery, but were very scarce in 4 mm long larvae. The mucin in these cells was strongly stained by alcian blue at pH 2.5 and weakly coloured by this dye at pH 1.0. It displayed a clean blue colour after high iron diamine followed by alcian blue (pH 2.5), except in some very few cells which displayed a purple-brown colour after this treatment. The mucus cells displayed various colours between purple-blue and magenta when the alcian blue (pH 2.5) was followed by periodic acid-Schiff (PAS) solution; the magenta-coloured cells were mainly confined to oesophagus. Together these findings suggest that the mucin in the digestive tract of prenatal platyfish consists mainly of non-sulphated, carboxylated glycoconjugates. The observations from the present lectin histochemistry suggest that the amount of galactosamine and glucosamine in this mucin varies much from cell to cell. Also, the various colours after PAS suggest a significant cellular heterogeneity in the mucus cell population. This may reflect different stages in development and maturation or a true and permanent cellular heterogeneity, suggesting that this mucus is able to play a number of important roles even a week before the larvae start to feed and digest.