The gut of the juvenile African lungfish Protopterus annectens: A light and scanning electron microscope study

We describe the microstructure of the alimentary canal of the juvenile lungfish Protopterus annectens. Following the oesophagus, the gut is formed by a long segment that extends down to the pyloric valve. This segment, classically named stomach, is lined by a transitional epithelium but lacks all characteristics of the vertebrate stomach. It has been defined here as the intestinal vestibule. The spiral valve is divided into a first large chamber, which contains mucosal ridges, and a second smooth portion. The entire spiral valve is lined with a pseudostratified columnar epithelium that contains approximately six cell types: enterocytes, goblet cells, ciliated cells, leukocytes, dark pigment cells, and vascular cells. Enterocytes and goblet cells show a high number of cytoplasmic vacuoles. The number and size of the vacuoles, and the number of ciliated cells, decreases from the anterior toward the posterior end, suggesting that most of the digestive processes take place in the anterior part of the spiral valve. The epithelium overlies a lamina propria in the first large chamber and a vascular plexus in the smooth portion. The cloaca has a thick muscular wall covered by a transitional epithelium. An extensive lymphatic system formed by capillaries and lymphatic micropumps is present along the entire wall of the alimentary canal. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Release of aggressive and capture behaviour in the antMyrmecia gulosa F. by exocrine products of the ant Camponotus

An account is given of the behaviour of workers of Myrmecia gulosa in the presence of formic acid and undecane (substances produced by its normal prey Camponotus). Comparative studies with three other species of Myrmecia are described.     

Chinese mantids gut toxic monarch caterpillars: avoidance of prey defence?

1. Monarch caterpillars, Danaus plexippus (Linnaeus), feed on milkweed plants in the genus Asclepias and sequester cardenolides as an anti–predator defence. However, some predators are able to consume this otherwise unpalatable prey. 2. Chinese mantids, Tenodera sinensis (Saussure), were observed consuming monarch caterpillars by ‘gutting’ them (i.e. removing the gut and associated internal organs). They then feed on the body of this herbivore without any apparent ill effects. 3. How adult T. sinensis handle and consume toxic (D. plexippus) and non–toxic [Ostrinia nubilalis (Hübner) and Galleria mellonella (Linnaeus)] caterpillars was explored. The differences in the carbon/nitrogen (C:N) ratio and cardenolide content of monarch tissue consumed or discarded by mantids were analysed. 4. Mantids gutted monarchs while wholly consuming non–toxic species. Monarch gut tissue had a higher C:N ratio than non–gut tissue, confirming the presence of plant material. Although there were more cardenolide peaks in the monarch body compared with gut tissue, the total cardenolide concentration and polarity index did not differ. 5. Although T. sinensis treated toxic prey differently than non–toxic prey, gutting did not decrease the mantid's total cardenolide intake. As other predators consume monarch caterpillars whole, this behaviour may be rooted in species–specific vulnerability to particular cardenolides or simply reflect a preference for high–N tissues.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Diet and phylogeny shape the gut microbiota of Antarctic seals: a comparison of wild and captive animals

The gut microbiota of mammals underpins the metabolic capacity and health of the host. Our understanding of what influences the composition of this community has been limited primarily to evidence from captive and terrestrial mammals. Therefore, the gut microbiota of southern elephant seals, Mirounga leonina, and leopard seals, Hydrurga leptonyx, inhabiting Antarctica were compared with captive leopard seals. Each seal exhibited a gut microbiota dominated by four phyla: Firmicutes (41.5 ± 4.0%), Fusobacteria (25.6 ± 3.9%), Proteobacteria (17.0 ± 3.2%) and Bacteroidetes (14.1 ± 1.7%). Species, age, sex and captivity were strong drivers of the composition of the gut microbiota, which can be attributed to differences in diet, gut length and physiology and social interactions. Differences in particular prey items consumed by seal species could contribute to the observed differences in the gut microbiota. The longer gut of the southern elephant seal provides a habitat reduced in available oxygen and more suitable to members of the phyla Bacteroidetes compared with other hosts. Among wild seals, 16 ‘core’ bacterial community members were present in the gut of at least 50% of individuals. As identified between southern elephant seal mother–pup pairs, ‘core’ members are passed on via vertical transmission from a young age and persist through to adulthood. Our study suggests that these hosts have co‐evolved with their gut microbiota and core members may provide some benefit to the host, such as developing the immune system. Further evidence of their strong evolutionary history is provided with the presence of 18 shared ‘core’ members in the gut microbiota of related seals living in the Arctic. The influence of diet and other factors, particularly in captivity, influences the composition of the community considerably. This study suggests that the gut microbiota has co‐evolved with wild mammals as is evident in the shared presence of ‘core’ members.     

Population genomics reveals evolution and variation of Saccharomyces cerevisiae in the human and insects gut

The quest to discover the variety of ecological niches inhabited by Saccharomyces cerevisiae has led to research in areas as diverse as wineries, oak trees and insect guts. The discovery of fungal communities in the human gastrointestinal tract suggested the host's gut as a potential reservoir for yeast adaptation. Here, we report the existence of yeast populations associated with the human gut (HG) that differ from those isolated from other human body sites. Phylogenetic analysis on 12 microsatellite loci and 1715 combined CDSs from whole-genome sequencing revealed three subclusters of HG strains with further evidence of clonal colonization within the host's gut. The presence of such subclusters was supported by other genomic features, such as copy number variation, absence/introgressions of CDSs and relative polymorphism frequency. Functional analysis of CDSs specific of the different subclusters suggested possible alterations in cell wall composition and sporulation features. The phenotypic analysis combined with immunological profiling of these strains further showed that sporulation was related with strain-specific genomic characteristics in the immune recognition pattern. We conclude that both genetic and environmental factors involved in cell wall remodelling and sporulation are the main drivers of adaptation in S. cerevisiae populations in the human gut.     

Coxal organs of Lithobius forficatus (Myriapoda,Chilopoda)

Summary In Lithobius forficatus each of the coxae of the four posterior trunk segments bear a pore field with several coxal pores. The surrounding single-layered epithelium is composed of four different cell types: the main epithelial cells having a fine-structural organization of transport cells with deep apical and basal folds of the cell surfaces and plasmalemma-mitochondrial complexes, junctional cells, exocrine glands, and the wall cells of the pore channel. The entire epithelium is separated from the hemolymph by an inner cellular sheath. It is assumed that the coxal organs participate in fluid uptake.     

Distribution of PACAP (pituitary adenylate cyclase-activating polypeptide)-like and helospectin-like peptides in the teleost gut

Pituitary adenylate cyclase-activating polypeptide (PACAP) and helospectin are two vasoactive intestinal polypeptide (VIP)-related neuropeptides that have recently been demonstrated in the mammalian gut; the aim of this study was to reveal their occurrence and localisation in the gastrointestinal tract, swimbladder, urinary bladder and the vagal innervation of the gut of teleosts, using immunohistochemical methods on whole-mounts and sections of these tissues from the Atlantic cod, Gadus morhua and the rainbow trout, Oncorhynchus mykiss. Both PACAP-like and helospectin-like peptides were present in the gut wall of the two species. Immunoreactive nerve fibres were found in all layers but were most frequent in the myenteric plexus and along the circular muscle fibres. Immunoreactivity was also demonstrated in nerves innervating the swimbladder wall, the urinary bladder and blood vessels to the gut. Immunoreactive nerve cell bodies were found in the myenteric plexus of the gut and in the muscularis mucosae of the swimbladder. In the vagus nerve, non-immunoreactive nerve cells were surrounded by PACAP-immunoreactive fibres. Double staining revealed the coexistence of PACAP-like and helospectin-like peptides with VIP in all visualized nerve fibres and in some endocrine cells. It is concluded that PACAP-like and helospectin-like peptides coexist with VIP in nerves innervating the gut of two teleost species. The distribution suggests that both PACAP and helospectin, like VIP, are involved in the control of gut motility and secretion.     

Fine Structure of the Hepatic Sacculations of Glossobalanus minutus (Enteropneusta,Hemichordata)

Abstract The hepatic region of Glossobalanus minutus is characterized by deep foldings of the dorsal side of the gut epithelium which affect the neighbouring tissues and structures: coelomic spaces, musculature and epidermis. The following cell types of the gut epithelium are described: vacuolated cells, undifferentiated cells, two types of mucous cells and two types of granular secretory cells. The nature and function of the different cell types are discussed. Data on the general ciliation and subepithelial nerve plexus of the gut epithelium are also given, with special mention of a possible neuroendocrine secretion towards the subjacent blood spaces. A well-developed blood sinus (gut sinus) lies between the gut and the visceral peritoneum. The ultrastructural features of the gut epithelium and its close association with the blood sinus point to an absorptive function. The coelomic cavity is reduced to a narrow space limited by two peritoneal sheets (visceral and parietal) of myoepithelial nature. Amoebocyte-like cells (coelomocytes) occur free in the coelomic fluid, and muscular, unicellular bridges are attached to both peritoneal walls across the coelomic space. The dorsal epidermis follows the gut foldings and is formed by flat, overlapping cells. The present observations are compared with previous histological, histochemical and ultrastructural data.     

Morphological and immunological confirmation of the presence of chlamydiae in the gut tissues of the chesapeake bay clam,Mercenaria mercenaria

The original electron microscopic identification by other investigators in 1977 of chlamydiae in the gut tissues of the Chesapeake Bay hard clam (Mercenaria mercenaria) is corroborated and further supported by evidence ofChlamydia-specific immunofluorescence (IF). Our electron microscopy demonstrated that gut tissue cells were heavily infected with chlamydiae in all stages of development but the intrachlamydial phage-like particles reported in 1977 were not seen. Tissue sections stained with IF reagents were strongly positive, and IF was blocked in varying degrees with chlamydial antisera produced in a goat and a turkey. The IF-positive tissue sections contained intracytoplasmic inclusions that stained darkly with Lugol's iodine (indicating the presence of glycogen) while IF-negative tissues had little if any iodinestaining material. Furthermore, electron micrographs of chlamydiae-containing phagosomes showed numerous rosettes of electron-dense particles typical of glycogen. The presence of iodine-positive phagosomes with electron dense rosettes suggests that the organisms are glycogen-producing chlamydiae biochemically related toChlamydia trachomatis. Repeated attempts to cultivate chlamydiae from the clam tissues in cell cultures and laboratory animals failed.     

The occurrence of argyrophilic and argentaffin cells in the gut of Ciona intestinalis L.

Summary Argyrophilic and argentaffin cells occur in the stomach and intestinal epithelium of the sea-squirt, Ciona intestinalis L.. These cells are characterized by their basal swelling which contains the nucleus surrounded by small secretory granules and by a filamentous cell-apex which reaches the gut lumen. The cells are scattered unevenly within the epithelium. Their number decreases rapidly towards the lower part of the intestine. The localization, size of granules and their shape are features which differentiate these cells from other secretory cells in the gut epithelium such as mucous cells. These cells are thought to possess an endocrine function.The excellent technical assistance of Mrs. R. Sprang is gratefully acknowledged     

Electron microscopic studies of the digestive tract and absorption from the gut lumen of a feather star,oligometra serripinna (Echinodermata)

Summary The gut of a crinoid echinoderm is described for the first time by transmission electron microscopy. The gut comprises a short esophagus, a relatively long intestine and a short rectum. From the luminal side to the coelomic side, the layers of the gut wall are an inner epithelium, an epineural plexus (much reduced or absent in the intestine and rectum), haemal fluid, smooth muscles mixed with a hyponeural plexus, and a visceral peritoneum. The inner epithelium of the esophagus consists of numerous flagellated enterocytes and some mucous cells containing abundant mucous granules. The luminal surface of the esophagus, but not that of the other gut regions, is covered by a conspicuous cuticle. The inner epithelium of the intestine consists of some exocrine cells, presumably exporting digestive enzymes to the gut lumen, and numerous vesicular enterocytes that are flagellated and contain a few apical mucous granules. The inner epithelium of the rectum is made up entirely of vesicular enterocytes most of which lack a flagellum. The uptake of macromolecules from the gut lumen was demonstrated by feeding the feather stars food mixed with ferritin. By 4 h after feeding, ferritin was identified in presumed secondary lysosomes within the enterocytes of the esophagus and within the vesicular enterocytes of the intestine and rectum. The functional implications of the new fine structural results are discussed.     

Morphology and ultrastructure of the gut in Spadella cephaloptera (chaetognatha)

Structural and ultrastructural studies on the gut of the chaetognath Spadella cephaloptera, as well as observations on the feeding behavior of specimens bred in the laboratory, were conducted. The gut displays four distinct zones: pharynx, esophagus, and intestine, to which are connected a pair of diverticula, and the rectum, differing in length, shape, and cellular composition. The intestine alone represents ∼90% of the gut length. Upon ingestion, food in the intestine is submitted to successive backward and forward peristaltic movements until digestion has ended. Ultrastructural observations have identified five distinct cell types from granule morphology and the presence or absence of cilia at the apex of the cells. Three of the types undoubtedly correspond to secretory cells. They are the (1) pharyngeal, (2) esophageal, and (3) light intestinal ciliated cells, which could be, respectively, implicated in (1) mucous, (2) enzyme, and (3) both mucous and enzyme secretions. The fourth type, which corresponds to dense intestinal ciliated cells, displays all the characteristics of cells specialized in the absorption of macromolecules and intracellular digestion. The products of this digestion could be temporarily stored inside dense granules before being utilized during vitellogenesis. Except for the presence of cilia, the fifth type, which is localized in the short rectum, represents a common polyhedral epithelial cell type. © 1996 Wiley-Liss, Inc.     

Studies on the gastrulation of amphibian embryos: Ultrastructure of the migrating cells of anurans

Summary In order to investigate the ultrastructure of the migrating cells in anuran gastrulae, three anurans, which belong to three different genera, were observed with transmission electron microscopy supported by light microscopy of the 1 m sections and scanning electron microscopy. Fine filopodial cell processes, as well as cell processes probably flattened against the inner surface of the blastocoel wall, were formed by the migrating cells. Blebs and lobopodial cell processes were frequently observed inBufo, sometimes inXenopus, but not observed inRana. Microfilaments were observed in the cell processes. Focal close contacts, probably having adhesive properties, were made between the migrating cells and the inner surface of the blastocoel wall. These observations suggest that the cells migrate along the inner surface of the blastocoel wall by forming filopodia and pseudopodia flattened against the wall. The role of the blebs and lobopodial cell processes requires more investigation.     

An electron microscopic study of the circulatory system in Nereis japonica

Blood vessels in Nereis japonica were studied by electron microscopy. It was found that blood vessels regardless of location were similar in the basic organization of the basal lamina and the usual presence of collagen fibrils on the vessel wall. Differences arise, depending on whether the outside of the basal lamina is covered by peritoneal cells, by gut epithelium, or by epidermis. These relate to the location of the vessels in mesenteries, gut or epidermis, but do not reflect basic structural differences in the vessels themselves. Furthermore, it was concluded that true endothelial cells do not exist in the circulatory system of Nereis japonica and that, in this respect, the system is essentially different from that of vertebrates, in which endothelial cells line the vessels of a closed circulatory system. These considerations lead to the further conclusion that the vascular lumen in Nereis is essentially interstitial space and that the system, which has been known as a typical “closed” circulatory system in annelids, is actually an open circulatory system. Peritoneal cells covering the walls of internal vessels show various degrees of muscular differentiation and those possessing myofilaments may be called “myomesothelial cells.”     

The natural diet of the Notonectidae: field trials using electrophoresis

ABSTRACT.

• 1 Field trials were conducted on populations of two sympatic species of the waterbug Notonecta (Hemiptera: Heteroptera), to examine their natural diet using the electrophoretic method of gut contents analysis.
• 2 Fingerprint esterase bands were identified from thirty-three potential aquatic prey types; gut contents of different instars of both species of Notonecta from the field were analysed.
• 3 The level of prey identification possible ranged from 73% in fifth instar N.glauca L. to 100% in third instar N.viridis Delcourt.
• 4 Type A errors, where no prey remains were detected from a full gut, were found in only 3% of the specimens analysed.
• 5 Data on gut states, the number of prey types per gut and details of aquatic prey found in the diet of different instars of field-collected Notonecta are presented.
• 6 These results are compared with previous data on notonectid diets, and the relative merits of different methods of diet analysis are discussed.

     

Endocrine cells in the gut of the ascidian Styela clava

Summary Ultrastructural studies have shown the presence of two types of granulated endocrine cell in the gut of Styela clava. Type I, which occurs in the stomach and intestine contains small irregular granules, each with a distinct halo. Type II, found only in the oesophagus contains larger rounded granules, often with little or no halo. The characteristics of these two cell types are compared with those of endocrine cells found in the digestive tracts of other protochordates and discussed with special reference to the evolution of gastrointestinal endocrine cells in vertebrates.The authors are grateful to Mr. R. Jones for photographic assistance. Animals were collected by courtesy of the Admiralty Marine Trials Station, Portsmouth, This research was carried out during the tenure of S.R.C. grant no. B/RG 82919 to one of us (M.C.T.). The localization of polypeptide hormones in the pharynx and gut of protochordates     

Ultrastructural localization of polysaccharides and N-actetyl-D-galactosamine in the secretory pathway of green algae (Desmidiaceae)

In order to characterize the secretory pathway leading to multipolar tip growth in green algae of the family Desmidiaceae, different general polysaccharide stainings, such as the periodic acid-silver hexamine method and the periodic acid-silver proteinate method as well as different lectins specific to defined sugar residues have been employed. General polysaccharide stainings label different kinds of secretory vesicles starting from the onset of vesicle production up to their delivery into the primary cell wall, however, the discrimination of Golgi products is possible using lectins. Both gold-labelled lectins from Helix pomatia and from Glycine max with affinity to N-acetyl-D-galactosamine only produce labelling of primary wall material containing 'dark vesicles' on the ultrathin sections of high-pressure frozen and freeze-substituted Micrasterias cells, whereas other vesicle types remain unstained. 'Dark vesicles' are labelled when still attached to trans-Golgi compartments, when distributed throughout the cytoplasm or when fusing with the plasma membrane with the same staining intensity which indicates that the sugars detected by the methods used are present from the onset of visible vesicle production. Gold-labelling of N-acetyl-D-galactosamine is also observed in the primary cell wall. In control experiments the staining vanishes when ultrathin sections are pre-incubated with N-acetyl-D-galactosamine. Various other lectins with affinity to different sugar residues than N-acetyl-D-galactosamine do not produce staining of the cell wall nor of any kind of secretory vesicles. As N-acetyl-D-galactosamine is usually not present in N-linked polysaccharides the results point towards the presence of O-linked-glycoproteins in the primary cell wall of desmids.Key words: Golgi, lectins, Micrasterias, N-acetyl-D-galactosamine, secretion, vesicles.      

Apoptosis in the digestive tract of herbivorous Rana pipiens larvae and carnivorous Ceratophrys ornata larvae: An immunohistochemical study

The lifespan of herbivorous Rana pipiens larvae is ～3 months, while that of carnivorous Ceratophrys ornata larvae is only about 2 weeks. During metamorphic climax, the larval gut shortens dramatically, especially in R. pipiens, and its luminal epithelium is replaced by adult‐type epithelium. To determine when programmed cell death occurs during the metamorphic restructuring of the gut, we prepared cross‐sections of the stomach, small intestine, and large intestine from representative larval stages and from juvenile frogs of both species. The sections were incubated with monoclonal antibody against active caspase‐3, one of the key enzymes in the apoptotic cascade. We observed apoptosis in some luminal epithelial cells in each of the three regions of the larval gastrointestinal tract of both species. However, apoptotic cells appeared earlier in larval stages of R. pipiens than C. ornata and few were seen in juvenile frogs of either species. The results demonstrate the occurrence of apoptosis in the metamorphic remodeling of the gut of both R. pipiens larvae and C. ornata larvae. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.