Light and electron microscopy studies of the midgut and salivary glands of second and third instars of the horse stomach bot,Gasterophilus intestinalis

A morphological study of the midgut and salivary glands of second and third instars of Gasterophilus intestinalis (De Geer) (Diptera: Oestridae) was conducted by light, scanning and transmission electron microscopy. The midgut is anteriorly delimited by a proventriculus, without caeca, and is composed of posterior foregut and anterior midgut tissue from which a double‐layered peritrophic matrix is produced. The midgut can be divided into anterior, median and posterior regions on the basis of the structural and physiological variations of the columnar cells which occur along its length. Two other types of cell were identified: regenerative cells scattered throughout the columnar cells, and, more rarely, endocrine cells of two structural types (closed and open). Different secretion mechanisms (merocrine, apocrine and microapocrine) occur along the midgut epithelium. Abundant microorganisms are observed in the endoperitrophic space of the anterior midgut. The origin and nature of these microorganisms remain unknown. No structural differences are observed between the second and third instar midguts. The salivary glands of G. intestinalis second and third instars consist of a pair of elongated tubular structures connected to efferent ducts which unite to form a single deferent duct linked dorsally to the pharynx. Several intermediate cells, without cuticle, make the junction with the salivary gland epithelium layer. Cytological characteristics of the gland epithelial cells demonstrate high cellular activity and some structural variations are noticed between the two larval stages.     

Conversion of cholic acid and chenodeoxycholic acid into their 7-oxo derivatives by Bacteroides intestinalis AM-1 isolated from human feces

Secondary bile acid-producing bacteria were isolated from human feces to improve our appreciation of the functional diversity and redundancy of the intestinal microbiota. In total, 619 bacterial colonies were isolated using a nutrient-poor agar medium and the level of secondary bile acid formation was examined in each by a liquid culture, followed by thin-layer chromatography. Of five strains analyzed by 16S rRNA gene sequencing and biochemical testing, one was identified as Bacteroides intestinalis AM-1, which was not previously recognized as a secondary bile-acid producer. GC-MS revealed that B. intestinalis AM-1 converts cholic acid (CA) and chenodeoxycholic acid into their 7-oxo derivatives, 7-oxo-deoxycholic acid (7-oxo-DCA) and 7-oxo-lithocholic acid, respectively. Thus, B. intestinalis AM-1 possesses 7α-hydroxysteroid dehydrogenase (7α-HSDH) activity. In liquid culture, B. intestinalis AM-1 showed a relatively higher productivity of 7-oxo-DCA than Escherichia coli HB101 and Bacteroides fragilis JCM11019^T, which are known to possess 7α-HSDH activity. The level of 7α-HSDH activity was higher in B. intestinalis AM-1 than in the other two strains under the conditions tested. The 7α-HSDH activity in each of the three strains is not induced by CA; instead, it is regulated in a growth phase-dependent manner.     

Characterization of the xylan-degrading microbial community from human faeces

In humans, plant cell wall polysaccharides represent an important source of dietary fibres that are digested by gut microorganisms. Despite the extensive degradation of xylan in the colon, the population structure and the taxonomy of the predominant bacteria involved in degradation of this polysaccharide have not been extensively explored. The objective of our study was to characterize the xylanolytic microbial community from human faeces, using xylan from different botanic origins. The xylanolytic population was enumerated at high level in all faecal samples studied. The predominant xylanolytic organisms further isolated (20 strains) were assigned to Roseburia and Bacteroides species. Some Bacteroides isolates corresponded to the two newly described species Bacteroides intestinalis and Bacteroides dorei. Other isolates were closely related to Bacteroides sp. nov., a cellulolytic bacterium recently isolated from human faeces. The remaining Bacteroides strains could be considered to belong to a new species of this genus. Roseburia isolates could be assigned to the species Roseburia intestinalis. The xylanase activity of the Bacteroides and Roseburia isolates was found to be higher than that of other gut xylanolytic species previously identified. Our results provide new insights to the diversity and activity of the human gut xylanolytic community. Four new xylan-degrading Bacteroides species were identified and the xylanolytic capacity of R. intestinalis was further shown.     

Cultivable bacterial diversity from the human colon

Knowledge of the composition of the colonic microbiota is important for our understanding of how the balance of these microbes is influenced by diet and the environment, and which bacterial groups are important in maintaining gut health or promoting disease. Molecular methodologies have advanced our understanding of the composition and diversity of the colonic microbiota. Importantly, however, it is the continued isolation of bacterial representatives of key groups that offers the best opportunity to conduct detailed metabolic and functional studies. This also permits bacterial genome sequencing which will accelerate the linkage to functionality. Obtaining new human colonic bacterial isolates can be challenging, because most of these are strict anaerobes and many have rather exact nutritional and physical requirements. Despite this many new species are being isolated and described that occupy distinct niches in the colonic microbial community. This review focuses on these under-studied yet important gut anaerobes.     

Caspase-dependent apoptosis of the HCT-8 epithelial cell line induced by the parasite Giardia intestinalis

Giardia intestinalis is a flagellated protozoan which causes enteric disease worldwide. Giardia trophozoites infect epithelial cells of the proximal small intestine and can cause acute or chronic diarrhea. The mechanism of epithelial injury in giardiasis remains unknown. A number of enteric pathogens, including protozoan parasites, are able to induce enterocyte apoptosis. The aim of this work was to assess whether G. intestinalis strain WB clone C6 is able to induce apoptosis in the human intestinal epithelial cell line HCT-8, and to investigate the role of caspases in this process. Results demonstrated that the parasite induces cell apoptosis, as confirmed by DNA fragmentation analysis, detection of active caspase-3 and degradation of the caspase-3 substrate PARP [poly(ADP-ribose) polymerase]. Furthermore, G. intestinalis infection induces activation of both the intrinsic and the extrinsic apoptotic pathways, down-regulation of the antiapoptotic protein Bcl-2 and up-regulation of the proapoptotic Bax, suggesting a possible role for caspase-dependent apoptosis in the pathogenesis of giardiasis.     

The ascidian homolog of the vertebrate homeobox gene Rx is essential for ocellus development and function

The tadpole larvae prosencephalon of the ascidian Ciona intestinalis contains a single large ventricle, along the inner walls of which lie two sensory organs: the otolith (a gravity-sensing organ) and the ocellus (a photo-sensing organ composed of a single cup-shaped pigment cell, about 20 photoreceptor cells, and three lens cells). Comparison has been drawn between the morphology and physiology of photoreceptor cells in the ascidian ocellus and the vertebrate eye. The development of vertebrate and invertebrate eyes requires the activity of several conserved genes and it is regulated by precise expression patterns and cell fate decisions common to several species. We have isolated a Ciona homeobox gene (Ci-Rx) that belongs to the paired-like class of homeobox genes. Rx genes have been identified from a variety of organisms and have been demonstrated to have a role in vertebrate eye formation. Ci-Rx is expressed in the anterior neural plate in the middle tailbud stage and subsequently in the larval stage in the sensory vesicle around the ocellus. Loss of Ci-Rx function leads to an ocellus-less phenotype that shows a loss of photosensitive swimming behavior, suggesting the important role played by Ci-Rx in basal chordate photoreceptor cell differentiation and ocellus formation. Furthermore, studies on Ci-Rx regulatory elements electroporated into Ciona embryos using LacZ or GFP as reporter genes indicate the presence of Ci-Rx in pigment cells, photoreceptors, and neurons surrounding the sensory vesicle. In Ci-Rx knocked-down larvae, neither basal swimming activity nor shadow responses develop. Thus, Rx has a role not only in pigment cells and photoreceptor formation but also in the correct development of the neuronal circuit that controls larval photosensitivity and swimming behavior. The results suggest that a Ci-Rx "retinal" territory exists, which consists of pigment cells, photoreceptors, and neurons involved in transducing the photoreceptor signals.     

Development of Pigment Cells in the Brain of Ascidian Tadpole Larvae: Insights into the Origins of Vertebrate Pigment Cells

In vertebrates, melanins produced in specialized pigment cells are required for visual acuity, camouflage, sexual display and protection from ultra violet (UV) radiation. There are three pigment cell types that are classified based on their distinct embryonic origins. Retinal pigment epithelium (RPE) cells originate from the outer layer of the optic cup. Pigment cells of the pineal organ are formed from the developing diencephalon. Melanocytes are derived from the neural crest unique to vertebrate embryos. Some of these pigment cells also play roles that are independent of the activity of tyrosinase, the key melanogenesis enzyme, or melanin: production of substrate(s) for catecholamine synthesis, maintenance of endolymph composition in the cochlea, maintenance of photoreceptor cells in the retina and retinoid metabolism essential for the visual cycle. To deduce the evolutionary origins of vertebrate pigment cells and a possible archetypal genetic circuitry, which may have been modified and utilized to generate multiple pigment cell types, comparison of developmental mechanisms of pigment cells between vertebrates and closely related invertebrate ascidians are proposed to provide useful information. The tadpole‐type larva of ascidians possesses two melanin‐containing pigment cells, termed the otolith and ocellus pigment cells, in the brain that are believed to be required for photo‐ and geotactic responses during swimming. In this review, current knowledge on the development of the two ascidian pigment cells is summarized, i.e. complete cell lineage, structure and expression of genes encoding two melanogenesis enzymes, and molecular developmental mechanisms involving BMP‐CHORDIN antagonism, and possible evolutionary relationships between ascidian and vertebrate pigment cells are discussed.