The salivary glands of the vector mosquito, Aedes aegypti, express a novel member of the amylase gene family

Structural and Functional Characterization of Drosophila melanogaster α-Amylase

Insects rely on carbohydrates such as starch and glycogen as an energy supply for growth of larvae and for longevity. In this sense α-amylases have essential roles under extreme conditions, e.g., during nutritional or temperature stress, thereby contributing to survival of the insect. This makes them interesting targets for combating insect pests. Drosophila melanogaster α-amylase, DMA, which belongs to the glycoside hydrolase family 13, sub family 15, has been studied from an evolutionary, biochemical, and structural point of view. Our studies revealed that the DMA enzyme is active over a broad temperature and pH range, which is in agreement with the fluctuating environmental changes with which the insect is confronted. Crystal structures disclosed a new nearly fully solvated metal ion, only coordinated to the protein via Gln263. This residue is only conserved in the subgroup of D. melanogaster and may thus contribute to the enzyme adaptive response to large temperature variations. Studies of the effect of plant inhibitors and the pseudo-tetrasaccharide inhibitor acarbose on DMA activity, allowed us to underline the important role of the so-called flexible loop on activity/inhibition, but also to suggest that the inhibition modes of the wheat inhibitors WI-1 and WI-3 on DMA, are likely different.

Toward a More Comprehensive View of α-Amylase across Decapods Crustaceans

Decapod crustaceans are a very diverse group and have evolved to suit a wide variety of diets. Alpha-amylases enzymes, responsible for starch and glycogen digestion, have been more thoroughly studied in herbivore and omnivore than in carnivorous species. We used information on the α-amylase of a carnivorous lobster as a connecting thread to provide a more comprehensive view of α-amylases across decapods crustaceans. Omnivorous crustaceans such as shrimps, crabs, and crayfish present relatively high amylase activity with respect to carnivorous crustaceans. Yet, contradictory results have been obtained and relatively high activity in some carnivores has been suggested to be a remnant trait from ancestor species. Here, we provided information sustaining that high enzyme sequence and overall architecture conservation do not allow high changes in activity, and that differences among species may be more related to number of genes and isoforms, as well as transcriptional and secretion regulation. However, recent evolutionary analyses revealed that positive selection might have also occurred among distant lineages with feeding habits as a selection force. Some biochemical features of decapod α-amylases can be related with habitat or gut conditions, while less clear patterns are observed for other enzyme properties. Likewise, while molt cycle variations in α-amylase activity are rather similar among species, clear relationships between activity and diet shifts through development cannot be always observed. Regarding the adaptation of α-amylase to diet, juveniles seem to exhibit more flexibility than larvae, and it has been described variation in α-amylase activity or number of isoforms due to the source of carbohydrate and its level in diets, especially in omnivore species. In the carnivorous lobster, however, no influence of the type of carbohydrate could be observed. Moreover, lobsters were not able to fine-regulate α-amylase gene expression in spite of large changes in carbohydrate content of diet, while retaining some capacity to adapt α-amylase activity to very low carbohydrate content in the diets. In this review, we raised arguments for the need of more studies on the α-amylases of less studied decapods groups, including carnivorous species which rely more on dietary protein and lipids, to broaden our view of α-amylase in decapods crustaceans.

Neurochemical regulation of Aedes aegypti salivary gland function

The salivary gland of hematophagous arthropods is critical for blood meal acquisition, blood vessel localization, and secretion of digestive enzymes. Thus, there is significant interest in the regulation of salivary gland function and mechanisms driving the secretion of saliva and digestive proteins. We aimed to gain a broader understanding of the regulatory role of aminergic, cholinergic, and octopaminergic neuromodulators to saliva and protein secretion from the female A. aegypti salivary gland. Quantification of saliva after injection with neuromodulators showed that dopamine, serotonin, and pilocarpine increased the secretory activity of the salivary gland with potency rankings dopamine = serotonin > pilocarpine. No change in saliva secretion was observed with octopamine or ergonovine, which indicates the A. aegypti salivary gland may be regulated by dopaminergic, serotonergic, and cholinergic systems, but are not likely regulated by octopaminergic or tryptaminergic systems. Next, we studied the regulatory control of dopamine-mediated salivation. Data indicate extracellular calcium flux, but not neural function, is critical for dopamine-mediated salivation, which suggests epithelial transport of ions and not neuronal control is responsible for dopamine-mediated salivation. For regulation of protein secretion, data indicate dopamine or serotonin exposure facilitates amylase secretion, whereas serotonin but not dopamine exposure increased apyrase concentrations in the secreted saliva. General immunoreactivity to anti-rat D1-dopamine receptor antibody was observed, yet immunoreactivity to the anti-rat D2-receptor antibody was identified in the proximal regions of the lateral lobes and slight immunoreactivity in the distal portion of the lateral lobe, with no expression in the medial lobe.

Horizontal Transfer and Gene Loss Shaped the Evolution of Alpha-Amylases in Bilaterians

The subfamily GH13_1 of alpha-amylases is typical of Fungi, but it is also found in some unicellular eukaryotes (e.g., Amoebozoa, choanoflagellates) and non-bilaterian Metazoa. Since a previous study in 2007, GH13_1 amylases were considered ancestral to the Unikonts, including animals, except Bilateria, such that it was thought to have been lost in the ancestor of this clade. The only alpha-amylases known to be present in Bilateria so far belong to the GH13_15 and 24 subfamilies (commonly called bilaterian alpha-amylases) and were likely acquired by horizontal transfer from a proteobacterium. The taxonomic scope of Eukaryota genomes in databases has been greatly increased ever since 2007. We have surveyed GH13_1 sequences in recent data from ca. 1600 bilaterian species, 60 non-bilaterian animals and also in unicellular eukaryotes. As expected, we found a number of those sequences in non-bilaterians: Anthozoa (Cnidaria) and in sponges, confirming the previous observations, but none in jellyfishes and in Ctenophora. Our main and unexpected finding is that such fungal (also called Dictyo-type) amylases were also consistently retrieved in several bilaterian phyla: hemichordates (deuterostomes), brachiopods and related phyla, some molluscs and some annelids (protostomes). We discuss evolutionary hypotheses possibly explaining the scattered distribution of GH13_1 across bilaterians, namely, the retention of the ancestral gene in those phyla only and/or horizontal transfers from non-bilaterian donors.

Transcriptome-wide responses of adult melon thrips (Thrips palmi) associated with capsicum chlorosis virus infection

Thrips palmi is a widely distributed major agricultural pest in the tropics and subtropics, causing significant losses in cucurbit and solanaceous crops through feeding damage and transmission of tospoviruses. Thrips palmi is a vector of capsicum chlorosis virus (CaCV) in Australia. The present understanding of transmission biology and potential effects of CaCV on T. palmi is limited. To gain insights into molecular responses to CaCV infection, we performed RNA-Seq to identify thrips transcripts that are differentially-abundant during virus infection of adults. De-novo assembly of the transcriptome generated from whole bodies of T. palmi adults generated 166,445 contigs, of which ~24% contained a predicted open reading frame. We identified 1,389 differentially-expressed (DE) transcripts, with comparable numbers up- (708) and down-regulated (681) in virus-exposed thrips compared to non-exposed thrips. Approximately 59% of these DE transcripts had significant matches to NCBI non-redundant proteins (Blastx) and Blast2GO identified provisional functional categories among the up-regulated transcripts in virus-exposed thrips including innate immune response-related genes, salivary gland and/or gut-associated genes and vitellogenin genes. The majority of the immune-related proteins are known to serve functions in lysosome activity and melanisation in insects. Most of the up-regulated oral and extra-oral digestion-associated genes appear to be involved in digestion of proteins, lipids and plant cell wall components which may indirectly enhance the likelihood or frequency of virus transmission or may be involved in the regulation of host defence responses. Most of the down-regulated transcripts fell into the gene ontology functional category of 'structural constituent of cuticle'. Comparison to DE genes responsive to tomato spotted wilt virus in Frankliniella occidentalis indicates conservation of some thrips molecular responses to infection by different tospoviruses. This study assembled the first transcriptome in the genus Thrips and provides important data to broaden our understanding of networks of molecular interactions between thrips and tospoviruses.

Silencing of sucrose hydrolase causes nymph mortality and disturbs adult osmotic homeostasis in Diaphorina citri (Hemiptera: Liviidae)

Plant piercing sucking insects mainly feed on phloem sap containing a high amount of sucrose. To enhance the absorption of sucrose from the midgut, sucrose hydrolase digests sucrose into glucose and fructose. In this study, a sucrose hydrolase homolog (DcSuh) was identified and targeted in Diaphorina citri, the vector of huanglongbing (HLB), by RNA interference (RNAi). In silico analysis revealed the presence of an Aamy domain in the DcSUH protein, which is characteristic of the glycoside hydrolase family 13 (GH13). Phylogenetic analysis showed DcSuh was closely related to the sucrose hydrolase of other Hemiptera members. The highest gene expression levels of DcSuh was found in the 4th and 5th instar nymphs. dsRNA-mediated RNAi of DcSuh was achieved through topical feeding. Our results showed that application of 0.2 μL of 500 ng μL^-1 (100 ng) dsRNA-DcSuh was sufficient to repress the expression of the targeted gene and cause nymph mortality and reduce adult lifespan. The reduction in gene expression, mortality, and lifespan was dose-dependent. In agreement with the gene expression results, treatment with dsRNA-DcSuh significantly reduced sucrose hydrolase activity in treated nymphs and emerged adults from treated nymphs. Interestingly, some emerged adults from treated nymphs showed a swollen abdomen phenotype, indicating that these insects were under osmotic stress. Although the percentage of swollen abdomens was low, their incidence was significantly correlated with the concentration of applied dsRNA-DcSuh. Metabolomic analyses using GC-MS showed an accumulation of sucrose and a reduction in fructose, glucose and trehalose in treated nymphs, confirming the inhibition of sucrose hydrolase activity. Additionally, most of the secondary metabolites were reduced in the treated nymphs, indicating a reduction in the biological activities in D. citri and that they are under stress. Our findings indicate that sucrose hydrolase might be a potential target for effective RNAi control of D. citri.

Anopheline salivary protein genes and gene families: an evolutionary overview after the whole genome sequence of sixteen Anopheles species

BACKGROUND

Mosquito saliva is a complex cocktail whose pharmacological properties play an essential role in blood feeding by counteracting host physiological response to tissue injury. Moreover, vector borne pathogens are transmitted to vertebrates and exposed to their immune system in the context of mosquito saliva which, in virtue of its immunomodulatory properties, can modify the local environment at the feeding site and eventually affect pathogen transmission. In addition, the host antibody response to salivary proteins may be used to assess human exposure to mosquito vectors. Even though the role of quite a few mosquito salivary proteins has been clarified in the last decade, we still completely ignore the physiological role of many of them as well as the extent of their involvement in the complex interactions taking place between the mosquito vectors, the pathogens they transmit and the vertebrate host. The recent release of the genomes of 16 Anopheles species offered the opportunity to get insights into function and evolution of salivary protein families in anopheline mosquitoes.

RESULTS

Orthologues of fifty three Anopheles gambiae salivary proteins were retrieved and annotated from 18 additional anopheline species belonging to the three subgenera Cellia, Anopheles, and Nyssorhynchus. Our analysis included 824 full-length salivary proteins from 24 different families and allowed the identification of 79 novel salivary genes and re-annotation of 379 wrong predictions. The comparative, structural and phylogenetic analyses yielded an unprecedented view of the anopheline salivary repertoires and of their evolution over 100 million years of anopheline radiation shedding light on mechanisms and evolutionary forces that contributed shaping the anopheline sialomes.

CONCLUSIONS

We provide here a comprehensive description, classification and evolutionary overview of the main anopheline salivary protein families and identify two novel candidate markers of human exposure to malaria vectors worldwide. This anopheline sialome catalogue, which is easily accessible as hyperlinked spreadsheet, is expected to be useful to the vector biology community and to improve the capacity to gain a deeper understanding of mosquito salivary proteins facilitating their possible exploitation for epidemiological and/or pathogen-vector-host interaction studies.

Molecular, Biochemical, and Dietary Regulation Features of α-Amylase in a Carnivorous Crustacean, the Spiny Lobster Panulirus argus

Alpha-amylases are ubiquitously distributed throughout microbials, plants and animals. It is widely accepted that omnivorous crustaceans have higher α-amylase activity and number of isoforms than carnivorous, but contradictory results have been obtained in some species, and carnivorous crustaceans have been less studied. In addition, the physiological meaning of α-amylase polymorphism in crustaceans is not well understood. In this work we studied α-amylase in a carnivorous lobster at the gene, transcript, and protein levels. It was showed that α-amylase isoenzyme composition (i.e., phenotype) in lobster determines carbohydrate digestion efficiency. Most frequent α-amylase phenotype has the lowest digestion efficiency, suggesting this is a favoured trait. We revealed that gene and intron loss have occurred in lobster α-amylase, thus lobsters express a single 1830 bp cDNA encoding a highly conserved protein with 513 amino acids. This protein gives rise to two isoenzymes in some individuals by glycosylation but not by limited proteolysis. Only the glycosylated isoenzyme could be purified by chromatography, with biochemical features similar to other animal amylases. High carbohydrate content in diet down-regulates α-amylase gene expression in lobster. However, high α-amylase activity occurs in lobster gastric juice irrespective of diet and was proposed to function as an early sensor of the carbohydrate content of diet to regulate further gene expression. We concluded that gene/isoenzyme simplicity, post-translational modifications and low Km, coupled with a tight regulation of gene expression, have arose during evolution of α-amylase in the carnivorous lobster to control excessive carbohydrate digestion in the presence of an active α-amylase.

Particularities of allergy in the Tropics

Allergic diseases are distributed worldwide and their risk factors and triggers vary according to geographical and socioeconomic conditions. Allergies are frequent in the Tropics but aspects of their prevalence, natural history, risk factors, sensitizers and triggers are not well defined and some are expected to be different from those in temperate zone countries. The aim of this review is to investigate if allergic diseases in the Tropics have particularities that deserve special attention for research and clinical practice. Such information will help to form a better understanding of the pathogenesis, diagnosis and management of allergic diseases in the Tropics. As expected, we found particularities in the Tropics that merit further study because they strongly affect the natural history of common allergic diseases; most of them related to climate conditions that favor permanent exposure to mite allergens, helminth infections and stinging insects. In addition, we detected several unmet needs in important areas which should be investigated and solved by collaborative efforts led by the emergent research groups on allergy from tropical countries.

A Deep Insight into the Sialome of Male and Female Aedes aegypti Mosquitoes

Only adult female mosquitoes feed on blood, while both genders take sugar meals. Accordingly, several compounds associated with blood feeding (i.e. vasodilators, anti-clotting, anti-platelets) are found only in female glands, while enzymes associated with sugar feeding or antimicrobials (such as lysozyme) are found in the glands of both sexes. We performed de novo assembly of reads from adult Aedes aegypti female and male salivary gland libraries (285 and 90 million reads, respectively). By mapping back the reads to the assembled contigs, plus mapping the reads from a publicly available Ae. aegypti library from adult whole bodies, we identified 360 transcripts (including splice variants and alleles) overexpressed tenfold or more in the glands when compared to whole bodies. Moreover, among these, 207 were overexpressed fivefold or more in female vs. male salivary glands, 85 were near equally expressed and 68 were overexpressed in male glands. We call in particular the attention to C-type lectins, angiopoietins, female-specific Antigen 5, the 9.7 kDa, 12–14 kDa, 23.5 kDa, 62/34 kDa, 4.2 kDa, proline-rich peptide, SG8, 8.7 kDa family and SGS fragments: these polypeptides are all of unknown function, but due to their overexpression in female salivary glands and putative secretory nature they are expected to affect host physiology. We have also found many transposons (some of which novel) and several endogenous viral transcripts (probably acquired by horizontal transfer) which are overexpressed in the salivary glands and may play some role in tissue-specific gene regulation or represent a mechanism of virus interference. This work contributes to a near definitive catalog of male and female salivary gland transcripts from Ae. aegypti, which will help to direct further studies aiming at the functional characterization of the many transcripts with unknown function and the understanding of their role in vector-host interaction and pathogen transmission.

Unraveling dual feeding associated molecular complexity of salivary glands in the mosquito Anopheles culicifacies

Mosquito salivary glands are well known to facilitate meal acquisition, however the fundamental question on how adult female salivary gland manages molecular responses during sugar versus blood meal uptake remains unanswered. To investigate these responses, we analyzed a total of 58.5 million raw reads generated from two independent RNAseq libraries of the salivary glands collected from 3–4 day-old sugar and blood fed Anopheles culicifacies mosquitoes. Comprehensive functional annotation analysis of 10,931 contigs unraveled that salivary glands may encode diverse nature of proteins in response to distinct physiological feeding status. Digital gene expression analysis and PCR validation indicated that first blood meal significantly alters the molecular architecture of the salivary glands. Comparative microscopic analysis also revealed that first blood meal uptake not only causes an alteration of at least 12–22% of morphological features of the salivary glands but also results in cellular changes e.g. apoptosis, confirming together that adult female salivary glands are specialized organs to manage meal specific responses. Unraveling the underlying mechanism of mosquito salivary gene expression, controlling dual feeding associated responses may provide a new opportunity to control vector borne diseases.

Immunological aspects of the immune response induced by mosquito allergens

Allergies caused by mosquito bites may produce local or systemic reactions. The inhalation of mosquito allergens may also cause asthma and/or allergic rhinoconjunctivitis in sensitized individuals. The mechanisms implicated in the development of these immune responses involve IgE antibodies, different subtypes of IgG and proinflammatory cytokines as well as basophils, eosinophils and mast cells. Several allergenic components have been identified in the saliva and bodies of mosquitoes and some of these are present in different mosquito species. The most common species implicated in allergic reactions belong to the genera Aedes, Culex and Anopheles. Several Aedes aegypti allergens have been cloned and sequenced. The recombinant molecules show IgE reactivity similar to that of the native allergens, making them good candidates for the diagnosis of mosquito allergies. Allergen-specific immunotherapy with mosquito extracts induces a protective response characterized by a decreased production of IgE antibodies, increased IgG levels, a reduction in the severity of cutaneous and respiratory symptoms and the need for medication. The aims of this review are to summarize the progress made in the characterization of mosquito allergens and discuss the types of immune responses induced by mosquito bites and the inhalation of mosquito allergens in atopic individuals.

Olive fly transcriptomics analysis implicates energy metabolism genes in spinosad resistance

Background

The olive fly, Bactrocera oleae, is the most devastating pest of cultivated olives. Its control has been traditionally based on insecticides, mainly organophosphates and pyrethroids. In recent years, the naturalyte spinosad is used against the olive fly. As with other insecticides, spinosad is subject to selection pressures that have led to resistance development. Mutations in the α6 subunit of the nicotinic acetylcholine receptor (nAChR) have been implicated in spinosad resistance in several species (e.g., Drosophila melanogaster) but excluded in others (e.g., Musca domestica). Yet, additional mechanisms involving enhanced metabolism of detoxification enzymes (such as P450 monooxygenases or mixed function oxidases) have also been reported. In order to clarify the spinosad resistance mechanisms in the olive fly, we searched for mutations in the α6-subunit of the nAChR and for up-regulated genes in the entire transcriptome of spinosad resistant olive flies.

Results

The olive fly α6-subunit of the nAChR was cloned from the laboratory sensitive strain and a spinosad selected resistant line. The differences reflected silent nucleotide substitutions or conserved amino acid changes. Additionally, whole transcriptome analysis was performed in the two strains in order to reveal any underlying resistance mechanisms. Comparison of over 13,000 genes showed that in spinosad resistant flies nine genes were significantly over-expressed, whereas ~40 were under-expressed. Further functional analyses of the nine over-expressed and eleven under-expressed loci were performed. Four of these loci (Yolk protein 2, ATP Synthase FO subunit 6, Low affinity cationic amino acid transporter 2 and Serine protease 6) showed consistently higher expression both in the spinosad resistant strain and in wild flies from a resistant California population. On the other side, two storage protein genes (HexL1 and Lsp1) and two heat-shock protein genes (Hsp70 and Hsp23) were unfailingly under-expressed in resistant flies.

Conclusion

The observed nucleotide differences in the nAChR-α6 subunit between the sensitive and spinosad resistant olive fly strains did not advocate for the involvement of receptor mutations in spinosad resistance. Instead, the transcriptome comparison between the two strains indicated that several immune system loci as well as elevated energy requirements of the resistant flies might be necessary to lever the detoxification process.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-714) contains supplementary material, which is available to authorized users.

Comparative transcriptome analysis of salivary glands of two populations of rice brown planthopper, Nilaparvata lugens, that differ in virulence

Background

The brown planthopper (BPH), Nilaparvata lugens (Stål), a destructive rice pest in Asia, can quickly overcome rice resistance by evolving new virulent populations. Herbivore saliva plays an important role in plant–herbivore interactions, including in plant defense and herbivore virulence. However, thus far little is known about BPH saliva at the molecular level, especially its role in virulence and BPH–rice interaction.

Methodology/Principal Findings

Using cDNA amplification in combination with Illumina short-read sequencing technology, we sequenced the salivary-gland transcriptomes of two BPH populations with different virulence; the populations were derived from rice variety TN1 (TN1 population) and Mudgo (M population). In total, 37,666 and 38,451 unigenes were generated from the salivary glands of these populations, respectively. When combined, a total of 43,312 unigenes were obtained, about 18 times more than the number of expressed sequence tags previously identified from these glands. Gene ontology annotations and KEGG orthology classifications indicated that genes related to metabolism, binding and transport were significantly active in the salivary glands. A total of 352 genes were predicted to encode secretory proteins, and some might play important roles in BPH feeding and BPH–rice interactions. Comparative analysis of the transcriptomes of the two populations revealed that the genes related to ‘metabolism,’ ‘digestion and absorption,’ and ‘salivary secretion’ might be associated with virulence. Moreover, 67 genes encoding putative secreted proteins were differentially expressed between the two populations, suggesting these genes may contribute to the change in virulence.

Conclusions/Significance

This study was the first to compare the salivary-gland transcriptomes of two BPH populations having different virulence traits and to find genes that may be related to this difference. Our data provide a rich molecular resource for future functional studies on salivary glands and will be useful for elucidating the molecular mechanisms underlying BPH feeding and virulence differences.

Transcriptome analysis of the salivary glands of potato leafhopper, Empoasca fabae

The potato leafhopper, Empoasca fabae, is a pest of economic crops in the United States and Canada, where it causes damage known as hopperburn. Saliva, along with mechanical injury, leads to decreases in gas exchange rates, stunting and chlorosis. Although E. fabae saliva is known to induce plant responses, little knowledge exists of saliva composition at the molecular level. We subjected the salivary glands of E. fabae to Roche 454-pyrosequencing which resulted significant number (30,893) of expressed sequence tags including 2805 contigs and 28,088 singletons. A high number of sequences (78%) showed similarity to other insect species in GenBank, including Triboliumcastaneum, Drosophilamelanogaster and Acrythosiphonpisum. KEGG analysis predicted the presence of pathways for purine and thiamine metabolic, biosynthesis of secondary metabolites, drug metabolism, and lysine degradation. Pfam analysis showed a high number of cellulase and carboxylesterase protein domains. Expression analysis of candidate genes (alpha amylase, lipase, pectin lyase, etc.) among different tissues revealed tissue-specific expression of digestive enzymes in E. fabae. This is the first study to characterize the sialotranscriptome of E. fabae and the first for any species in the family of Cicadellidae. Due to the status of these insects as economic pests, knowledge of which genes are active in the salivary glands is important for understanding their impact on host plants.

Characterization of two closely related α-amylase paralogs in the bark beetle, Ips typographus (L.)

Ips typographus (L.), the eight-spined spruce bark beetle, causes severe damage throughout Eurasian spruce forests and suitable nuclear markers are needed in order to study its population structure on a genetic level. Two closely related genes encoding α-amylase in I. typographus were characterized and named AmyA and AmyB. Both α-amylase paralogs consisted of six exons and five introns. AmyA encodes a polypeptide of 483 amino acids, whereas AmyB has two alternative transcripts encoding polypeptides of 483 and 370 amino acids. The expression levels of both genes were high during larval stage and adulthood. The AmyB transcripts were absent in the pupal stage. A modification of the allozyme staining method allowed us to detect two clusters of bands on the electrophoretic gel that may correspond to the two α-amylase genes. There was a correlation between the lack of AmyB expression in pupa and the absence of the fast migrating isozyme cluster at this stage, suggesting that the faster migrating isoforms are products of the AmyB gene, whereas the slowly migrating bands are derived from the AmyA.

Comparative genomic analysis of Drosophila melanogaster and vector mosquito developmental genes

Genome sequencing projects have presented the opportunity for analysis of developmental genes in three vector mosquito species: Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae. A comparative genomic analysis of developmental genes in Drosophila melanogaster and these three important vectors of human disease was performed in this investigation. While the study was comprehensive, special emphasis centered on genes that 1) are components of developmental signaling pathways, 2) regulate fundamental developmental processes, 3) are critical for the development of tissues of vector importance, 4) function in developmental processes known to have diverged within insects, and 5) encode microRNAs (miRNAs) that regulate developmental transcripts in Drosophila. While most fruit fly developmental genes are conserved in the three vector mosquito species, several genes known to be critical for Drosophila development were not identified in one or more mosquito genomes. In other cases, mosquito lineage-specific gene gains with respect to D. melanogaster were noted. Sequence analyses also revealed that numerous repetitive sequences are a common structural feature of Drosophila and mosquito developmental genes. Finally, analysis of predicted miRNA binding sites in fruit fly and mosquito developmental genes suggests that the repertoire of developmental genes targeted by miRNAs is species-specific. The results of this study provide insight into the evolution of developmental genes and processes in dipterans and other arthropods, serve as a resource for those pursuing analysis of mosquito development, and will promote the design and refinement of functional analysis experiments.

Spatial mapping of gene expression in the salivary glands of the dengue vector mosquito, Aedes aegypti

BACKGROUND

Aedes aegypti mosquitoes are the main vectors of dengue viruses to humans. Understanding their biology and interactions with the pathogen are prerequisites for development of dengue transmission control strategies. Mosquito salivary glands are organs involved directly in pathogen transmission to vertebrate hosts. Information on the spatial distribution of gene expression in these organs is expected to assist in the development of novel disease control strategies, including those that entail the release of transgenic mosquitoes with impaired vector competence.

RESULTS

We report here the hybridization in situ patterns of 30 transcripts expressed in the salivary glands of adult Ae. aegypti females. Distinct spatial accumulation patterns were identified. The products of twelve genes are localized exclusively in the proximal-lateral lobes. Among these, three accumulate preferentially in the most anterior portion of the proximal-lateral lobe. This pattern revealed a salivary gland cell type previously undescribed in Ae. aegypti, which was validated by transmission electron microscopy. Five distinct gene products accumulate in the distal-lateral lobes and another five localize in the medial lobe. Seven transcripts are found in the distal-lateral and medial lobes. The transcriptional product of one gene accumulates in proximal- and distal-lateral lobes. Seven genes analyzed by quantitative PCR are expressed constitutively. The most abundant salivary gland transcripts are those localized within the proximal-lateral lobes, while previous work has shown that the distal-lateral lobes are the most active in protein synthesis. This incongruity suggests a role for translational regulation in mosquito saliva production.

CONCLUSIONS

Transgenic mosquitoes with reduced vector competence have been proposed as tools for the control of dengue virus transmission. Expression of anti-dengue effector molecules in the distal-lateral lobes of Ae. aegypti salivary glands has been shown to reduce prevalence and mean intensities of viral infection. We anticipate greater efficiency of viral suppression if effector genes are expressed in all lobes of the salivary glands. Based on our data, a minimum of two promoters is necessary to drive the expression of one or more anti-dengue genes in all cells of the female salivary glands.

Cloning and expression analysis of the Bombyx mori α-amylase gene (Amy) from the indigenous Thai silkworm strain, Nanglai

α-Amylase is a common enzyme for hydrolyzing starch. In the silkworm, Bombyx mori L. (Lepidoptera: Bombycidae), α-amylase is found in both digestive fluid and hemolymph. Here, the complete genomic sequence of the Amy gene encoding α-amylase from a local Thai silkworm, the Nanglai strain, was obtained. This gene was 7981 bp long with 9 exons. The full length Amy cDNA sequence was 1749 bp containing a 1503 bp open reading frame. The ORF encoded 500 amino acid residues. The deduced protein showed 81-54% identity to other insect α-amylases and more than 50% identity to mammalian enzymes. Southern blot analysis revealed that in the Nanglai strain Amy is a single-copy gene. RT- PCR showed that Amy was transcribed only in the foregut. Transgenic B. mori also showed that the Amy promoter activates expression of the transgene only in the foregut.

Insight into the sialome of the Black Fly, Simulium vittatum

Adaptation to vertebrate blood feeding includes development of a salivary "magic potion" that can disarm host hemostasis and inflammatory reactions. Within the lower Diptera, a vertebrate blood-sucking mode evolved in the Psychodidae (sand flies), Culicidae (mosquitoes), Ceratopogonidae (biting midges), Simuliidae (black flies), and the frog-feeding Corethrellidae. Sialotranscriptome analyses from several species of mosquitoes and sand flies and from one biting midge indicate divergence in the evolution of the blood-sucking salivary potion, manifested in the finding of many unique proteins within each insect family, and even genus. Gene duplication and divergence events are highly prevalent, possibly driven by vertebrate host immune pressure. Within this framework, we describe the sialome (from Greek sialo, saliva) of the black fly Simulium vittatum and discuss the findings within the context of the protein families found in other blood-sucking Diptera. Sequences and results of Blast searches against several protein family databases are given in Supplemental Tables S1 and S2, which can be obtained from http://exon.niaid.nih.gov/transcriptome/S_vittatum/T1/SV-tb1.zip and http://exon.niaid.nih.gov/transcriptome/S_vittatum/T2/SV-tb2.zip .

The Anopheles gambiae salivary protein gSG6: an anopheline-specific protein with a blood-feeding role

The Anopheles gambiae salivary gland protein 6 (gSG6) is a small protein specifically found in the salivary glands of adult female mosquitoes. We report here the expression of a recombinant form of the protein and we show that in vivo gSG6 is expressed in distal-lateral lobes and is secreted with the saliva while the female mosquito probes for feeding. Injection of gSG6 dsRNA into adult A. gambiae females results in decreased gSG6 protein levels, increased probing time and reduced blood feeding ability. gSG6 orthologs have been found so far only in the salivary glands of Anopheles stephensi and Anopheles funestus, both members of the Cellia subgenus. We report here the gSG6 sequence from five additional anophelines, four species of the A. gambiae complex and Anopheles freeborni, a member of the subgenus Anopheles. We conclude that gSG6 plays some essential blood feeding role and was recruited in the anopheline subfamily most probably after the separation of the lineage which gave origin to Cellia and Anopheles subgenera.

The salivary gland transcriptome of the neotropical malaria vector Anopheles darlingi reveals accelerated evolution of genes relevant to hematophagy

BACKGROUND

Mosquito saliva, consisting of a mixture of dozens of proteins affecting vertebrate hemostasis and having sugar digestive and antimicrobial properties, helps both blood and sugar meal feeding. Culicine and anopheline mosquitoes diverged ~150 MYA, and within the anophelines, the New World species diverged from those of the Old World ~95 MYA. While the sialotranscriptome (from the Greek sialo, saliva) of several species of the Cellia subgenus of Anopheles has been described thoroughly, no detailed analysis of any New World anopheline has been done to date. Here we present and analyze data from a comprehensive salivary gland (SG) transcriptome of the neotropical malaria vector Anopheles darlingi (subgenus Nyssorhynchus).

RESULTS

A total of 2,371 clones randomly selected from an adult female An. darlingi SG cDNA library were sequenced and used to assemble a database that yielded 966 clusters of related sequences, 739 of which were singletons. Primer extension experiments were performed in selected clones to further extend sequence coverage, allowing for the identification of 183 protein sequences, 114 of which code for putative secreted proteins.

CONCLUSION

Comparative analysis of sialotranscriptomes of An. darlingi and An. gambiae reveals significant divergence of salivary proteins. On average, salivary proteins are only 53% identical, while housekeeping proteins are 86% identical between the two species. Furthermore, An. darlingi proteins were found that match culicine but not anopheline proteins, indicating loss or rapid evolution of these proteins in the old world Cellia subgenus. On the other hand, several well represented salivary protein families in old world anophelines are not expressed in An. darlingi.

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 mosquito-specific protein family includes candidate receptors for malaria sporozoite invasion of salivary glands

We describe a previously unrecognized protein family from Aedes and Anopheles mosquitoes, here named SGS proteins. There are no SGS homologues in Drosophila or other eukaryotes, but SGS presence in two mosquito genera suggests that the protein family is widespread among mosquitoes. Ae. aegypti aaSGS1 mRNA and protein are salivary gland specific, and protein is localized in the basal lamina covering the anatomical regions that are preferentially invaded by malaria sporozoites. Anti-aaSGS1 antibodies inhibited sporozoite invasion into the salivary glands in vivo, confirming aaSGS1 as a candidate sporozoite receptor. By homology to aaSGS1 we identified the complete complement of four SGS genes in An. gambiae, which were not recognized in the genome annotation. Two An. gambiae SGS genes display salivary gland specific expression like aaSGS1. Bioinformatic analysis predicts that SGS proteins possess heparin-binding domains, and have among the highest density of tyrosine sulphation sites of all An. gambiae proteins. The major sporozoite surface proteins (CS and TRAP) also bind heparin, and interact with sulphoconjugates during liver cell invasion. Thus, we speculate that sporozoite invasion of mosquito salivary glands and subsequently the vertebrate liver may share similar mechanisms based on sulphation. Phylogenomic analysis suggests that an SGS ancestor was involved in a lateral gene transfer.

A proteomic analysis of salivary glands of female Anopheles gambiae mosquito

Understanding the development of the malaria parasite within the mosquito vector at the molecular level should provide novel targets for interrupting parasitic life cycle and subsequent transmission. Availability of the complete genomic sequence of the major African malaria vector, Anopheles gambiae, allows discovery of such targets through experimental as well as computational methods. In the female mosquito, the salivary gland tissue plays an important role in the maturation of the infective form of the malaria parasite. Therefore, we carried out a proteomic analysis of salivary glands from female An. gambiae mosquitoes. Salivary gland extracts were digested with trypsin using two complementary approaches and analyzed by LC-MS/MS. This led to identification of 69 unique proteins, 57 of which were novel. We carried out a functional annotation of all proteins identified in this study through a detailed bioinformatics analysis. Even though a number of cDNA and Edman degradation-based approaches to catalog transcripts and proteins from salivary glands of mosquitoes have been published previously, this is the first report describing the application of MS for characterization of the salivary gland proteome. Our approach should prove valuable for characterizing proteomes of parasites and vectors with sequenced genomes as well as those whose genomes are yet to be fully sequenced.

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.

Isolation and characterization of a C-type lectin cDNA specifically expressed in the tip of mouthparts of the flesh fly Sarcophaga peregrina

We have isolated a novel gene, CLEM 36, of the flesh fly Sarcophaga peregrina, which shows significant homology to the C-type lectin family. CLEM 36 mRNA was transcribed excessively from the second day after eclosion only in the tip of mouthparts. Whole mount in situ hybridization showed that CLEM 36 mRNA was expressed in the C-type lectin-producing tissue (CLPT) located at the entrance of the food canal and between the labellum and haustellum. Immunoblot analysis showed that the mature form of CLEM 36 protein was synthesized in the CLPT, then secreted into saliva. Our results indicate that CLEM 36 protein may play an important role in biological defence against pathogens during the food intake of this insect.

Identification and characterization of gp65, a salivary-gland-specific molecule expressed in the malaria vector Anopheles albimanus

A group of salivary-gland-specific proteins, designated gp65, were identified in the mosquito Anopheles albimanus. Two-dimensional gel electrophoresis resolved this group into at least four molecules with pI 6.4-6.5. The N-terminal amino acid sequence was determined for the major species, gp65-1, and degenerate oligonucleotide primers were used to amplify a specific probe for library screening. A 1312 bp cDNA clone encoding a predicted translation product of 386 amino acids was recovered. gp65-1 is expressed abundantly in the medial and distal-lateral lobes of the adult female glands, and is secreted in the saliva. The amino acid sequence has potential sites for N-glycosylation, phosphorylation and myristylation, and is similar to a number of proteins of unknown function from other mosquito species.

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/

Expression of functional Anopheles merus alpha-amylase in the baculovirus/Spodoptera frugiperda system

The Anopheles merus (Diptera, Nematocera, Culicoidea) alpha-amylase gene (AmerAmy, GenBank Accession Number U01210) was amplified with its own or with the Zabrotes subfasciatusalpha-amylase signal peptide (ZsAmerAmy, GenBank Accession Number AY270183) by PCR, using designed primers. The AmerAmy gene was sequenced from its promotor to the TGA codon. As a positive control, the Z. subfasciatusalpha-amylase gene with its own signal peptide (ZsAmy, GenBank Accession Number AF255722) was also amplified by PCR. These three sequences were inserted into the baculovirus genome using the Bac-to-Bac trade mark system. Recombinant baculovirus preparations were used to infect Sf9 Spodoptera frugiperda insect cells. The A. merusalpha-amylase was successfully expressed as an active enzyme detected mainly in cell culture supernatants.

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.

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.

Integration of the Aedes aegypti mosquito genetic linkage and physical maps

Two approaches were used to correlate the Aedes aegypti genetic linkage map to the physical map. STS markers were developed for previously mapped RFLP-based genetic markers so that large genomic clones from cosmid libraries could be found and placed to the metaphase chromosome physical maps using standard FISH methods. Eight cosmids were identified that contained eight RFLP marker sequences, and these cosmids were located on the metaphase chromosomes. Twenty-one cDNAs were mapped directly to metaphase chromosomes using a FISH amplification procedure. The chromosome numbering schemes of the genetic linkage and physical maps corresponded directly and the orientations of the genetic linkage maps for chromosomes 2 and 3 were inverted relative to the physical maps. While the chromosome 2 linkage map represented essentially 100% of chromosome 2, approximately 65% of the chromosome 1 linkage map mapped to only 36% of the short p-arm and 83% of the chromosome 3 physical map contained the complete genetic linkage map. Since the genetic linkage map is a RFLP cDNA-based map, these data also provide a minimal estimate for the size of the euchromatic regions. The implications of these findings on positional cloning in A. aegypti are discussed.

Phlebotomus papatasi and Leishmania major parasites express alpha-amylase and alpha-glucosidase

Alpha-amylase and alpha-glucosidase activities were found in homogenates of young, unfed male and female Phlebotomus papatasi and in gut and salivary gland preparations. A significant increase in both enzyme activities in females and of alpha-amylase in males was recorded for flies that had fed overnight on a plant (Capparis spinosa). After plant feeding, alpha-amylase activity was relatively lower in female salivary glands and higher in guts, while in the males the activity in the salivary glands had increased. Alpha-glucosidase activity increased in guts of both sexes and in the salivary glands of the females. In addition, alpha-amylase activity was found in preparations of Leishmania major and L. infantum promastigotes, but not in those of L. donovani or L. tropica. Alpha-glucosidase activity was present in promastigote preparations of L. major, L. infantum, L. donovani, L. braziliensis, Crithidia fasciculata and Herpetomonas muscarum. It was lacking in similar preparations of L. tropica, Sauroleishmania agamae or Leptomonas seymouri. The growth rate of L. major promastigotes in medium supplemented with starch or with glucose was similar and it was significantly higher than in glucose poor medium. In this study, we demonstrate that P. papatasi and L. major possess the enzymes for hydrolyzing starch grains that are included in the plant tissue-diet of the sand flies.

Salivary amylase activity of the phlebotomine sand fly, Lutzomyia longipalpis

Both male and female adult stages of the sand fly Lutzomyia longipalpis have detectable amylase activity in their salivary glands, as indicated by formation of p-nitrophenyl-alpha-D-maltoside from p-nitrophenyl-alpha-D-octoside and by hydrolysis of 4-nitrophenyl-alpha-D-maltoheptaoside-4,6,-O-ethylidene. No salivary alpha-glucosidase was detected. Amylase activity was also found in the crop and midgut of female flies, although in a smaller amount. Salivary amylase is significantly reduced from the salivary glands immediately after a blood meal, as is the case with salivary alpha-glucosidases in mosquitoes. Presence of salivary gland amylase in these sand flies, and absence of salivary alpha-glucosidase, indicates that in nature these insects may have a significant intake of carbohydrates in the form of starch, as suggested by their plant-feeding behavior, previously demonstrated by Schlein and Warburg (Schlein, Y., Warburg, A., 1986. Phytophagy and the feeding cycle of Phlebotomus papatasi (Diptera: Psychodidae) under experimental conditions. Journal of Medical Entomology 23, 11-15), and Alexander and Usma (Alexander, B., Usma, M.C., 1994. Potential sources of sugar for the phlebotomine sandfly Lutzomyia youngi (Diptera: Psychodidae) in a Columbia coffee plantation. Ann. Trop. Med. Parasitol. 88, 543-549).

Toward an understanding of the biochemical and pharmacological complexity of the saliva of a hematophagous sand fly Lutzomyia longipalpis

The saliva of blood-sucking arthropods contains powerful pharmacologically active substances and may be a vaccine target against some vector-borne diseases. Subtractive cloning combined with biochemical approaches was used to discover activities in the salivary glands of the hematophagous fly Lutzomyia longipalpis. Sequences of nine full-length cDNA clones were obtained, five of which are possibly associated with blood-meal acquisition, each having cDNA similarity to: (i) the bed bug Cimex lectularius apyrase, (ii) a 5'-nucleotidase/phosphodiesterase, (iii) a hyaluronidase, (iv) a protein containing a carbohydrate-recognition domain (CRD), and (v) a RGD-containing peptide with no significant matches to known proteins in the BLAST databases. Following these findings, we observed that the salivary apyrase activity of L. longipalpis is indeed similar to that of Cimex apyrase in its metal requirements. The predicted isoelectric point of the putative apyrase matches the value found for Lutzomyia salivary apyrase. A 5'-nucleotidase, as well as hyaluronidase activity, was found in the salivary glands, and the CRD-containing cDNA matches the N-terminal sequence of the HPLC-purified salivary anticlotting protein. A cDNA similar to alpha-amylase was discovered and salivary enzymatic activity demonstrated for the first time in a blood-sucking arthropod. Full-length clones were also found coding for three proteins of unknown function matching, respectively, the N-terminal sequence of an abundant salivary protein, having similarity to the CAP superfamily of proteins and the Drosophila yellow protein. Finally, two partial sequences are reported that match possible housekeeping genes. Subtractive cloning will considerably enhance efforts to unravel the salivary pharmacopeia of blood-sucking arthropods.

Characterization of the Sialokinin I gene encoding the salivary vasodilator of the yellow fever mosquito, Aedes aegypti

The gene encoding sialokinin I, the principal vasodilatory peptide of Aedes aegypti, has been isolated and characterized. Degenerate oligonucleotide primers based on peptide amino acid sequence were used to amplify a gene fragment from messenger RNA (mRNA) isolated from female salivary glands. The amplification product was used to probe a salivary gland complementary DNA (cDNA) library, and a number of corresponding cDNAs were isolated and their primary sequence determined. Analysis of the conceptual translation product of a 406-bp cDNA indicates that sialokinin I is expressed as a preprosialokinin and is subsequently post-translationally processed to the active peptide. Northern analysis revealed a 490-bp transcription product expressed exclusively in female salivary glands, and hybridization in situ of probes to RNA in whole tissues localized gene expression to the medial lobe of female salivary glands. Screening of an Ae. aegypti genomic library with the cDNA resulted in the isolation of a clone containing the gene, designated Sialokinin I (Sia I). Comparison of the cDNA with the genomic clone reveals two introns of 62 bp and 833 bp. Primer extension analysis showed that several transcription initiation sites are present. Southern analysis of genomic DNA shows that Sia I is most probably a single-copy gene. Similarities of the Sia I gene product with other genes are confined to the region encoding the active decapeptide.

Identification of surface molecules on salivary glands of the mosquito, Aedes aegypti, by a panel of monoclonal antibodies

Malaria transmission by the mosquito vector requires sporozoite invasion into mosquito salivary glands. Parasites probably enter the glands by specific receptor-ligand interactions with molecules on the surface of the glands. We have undertaken the characterization of salivary gland surface molecules of Aedes aegypti to identify candidate receptors for Plasmodium gallinaceum sporozoite invasion. Monoclonal antibodies (mAbs) were generated against antigen enriched for salivary gland membranes and basal lamina. A panel of 44 mAbs were generated that bound to surface molecules of mosquito tissues. Twenty-four mAbs bound exclusively to salivary glands, six bound to salivary glands and ovaries, one bound to salivary gland and midgut, and 13 bound to all tissues tested. We present data on the immunolocalization and biochemical characteristics of the antigens. Many of the salivary gland-specific mAbs bound preferentially to the median and distal lateral lobes of the salivary glands, indicating that there are anatomical region-specific biochemical differences on the gland surface. These lobes of the salivary glands are the preferential sites of malaria sporozoite invasion. Therefore, antigens specific for these regions are promising candidate receptors for sporozoite invasion. The present identification of surface molecules of mosquito salivary glands by means of monoclonal antibodies represents the first description of individual molecules on the mosquito salivary gland surface. This work lays the basis for further studies on the molecular mechanisms involved in malaria sporozoite invasion of mosquito salivary glands.

Trapping cDNAs encoding secreted proteins from the salivary glands of the malaria vector Anopheles gambiae

The signal sequence trap method was used to isolate cDNAs corresponding to proteins containing secretory leader peptides and whose genes are expressed specifically in the salivary glands of the malaria vector Anopheles gambiae. Fifteen unique cDNA fragments, ranging in size from 150 to 550 bp, were isolated and sequenced in a first round of immunoscreening in COS-7 cells. All but one of the cDNAs contained putative signal sequences at their 5' ends, suggesting that they were likely to encode secreted or transmembrane proteins. Expression analysis by reverse transcription-PCR showed that at least six cDNA fragments were expressed specifically in the salivary glands. Fragments showing a high degree of similarity to D7 and apyrase, two salivary gland-specific genes previously found in Aedes aegypti, were identified. Of interest, three different D7-related cDNAs that are likely to represent a new gene family were found in An. gambiae. Moreover, three salivary gland-specific cDNA fragments that do not show similarity to known proteins in the databases were identified, and the corresponding full length cDNAs were cloned and sequenced. RNA in situ hybridization to whole female salivary glands showed patterns of expression that overlap only in part those observed in the culicine mosquito A. aegypti.

Promoter-directed expression of recombinant fire-fly luciferase in the salivary glands of Hermes-transformed Aedes aegypti

Molecular genetic analyses of biological properties characteristic of insect vectors of disease, such as hematophagy and competence for pathogens, require the ability to isolate and characterize genes involved in these processes. We have been working to develop molecular approaches for studying the promoter function of genes that are expressed specifically in the adult salivary glands of the yellow fever mosquito, Aedes aegypti. Genomic DNA fragments containing cis-acting promoter elements from the Maltase-like I (MalI) and Apyrase (Apy) genes were cloned so as to direct the expression of the reporter gene, luciferase (luc). The function of the promoters was assayed transiently in cultured insect cells and by germ-line transformation of Ae. aegypti. MalI and Apy DNA fragments consisting of at least 650 nucleotides (nt) of DNA immediately adjacent to the 5'-end of the initiation codon of the mosquito genes directed constitutive expression of the luc reporter gene in cultured cells. When introduced into Ae. aegypti chromosomes, approximately 1.5 kilobases (kb) of each promoter were able to direct the predicted developmental-, sex- and tissue-specific expression of the reporter gene in patterns identical to those determined for the respective endogenous genes.

Isolation and characterization of the gene encoding a novel factor Xa-directed anticoagulant from the yellow fever mosquito, Aedes aegypti

Mosquito salivary glands secrete a number of proteins that inhibit mammalian hemostasis and facilitate blood feeding. We have isolated the protein product and corresponding cDNA of a gene designated Anticoagulant-factor Xa (AFXa), that encodes the factor Xa (FXa)-directed anticoagulant of the yellow fever mosquito, Aedes aegypti. The protein was purified partially by cation exchange chromatography and shown by enzyme activity profiles and SDS-polyacrylamide gel electrophoresis analysis to have an Mr = 54, 000. The protein was purified further by preparative SDS-polyacrylamide gel electrophoresis and subjected to internal protein sequencing, and the sequence of five peptides was determined. Degenerate oligonucleotides were designed based on three of the peptide sequences, and these were used to screen an adult female salivary gland cDNA library from A. aegypti. A 1.8-kilobase pair cDNA was isolated and shown to encode a 415-amino acid conceptual translation product with a predicted molecular mass of 47.8 kDa that contains the five sequenced peptides. Hydrophobicity analysis predicts a 19-amino acid signal peptide typical for secreted proteins. Northern analysis demonstrated that AFXa is expressed only in female salivary glands. Baculovirus-expressed AFXa protein has the appropriate size and expected FXa-directed anticoagulant activity. Analysis of the primary amino acid sequence shows that the AFXa gene product has similarities to the serpin superfamily of serine protease inhibitors and may represent a novel, highly diverged member of this family.

Evidence for two distinct members of the amylase gene family in the yellow fever mosquito, Aedes aegypti

Genomic DNA fragments encoding a salivary gland-specific alpha-amylase gene, Amylase I (Amy I), and an additional amylase, Amylase II (AmyII) of the yellow fever mosquito, Aedes aegypti, were isolated and characterized. Two independently isolated DNA fragments, G34-F and G34-14A, encode polymorphic alleles of Amy I. A 3.2 kilobase (kb) EcoR I fragment of G34-F, F2, has been sequenced in its entirety and contains 832 base pairs (bp) of the 5'-end, non-coding and putative promoter regions that are adjacent to 2.4 kb of the Amy I coding region. One intron, 59 bp in length, is found towards the 3'-end of the clone. A third genomic clone, 3A, corresponding to Amy II, was sequenced and shown not to contain the primary DNA sequence that encodes the 260 amino acid region that uniquely characterizes the amino terminal end of the Amy I product. Amy I was assigned by restriction fragment length polymorphism (RFLP) mapping to chromosome 2 (23.0 cM) and Amy II to chromosome 1 (44.0 cM). Amy I and Amy II are highly polymorphic and there may be multiple linked copies at each locus. Comparisons between Amy I and Amy II are presented for the putative promoter and conceptual translation products. The identification of two distinct amylase genes and their separate linkage assignments provides evidence for a multigene family of alpha-amylases in Ae. aegypti.

Cloning and sequencing analysis of three amylase cDNAs in the shrimp Penaeus vannamei (Crustacea decapoda): evolutionary aspects

In Penaeus vannamei, alpha-amylase is the most important glucosidase and is present as at least two major isoenzymes which have been purified. In order to obtain information on their structure, a hepatopancreas cDNA library constructed in phage lambda-Zap II (Strategene) was screened using a synthetic oligonucleotide based on the amino acid sequence of a V8 staphylococcal protease peptide of P. vannamei alpha-amylase. Three clones were selected: AMY SK 37 (EMBL sequence accession number: X 77318) is the most complete of the analyzed clones and was completely sequenced. It contains the complete cDNA sequence coding for one of the major isoenzymes of shrimp amylase. The deduced amino acid sequence shows the existence of a 511-residue-long pre-enzyme containing a highly hydrophobic signal peptide of 16 amino acids. Northern hybridization of total RNA with the amylase cDNA confirms the size of the messenger at around 1,600 bases. AMY SK 28, which contains the complete mature sequence of amylase, belonged to the same family characterized by a common 3' terminus and presented four amino acid changes. Some other variants of this family were also partially sequenced. AMY SK 20 was found to encode a minor variant of the protein with a different 3' terminus and 57 amino acid changes. Phylogenetic analysis established with the conserved amino acid regions of the (beta/alpha) eight-barrel domain and with the total sequence of P. vannamei showed close evolutionary relationships with mammals (59-63% identity) and with insect alpha-amylase (52-62% identity). The use of conserved sequences increased the level of similarity but it did not alter the ordering of the groupings. Location of the secondary structure elements confirmed the high level of sequence similarity of shrimp alpha-amylase with pig alpha-amylase.

The salivary gland-specific apyrase of the mosquito Aedes aegypti is a member of the 5'-nucleotidase family

The saliva of hematophagous insects contains a variety of pharmacologically active substances that counteract the normal hemostatic response to injury in vertebrate hosts. The yellow-fever mosquito, Aedes aegypti, secretes an apyrase that inhibits ADP-dependent platelet aggregation. Apyrase was purified as an active enzyme from adult female salivary glands and subjected to tryptic digestion, and the resulting peptides were sequenced. The amino acid sequences obtained match the conceptual translation product of a cDNA clone isolated from an adult female salivary gland library. Sequence comparisons indicate similarities with a ubiquitous family of 5'-nucleotidases. The mosquito protein differs from other members of the family by lacking a carboxyl-terminal hydrophobic domain. The apparent conversion of a gene encoding an enzyme involved in a common metabolic event at the cellular level to a gene involved in the antihemostatic response of mosquitoes illustrates one way this particular insect has adapted to the challenges of bloodfeeding.