Emergence of Thamugadia ivaschkini microfilaria from the stomach into the hemocoel of Sergentomyia arpaklensis sandflies

Regularities of migration of microfilarians from the stomach to haemocoel in connection with blood digestion and peritrophic membrane formation were studied in sandflies of S. arpaklensis experimentally infected with larvae of Th. ivaschkini. Whatever the number of swallowed parasites, the average number of larvae reaching the haemocoel does not exceed 5. Factors limiting the invasion are the thick layer of prosecretion of the peritrophic membrane and a peculiar way of clot formation during the feeding of S. arpaklensis sandflies with blood of reptiles. The results obtained are compared with data on members of the genus Phlebotomus and other bloodsucking Diptera.     

Distribution of digestive enzymes among the endo- and ectoperitrophic spaces and midgut cells of Rhynchosciara and its physiological significance

Determinations of carbohydrases, proteases, carboxylesterases and phosphatases in the midgut cells and in the luminal spaces outside and inside the peritrophic membrane of Rhynchosciara americana larvae have been carried out. The data show that alpha-amylase, cellulase and proteinases are present in cells, ecto- and endoperitrophic spaces; aminopeptidases and trehalase in cells and ectoperitrophic space; and finally disaccharidases (except trehalase), carboxypeptidases, dipeptidases, carboxylesterases and phosphatases only in cells. The results support the conclusion that digestion takes place in three spatially organized steps. The first one occurs inside the peritrophic membrane and comprises the dispersion and/or decrease in molecular weight of the food molecules. The second is the hydrolysis of the polymeric food molecules in the ectoperitrophic space to dimers and/or small oligomers. Finally, terminal digestion occurs in the midgut caeca and posterior ventriculus cells by enzymes presumed to be plasma membrane bound. The existence of two extracellular sites for digestion in R. americana is considered to be an adaptation to conserve secreted enzymes, since only those penetrating the endoperitrophic space are lost quickly in the faeces.     

Resistance of the alimentary canal of Daphnia magna Straus to the effect of enteropathogenic NAG-vibrios

The interrelations between 30 Daphnias and enteropathogenic NAG-vibrios were experimentally investigated. Using histological and immunoserological techniques, NAG-vibrio administration into the medium inhabited by Crustaceous was shown to cause no pathological changes in the animal alimentary canal. Daphnias used these organisms as food. The intestinal epithelium is well protected from mechanical injury by peritrophic membrane, chitinous lining and peritrophic cavity where digestion takes place.     

Digestive enzymes in midgut cells,endo-and ectoperitrophic contents,and peritrophic membranes of Spodoptera frugiperda (lepidoptera) larvae

In the midgut of Spodoptera frugiperda larvae, subcellular fractionation data suggest that aminopeptidase and part of amylase, carboxypeptidase A, dipeptidase, and trypsin are bound to the microvillar membranes; that major amounts of soluble dipeptidase, cellobiase, and maltase are trapped in the cell glycocalyx; and finally that soluble carboxypeptidase, amylase, and trypsin occur in intracellular vesicles. Most luminal acetylglucosaminidase is soluble and restricted to the ectoperitrophic contents. Aminopeptidase occurs in minor amounts bound to membranes both in the ectoperitrophic contents and incorporated in the peritrophic membrane. Amylase, carboxypeptidase A, and trypsin are found in minor amounts in the ectoperitrophic contents (both soluble and membrane-bound) and in major amounts in the peritrophic membrane with contents. Part of the activities recovered in the last mentioned contents corresponds to enzyme molecules incorporated in the peritrophic membrane. The results suggest that initial digestion is carried out in major amounts by enzymes in the endoperitrophic space and, in minor amounts, by enzymes immobilized in the peritrophic membrane. Intermediate and final digestion occur at the ectoperitrophic space or at the surface of midgut cells. The results also lend support to the hypothesis that amylase and trypsin are derived from membrane-bound forms, are released in soluble form by a microapocrine mechanism, and are partly incorporated into the peritrophic membrane. © 1994 Wiley-Liss, Inc.     

Evidence for a sugar receptor (lectin) in the peritrophic membrane of the blowfly larva, Calliphora erythrocephala Mg. (Diptera)

For the first time a sugar receptor (lectin) has been localized by electron microscopy in an invertebrate. The peritrophic membrane of the blowfly larva, Calliphora erythrocephala, is shown here to express lectins with high specificity for mannose. The lectin is restricted to the lumen side of the peritrophic membrane. The surface of the midgut epithelium is devoid of mannose-specific lectins. It is suggested that the midgut epithelium has lost these lectins during the course of evolution in favour of the peritrophic membrane which is secreted by specialized cells only at the beginning of the midgut.Peritrophic membranes and the midgut epithelium lack lectins specific for galactose. The lumen side of the peritrophic membrane of the larvae has mannose and/or glucose residues, and it is densely packed with two species of bacteria, Proteus vulgaris and P. morganii. These also have mannose-specific lectins as well as mannose residues on their pili. The existence of mannose-specific receptors and mannose residues on both, peritrophic membranes and bacteria, leads to the assumption of mutual adherence between the two surfaces.     

The physiological role of the peritrophic membrane and trehalase: Digestive enzymes in the midgut and excreta of starved larvae of Rhynchosciara

Amylase, cellulase, trehalase, aminopeptidase and trypsin were determined using the midgut and trehalose using the haemolymph of starved and of subsequently fed larvae of Rhynchosciara americana. Midgut trehalase activity decreases steadily during starvation and increases again on feeding, whereas haemolymph trehalose titres remain constant, suggesting that trehalase is a true digestive enzyme. The decrease in amylase, cellulase and trypsin activity in the midgut during starvation is of the same order as that recovered from the excreta. Since this finding is exactly what one would expect if enzyme production stops in response to starvation, this supports the hypothesis that synthesis that synthesis of these enzymes is controlled. The excretion rate of amylase, cellulase and trypsin is very low in comparison to their activity inside the peritrophic membrane and the travel time of the food bolus through the gut. It is proposed that the peritrophic membrane separates two extracellular sites for digestion as an adaptation to conserve secreted enzymes. This could be accomplished by the existence of an endo-ectoperitrophic circulation of the enzymes involved in the initial attack on the food and by restricting to the ectoperitrophic fluid the enzymes which participate only in intermediary digestion of food.     

Epithelial ultrastructure of the midgut of the horsefly, Hybomitra schineri (Tabanidae)

The study of the midgut of Hybomitra schineri by means of electron microscopy has shown that epithelial cells are of cylindrical shape. According to the electron density of cytoplasm the cells can be arranged into three subtypes. The apical surface of all the cells is covered by microvilli with filamentous glycocalyx. The peritrophic membrane of the 1st type is formed in females only during the blood digestion. Two types of secretion of digestive enzymes (merocrine and macroapocrine ones) were found, the latter being prevalent at the carbohydrate feeding.     

Secretion of the type 2 peritrophic matrix protein, peritrophin-15, from the cardia

The midgut of most insects is lined with a peritrophic matrix, which is thought to facilitate digestion and protect the midgut digestive epithelial cells from abrasive damage and invasion by ingested micro-organisms. The type 2 peritrophic matrix is synthesised by a complex and highly specialised organ called the cardia typically located at the junction of the cuticle-lined foregut and midgut. Although the complex anatomy of this small organ has been described, virtually nothing is known of the molecular processes that lead to the assembly of the type 2 peritrophic matrix in the cardia. As a step towards understanding the synthesis of the peritrophic matrix, the synthesis and secretion of the intrinsic peritrophic matrix protein, peritrophin-15 has been followed in the cardia of Lucilia cuprina larvae using immuno-gold localisations. The protein is synthesised by cardia epithelial cells, which have abundant rough endoplasmic reticulum, Golgi, and vesicles indicative of a general secretory function. Peritrophin-15 is packaged into secretory vesicles probably produced from Golgi and transported to the cytoplasmic face of the apical plasma membrane. The vesicles fuse with the plasma membrane at the base of the microvilli and release peritrophin-15 into the inter-microvilli spaces. The protein then becomes associated with the nascent peritrophic matrix, which lies along the tips of the epithelial cell microvilli. It is proposed that peritrophin-15 binds to the ends of chitin fibrils present in the nascent peritrophic matrix, thereby protecting the fibril from the action of exochitinases.     

Feeding, nutrient flow, and functional gut morphology in the cricket Gryllus bimaculatus

The flow of nutrients through the digestive tract of Gryllus bimaculatus is regulated by the proventriculus, which effectively triturates the partially digested food coming from the crop and shoves the mushy nutrient mass into the space between the paired caeca. The many folds at the base of the caeca form a sieve, and only fine food particles (4-10 microm) and fluids in the mush are filtered under pressure (produced by proventricular peristalsis) into the caeca. Combined with the release of enzymes in the caeca and the influx of water, the caeca are rapidly inflated on day 1 after the terminal molt. The remaining, mostly undigested food is shoved into a tube formed by the peritrophic membrane, which is first formed at the anterior end of the ventriculus. A mucous membrane (peritrophic gel) covers the caecal epithelium, and seems to merge with the true peritrophic membrane at the beginning of the ventriculus. The Type I peritrophic membrane is dragged posteriorly through the entire ventriculus and ileum by the posterior movement of the food bolus, which is shoved posteriorly at a rate of 6 mm/h by proventricular pressure. The growth rate of the peritrophic membrane is about 3 mm/h. Peristalsis does not occur in the midgut or ileum; the muscles in these regions function solely to counteract the internal pressure produced by the proventriculus. The exo- and endoperitrophic space in newly molted animals is open and fluids can flow in both directions. The endoperitrophic space becomes filled on day 1, and leads to a great reduction of the exoperitrophic space. In the ileal pouch (exoperitrophic space) the peritrophic membrane separates the mass of bacteria from the waste bolus within the endoperitrophic space. Feathery bristles arising from the cuticular covering of the finger-like invaginations of the ileal wall hold most of the bacterial mass in place. The crop weight decreases from day 1 to day 3 as the weight of caeca, ventriculus, and ileum increases. After day 3, food uptake and the weight of the entire gut system decrease in female crickets, partly in response to space restrictions in the abdomen caused by rapid ovarial growth.     

Plant resistance and its effect on the peritrophic membrane of southwestern corn borer (Lepidoptera: Crambidae) larvae

The southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), is a serious pest of corn, Zea mays L., in the southern United States. Corn germplasm lines with conventional genetic leaf-feeding resistance to this pest, the fall armyworm, Spodoptera frugiperda (J.E. Smith), and other lepidopterans have been released to the public by USDA-ARS scientists located in Mississippi. Recent studies suggest the insect resistant lines disrupt the integrity of the peritrophic membrane of the fall armyworm. The objectives of this study were to investigate any morphological differences in the structure of the peritrophic membrane of southwestern corn borer larvae feeding on resistant and susceptible corn hybrids and to quantify the damage. Larvae were reared under field and laboratory conditions on three corn hybrids (two resistant and one susceptible). Scanning electron microscopy was used to examine the peritrophic membrane for abnormalities such as holes or tears and to count the holes or tears in the membrane. Differences in the degree of damage to peritrophic membrane of larvae fed on resistant and susceptible plants were not detected. Up to five distinct layers of the membrane were observed in each larva. Variation in the amounts of damage to the peritrophic membrane observed from larvae feeding on all plant material was high. Plant resistance adversely affects growth and development of southwestern corn borer larvae, and further investigations are needed to explain the role of plant resistance and its relation to peritrophic membrane in southwestern corn borer larvae.     

The ultrastructure of the digestive cells of Argulus japonicus, Thiele 1900 (Crustacea: Branchiura)

The ultrastructure of the cells of the digestive system of Argulus japonicus is described with the use of transmission electron microscopy. Specimens of Argulus japonicus were collected from the Vaal Dam in South Africa and fixed in Todd's fixative. The samples were post fixed in osmium tetroxide and embedded in resin. The anterior midgut is composed mostly of R cells while the enteral diverticula are composed mainly of R cells in the proximal diverticules and of F cells in the distal diverticula. The posterior midgut is composed of very large papilliform B cells and of R cells. The R cells in the anterior midgut probably absorb nutrients including lipids. The F cells are filled mostly with rough endoplasmic reticulum, suggesting enzyme synthesis, while the B cells portrayed endocytotic vesicles, indicating intracellular digestion of predigested food. The R cells of the posterior midgut are less active than cells present in the anterior midgut. E cells and peritrophic membrane were not observed.     

A study of tolerance of ingested tannin in Schistocerca gregaria

A study has been made on the effects of ingestion of tannic acid on growth and development of Schistocerca gregaria. No deleterious effects were found on digestion or utilisation of food, even when food protein levels were very low. At high concentrations consumption rates were relatively low over the first day, but this effect was not sustained. The lack of ‘antidigestive’ effects is shown to be due partly to the hydrolysis of tannic acid to gallic acid and glucose, and partly to the adsorptive properties of the peritrophic membrane. Insects reared on food with high levels of tannic acid took a longer time to reach sexual maturity than did the controls, although fecundity was not affected thereafter.     

Cellular organization and peritrophic membrane formation in the cardia (Proventriculus) of Drosophila melanogaster

The peritrophic membrane of Drosophila melanogaster consists of four layers, each associated with a specific region of the folded epithelial lining of the cardia. The epithelium is adapted to produce this multilaminar peritrophic membrane by bringing together several regions of foregut and midgut, each characterized by a distinctively differentiated cell type. The very thin, electron-dense inner layer of the peritrophic membrane originates adjacent to the cuticular surface of the stomadeal valve and so appears to require some contribution by the underlying foregut cells. These foregut cells are characterized by dense concentrations of glycogen, extensive arrays of smooth endoplasmic reticulum, and pleated apical plasma membranes. The second and thickest layer of the peritrophic membrane coalesces from amorphous, periodic acid-Schiff-positive material between the microvilli of midgut cells in the neck of the valve. The third layer of the peritrophic membrane is composed of fine electron-dense granules associated with the tall midgut cells of the outer cardia wall. These columnar cells are characterized by cytoplasm filled with extensive rough endoplasmic reticulum and numerous Golgi bodies and by an apical projection filled with secretory vesicles and covered by microvilli. The fourth, outer layer of the peritrophic membrane originates over the brush border of the cuboidal midgut cells, which connect the cardia with the ventriculus.     

Chitin in the peritrophic membrane of Acarus siro (Acari: Acaridae) as a target for novel acaricides

The peritrophic membrane in Acarus siro L. (Acari: Acaridae) is produced by distinct cells located in the ventriculus. In this study, the chitin inside the peritrophic membrane was detected using wheat germ-lectin conjugated with colloidal gold (10 nm). The chitin fibrils of the peritrophic membrane were a target for chitin effectors, including 1) chitinase, which hydrolyzes chitin fibers inside the peritrophic membrane; 2) calcofluor, which binds to chitin and destroys the peritrophic membrane mesh structure; and 3) diflubenzuron, which inhibits chitin synthesis. In addition, soybean trypsin protease inhibitor (STI) and cocktails of chitinase/calcofluor, diflubenzuron/calcofluor and chitinase/STI were tested. These compounds were supplemented in diets and an increase of population initiated from 50 individuals was observed after 21 d of cultivation. Final A. siro densities on experimental and control diets were compared. The chitin in the peritrophic membrane was determined to be a suitable target for novel acaricidal compounds for suppressing the population growth of A. siro. The most effective compounds were calcofluor and diflubenzuron, whereas the suppressive effects of chitinase and STI were low. The failure of chitinase could be due to its degradation by endogenous proteases. The combination of chitinase and STI suppressed A. siro population growth more effectively than when they were tested in oral admission separately. The combinations of calcofluor/chitinase or calcofluor/difluorbenzuron showed no additive effects on final A. siro density. The presence of chitin in peritrophic membrane provides a target for novel acaricidal compounds, which disrupt peritrophic membrane structure. The suitability of chitin effectors and their practical application in the management of stored product mites is discussed.     

Ultrastructure of the digestive tract in Acarus siro (Acari: Acaridida)

The gut of the mite Acarus siro is characterized on the ultrastructural level. It consists of the foregut (pharynx, esophagus), midgut (ventriculus, caeca, colon, intercolon, postcolonic diverticula, postcolon), and hindgut (anal atrium). The gut wall is formed by a single-layered epithelium; only regenerative cells are located basally and these have no contact with the lumen. Eight cell types form the whole gut: (i) simple epithelial cells forming fore- and hindgut; (ii) cells that probably produce the peritrophic membrane; (iii) regenerative cells occurring in the ventriculus, caeca, colon, and intercolon; (iv) spherite cells and (v) digestive cells forming the ventriculus and caeca; (vi) colonic cells and (vii) intercolonic cells; and (viii) cells forming the walls of postcolonic diverticula and postcolon. Spherite and digestive cells change in structure during secretory cycles, which are described and discussed. The cycle of spherite, colonic, and intercolonic cells is terminated by apoptosis. Ingested food is packed into a food bolus surrounded by a single homogeneous peritrophic membrane formed by addition of lamellae that subsequently fuse together. The postcolonic diverticula serve as a shelter for filamentous bacteria, which also are abundant in the intercolon.     

Ultrastructure of American foulbrood disease pathogenesis in larvae of the worker honey bee,Apis mellifera

Using electron microscopy, the pathogenesis of American foulbrood disease was followed from ingestion of Bacillus larvae spores by young, susceptible honey bee larvae to death of the host and sporulation of the pathogen. Interaction between the host peritrophic membrane and B. larvae vegetatives is described. Phagocytosis was demonstrated to be a mechanism of entry of pathogen into host midgut cells. No evidence of enzymatic digestion of peritrophic membrane or host-cell microvilli was found during the initial interaction of pathogen and host midgut cell, although eventual lysis of host gut cells may have been the result of enzymatic activity. Following entry of bacteria into the hemocoel, host death resulted from systemic bacteremia.     

The peritrophic matrix limits the rate of digestion in adult Anopheles stephensi and Aedes aegypti mosquitoes

The peritrophic matrix (PM) is a chitin-containing acellular sheath that surrounds the blood meal and separates the food bolus from the midgut epithelium. Intense molecular traffic through the PM occurs during digestion. Digestive enzymes secreted by the midgut epithelium must traverse the PM to reach their substrates in the food bolus, and digestion products must cross the PM in the opposite direction to be absorbed by the epithelial cells. Here we report that the PM limits the rate of digestion. PM disruption by two independent means (chitinase and anti-PM antibodies) consistently increases the rate of blood digestion. The significance of these results in relation to PM function is discussed.     

棉铃虫围食膜的蛋白质组鉴定

【目的】围食膜(peritrophic membrane, PM)是昆虫抵御随食物摄入的病原微生物入侵的第一道天然屏障。本研究旨在鉴定出农业重大害虫棉铃虫Helicoverpa armigera围食膜的总蛋白成分,为进一步揭示昆虫围食膜的形成机制及研发新颖的害虫控制策略奠定基础。【方法】剥离棉铃虫5龄幼虫PM,用三氟甲磺酸(trifluoromethane sulfonic acid, TFMS)处理,采用液质联用技术(LC-MS/MS)鉴定围食膜蛋白质组,然后对鉴定结果进行生物信息学分析。【结果】本研究共鉴定出棉铃虫幼虫围食膜蛋白质169个,是目前鉴定最多的棉铃虫围食膜蛋白。通过GO分析,可以将这些鉴定的蛋白分为细胞组分、分子功能和生物学过程三大类;KEGG富集结果显示,鉴定蛋白可以富集在12条代谢通路中;蛋白互作分析(protein protein interaction, PPI)结果表明,以ACC和CG3011等蛋白为核心可以形成蛋白互作网络。【结论】本研究鉴定了169个棉铃虫幼虫围食膜蛋白质,并对其进行了GO, KEGG和PPI分析,结果有助于人们全面理解昆虫围食膜的分子结构和功能。     

The ultrastructure of the midgut and the formation of peritrophic membranes in a harvestman,Phalangium opilio (Chelicerata Phalangida)

Summary The ultrastructure of the midgut epithelium of Phalangium opilio was examined. In the anterior part of the midgut the epithelium consists of three different types of cells, called resorption, digestion, and excretion cells according to their presumed functions. Excretion cells may represent old digestion cells. The relation between resorption and digestion cells needs further investigation. The epithelium of the posterior part of the midgut consists of two types, transport and secretion cells, which seem to serve mainly for the resorption of water and the secretion of peritrophic membranes, respectively.Peritrophic membranes are secreted by the anterior midgut epithelium mainly in a period between 2 and 4 h after feeding. Chitin or chitin precursors could be localized in vesicles and in the brush border of midgut cells, and in the peritrophic membranes, using colloidal gold labelled with wheat germ agglutinin. Two different textures of chitin-containing microfibrils were found in the peritrophic membranes, either a random or a hexagonal texture. The latter results if the microfibrils polymerize between the basal parts of the microvilli. Irregularities of the hexagonal texture can be correlated with an irregular pattern of the microvilli. In the posterior midgut peritrophic membranes with a random texture, chitin-containing microfibrils are continuously secreted in the form of patches.     

The origin and functions of the insect peritrophic membrane and peritrophic gel

There is a a fluid (peritrophic gel) or membranous (peritrophic membrane, PM) film surrounding the food bolus in most insects. The PM is composed of chitin and proteins, of which peritrophins are the most important. It is proposed here that, during evolution, midgut cells initially synthesized chitin and peritrophins derived from mucins by acquiring chitin-binding domains, thus permitting the formation of PM. Since PM compartmentalizes the midgut, new physiological roles were added to those of the ancestral mucus (protection against abrasion and microorganism invasion). These new roles are reviewed in the light of data on PM permeability and on enzyme compartmentalization, fluid fluxes, and ultrastructure of the midgut. The importance of the new roles in relation to those of protection is evaluated from data obtained with insects having disrupted PM. Finally, there is growing evidence suggesting that a peritrophic gel occurs when a highly permeable peritrophic structure is necessary or when chitin-binding molecules or chitinase are present in food.