Characterization of genes expressed in the salivary glands of the tsetse fly, Glossina morsitans morsitans

Tsetse salivary glycoproteins are modified with paucimannosidic N-glycans, are recognised by C-type lectins and bind to trypanosomes

African sleeping sickness is caused by Trypanosoma brucei, a parasite transmitted by the bite of a tsetse fly. Trypanosome infection induces a severe transcriptional downregulation of tsetse genes encoding for salivary proteins, which reduces its anti-hemostatic and anti-clotting properties. To better understand trypanosome transmission and the possible role of glycans in insect bloodfeeding, we characterized the N-glycome of tsetse saliva glycoproteins. Tsetse salivary N-glycans were enzymatically released, tagged with either 2-aminobenzamide (2-AB) or procainamide, and analyzed by HILIC-UHPLC-FLR coupled online with positive-ion ESI-LC-MS/MS. We found that the N-glycan profiles of T. brucei-infected and naïve tsetse salivary glycoproteins are almost identical, consisting mainly (>50%) of highly processed Man₃GlcNAc₂ in addition to several other paucimannose, high mannose, and few hybrid-type N-glycans. In overlay assays, these sugars were differentially recognized by the mannose receptor and DC-SIGN C-type lectins. We also show that salivary glycoproteins bind strongly to the surface of transmissible metacyclic trypanosomes. We suggest that although the repertoire of tsetse salivary N-glycans does not change during a trypanosome infection, the interactions with mannosylated glycoproteins may influence parasite transmission into the vertebrate host.

In addition to helping the ingestion of a bloodmeal, the saliva of vector insects can modulate vertebrate immune responses. However, most research has focused on the salivary proteins, while the sugars (glycans) that modify them remain unexplored. Here we studied N-glycosylation, a common post-translational modification where sugar structures are attached to specific sites of a protein. Insect salivary N-glycans may affect how the saliva is recognized by the host, possibly playing a role during pathogen transmission. In this manuscript, we present the first detailed structural characterization of the salivary N-glycans in the tsetse fly Glossina morsitans, vector of African trypanosomiasis. We found that tsetse fly glycoproteins are mainly modified by simple N-glycans with short mannose modifications, which are recognised by mammalian C-type lectins (mannose receptor and DC-SIGN). Furthermore, we show that salivary glycoproteins bind to the surface of the trypanosomes that are transmitted to the vertebrate host; this opens up interesting questions as to the role of these glycoproteins in the successful establishment of infection by this parasite. Overall, our work represents a novel contribution towards the salivary N-glycome of an important insect vector, and towards the understanding of vector saliva and its complex effects in the vertebrate host.

The functions of CAP superfamily proteins in mammalian fertility and disease

BACKGROUND

Members of the cysteine-rich secretory proteins (CRISPS), antigen 5 (Ag5) and pathogenesis-related 1 (Pr-1) (CAP) superfamily of proteins are found across the bacterial, fungal, plant and animal kingdoms. Although many CAP superfamily proteins remain poorly characterized, over the past decade evidence has accumulated, which provides insights into the functional roles of these proteins in various processes, including fertilization, immune defence and subversion, pathogen virulence, venom toxicology and cancer biology.

OBJECTIVE AND RATIONALE

The aim of this article is to summarize the current state of knowledge on CAP superfamily proteins in mammalian fertility, organismal homeostasis and disease pathogenesis.

SEARCH METHODS

The scientific literature search was undertaken via PubMed database on all articles published prior to November 2019. Search terms were based on following keywords: 'CAP superfamily', 'CRISP', 'Cysteine-rich secretory proteins', 'Antigen 5', 'Pathogenesis-related 1', 'male fertility', 'CAP and CTL domain containing', 'CRISPLD1', 'CRISPLD2', 'bacterial SCP', 'ion channel regulator', 'CatSper', 'PI15', 'PI16', 'CLEC', 'PRY proteins', 'ASP proteins', 'spermatogenesis', 'epididymal maturation', 'capacitation' and 'snake CRISP'. In addition to that, reference lists of primary and review article were reviewed for additional relevant publications.

OUTCOMES

In this review, we discuss the breadth of knowledge on CAP superfamily proteins with regards to their protein structure, biological functions and emerging significance in reproduction, health and disease. We discuss the evolution of CAP superfamily proteins from their otherwise unembellished prokaryotic predecessors into the multi-domain and neofunctionalized members found in eukaryotic organisms today. At least in part because of the rapid evolution of these proteins, many inconsistencies in nomenclature exist within the literature. As such, and in part through the use of a maximum likelihood phylogenetic analysis of the vertebrate CRISP subfamily, we have attempted to clarify this confusion, thus allowing for a comparison of orthologous protein function between species. This framework also allows the prediction of functional relevance between species based on sequence and structural conservation.

WIDER IMPLICATIONS

This review generates a picture of critical roles for CAP proteins in ion channel regulation, sterol and lipid binding and protease inhibition, and as ligands involved in the induction of multiple cellular processes.

A proteomics approach reveals molecular manipulators of distinct cellular processes in the salivary glands of Glossina m. morsitans in response to Trypanosoma b. brucei infections

Background

Glossina m. morsitans is the primary vector of the Trypanosoma brucei group, one of the causative agents of African trypanosomoses. The parasites undergo metacyclogenesis, i.e. transformation into the mammalian-infective metacyclic trypomastigote (MT) parasites, in the salivary glands (SGs) of the tsetse vector. Since the MT-parasites are largely uncultivable in vitro, information on the molecular processes that facilitate metacyclogenesis is scanty.

Methods

To bridge this knowledge gap, we employed tandem mass spectrometry to investigate protein expression modulations in parasitized (T. b. brucei-infected) and unparasitized SGs of G. m. morsitans. We annotated the identified proteins into gene ontologies and mapped the up- and downregulated proteins within protein-protein interaction (PPI) networks.

Results

We identified 361 host proteins, of which 76.6 % (n = 276) and 22.3 % (n = 81) were up- and downregulated, respectively, in parasitized SGs compared to unparasitized SGs. Whilst 32 proteins were significantly upregulated (> 10-fold), only salivary secreted adenosine was significantly downregulated. Amongst the significantly upregulated proteins, there were proteins associated with blood feeding, immunity, cellular proliferation, homeostasis, cytoskeletal traffic and regulation of protein turnover. The significantly upregulated proteins formed major hubs in the PPI network including key regulators of the Ras/MAPK and Ca²⁺/cAMP signaling pathways, ubiquitin-proteasome system and mitochondrial respiratory chain. Moreover, we identified 158 trypanosome-specific proteins, notable of which were proteins in the families of the GPI-anchored surface glycoproteins, kinetoplastid calpains, peroxiredoxins, retrotransposon host spot multigene and molecular chaperones. Whilst immune-related trypanosome proteins were over-represented, membrane transporters and proteins involved in translation repression (e.g. ribosomal proteins) were under-represented, potentially reminiscent of the growth-arrested MT-parasites.

Conclusions

Our data implicate the significantly upregulated proteins as manipulators of diverse cellular processes in response to T. b. brucei infection, potentially to prepare the MT-parasites for invasion and evasion of the mammalian host immune defences. We discuss potential strategies to exploit our findings in enhancement of trypanosome refractoriness or reduce the vector competence of the tsetse vector.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1714-z) contains supplementary material, which is available to authorized users.

Escaping Deleterious Immune Response in Their Hosts: Lessons from Trypanosomatids

The Trypanosomatidae family includes the genera Trypanosoma and Leishmania, protozoan parasites displaying complex digenetic life cycles requiring a vertebrate host and an insect vector. Trypanosoma brucei gambiense, Trypanosoma cruzi, and Leishmania spp. are important human pathogens causing human African trypanosomiasis (HAT or sleeping sickness), Chagas' disease, and various clinical forms of Leishmaniasis, respectively. They are transmitted to humans by tsetse flies, triatomine bugs, or sandflies, and affect millions of people worldwide. In humans, extracellular African trypanosomes (T. brucei) evade the hosts' immune defenses, allowing their transmission to the next host, via the tsetse vector. By contrast, T. cruzi and Leishmania sp. have developed a complex intracellular lifestyle, also preventing several mechanisms to circumvent the host's immune response. This review seeks to set out the immune evasion strategies developed by the different trypanosomatids resulting from parasite-host interactions and will focus on: clinical and epidemiological importance of diseases; life cycles: parasites-hosts-vectors; innate immunity: key steps for trypanosomatids in invading hosts; deregulation of antigen-presenting cells; disruption of efficient specific immunity; and the immune responses used for parasite proliferation.

Immunogenicity and Serological Cross-Reactivity of Saliva Proteins among Different Tsetse Species

Tsetse are vectors of pathogenic trypanosomes, agents of human and animal trypanosomiasis in Africa. Components of tsetse saliva (sialome) are introduced into the mammalian host bite site during the blood feeding process and are important for tsetse’s ability to feed efficiently, but can also influence disease transmission and serve as biomarkers for host exposure. We compared the sialome components from four tsetse species in two subgenera: subgenus Morsitans: Glossina morsitans morsitans (Gmm) and Glossina pallidipes (Gpd), and subgenus Palpalis: Glossina palpalis gambiensis (Gpg) and Glossina fuscipes fuscipes (Gff), and evaluated their immunogenicity and serological cross reactivity by an immunoblot approach utilizing antibodies from experimental mice challenged with uninfected flies. The protein and immune profiles of sialome components varied with fly species in the same subgenus displaying greater similarity and cross reactivity. Sera obtained from cattle from disease endemic areas of Africa displayed an immunogenicity profile reflective of tsetse species distribution. We analyzed the sialome fractions of Gmm by LC-MS/MS, and identified TAg5, Tsal1/Tsal2, and Sgp3 as major immunogenic proteins, and the 5'-nucleotidase family as well as four members of the Adenosine Deaminase Growth Factor (ADGF) family as the major non-immunogenic proteins. Within the ADGF family, we identified four closely related proteins (TSGF-1, TSGF-2, ADGF-3 and ADGF-4), all of which are expressed in tsetse salivary glands. We describe the tsetse species-specific expression profiles and genomic localization of these proteins. Using a passive-immunity approach, we evaluated the effects of rec-TSGF (TSGF-1 and TSGF-2) polyclonal antibodies on tsetse fitness parameters. Limited exposure of tsetse to mice with circulating anti-TSGF antibodies resulted in a slight detriment to their blood feeding ability as reflected by compromised digestion, lower weight gain and less total lipid reserves although these results were not statistically significant. Long-term exposure studies of tsetse flies to antibodies corresponding to the ADGF family of proteins are warranted to evaluate the role of this conserved family in fly biology.

Insect saliva contains many proteins that are injected into the mammalian host during the blood feeding process. Saliva proteins enhance the blood feeding ability of insects, but they can also induce mammalian immune responses that inhibit successful feeding, or modulate the bite site to benefit pathogen transmission. Here we studied saliva from four different tsetse species that belong to two distant species groups. We show that the saliva protein profiles of different species groups vary. Experimental mice subjected to fly bites display varying immunological responses against the abundant saliva proteins and the antigenicity of the shared saliva proteins in different tsetse species differs. We show that one member of the ADGF family with adenosine deaminase motifs, TSGF-2, is non-immunogenic in Glossina morsitans in mice, while the same protein from Glossina fuscipes is highly immunogenic. Such species-specific immune responses could be exploited as biomarkers of host exposures in the field. We also show that short-term exposure of G. morsitans to mice passively immunized by anti-TSGF antibodies leads to slight but not statistically significant negative fitness effects. Thus, future investigations with non-antigenic saliva proteins are warranted as they can lead to novel mammalian vaccine targets to reduce tsetse populations in the field.

Quo vadis venomics? A roadmap to neglected venomous invertebrates

Venomics research is being revolutionized by the increased use of sensitive -omics techniques to identify venom toxins and their transcripts in both well studied and neglected venomous taxa. The study of neglected venomous taxa is necessary both for understanding the full diversity of venom systems that have evolved in the animal kingdom, and to robustly answer fundamental questions about the biology and evolution of venoms without the distorting effect that can result from the current bias introduced by some heavily studied taxa. In this review we draw the outlines of a roadmap into the diversity of poorly studied and understood venomous and putatively venomous invertebrates, which together represent tens of thousands of unique venoms. The main groups we discuss are crustaceans, flies, centipedes, non-spider and non-scorpion arachnids, annelids, molluscs, platyhelminths, nemerteans, and echinoderms. We review what is known about the morphology of the venom systems in these groups, the composition of their venoms, and the bioactivities of the venoms to provide researchers with an entry into a large and scattered literature. We conclude with a short discussion of some important methodological aspects that have come to light with the recent use of new -omics techniques in the study of venoms.

Insights into the trypanosome-host interactions revealed through transcriptomic analysis of parasitized tsetse fly salivary glands

The agents of sleeping sickness disease, Trypanosoma brucei complex parasites, are transmitted to mammalian hosts through the bite of an infected tsetse. Information on tsetse-trypanosome interactions in the salivary gland (SG) tissue, and on mammalian infective metacyclic (MC) parasites present in the SG, is sparse. We performed RNA-seq analyses from uninfected and T. b. brucei infected SGs of Glossina morsitans morsitans. Comparison of the SG transcriptomes to a whole body fly transcriptome revealed that only 2.7% of the contigs are differentially expressed during SG infection, and that only 263 contigs (0.6%) are preferentially expressed in the SGs (SG-enriched). The expression of only 37 contigs (0.08%) and 27 SG-enriched contigs (10%) were suppressed in infected SG. These suppressed contigs accounted for over 55% of the SG transcriptome, and included the most abundant putative secreted proteins with anti-hemostatic functions present in saliva. In contrast, expression of putative host proteins associated with immunity, stress, cell division and tissue remodeling were enriched in infected SG suggesting that parasite infections induce host immune and stress response(s) that likely results in tissue renewal. We also performed RNA-seq analysis from mouse blood infected with the same parasite strain, and compared the transcriptome of bloodstream form (BSF) cells with that of parasites obtained from the infected SG. Over 30% of parasite transcripts are differentially regulated between the two stages, and reflect parasite adaptations to varying host nutritional and immune ecology. These differences are associated with the switch from an amino acid based metabolism in the SG to one based on glucose utilization in the blood, and with surface coat modifications that enable parasite survival in the different hosts. This study provides a foundation on the molecular aspects of the trypanosome dialogue with its tsetse and mammalian hosts, necessary for future functional investigations.

Tsetse flies transmit the causative agents of African sleeping sickness and nagana in sub-Saharan Africa. The parasites are acquired when tsetse flies feed on an infected host, undergo multiplication in the fly gut and migrate to the salivary glands (SG). The cycle resumes once this infected fly transmits the parasites in conjunction with saliva to another host when feeding. We compared gene expression changes between parasitized and uninfected tsetse SG. We also assessed changes in parasite gene expression in the tsetse SG in relation to those present within vertebrate blood. We found that parasite infections increase expression of host proteins associated with stress and cell division, indicative of extensive cellular damage in SG. We also found that parasite infections reduce expression of the most highly expressed SG-specific secreted proteins, suggesting modification of saliva composition. The parasite transcriptome reveals changes in specific cell surface proteins and in metabolism related to glucose-amino acid utilization in the different host environments. This study provides information for critical understanding of tsetse-trypanosome interactions, and transcriptional changes that likely enable the parasite to persist in the varying environment of its insect and vertebrate hosts.

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.

Dracula's children: molecular evolution of vampire bat venom

While vampire bat oral secretions have been the subject of intense research, efforts have concentrated only on two components: DSPA (Desmodus rotundus salivary plasminogen activator) and Draculin. The molecular evolutionary history of DSPA has been elucidated, while conversely draculin has long been known from only a very small fragment and thus even the basic protein class was not even established. Despite the fact that vampire bat venom has a multitude of effects unaccounted by the documented bioactivities of DSPA and draculin, efforts have not been made to establish what other bioactive proteins are secreted by their submaxillary gland. In addition, it has remained unclear whether the anatomically distinct anterior and posterior lobes of the submaxillary gland are evolving on separate gene expression trajectories or if they remain under the shared genetic control. Using a combined proteomic and transcriptomic approach, we show that identical proteins are simultaneously expressed in both lobes. In addition to recovering the known structural classes of DSPA, we recovered a novel DSPA isoform as well as obtained a very large sequence stretch of draculin and thus established that it is a mutated version of the lactotransferrin scaffold. This study reveals a much more complex secretion profile than previously recognised. In addition to obtaining novel versions of scaffolds convergently recruited into other venoms (allergen-like, CRiSP, kallikrein, Kunitz, lysozyme), we also documented novel expression of small peptides related to calcitonin, PACAP, and statherin. Other overexpressed protein types included BPI-fold, lacritin, and secretoglobin. Further, we investigate the molecular evolution of various vampire bat venom-components and highlight the dominant role of positive selection in the evolution of these proteins. Conspicuously many of the proteins identified in the proteome were found to be homologous to proteins with known activities affecting vasodilation and platelet aggregation. We show that vampire bat venom proteins possibly evade host immune response by the mutation of the surface chemistry through focal mutagenesis under the guidance of positive Darwinian selection. These results not only contribute to the body of knowledge regarding haematophagous venoms but also provide a rich resource for novel lead compounds for use in drug design and development.

BIOLOGICAL SIGNIFICANCE

These results have direct implications in understanding the molecular evolutionary history of vampire bat venom. The unusual peptides discovered reinforce the value of studying such neglected taxon for biodiscovery.

Identification of Glossina palpalis gambiensis specific salivary antigens: towards the development of a serologic biomarker of human exposure to tsetse flies in West Africa

The saliva of blood sucking arthropods contains a number of pharmacologically active compounds that induce an antibody response in exposed human individuals. The objectives of the present study were (i) to assess the human IgG response directed against salivary antigens of Glossina palpalis gambiensis, the main vector of Trypanosoma brucei gambiense in West Africa, as a biomarker of human-tsetse contacts; and (ii) to identify specific salivary antigens. Immune reactivity of human plasma collected within active human African trypanosomiasis (HAT) foci (coastal Guinea), historical foci where tsetse flies are still present (South-West Burkina Faso) and a tsetse free area (Bobo-Dioulasso, Burkina Faso), was measured by ELISA against whole saliva extracts. In the active HAT foci and areas where tsetse flies were present in high densities, specific IgG responses were significantly higher (p < 0.0001) to those in Bobo-Dioulasso or in Loropeni, where tsetse flies were either absent or only present at low densities. Furthermore, 2D-electrophoresis combined with mass spectrometry enabled to reveal that several antigens were specifically recognized by plasma from exposed individuals. Among them, four salivary proteins were successfully identified (Ada, 5'Nuc, Ag5 and Tsgf1). These results represent a first attempt to identify Glossina salivary proteins or synthetic peptides to develop a standardized and specific biomarker of tsetse exposure in West Africa.

Tsetse salivary gland proteins 1 and 2 are high affinity nucleic acid binding proteins with residual nuclease activity

Analysis of the tsetse fly salivary gland EST database revealed the presence of a highly enriched cluster of putative endonuclease genes, including tsal1 and tsal2. Tsal proteins are the major components of tsetse fly (G. morsitans morsitans) saliva where they are present as monomers as well as high molecular weight complexes with other saliva proteins. We demonstrate that the recombinant tsetse salivary gland proteins 1&2 (Tsal1&2) display DNA/RNA non-specific, high affinity nucleic acid binding with K_D values in the low nanomolar range and a non-exclusive preference for duplex. These Tsal proteins exert only a residual nuclease activity with a preference for dsDNA in a broad pH range. Knockdown of Tsal expression by in vivo RNA interference in the tsetse fly revealed a partially impaired blood digestion phenotype as evidenced by higher gut nucleic acid, hematin and protein contents.

Platyhelminth Venom Allergen-Like (VAL) proteins: revealing structural diversity, class-specific features and biological associations across the phylum

During platyhelminth infection, a cocktail of proteins is released by the parasite to aid invasion, initiate feeding, facilitate adaptation and mediate modulation of the host immune response. Included amongst these proteins is the Venom Allergen-Like (VAL) family, part of the larger sperm coating protein/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) superfamily. To explore the significance of this protein family during Platyhelminthes development and host interactions, we systematically summarize all published proteomic, genomic and immunological investigations of the VAL protein family to date. By conducting new genomic and transcriptomic interrogations to identify over 200 VAL proteins (228) from species in all 4 traditional taxonomic classes (Trematoda, Cestoda, Monogenea and Turbellaria), we further expand our knowledge related to platyhelminth VAL diversity across the phylum. Subsequent phylogenetic and tertiary structural analyses reveal several class-specific VAL features, which likely indicate a range of roles mediated by this protein family. Our comprehensive analysis of platyhelminth VALs represents a unifying synopsis for understanding diversity within this protein family and a firm context in which to initiate future functional characterization of these enigmatic members.

The salivary secretome of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) infected by salivary gland hypertrophy virus

BACKGROUND

The competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.

METHODOLOGY/PRINCIPAL FINDINGS

After electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.

CONCLUSIONS/SIGNIFICANCE

SGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.

Insight into the salivary transcriptome and proteome of Dipetalogaster maxima

Dipetalogaster maxima is a blood-sucking Hemiptera that inhabits sylvatic areas in Mexico. It usually takes its blood meal from lizards, but following human population growth, it invaded suburban areas, feeding also on humans and domestic animals. Hematophagous insect salivary glands produce potent pharmacologic compounds that counteract host hemostasis, including anticlotting, antiplatelet, and vasodilatory molecules. To obtain further insight into the salivary biochemical and pharmacologic complexity of this insect, a cDNA library from its salivary glands was randomly sequenced. Salivary proteins were also submitted to one- and two-dimensional gel electrophoresis (1DE and 2DE) followed by mass spectrometry analysis. We present the analysis of a set of 2728 cDNA sequences, 1375 of which coded for proteins of a putative secretory nature. The saliva 2DE proteome displayed approximately 150 spots. The mass spectrometry analysis revealed mainly lipocalins, pallidipins, antigen 5-like proteins, and apyrases. The redundancy of sequence identification of saliva-secreted proteins suggests that proteins are present in multiple isoforms or derive from gene duplications.

Diet-specific salivary gene expression and glucose oxidase activity in Spodoptera exigua (Lepidoptera: Noctuidae) larvae

Saliva secreted during caterpillar feeding contains enzymes to initiate digestion or detoxify noxious plant compounds. Activity of some salivary enzymes is diet-dependent and may be transcriptionally regulated. In this study, cDNA-amplified fragment length polymorphism was used to identify beet armyworm, Spodoptera exigua Hübner, labial salivary genes that are differentially expressed in response to diet. In addition, SeGOX was sequenced based on homology and characterized to confirm that the transcript encodes a functional enzyme. Three labial salivary transcripts, encoding glucose oxidase (GOX) and two proteins of unknown function (Se1H and Se2J), were expressed in a diet-specific manner. Since diet, particularly the protein to digestible carbohydrate levels and ratio, may affect labial salivary enzyme activity, the influence of nutritional quality on gene expression was determined. Transcript levels of the labial salivary genes Se1H, Se2J and SeGOX increased with dietary carbohydrate levels, regardless of protein concentrations. In contrast GOX enzymatic activity increased with increasing dietary carbohydrates when caterpillars were fed protein-rich diets, but not when caterpillars were fed protein-poor diets. Our results suggest that dietary carbohydrates affect SeGOX, Se1H and Se2J transcription, but dietary protein or amino acid levels affect translational and/or post-translational regulation of the enzyme GOX.

Trypanosoma brucei modifies the tsetse salivary composition, altering the fly feeding behavior that favors parasite transmission

Tsetse flies are the notorious transmitters of African trypanosomiasis, a disease caused by the Trypanosoma parasite that affects humans and livestock on the African continent. Metacyclic infection rates in natural tsetse populations with Trypanosoma brucei, including the two human-pathogenic subspecies, are very low, even in epidemic situations. Therefore, the infected fly/host contact frequency is a key determinant of the transmission dynamics. As an obligate blood feeder, tsetse flies rely on their complex salivary potion to inhibit host haemostatic reactions ensuring an efficient feeding. The results of this experimental study suggest that the parasite might promote its transmission through manipulation of the tsetse feeding behavior by modifying the saliva composition. Indeed, salivary gland Trypanosoma brucei-infected flies display a significantly prolonged feeding time, thereby enhancing the likelihood of infecting multiple hosts during the process of a single blood meal cycle. Comparison of the two major anti-haemostatic activities i.e. anti-platelet aggregation and anti-coagulation activity in these flies versus non-infected tsetse flies demonstrates a significant suppression of these activities as a result of the trypanosome-infection status. This effect was mainly related to the parasite-induced reduction in salivary gland gene transcription, resulting in a strong decrease in protein content and related biological activities. Additionally, the anti-thrombin activity and inhibition of thrombin-induced coagulation was even more severely hampered as a result of the trypanosome infection. Indeed, while naive tsetse saliva strongly inhibited human thrombin activity and thrombin-induced blood coagulation, saliva from T. brucei-infected flies showed a significantly enhanced thrombinase activity resulting in a far less potent anti-coagulation activity. These data clearly provide evidence for a trypanosome-mediated modification of the tsetse salivary composition that results in a drastically reduced anti-haemostatic potential and a hampered feeding performance which could lead to an increase of the vector/host contact and parasite transmission in field conditions.

Human African Trypanosomiasis, or sleeping sickness, is a devastating parasitic disease that is fatal if left untreated. Infections are acquired via the bite of an obligate blood feeding fly, the tsetse fly, that is exclusively present on the African continent. In this insect vector, the trypanosome parasite has a complex development ending in the salivary glands. In this experimental study we demonstrate that the Trypanosoma brucei parasites change the composition of the tsetse fly saliva making it less efficient to keep the blood fluid at the biting site in the mammalian host. This results in a more difficult blood feeding process and favors the fly biting activity on multiple hosts, thereby promoting the survival and circulation of the parasite within the natural host population. These findings give us a better understanding of how trypanosome infections in the human population can be maintained given the fact that only very few tsetse flies are actually carrying the parasite.

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.

The Toxicogenomic Multiverse: Convergent Recruitment of Proteins Into Animal Venoms

Throughout evolution, numerous proteins have been convergently recruited into the venoms of various animals, including centipedes, cephalopods, cone snails, fish, insects (several independent venom systems), platypus, scorpions, shrews, spiders, toxicoferan reptiles (lizards and snakes), and sea anemones. The protein scaffolds utilized convergently have included AVIT/colipase/prokineticin, CAP, chitinase, cystatin, defensins, hyaluronidase, Kunitz, lectin, lipocalin, natriuretic peptide, peptidase S1, phospholipase A2, sphingomyelinase D, and SPRY. Many of these same venom protein types have also been convergently recruited for use in the hematophagous gland secretions of invertebrates (e.g., fleas, leeches, kissing bugs, mosquitoes, and ticks) and vertebrates (e.g., vampire bats). Here, we discuss a number of overarching structural, functional, and evolutionary generalities of the protein families from which these toxins have been frequently recruited and propose a revised and expanded working definition for venom. Given the large number of striking similarities between the protein compositions of conventional venoms and hematophagous secretions, we argue that the latter should also fall under the same definition.

Identification of a functional Antigen5-related allergen in the saliva of a blood feeding insect, the tsetse fly

Our previous screening of a Glossina morsitans morsitans lamdagt11 salivary gland expression library with serum of a tsetse fly exposed rabbit identified a cDNA encoding Tsetse Antigen5 (TAg5, 28.9 kDa), a homologue of Antigen5 sting venom allergens. Recombinant TAg5 was produced in Sf9 cells in order to assess its immunogenic properties in humans. Plasma from a patient that previously exhibited anaphylactic reactions against tsetse fly bites contained circulating anti-TAg5 and anti-saliva IgEs. In a significant proportion of plasma samples of African individuals, TAg5 and saliva binding IgEs (respectively 56 and 65%) can be detected. Saliva, harvested from flies that were subjected to TAg5- specific RNA interference (RNAi), displayed significantly reduced IgE binding potential. Allergenic properties of TAg5 and tsetse fly saliva were further illustrated in immunized mice, using an immediate cutaneous hypersensitivity and passive cutaneous anaphylaxis assay. Collectively, TAg5 was illustrated to be a tsetse fly salivary allergen, demonstrating that Antigen5-related proteins are represented as functional allergens not only in stinging but also in blood feeding insects.

A portrait of the "SCP/TAPS" proteins of eukaryotes--developing a framework for fundamental research and biotechnological outcomes

A wide range of proteins belonging to the SCP/TAPS "family" has been described for various eukaryotic organisms, including plants and animals (vertebrates and invertebrates, such as helminths). Although SCP/TAPS proteins have been proposed to play key roles in a number of fundamental biological processes, such as host-pathogen interactions and defence mechanisms, there is a paucity of information on their genetic relationships, structures and functions, and there is no standardised nomenclature for these proteins. A detailed analysis of the relationships of members of the SCP/TAPS family of proteins, based on key protein signatures, could provide a foundation for investigating these areas. In this article, we review the current state of knowledge of key SCP/TAPS proteins of eukaryotes, with an emphasis on those from parasitic helminths, and undertake a comprehensive, systematic phylogenetic analysis of currently available full-length protein sequence data (considering characteristic protein signatures or motifs) to infer relationships and provide a framework (based on statistical support) for the naming of these proteins. This framework is intended to guide genomic and molecular biological explorations of key SCP/TAPS molecules associated with infectious diseases of plants and animals. In particular, fundamental investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the control of parasitic diseases, with important biotechnological outcomes.

An insight into the sialotranscriptome of the non-blood feeding Toxorhynchites amboinensis mosquito

All adult mosquitoes take sugar meals, and most adult females also take blood meals to develop eggs. Salivary glands (SG) of males are thus much smaller and do not contain many of the antihemostatic and antiinflammatory compounds found in females. In the past 5 years, transcriptome analyses have identified nearly 70 different genes expressed in adult female SG. For most of these, no function can be assigned in either blood or sugar feeding. Exceptionally, Toxorhynchites mosquitoes are unusual in that they never feed on blood, and the SG of adults are identical in both sexes. Transcriptome analysis of the adult SG of this mosquito was performed to increase knowledge of the evolution of blood feeding--and to identify polypeptide families associated with sugar feeding--in mosquitoes.

An insight into the sialome of the blood-sucking bug Triatoma infestans, a vector of Chagas' disease

Triatoma infestans is a hemiptera, vector of Chagas' disease that feeds exclusively on vertebrate blood in all life stages. Hematophagous insects' salivary glands (SG) produce potent pharmacological compounds that counteract host hemostasis, including anticlotting, antiplatelet, and vasodilatory molecules. To obtain a further insight into the salivary biochemical and pharmacological complexity of this insect, a cDNA library from its SG was randomly sequenced. Also, salivary proteins were submitted to two-dimensional gel (2D-gel) electrophoresis followed by MS analysis. We present the analysis of a set of 1534 (SG) cDNA sequences, 645 of which coded for proteins of a putative secretory nature. Most salivary proteins described as lipocalins matched peptide sequences obtained from proteomic results.

The Glossina morsitans tsetse fly saliva: general characteristics and identification of novel salivary proteins

The tsetse fly (Glossina spp.) is an obligate blood-sucking insect that transmits different human-pathogenic and livestock threatening trypanosome species in Africa. To obtain more insight in the tsetse salivary function, some general aspects of the tsetse fly saliva and its composition were studied. Direct pH and protein content measurements revealed a moderately alkaline (pH approximately 8.0) salivary environment with approximately 4.3 microg soluble proteins per gland and a constant representation of the major saliva proteins throughout the blood-feeding cycle. Although major salivary genes are constitutively expressed, upregulation of salivary protein synthesis within 48 h after the blood meal ensures complete protein replenishment from day 3 onwards. Screening of a non-normalised Glossina morsitans morsitans lambdagt11 salivary gland expression library with serum from a saliva-immunized rabbit identified three full-length cDNAs encoding for novel salivary proteins with yet unknown functions: a 8.3 kDa glycine/glutamate-rich protein (G. morsitans morsitans salivary gland protein Gmmsgp1), a 12.0 kDa proline-rich protein (Gmmsgp2), and a 97.4 kDa protein composed of a metallophosphoesterase/5'nucleotidase region with a glutamate/aspartate/asparagines-rich region (Gmmsgp3).

The sialotranscriptome of the blood-sucking bug Triatoma brasiliensis (Hemiptera, Triatominae)

Triatoma brasiliensis is the most important autochthon vector of Trypanosoma cruzi in Brazil, where it is widely distributed in the semiarid areas of the Northeast. In order to advance the knowledge of the salivary biomolecules of Triatominae, a salivary gland cDNA library of T. brasiliensis was mass sequenced and analyzed. Polypeptides were sequenced by HPLC/Edman degradation experiments. Then 1712 cDNA sequences were obtained and grouped in 786 clusters. The housekeeping category had 24.4% and 17.8% of the clusters and sequences, respectively. The putatively secreted category contained 47.1% of the clusters and 68.2% of the sequences. Finally, 28.5% of the clusters, containing 14% of all sequences, were classified as unknown. The sialoma of T. brasiliensis showed a high amount and great variety of different lipocalins (93.8% of secreted proteins). Remarkably, a great number of serine proteases that were not observed in previous blood-sucking sialotranscriptomes were found. Nine Kazal peptides were identified, among them one with high homology to the tabanid vasodilator vasotab, suggesting that the Triatoma vasodilator could be a Kazal protein.

An insight into the sialome of the oriental rat flea, Xenopsylla cheopis (Rots)

BACKGROUND

The salivary glands of hematophagous animals contain a complex cocktail that interferes with the host hemostasis and inflammation pathways, thus increasing feeding success. Fleas represent a relatively recent group of insects that evolved hematophagy independently of other insect orders.

RESULTS

Analysis of the salivary transcriptome of the flea Xenopsylla cheopis, the vector of human plague, indicates that gene duplication events have led to a large expansion of a family of acidic phosphatases that are probably inactive, and to the expansion of the FS family of peptides that are unique to fleas. Several other unique polypeptides were also uncovered. Additionally, an apyrase-coding transcript of the CD39 family appears as the candidate for the salivary nucleotide hydrolysing activity in X.cheopis, the first time this family of proteins is found in any arthropod salivary transcriptome.

CONCLUSION

Analysis of the salivary transcriptome of the flea X. cheopis revealed the unique pathways taken in the evolution of the salivary cocktail of fleas. Gene duplication events appear as an important driving force in the creation of salivary cocktails of blood feeding arthropods, as was observed with ticks and mosquitoes. Only five other flea salivary sequences exist at this time at NCBI, all from the cat flea C. felis. This work accordingly represents the only relatively extensive sialome description of any flea species. Sialotranscriptomes of additional flea genera will reveal the extent that these novel polypeptide families are common throughout the Siphonaptera.

An annotated catalogue of salivary gland transcripts in the adult female mosquito, Aedes aegypti

Background

Saliva of blood-sucking arthropods contains a cocktail of antihemostatic agents and immunomodulators that help blood feeding. Mosquitoes additionally feed on sugar meals and have specialized regions of their glands containing glycosidases and antimicrobials that might help control bacterial growth in the ingested meals. To expand our knowledge on the salivary cocktail of Ædes ægypti, a vector of dengue and yellow fevers, we analyzed a set of 4,232 expressed sequence tags from cDNA libraries of adult female mosquitoes.

Results

A nonredundant catalogue of 614 transcripts (573 of which are novel) is described, including 136 coding for proteins of a putative secretory nature. Additionally, a two-dimensional gel electrophoresis of salivary gland (SG) homogenates followed by tryptic digestion of selected protein bands and MS/MS analysis revealed the expression of 24 proteins. Analysis of tissue-specific transcription of a subset of these genes revealed at least 31 genes whose expression is specific or enriched in female SG, whereas 24 additional genes were expressed in female SG and in males but not in other female tissues. Most of the 55 proteins coded by these SG transcripts have no known function and represent high-priority candidates for expression and functional analysis as antihemostatic or antimicrobial agents. An unexpected finding is the occurrence of four protein families specific to SG that were probably a product of horizontal transfer from prokaryotic organisms to mosquitoes.

Conclusion

Overall, this paper contributes to the novel identification of 573 new transcripts, or near 3% of the Æ. ægypti proteome assuming a 20,000-protein set, and to the best-described sialome of any blood-feeding insect.

A novel secreted endonuclease from Culex quinquefasciatus salivary glands

Previous analysis of the salivary gland transcriptome of Culex quinquefasciatus showed the potential presence of an endonuclease with sequence similarities to shrimp, crab and two tsetse salivary proteins. Indeed, not only was the cloned cDNA shown to encode an active double-stranded endonuclease, but also the same activity was demonstrated to be secreted by salivary glands of Cx. quinquefasciatus. Preliminary studies with salivary gland extracts confirmed the presence of a highly active nuclease. This enzyme was shown to be present in the saliva of female mosquitoes by allowing starved mosquitoes to probe DNA-containing agarose gel. The recombinant Cx. quinquefasciatus endonuclease (CuquEndo) produced in mammalian cells showed no sequence specificity for DNA substrate except that it only cleaves double-stranded DNA. Recombinant Cx. quinquefasciatus endonuclease was active in the presence of Mg(2+) ions at pH 7.0-8.0, but no endonuclease activity was detected in the presence of calcium ions. The final hydrolysis products of this enzyme, detected by ion exchange chromatography, yielded DNA fragments ranging form 8-12 base pairs. Although endonucleases have been associated with a variety of cellular functions, their role in mosquito saliva is not clear. This female-specific secreted endonuclease may assist blood meal intake by lowering the local viscosity created by the release of host DNA in the bite site and/or acting as an indirect anticoagulant factor by producing a defibrotide-like mixture of DNA haptamers.

Comparative salivary gland transcriptomics of sandfly vectors of visceral leishmaniasis

Background

Immune responses to sandfly saliva have been shown to protect animals against Leishmania infection. Yet very little is known about the molecular characteristics of salivary proteins from different sandflies, particularly from vectors transmitting visceral leishmaniasis, the fatal form of the disease. Further knowledge of the repertoire of these salivary proteins will give us insights into the molecular evolution of these proteins and will help us select relevant antigens for the development of a vector based anti-Leishmania vaccine.

Results

Two salivary gland cDNA libraries from female sandflies Phlebotomus argentipes and P. perniciosus were constructed, sequenced and proteomic analysis of the salivary proteins was performed. The majority of the sequenced transcripts from the two cDNA libraries coded for secreted proteins. In this analysis we identified transcripts coding for protein families not previously described in sandflies. A comparative sandfly salivary transcriptome analysis was performed by using these two cDNA libraries and two other sandfly salivary gland cDNA libraries from P. ariasi and Lutzomyia longipalpis, also vectors of visceral leishmaniasis. Full-length secreted proteins from each sandfly library were compared using a stand-alone version of BLAST, creating formatted protein databases of each sandfly library. Related groups of proteins from each sandfly species were combined into defined families of proteins. With this comparison, we identified families of salivary proteins common among all of the sandflies studied, proteins to be genus specific and proteins that appear to be species specific. The common proteins included apyrase, yellow-related protein, antigen-5, PpSP15 and PpSP32-related protein, a 33-kDa protein, D7-related protein, a 39- and a 16.1- kDa protein and an endonuclease-like protein. Some of these families contained multiple members, including PPSP15-like, yellow proteins and D7-related proteins suggesting gene expansion in these proteins.

Conclusion

This comprehensive analysis allows us the identification of genus- specific proteins, species-specific proteins and, more importantly, proteins common among these different sandflies. These results give us insights into the repertoire of salivary proteins that are potential candidates for a vector-based vaccine.

An updated catalogue of salivary gland transcripts in the adult female mosquito, Anopheles gambiae

Salivary glands of blood-sucking arthropods contain a variety of compounds that prevent platelet and clotting functions and modify inflammatory and immunological reactions in the vertebrate host. In mosquitoes, only the adult female takes blood meals, while both sexes take sugar meals. With the recent description of the Anopheles gambiae genome, and with a set of approximately 3000 expressed sequence tags from a salivary gland cDNA library from adult female mosquitoes, we attempted a comprehensive description of the salivary transcriptome of this most important vector of malaria transmission. In addition to many transcripts associated with housekeeping functions, we found an active transposable element, a set of Wolbachia-like proteins, several transcription factors, including Forkhead, Hairy and doublesex, extracellular matrix components and 71 genes coding for putative secreted proteins. Fourteen of these 71 proteins had matching Edman degradation sequences obtained from SDS-PAGE experiments. Overall, 33 transcripts are reported for the first time as coding for salivary proteins. The tissue and sex specificity of these protein-coding transcripts were analyzed by RT-PCR and microarray experiments for insight into their possible function. Notably, two gene products appeared to be differentially spliced in the adult female salivary glands, whereas 13 contigs matched predicted intronic regions and may include additional alternatively spliced transcripts. Most An. gambiae salivary proteins represent novel protein families of unknown function, potentially coding for pharmacologically or microbiologically active substances. Supplemental data to this work can be found at http://www.ncbi.nlm.nih.gov/projects/omes/index.html#Ag2.

Characterization of the SCP/TAPS gene family in Drosophila melanogaster

The SCP/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) gene family encodes proteins found in many eukaryotes. SCP/TAPS proteins are defined by the presence of an SCP/TAPS domain, and many participate in important physiological processes. Five SCP/TAPS genes were previously identified in Drosophila melanogaster and are expressed in the digestive tract or in the testes. Sequence databases were searched to determine if other SCP/TAPS genes were present in D. melanogaster, and an additional 21 SCP/TAPS genes were identified. To further define the roles of these genes, the structures of each gene and protein were analyzed. Based on these analyses, 25 SCP/TAPS genes could be placed into one of two groups. Each group contained conserved intron positions that were not shared with the other group. Proteins encoded by group 1 genes also shared additional sequence motifs and conserved cysteines not found in group 2 proteins. To determine if the two groups were expressed differently, reverse transcriptase (RT)-polymerase chain reaction (PCR) was used to examine expression in adult flies. The results indicated that most genes were preferentially expressed in adult males, suggesting a role for these genes in male reproduction. Members of both groups displayed this preferential expression, so it was not group-specific. The two groups may differ in localization rather than function.

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.

Midgut and salivary gland transcriptomes of the arbovirus vector Culicoides sonorensis (Diptera: Ceratopogonidae)

Numerous Culicoides spp. are important vectors of livestock or human disease pathogens. Transcriptome information from midguts and salivary glands of adult female Culicoides sonorensis provides new insight into vector biology. Of 1719 expressed sequence tags (ESTs) from adult serum-fed female midguts harvested within 5 h of feeding, twenty-eight clusters of serine proteases were derived. Four clusters encode putative iron binding proteins (FER1, FERL, PXDL1, PXDL2), and two clusters encode metalloendopeptidases (MDP6C, MDP6D) that probably function in bloodmeal catabolism. In addition, a diverse variety of housekeeping cDNAs were identified. Selected midgut protease transcripts were analysed by quantitative real-time PCR (q-PCR): TRY1_115 and MDP6C mRNAs were induced in adult female midguts upon feeding, whereas TRY1_156 and CHYM1 were abundant in midguts both before and immediately after feeding. Of 708 salivary gland ESTs analysed, clusters representing two new classes of protein families were identified: a new class of D7 proteins and a new class of Kunitz-type protease inhibitors. Additional cDNAs representing putative immunomodulatory proteins were also identified: 5' nucleotidases, antigen 5-related proteins, a hyaluronidase, a platelet-activating factor acetylhydrolase, mucins and several immune response cDNAs. Analysis by q-PCR showed that all D7 and Kunitz domain transcripts tested were highly enriched in female heads compared with other tissues and were generally absent from males. The mRNAs of two additional protease inhibitors, TFPI1 and TFPI2, were detected in salivary glands of paraffin-embedded females by in situ hybridization.

Identification of the most abundant secreted proteins from the salivary glands of the sand fly Lutzomyia longipalpis, vector of Leishmania chagasi

Using massive cDNA sequencing, proteomics and customized computational biology approaches, we have isolated and identified the most abundant secreted proteins from the salivary glands of the sand fly Lutzomyia longipalpis. Out of 550 randomly isolated clones from a full-length salivary gland cDNA library, we found 143 clusters or families of related proteins. Out of these 143 families, 35 were predicted to be secreted proteins. We confirmed, by Edman degradation of Lu. longipalpis salivary proteins, the presence of 17 proteins from this group. Full-length sequence for 35 cDNA messages for secretory proteins is reported, including an RGD-containing peptide, three members of the yellow-related family of proteins, maxadilan, a PpSP15-related protein, six members of a family of putative anticoagulants, an antigen 5-related protein, a D7-related protein, a cDNA belonging to the Cimex apyrase family of proteins, a protein homologous to a silk protein with amino acid repeats resembling extracellular matrix proteins, a 5'-nucleotidase, a peptidase, a palmitoyl-hydrolase, an endonuclease, nine novel peptides and four different groups of proteins with no homologies to any protein deposited in accessible databases. Sixteen of these proteins appear to be unique to sand flies. With this approach, we have tripled the number of isolated secretory proteins from this sand fly. Because of the relationship between the vertebrate host immune response to salivary proteins and protection to parasite infection, these proteins are promising markers for vector exposure and attractive targets for vaccine development to control Leishmania chagasi infection.

Kinetics of expression of the salivary apyrases in Triatoma infestans

Apyrases are nucleoside triphosphate-diphosphohydrolases that remove Pi from ATP and ADP. The blood feeding reduviid Triatoma infestans, which transmits the Trypanosoma cruzi agent of Chagas disease to animals and man, presents in its salivary glands five apyrases with molecular masses of 88, 82, 79, 68 and 67 kDa. These triatomine apyrases have been associated with the prevention of ADP induced platelet aggregation in the host. Here we provide biochemical data showing that these apyrases are stored in the lumen of the salivary gland D1 pairs, and that about one half of the pool of the enzyme is consumed during feeding. After the feeding recovery of apyrases to maximal activity level takes days, thus suggesting de novo protein synthesis. This hypothesis is supported by quantitative RT-PCR analysis which shows an upregulation of the 79 kDa apyrase mRNA level after feeding.

An insight into the salivary transcriptome and proteome of the adult female mosquito Culex pipiens quinquefasciatus

To obtain an insight into the salivary transcriptome and proteome (sialome) of the adult female mosquito Culex quinquefasciatus, a cDNA library was randomly sequenced, and aminoterminal information for selected proteins and peptides was obtained. cDNA sequence clusters coding for secreted proteins were further analyzed. The transcriptome revealed messages coding for several proteins of known families previously reported in the salivary glands of other blood-feeding insects as well as immune-related products such as C-type lectin, gambicin, and members of the prophenol oxidase cascade. Additionally, several transcripts coding for low-complexity proteins were found, some clearly coding for mucins. Many novel transcripts were found, including a novel endonuclease previously described in crabs and shrimps but not in insects; a hyaluronidase, not described before in mosquito salivary glands but found in venom glands and in salivary glands of sand flies and black flies; several cysteine-rich peptides with possible anticlotting function, including one similar to a previously described nematode family of anti-proteases; and a completely novel family of cysteine- and tryptophane-rich proteins (CWRC family) for which 12 full-length sequences are described. Also described are 14 additional novel proteins and peptides whose function and/or family affiliation are unknown. In total, 54 transcripts coding for full-length proteins are described. That several of these are translated into proteins was confirmed by finding the corresponding aminoterminal sequences in the SDS-PAGE/Edman degradation experiments. Electronic versions of all tables and sequences can be found at http://www.ncbi.nlm.nih.gov/projects/Mosquito/C_quinquefasciatus_sialome.

OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands

Outer surface protein C (OspC) is a differentially expressed major surface lipoprotein of Borrelia burgdorferi. ospC is swiftly upregulated when spirochetes leave the Ixodes scapularis tick gut, migrate to the salivary gland, and exit the arthropod vector. Here we show that OspC strongly binds to the tick salivary gland, suggesting a role for OspC in spirochete adherence to this tissue. In vivo studies using a murine model of Lyme borreliosis showed that while OspC F(ab)(2) fragments did not influence either the viability of spirochetes or ospC gene expression, they did interfere with B. burgdorferi invasion of tick salivary glands. We then generated ospC knockout spirochetes in an infectious clone of B. burgdorferi and examined them within the vector. OspC-deficient or wild-type spirochetes persisted equally within the gut of unfed ticks and multiplied during the tick engorgement; however, unlike wild-type B. burgdorferi, the mutants were unable to invade salivary glands. Salivary gland colonization of OspC-deficient spirochetes was completely restored when this mutant was complemented in trans with a plasmid harboring the wild-type ospC gene. These studies conclusively demonstrate the importance of OspC in the invasion of tick salivary glands by B. burgdorferi, a critical step in the transmission of spirochetes from the arthropod vector to the mammalian host.

The transcriptome of adult female Anopheles darlingi salivary glands

Anopheles (Nyssorhynchus) darlingi is an important malaria vector in South and Central America; however, little is known about molecular aspects of its biology. Genomic and proteomic analyses were performed on the salivary gland products of Anopheles darlingi. A total of 593 randomly selected, salivary gland-derived cDNAs were sequenced and assembled based on their similarities into 288 clusters. The putative translated proteins were classified into three categories: (S) secretory products, (H) housekeeping products and (U) products with unknown cell location and function. Ninety-three clusters encode putative secreted proteins and several of them, such as an anophelin, a thrombin inhibitor, apyrases and several new members of the D7 protein family, were identified as molecules involved in haematophagy. Sugar-feeding related enzymes (alpha-glucosidases and alpha-amylase) also were found among the secreted salivary products. Ninety-nine clusters encode housekeeping proteins associated with energy metabolism, protein synthesis, signal transduction and other cellular functions. Ninety-seven clusters encode proteins with no similarity with known proteins. Comparison of the sequence divergence of the S and H categories of proteins of An. darlingi and An. gambiae revealed that the salivary proteins are less conserved than the housekeeping proteins, and therefore are changing at a faster evolutionary rate. Tabular and supplementary material containing the cDNA sequences and annotations are available at http://www.ncbi.nlm.nih.gov/projects/Mosquito/A_darlingi_sialome/

Exploring the sialome of the blood-sucking bug Rhodnius prolixus

Rhodnius prolixus is a Hemiptera that feeds exclusively on vertebrate blood in all life stages. Its salivary glands produce potent pharmacological substances that counteract host hemostasis, including anti-clotting, anti-platelet, and vasodilatory substances. To obtain a further insight into the salivary biochemical and pharmacological complexity of this insect, a cDNA library was randomly sequenced, and salivary gland homogenates were fractionated by HPLC to obtain aminoterminal sequences of abundantly expressed proteins. Results indicate a remarkable expansion of the lipocalin family in Rhodnius salivary glands, among other protein sequences described. A summary of 31 new full length proteins deducted from their mRNA sequence is described, including several new members of the nitrophorin, triabin, and pallidipin families. The electronic version of the complete tables is available at http://www.ncbi.nlm.nih.gov/projects/vectors/rhodnius_prolixus.

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.

Exploring the salivary gland transcriptome and proteome of the Anopheles stephensi mosquito

Anopheles stephensi is the main urban mosquito vector of malaria in the Indian subcontinent, and belongs to the same subgenus as Anopheles gambiae, the main malaria vector in Africa. Recently the genome and proteome sets of An. gambiae have been described, as well as several protein sequences expressed in its salivary glands, some of which had their expression confirmed by amino terminal sequencing. In this paper, we randomly sequenced a full-length cDNA library of An. stephensi and performed Edman degradation of polyvinylidene difluoride (PVDF)-transferred protein bands from salivary homogenates. Twelve of 13 proteins found by aminoterminal degradation were found among the cDNA clusters of the library. Thirty-three full-length novel cDNA sequences are reported, including a novel secreted galectin; the homologue of anophelin, a thrombin inhibitor; a novel trypsin/chymotrypsin inhibitor; an apyrase; a lipase; and several new members of the D7 protein family. Most of the novel proteins have no known function. Comparison of the putatively secreted and putatively housekeeping proteins of An. stephensi with An. gambiae proteins indicated that the salivary gland proteins are at a faster evolutionary pace. The possible role of these proteins in blood and sugar feeding by the mosquito is discussed. The electronic tables and supplemental material are available at http://www.ncbi.nlm.nih.gov/projects/Mosquito/A_stephensi_sialome/ .

Inhibition mechanisms of hematophagous invertebrate compounds acting on the host blood coagulation and platelet aggregation pathways

To facilitate blood feeding, hematophagous invertebrates have evolved a sophisticated array of physiological compounds that counteract homeostatic systems and inflammatory reactions of the vertebrate host. For this reason, hematophagous invertebrates possess a variety of anticoagulation components that are inhibitors of coagulant factors or antagonists of the platelet receptor. The examination of kinetic data and the crystal structure analysis have exposed the inhibition mechanisms for many of these anticoagulant reagents. Here, we attempt to classify the antihemostatic molecules and to focus on the kinetic approaches that have been instrumental in defining these mechanisms.

Toward a description of the sialome of the adult female mosquito Aedes aegypti

To describe the set of mRNA and protein expressed in the salivary glands (sialome) of Aedes aegypti mosquitoes, we randomly sequenced a full-length cDNA library of this insect and performed Edman degradation of PVDF-transferred protein bands from salivary homogenates. We found 238 cDNA clusters which contained those coding for 10 of the 11 proteins found by aminoterminal degradation. All six previously described salivary proteins were found in this library. Full-length sequences of 32 novel cDNA sequences are reported, one of which is the product of a transposable element. Among the 31 novel protein sequences are 4 additional members of the D7 protein family; 4 novel members of the antigen 5 family (a protein family not reported in Aedes); a novel serpin; a novel member of the 30-kDa allergen of Ae. Aegypti; a secreted calreticulin; 2 proteins similar to mammalian angiopoietins; adenosine deaminase; purine hydrolase; lysozyme; a C-type lectin; 3 serine proteases, including one with high similarity to Bombyx prophenoloxidase activating enzyme; 2 proteins related to invertebrate immunity; and several sequences that have no significant matches to known proteins. The possible role of these proteins in blood and sugar feeding by the mosquito is discussed.

Identification of major soluble salivary gland proteins in teneral Glossina morsitans morsitans

Salivary glands of tsetse flies (Diptera: Glossinidiae) contain molecules that are involved in preventing blood clotting during feeding as well as molecules thought to be intimately associated with trypanosome development and maturation. Here we present a protein microchemical analysis of the major soluble proteins of the salivary glands of Glossina morsitans morsitans, an important vector of African trypanosomes. Differential solubilization of salivary proteins was followed by reverse-phase, high-performance liquid chromatography (HPLC) and analysis of fractions by 1-D gel electrophoresis to reveal four major proteins. Each protein was subjected to amino acid microanalysis and N-terminal microsequencing. A protein chemical approach using high-resolution 2-D gel electrophoresis and mass spectrometry was also used to identify the salivary proteins. Matrix-assisted, laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and quadrupole time-of-flight (Q-TOF) tandem mass spectrometry methods were used for peptide mass mapping and sequencing, respectively. Sequence information and peptide mass maps queried against the NCBI non-redundant database confirmed the identity of the first protein as tsetse salivary gland growth factor-1 (TSGF-1). Two proteins with no known function were identified as tsetse salivary gland protein 1 (Tsal 1) and tsetse salivary gland protein 2 (Tsal 2). The fourth protein was identified as Tsetse antigen-5 (TAg-5), which is a member of a large family of anti-haemostatic proteins. The results show that these four proteins are the most abundant soluble gene products present in salivary glands of teneral G. m. morsitans. We discuss the possible functions of these major proteins in cyclical transmission of African trypanosomes.

Toward a catalog for the transcripts and proteins (sialome) from the salivary gland of the malaria vectorAnopheles gambiae

Hundreds of Anopheles gambiae salivary gland cDNA library clones have been sequenced. A cluster analysis based on sequence similarity at e-60 grouped the 691 sequences into 251 different clusters that code for proteins with putative secretory, housekeeping, or unknown functions. Among the housekeeping cDNAs, we found sequences predicted to code for novel thioredoxin, tetraspanin, hemopexin, heat shock protein, and TRIO and MBF proteins. Among secreted cDNAs, we found 21 novel A. gambiaesalivary sequences including those predicted to encode amylase, calreticulin,selenoprotein, mucin-like protein and 30-kDa allergen, in addition to antigen 5- and D7-related proteins, three novel salivary gland (SG)-like proteins and eight unique putative secreted proteins (Hypothetical Proteins, HP). The electronic version of this paper contains hyperlinks to FASTA-formatted files for each cluster with the best match to the nonredundant (NR) and conserved domain databases (CDD) in addition to CLUSTAL alignments of each cluster. The N terminus of 12 proteins (SG-1, SG-1-like 2, SG-6, HP 8, HP 9-like, 5′nucleotidase, 30-kDa protein, antigen 5- and four D7-related proteins) has been identified by Edman degradation of PVDF-transferred, SDS/PAGE-separated salivary gland proteins. Therefore, we contribute to the generation of a catalog of A. gambiae salivary transcripts and proteins. These data are freely available and will eventually become an invaluable tool to study the role of salivary molecules in parasite-host/vector interactions.

Role of arthropod saliva in blood feeding: sialome and post-sialome perspectives

This review addresses the problems insects and ticks face to feed on blood and the solutions these invertebrates engender to overcome these obstacles, including a sophisticated salivary cocktail of potent pharmacologic compounds. Recent advances in transcriptome and proteome research allow an unprecedented insight into the complexity of these compounds, indicating that their molecular diversity as well as the diversity of their targets is still larger than previously thought.

Identification and phylogeny of a non-specific endonuclease gene of white spot syndrome virus of shrimp

White spot syndrome virus (WSSV) is a taxonomically unclassified virus which causes a disease in shrimps worldwide. A 936 bp long open reading frame (ORF) was found on a 7.2 kb HindIII fragment of the DNA genome of WSSV located adjacent to the ribonucleotide reductase small subunit gene. This putative ORF showed homology to prokaryotic and eukaryotic endonucleases, which contain a non-specific endonuclease motif. Alignment with viral and eukaryotic endonuclease ORFs revealed that most catalytically and structurally important amino acid residues were present in the putative WSSV non-specific endonuclease gene. An unrooted parsimonous phylogenetic tree of non-specific endonucleases indicated that the WSSV ORF was located in a well bootstrap supported clade containing only arthopods, including one of WSSV's natural hosts, Penaeus japonicus. A similar conjunction was found for the only other viral homologue, present in Fowlpox virus, which was also found in a well bootstrap-supported clade with its natural host, Gallus gallus. This clustering of virus and host suggests that both WSSV and Fowlpox virus may have acquired their nuclease genes from their respective natural hosts. Because the motif for non-specific nucleases is found in only two viruses, this gene cannot be used to clarify the taxonomic position of WSSV. However, the presence of this type of nuclease rarely found in viruses adds a novel feature to WSSV.