Proventriculus-specific cDNAs characterized from the tsetse, Glossina morsitans morsitans

Peritrophins are involved in the defense against Bacillus thuringiensis and nucleopolyhedrovirus formulations in Spodoptera littoralis (Lepidoptera: Noctuidae)

The peritrophic matrix (or peritrophic membrane, PM) is present in most insects where it acts as a barrier to mechanical insults and pathogens, as well as a facilitator of digestive processes. The PM is formed by the binding of structural PM proteins, referred to as peritrophins, to chitin fibrils and spans the entire midgut in lepidopterans. To investigate the role of peritrophins in a highly polyphagous lepidopteran pest, namely the cotton leafworm (Spodoptera littoralis), we generated Insect Intestinal Mucin (IIM-) and non-mucin Peritrophin (PER-) mutant strains via CRISPR/Cas9 mutagenesis. Both strains exhibited deformed PMs and retarded developmental rates. Bioassays conducted with Bacillus thuringiensis (Bt) and nucleopolyhedrovirus (SpliNPV) formulations showed that both the IIM- and PER- mutant larvae were more susceptible to these bioinsecticides compared to the wild-type (WT) larvae with intact PM. Interestingly, the provision of chitin-binding agent Calcofluor (CF) in the diet lowered the toxicity of Bt formulations in both WT and IIM- larvae and the protective effect of CF was significantly lower in PER- larvae. This suggested that the interaction of CF with PER is responsible for Bt resistance mediated by CF. In contrast, the provision of CF caused increased susceptibility to SpliNPV in both mutants and WT larvae. The study showed the importance of peritrophins in the defense against pathogens in S. littoralis and revealed novel insights into CF-mediated resistance to Cry toxin.

Peritrophin-like Genes Are Associated with Delousing Drug Response and Sensitivity in the Sea Louse Caligus rogercresseyi

Caligus rogercresseyi is the main ectoparasite that affects the salmon industry in Chile. The mechanisms used by the parasite to support its life strategy are of great interest for developing control strategies. Due to the critical role of insect peritrophins in host–parasite interactions and response to pest control drugs, this study aimed to identify and characterize the peritrophin-like genes present in C. rogercresseyi. Moreover, the expression of peritrophin-like genes was evaluated on parasites exposed to delousing drugs such as pyrethroids and azamethiphos. Peritrophin genes were identified by homology analysis among the sea louse transcriptome database and arthropods peritrophin-protein database obtained from GenBank and UniProt. Moreover, the gene loci in the parasite genome were located. Furthermore, peritrophin gene expression levels were evaluated by RNA-Seq analysis in sea louse developmental stages and sea lice exposed to delousing drugs deltamethrin, cypermethrin, and azamethiphos. Seven putative peritrophin-like genes were identified in C. rogercresseyi with high homology with other crustacean peritrophins. Differences in the presence of signal peptides, the number of chitin-binding domains, and the position of conserved cysteines were found. In addition, seven peritrophin-like gene sequences were identified in the C. rogercresseyi genome. Gene expression analysis revealed a stage-dependent expression profile. Notably, differential regulation of peritrophin genes in resistant and susceptible populations to delousing drugs was found. These data are the first report and characterization of peritrophin genes in the sea louse C. rogercresseyi, representing valuable knowledge to understand sea louse biology. Moreover, this study provides evidence for a deeper understanding of the molecular basis of C. rogercresseyi response to delousing drugs.

Identifying and Characterizing a Novel Peritrophic Matrix Protein (MdPM-17) Associated With Antibacterial Response From the Housefly, Musca domestica (Diptera: Muscidae)

Peritrophic matrix/membrane (PM) critically prevents the midgut of insects from external invasion by microbes. The proteins in the peritrophic membrane are its major structural components. Additionally, they determine the formation and function of this membrane. However, the role of PM proteins in immune regulation is unclear. Herein, we isolated a novel PM protein (MdPM-17) from Musca domestica larvae. Further, the function of MdPM-17 in regulating host innate immunity was identified. Results showed that the cDNA of MdPM-17 full is 635 bp in length. Moreover, it consists of a 477-bp open reading frame encoding 158 amino acid residues. These amino acid residues are composed of two Chitin-binding type-2 domain (ChtBD2) and 19 amino acids as a signal peptide. Moreover, tissue distribution analysis indicates that MdPM-17 was enriched expressed in midgut, and moderate levels in the fat body, foregut, and malpighian tubule. Notably, MdPM-17 recombinant protein showed high chitin-binding capacity, thus belongs to the Class III PM protein group. MdPM-17 protein silencing via RNA interference resulted in the expression of antimicrobial peptide (defensin, cecropins, and diptericin) genes, and this occurred after oral inoculation with exogenous microbes Escherichia coli (Enterobacteriales:Enterobacteriaceae), Staphylococcus aureus (Bacillales:Staphylococcaceae), and Candida albicans (Endomycetales:Saccharomycetaceae)). Therefore, all the antimicrobial peptide (AMP) gene expression levels are high in MdPM-17-depleted larvae during microbial infection compared to controls. Consequently, these findings indicate that MdPM-17 protein is associated with the antibacterial response from the housefly.

A fine-tuned vector-parasite dialogue in tsetse's cardia determines peritrophic matrix integrity and trypanosome transmission success

Arthropod vectors have multiple physical and immunological barriers that impede the development and transmission of parasites to new vertebrate hosts. These barriers include the peritrophic matrix (PM), a chitinous barrier that separates the blood bolus from the midgut epithelia and modulates vector-pathogens interactions. In tsetse flies, a sleeve-like PM is continuously produced by the cardia organ located at the fore- and midgut junction. African trypanosomes, Trypanosoma brucei, must bypass the PM twice; first to colonize the midgut and secondly to reach the salivary glands (SG), to complete their transmission cycle in tsetse. However, not all flies with midgut infections develop mammalian transmissible SG infections—the reasons for which are unclear. Here, we used transcriptomics, microscopy and functional genomics analyses to understand the factors that regulate parasite migration from midgut to SG. In flies with midgut infections only, parasites fail to cross the PM as they are eliminated from the cardia by reactive oxygen intermediates (ROIs)—albeit at the expense of collateral cytotoxic damage to the cardia. In flies with midgut and SG infections, expression of genes encoding components of the PM is reduced in the cardia, and structural integrity of the PM barrier is compromised. Under these circumstances trypanosomes traverse through the newly secreted and compromised PM. The process of PM attrition that enables the parasites to re-enter into the midgut lumen is apparently mediated by components of the parasites residing in the cardia. Thus, a fine-tuned dialogue between tsetse and trypanosomes at the cardia determines the outcome of PM integrity and trypanosome transmission success.

Insects are responsible for transmission of parasites that cause deadly diseases in humans and animals. Understanding the key factors that enhance or interfere with parasite transmission processes can result in new control strategies. Here, we report that a proportion of tsetse flies with African trypanosome infections in their midgut can prevent parasites from migrating to the salivary glands, albeit at the expense of collateral damage. In a subset of flies with gut infections, the parasites manipulate the integrity of a midgut barrier, called the peritrophic matrix, and reach the salivary glands for transmission to the next mammal. Either targeting parasite manipulative processes or enhancing peritrophic matrix integrity could reduce parasite transmission.

Ironing out the Details: Exploring the Role of Iron and Heme in Blood-Sucking Arthropods

Heme and iron are essential molecules for many physiological processes and yet have the ability to cause oxidative damage such as lipid peroxidation, protein degradation, and ultimately cell death if not controlled. Blood-sucking arthropods have evolved diverse methods to protect themselves against iron/heme-related damage, as the act of bloodfeeding itself is high risk, high reward process. Protective mechanisms in medically important arthropods include the midgut peritrophic matrix in mosquitoes, heme aggregation into the crystalline structure hemozoin in kissing bugs and hemosomes in ticks. Once heme and iron pass these protective mechanisms they are presumed to enter the midgut epithelial cells via membrane-bound transporters, though relatively few iron or heme transporters have been identified in bloodsucking arthropods. Upon iron entry into midgut epithelial cells, ferritin serves as the universal storage protein and transport for dietary iron in many organisms including arthropods. In addition to its role as a nutrient, heme is also an important signaling molecule in the midgut epithelial cells for many physiological processes including vitellogenesis. This review article will summarize recent advancements in heme/iron uptake, detoxification and exportation in bloodfeeding arthropods. While initial strides have been made at ironing out the role of dietary iron and heme in arthropods, much still remains to be discovered as these molecules may serve as novel targets for the control of many arthropod pests.

Mammalian African trypanosome VSG coat enhances tsetse's vector competence

Tsetse flies are biological vectors of African trypanosomes, the protozoan parasites responsible for causing human and animal trypanosomiases across sub-Saharan Africa. Currently, no vaccines are available for disease prevention due to antigenic variation of the Variant Surface Glycoproteins (VSG) that coat parasites while they reside within mammalian hosts. As a result, interference with parasite development in the tsetse vector is being explored to reduce disease transmission. A major bottleneck to infection occurs as parasites attempt to colonize tsetse's midgut. One critical factor influencing this bottleneck is the fly's peritrophic matrix (PM), a semipermeable, chitinous barrier that lines the midgut. The mechanisms that enable trypanosomes to cross this barrier are currently unknown. Here, we determined that as parasites enter the tsetse's gut, VSG molecules released from trypanosomes are internalized by cells of the cardia-the tissue responsible for producing the PM. VSG internalization results in decreased expression of a tsetse microRNA (mir-275) and interferes with the Wnt-signaling pathway and the Iroquois/IRX transcription factor family. This interference reduces the function of the PM barrier and promotes parasite colonization of the gut early in the infection process. Manipulation of the insect midgut homeostasis by the mammalian parasite coat proteins is a novel function and indicates that VSG serves a dual role in trypanosome biology-that of facilitating transmission through its mammalian host and insect vector. We detail critical steps in the course of trypanosome infection establishment that can serve as novel targets to reduce the tsetse's vector competence and disease transmission.

CONSTRUCTION OF SILKWORM MIDGUT cDNA LIBRARY FOR SCREEN AND SEQUENCE ANALYSIS OF PERITROPHIC MEMBRANE PROTEIN GENES

Silkworm is an important economic insect and the model species for Lepidoptera. The midgut of silkworm is an important physiological barrier, as its peritrophic membrane (PM) can resist pathogen invasion. In this study, a silkworm midgut cDNA library was constructed in order to identify silkworm PM genes. The capacity of the initial library was 6.92 × 10(6) pfu/ml, along with a recombination rate of 92.14% and a postamplification titer of 4.10 × 10(9) pfu/ml. Three silkworm PM protein genes were obtained by immunoscreening, two of which were chitin-binding protein (CBP) genes and one of which was a chitin deacetylase (CDA) gene as revealed by sequence analysis. Three genes were named BmCBP02, BmCBP13, and BmCDA17, and their ORF sizes are 678, 1,029, and 645 bp, respectively; all of them contain sequences of chitin-binding domains. Phylogenetic analysis indicated that BmCBP02 has the highest consensus with Mamestra configurata CBP at 61.0%; BmCBP13 has the highest consensus with Loxostege sticticalis PM CBP at 53.35%; BmCDA17 has the highest consensus with Helicoverpa armigera CDA5a at 70.83%. Tissue transcriptional analysis revealed that all three genes were specifically expressed in the midgut, and during the developmental process of fifth-instar silkworms, the transcription of all the genes showed an upward trend. This study laid a foundation for further studies on the functions of silkworm PM genes.

Identification and molecular characterization of a chitin-binding protein from the beet webworm, Loxostege sticticalis L

As the first crucial barrier in the midgut of insects, the peritrophic membrane (PM) plays an important role in preventing external invasion. PM proteins, as the major components of the PM, determine the structure and function of this membrane. A new PM protein, named LstiCBP, from the PM of Loxostege sticticalis larvae was identified using cDNA library screening. The full cDNA of LstiCBP is 2606 bp in length and contains a 2403 bp ORF that encodes an 808-amino acid preprotein with a 15-amino acid as signal peptide. The deduced protein sequence of the cDNA contains 8 cysteine-rich chitin-binding domains (CBDs). Recombinant LstiCBP was successfully expressed in BL21 cells using recombinant plasmid DNA and showed high chitin-binding activity. LstiCBP expression was detected in the midgut at both the transcriptional and translational levels; however, the biochemical and physiological functions of LstiCBP in L. sticticalis require further investigation.

The peritrophic matrix mediates differential infection outcomes in the tsetse fly gut following challenge with commensal, pathogenic, and parasitic microbes

The insect gut is lined by a protective, chitinous peritrophic matrix (PM) that separates immunoreactive epithelial cells from microbes present within the luminal contents. Tsetse flies (Glossina spp.) imbibe vertebrate blood exclusively and can be exposed to foreign microorganisms during the feeding process. We used RNA interference-based reverse genetics to inhibit the production of a structurally robust PM and then observed how this procedure impacted infection outcomes after per os challenge with exogenous bacteria (Enterobacter sp. and Serratia marcescens strain Db11) and parasitic African trypanosomes. Enterobacter and Serratia proliferation was impeded in tsetse that lacked an intact PM because these flies expressed the antimicrobial peptide gene, attacin, earlier in the infection process than did their counterparts that housed a fully developed PM. After challenge with trypanosomes, attacin expression was latent in tsetse that lacked an intact PM, and these flies were thus highly susceptible to parasite infection. Our results suggest that immunodeficiency signaling pathway effectors, as opposed to reactive oxygen intermediates, serve as the first line of defense in tsetse's gut after the ingestion of exogenous microorganisms. Furthermore, tsetse's PM is not a physical impediment to infection establishment, but instead serves as a barrier that regulates the fly's ability to immunologically detect and respond to the presence of these microbes. Collectively, our findings indicate that effective insect antimicrobial responses depend largely upon the coordination of multiple host and microbe-specific developmental factors.

An investigation into the protein composition of the teneral Glossina morsitans morsitans peritrophic matrix

Background

Tsetse flies serve as biological vectors for several species of African trypanosomes. In order to survive, proliferate and establish a midgut infection, trypanosomes must cross the tsetse fly peritrophic matrix (PM), which is an acellular gut lining surrounding the blood meal. Crossing of this multi-layered structure occurs at least twice during parasite migration and development, but the mechanism of how trypanosomes do so is not understood. In order to better comprehend the molecular events surrounding trypanosome penetration of the tsetse PM, a mass spectrometry-based approach was applied to investigate the PM protein composition using Glossina morsitans morsitans as a model organism.

Methods

PMs from male teneral (young, unfed) flies were dissected, solubilised in urea/SDS buffer and the proteins precipitated with cold acetone/TCA. The PM proteins were either subjected to an in-solution tryptic digestion or fractionated on 1D SDS-PAGE, and the resulting bands digested using trypsin. The tryptic fragments from both preparations were purified and analysed by LC-MS/MS.

Results

Overall, nearly 300 proteins were identified from both analyses, several of those containing signature Chitin Binding Domains (CBD), including novel peritrophins and peritrophin-like glycoproteins, which are essential in maintaining PM architecture and may act as trypanosome adhesins. Furthermore, 27 proteins from the tsetse secondary endosymbiont, Sodalis glossinidius, were also identified, suggesting this bacterium is probably in close association with the tsetse PM.

Conclusion

To our knowledge this is the first report on the protein composition of teneral G. m. morsitans, an important vector of African trypanosomes. Further functional analyses of these proteins will lead to a better understanding of the tsetse physiology and may help identify potential molecular targets to block trypanosome development within the tsetse.

African trypanosomes are transmitted by the haematophagous tsetse vector. For transmission to occur, bloodmeal ingested trypanosomes must overcome numerous barriers imposed by the fly. The first obstacle is the crossing of peritrophic matrix (PM), a cell-free structure that protects the midgut epithelial cells from coming under attack by the hosts' digestive enzymes, aids in water retention and helps prevent harmful pathogens from establishing a systemic infection. Trypanosomes cross the tsetse PM at least twice in their development but how they do so remains to be elucidated. Despite being a recognised barrier to trypanosome infections, there is limited knowledge of the molecular components of the tsetse PM. In this study we identified nearly 300 PM proteins using two mass spectrometry approaches. Several of the identified components were peritrophins, which are a key group of glycoproteins essential for PM integrity. In addition, we detected proteins from Sodalis glossinidius, a commensal bacterium linked to increased susceptibility to trypanosome infection in tsetse. Our study provides the first comprehensive identification of proteins from the tsetse PM, which provides a starting point for research into potential targets for vector control.

Post eclosion age predicts the prevalence of midgut trypanosome infections in Glossina

The teneral phenomenon, as observed in Glossina sp., refers to the increased susceptibility of the fly to trypanosome infection when the first bloodmeal taken is trypanosome-infected. In recent years, the term teneral has gradually become synonymous with unfed, and thus fails to consider the age of the newly emerged fly at the time the first bloodmeal is taken. Furthermore, conflicting evidence exists of the effect of the age of the teneral fly post eclosion when it is given the infected first bloodmeal in determining the infection prevalence. This study demonstrates that it is not the feeding history of the fly but rather the age (hours after eclosion of the fly from the puparium) of the fly when it takes the first (infective) bloodmeal that determines the level of fly susceptibility to trypanosome infection. We examine this phenomenon in male and female flies from two distinct tsetse clades (Glossina morsitans morsitans and Glossina palpalis palpalis) infected with two salivarian trypanosome species, Trypanosoma (Trypanozoon) brucei brucei and Trypanosoma (Nannomonas) congolense using Fisher's exact test to examine differences in infection rates. Teneral tsetse aged less than 24 hours post-eclosion (h.p.e.) are twice as susceptible to trypanosome infection as flies aged 48 h.p.e. This trend is conserved across sex, vector clade and parasite species. The life cycle stage of the parasite fed to the fly (mammalian versus insect form trypanosomes) does not alter this age-related bias in infection. Reducing the numbers of parasites fed to 48 h.p.e., but not to 24 h.p.e. flies, increases teneral refractoriness. The importance of this phenomenon in disease biology in the field as well as the necessity of employing flies of consistent age in laboratory-based infection studies is discussed.

Identification and molecular characterization of a new member of the peritrophic membrane proteins from the meadow moth, loxostege sticticalis

The peritrophic membrane (PM) plays an important role in protecting insects. The PM proteins are important to determinate the formation and function of the PM. A new PM protein, named Lsti99, was identified from the PM of Loxostege sticticalis larvae by cDNA library screening. The full cDNA of Lsti99 is 1392 bp in length, contains an open reading frame (ORF) of 1245 bp that encodes a preprotein of 415 amino acid residues with a 17-amino acid signal peptide. The sequence of Lsti99 showed no homology to other known PM proteins. The recombinant Lsti99 was successfully expressed in insect cells (Sf9) using recombinant baculoviruses and was used to isolate the antibodies to Lsti99 from the polyclonal antiserum. Lsti99 was expressed mainly in the PM, but weaker bands could be detected in the head and integument as well. The Lsti99 protein could be separated from the PM complex by chitinase in vitro, but M2R did not show effect in vitro confirming the chitin-binding activity of Lsti99. The biochemical and physiological functions of Lsti99 in L. sticticalis require further investigation.

An insight into the sialome of Glossina morsitans morsitans

BACKGROUND

Blood feeding evolved independently in worms, arthropods and mammals. Among the adaptations to this peculiar diet, these animals developed an armament of salivary molecules that disarm their host's anti-bleeding defenses (hemostasis), inflammatory and immune reactions. Recent sialotranscriptome analyses (from the Greek sialo = saliva) of blood feeding insects and ticks have revealed that the saliva contains hundreds of polypeptides, many unique to their genus or family. Adult tsetse flies feed exclusively on vertebrate blood and are important vectors of human and animal diseases. Thus far, only limited information exists regarding the Glossina sialome, or any other fly belonging to the Hippoboscidae.

RESULTS

As part of the effort to sequence the genome of Glossina morsitans morsitans, several organ specific, high quality normalized cDNA libraries have been constructed, from which over 20,000 ESTs from an adult salivary gland library were sequenced. These ESTs have been assembled using previously described ESTs from the fat body and midgut libraries of the same fly, thus totaling 62,251 ESTs, which have been assembled into 16,743 clusters (8,506 of which had one or more EST from the salivary gland library). Coding sequences were obtained for 2,509 novel proteins, 1,792 of which had at least one EST expressed in the salivary glands. Despite library normalization, 59 transcripts were overrepresented in the salivary library indicating high levels of expression. This work presents a detailed analysis of the salivary protein families identified. Protein expression was confirmed by 2D gel electrophoresis, enzymatic digestion and mass spectrometry. Concurrently, an initial attempt to determine the immunogenic properties of selected salivary proteins was undertaken.

CONCLUSIONS

The sialome of G. m. morsitans contains over 250 proteins that are possibly associated with blood feeding. This set includes alleles of previously described gene products, reveals new evidence that several salivary proteins are multigenic and identifies at least seven new polypeptide families unique to Glossina. Most of these proteins have no known function and thus, provide a discovery platform for the identification of novel pharmacologically active compounds, innovative vector-based vaccine targets, and immunological markers of vector exposure.

New insights into peritrophic matrix synthesis, architecture, and function

The peritrophic matrix (PM) is a chitin and glycoprotein layer that lines the invertebrate midgut. Although structurally different, it is functionally similar to the mucous secretions of the vertebrate digestive tract. The PM is a physical barrier, protecting the midgut epithelium from abrasive food particles, digestive enzymes, and pathogens infectious per os. It is also a biochemical barrier, sequestering and, in some cases, inactivating ingested toxins. Finally, the PM compartmentalizes digestive processes, allowing for efficient nutrient acquisition and reuse of hydrolytic enzymes. The PM consists of an organized lattice of chitin fibrils held together by chitin binding proteins. Glycans fill the interstitial spaces, creating a molecular sieve, the properties of which are dependent on the immediate ion content and pH. In this review, we have integrated recent structural and functional information to create a holistic model for the PM. We also show how this information may generate novel technologies for use in insect pest management.

A novel chitin-binding protein identified from the peritrophic membrane of the cabbage looper, Trichoplusia ni

A novel midgut peritrophic membrane (PM) protein, TnPM-P42, was identified from the cabbage looper, Trichoplusia ni. TnPM-P42 was shown as a 42kDa protein by SDS-PAGE analysis and appeared to be associated with the PM throughout its entire length. In T. ni larvae, the midgut is the only tissue where TnPM-P42 could be detected during the feeding period of the larvae. TnPM-P42 has chitin-binding activity and is strongly associated with the PM, which is similar to the currently known peritrophin type PM proteins. However, TnPM-P42 represents a unique family of proteins distinctly different from the peritrophin type PM proteins in its sequence characteristics. TnPM-P42 does not contain the peritrophin domain which is present in all the currently known PM proteins, but instead has a chitin deacetylase-like domain. Sequence similarity search of the GenBank database did not result in identification of any known proteins with a significant overall sequence similarity to the TnPM-P42. However, expressed sequence tags (ESTs) from various arthropods were identified to code for proteins with high sequence similarities to TnPM-P42, indicating the presence of TnPM-P42 homologs in other arthropods. Consistent with the identification of various ESTs from arthropods, Western blot analysis demonstrated the presence of a TnPM-P42-like protein in the PMs from Heliothis virescens and Helicoverpa zea larvae. The sequence characteristics of TnPM-P42 indicate that TnPM-P42 represents a novel family of insect proteins. However, its biochemical and physiological functions require further investigation.

Increased expression of unusual EP repeat-containing proteins in the midgut of the tsetse fly (Glossina) after bacterial challenge

Proteins containing a glutamic acid-proline (EP) repeat epitope were immunologically detected in midguts from eight species of Glossina (tsetse flies). The molecular masses of the tsetse EP proteins differed among species groups. The amino acid sequence of one of these proteins, from Glossina palpalis palpalis, was determined and compared to the sequence of a homologue, the tsetse midgut EP protein of Glossina m. morsitans. The extended EP repeat domains comprised between 36% (G. m. morsitans) and 46% (G. p. palpalis) of the amino acid residues, but otherwise the two polypeptide chains shared most of their sequences and predicted functional domains. The levels of expression of tsetse EP protein in adult teneral midguts were markedly higher than in midguts from larvae. The EP protein was detected by immunoblotting in the fat body, proventriculus and midgut, the known major immune tissues of tsetse and is likely secreted as it was also detected in hemolymph. The EP protein was not produced by the bacterial symbionts of tsetse midguts as determined by genome analysis of Wigglesworthia glossinidia and immunoblot analysis of Sodalis glossinidius. Bacterial challenge of G. m. morsitans, by injection of live E. coli, induced augmented expression of the tsetse EP protein. The presence of EP proteins in a wide variety of tsetse, their constitutive expression in adult fat body and midguts and their upregulation after immunogen challenge suggest they play an important role as a component of the immune system in tsetse.

Identification of midgut proteins that are differentially expressed in trypanosome-susceptible and normal tsetse flies (Glossina morsitans morsitans)

Molecules in the midgut of tsetse flies (Diptera: Glossinidiae) are thought to play important roles in the life cycle of African trypanosomes by influencing initial parasite establishment and subsequent differentiation events that ultimately lead to maturation of mammal-infective trypanosomes. The molecular composition of the tsetse midgut is, therefore, of critical importance to disease transmission by these medically important vectors. In this study we compared protein expression profiles of midguts of the salmon mutant and wild type Glossina morsitans morsitans Westwood that display marked differences in their susceptibility to infection by African trypanosomes. Isotope coded affinity tag (ICAT) technology was used to identify 207 proteins including 17 that were up regulated and nine that were down regulated in the salmon mutants. Several of the up regulated molecules were previously described as tsetse midgut or salivary gland proteins. Of particular interest was the up regulation in the salmon flies of tsetse midgut EP protein, a recently described molecule with lectin-like activity that was also found to be induced in tsetse by bacterial challenge. The up regulation of the EP protein in midguts of salmon mutants was confirmed by two-dimensional gel electrophoresis and tandem mass spectrometry.

Modeling the structure of the type I peritrophic matrix: characterization of a Mamestra configurata intestinal mucin and a novel peritrophin containing 19 chitin binding domains

Twelve to fourteen integral proteins were found to reside in the Type I peritrophic matrix (PM) of Mamestra configurata (bertha armyworm) larvae. Several methods were employed, including de novo peptide sequencing, the generation of a midgut-specific EST database and immunological screening, which led to the isolation of cDNAs encoding two integral PM proteins. McPM1, the largest PM protein described to date at 202 kDa, was comprised of a concatamer of 19 chitin binding domains (CBD), 12 of which resided within a central repetitive region consisting of six iterations of a two CBD module. The protein was found to reside within the PM primarily as several lower molecular weight, presumably proteolytically processed, forms. McMUC1 was similar in structure to other insect intestinal mucins (IIM) and was highly glycosylated. The expression of both proteins was restricted to the larval midgut. Lower molecular weight proteins that may represent non- and partially glycosylated forms of McMUC1 were also recognized by an anti-McMUC1 antiserum. These were preferentially degraded upon ingestion of M. configurata multi-capsid nucleopolyhedrovirus by larvae, possibly by a viral-encoded metalloprotease. A molecular model of PM structure is presented featuring the interaction of McPM1 with chitin inter-fibril junctions and McMUC1 with the extended chains in the internodal regions. The potential for interaction between PM proteins via intermolecular disulfide bond formation and through association of CBD with N-linked glycans is discussed.

Interactions between tsetse and trypanosomes with implications for the control of trypanosomiasis

Tsetse flies (Diptera: Glossinidae) are vectors of several species of pathogenic trypanosomes in tropical Africa. Human African trypanosomiasis (HAT) is a zoonosis caused by Trypanosoma brucei rhodesiense in East Africa and T. b. gambiense in West and Central Africa. About 100000 new cases are reported per year, with many more probably remaining undetected. Sixty million people living in 36 countries are at risk of infection. Recently, T. b. gambiense trypanosomiasis has emerged as a major public health problem in Central Africa, especially in the Democratic Republic of Congo, Angola and southern Sudan where civil war has hampered control efforts. African trypanosomes also cause nagana in livestock. T. vivax and T. congolense are major pathogens of cattle and other ruminants, while T. simiae causes high mortality in domestic pigs; T. brucei affects all livestock, with particularly severe effects in equines and dogs. Central to the control of these diseases is control of the tsetse vector, which should be very effective since trypanosomes rely on this single insect for transmission. However, the area infested by tsetse has increased in the past century. Recent advances in molecular technologies and their application to insects have revolutionized the field of vector biology, and there is hope that such new approaches may form the basis for future tsetse control strategies. This article reviews the known biology of trypanosome development in the fly in the context of the physiology of the digestive system and interactions of the immune defences and symbiotic flora.

Proventriculus (cardia) plays a crucial role in immunity in tsetse fly (Diptera: Glossinidiae)

Fat body and hemocytes play a central role in cellular and humoral responses for systemic infections in invertebrates, similar to the mammalian liver and blood cells. Epithelial surfaces, in particular the midgut, participate in the initial local immune responses in order to aid in the generation of the terminal cytotoxic molecules that mediate non-self recognition. Here, we describe for the first time the immune responses of a cluster of cells at the foregut/midgut junction--known as proventriculus (cardia) in the medically and agriculturally important insect, tsetse fly (Diptera: Glossinidae). We provide evidence for the transcriptional induction of the antimicrobial peptides attacin and defensin as well as for the reactive nitrogen intermediate (RNI) nitric oxide synthase (NOS) upon microbial challenge by either microinjection or feeding. Proventriculus from immune challenged flies also has higher NOS and nitric oxide (NO) activities as well as increased levels of the reactive oxygen intermediate (ROI), hydrogen peroxide (H2O2). In several vector pathogen systems, including tsetse flies and African trypanosomes, stimulation of systemic responses prior to pathogen acquisition has been shown to reduce disease transmission. Furthermore, the induction of systemic immune responses has been documented while pathogens are still differentiating within the midgut environment. While evidence for a close molecular communication between the local and systemic responses is accumulating, the molecular signals that mediate these interactions are at present unknown. Reactive intermediates such as NO or H2O2 may function as immunological signals for mediating the molecular communication between the different insect compartments. We discuss the putative role of the proventriculus in invertebrate immunity and specifically speculate on its significance for trypanosome transmission in tsetse.

Control of tsetse flies and trypanosomes using molecular genetics

TSETSE FLIES (DIPTERA: Glossinidae) are important agricultural and medical vectors transmitting the African trypanosomes, the agents of sleeping sickness disease in humans and various diseases in animals (nagana). While the prevalence of disease has increased to epidemic proportions, lack of a mammalian vaccine and affordable and effective drugs have hindered disease control. Trypanosomiasis management relies heavily on the control of its single insect vector, the tsetse fly. Despite the effectiveness of some of these tools, their impact on disease control has not been sustainable due to their local nature and extensive dependence on community participation. Recent advances in molecular technologies and their application to insects have revolutionized the field of vector biology, and there is hope that such new approaches may form the basis for future tsetse interventions. The success of the genetic approaches aiming to disrupt the transmission cycle of the parasite in their invertebrate host depends on full understanding of the interaction between tsetse and trypanosomes. This article reviews the biology of trypanosome development in the fly and the multiple bacterial symbionts that inhabit the same gut environment. The availability of a genetic transformation system for the midgut symbiont allows for gene products to be expressed in vivo in the tsetse gut where they can produce a hostile environment for pathogen transmission. The characterization of gene product(s) with anti-pathogenic properties and their expression in vivo is discussed. A strategy is outlined where the replacement of susceptible insect phenotypes with their engineered refractory counterparts can result in decreased disease transmission.