Expression profiling and comparative analyses of seven midgut serine proteases from the yellow fever mosquito, Aedes aegypti

Cytoskeleton-associated gelsolin responds to the midgut distention process in saline meal-fed Aedes aegypti and affects arbovirus dissemination from the midgut

The mosquito, Aedes aegypti, is the principal vector for several arboviruses. The mosquito midgut is the initial tissue that gets infected with an arbovirus acquired along with a blood meal from a vertebrate host. Blood meal ingestion leads to midgut tissue distention thereby increasing the pore size of the surrounding basal lamina. This allows newly synthesized virions to exit the midgut by traversing the distended basal lamina to infect secondary tissues of the mosquito. We conducted a quantitative label-free proteomic time course analysis with saline meal-fed Ae. aegypti females to identify host factors involved in midgut tissue distention. Around 2000 proteins were detected during each of the seven sampling time points and 164 of those were uniquely expressed. Forty-five of 97 differentially expressed proteins were upregulated during the 96-h time course and most of those were involved in cytoskeleton modulation, metabolic activity, and vesicle/vacuole formation. The F-actin-modulating Ae. aegypti (Aa)-gelsolin was selected for further functional studies. Stable knockout of Aa-gelsolin resulted in a mosquito line, which showed distorted actin filaments in midgut-associated tissues likely due to diminished F-actin processing by gelsolin. Zika virus dissemination from the midgut of these mosquitoes was diminished and delayed. The loss of Aa-gelsolin function was associated with an increased induction of apoptosis in midgut tissue indicating an involvement of Aa-gelsolin in apoptotic signaling in mosquitoes. Here, we used proteomics to discover a novel host factor, Aa-gelsolin, which affects the midgut escape barrier for arboviruses in mosquitoes and apoptotic signaling in the midgut.

Hybridization between Aedes aegypti and Aedes mascarensis mosquitoes leads to disruption of male sex determination

Understanding the sex determination pathway and its disruptions in mosquitoes is critical for the effective control of disease vectors through genetic manipulations based on sex separation. When male hybrids of Aedes aegypti females and Ae. mascarensis males are backcrossed to Ae. aegypti females, a portion of the backcross progeny manifests as males with abnormal sexual differentiation. We discovered a significant correlation between pupal abnormalities and the feminization of subsequent adults exemplified by the relative abundance of ovarian and testicular tissues. All intersex individuals were genetic males as they expressed a male determining factor, Nix. Further, our analysis of the sex-specific splicing of doublesex and fruitless transcripts demonstrated the presence of both male and female splice variants indicating that sex determination is disrupted. A comparative transcriptomic analysis revealed similar expression levels of most female-associated genes in reproductive organs and carcasses between intersexual males and normal females. Moreover, intersexes had largely normal gene expression in testes but significant gene downregulation in male accessory glands when compared with normal males. We conclude that evolving hybrid incompatibilities between Ae. aegypti and Ae. mascarensis involve disruption of sex determination and are accompanied by changes in gene expression associated with sexual differentiation.

Effect of nanoformulation Azadirachta indica on some factors associated with the vectorial capacity and competence of Anopheles aquasalis experimentally infected with Plasmodium vivax

Malaria remains a highly prevalent infectious disease worldwide, particularly in tropical and subtropical regions. Effectively controlling of mosquitoes transmitting of Plasmodium spp. is crucial in to control this disease. A promising strategy involves utilizing plant-derived products, such as the Neem tree (Azadirachta indica), known for its secondary metabolites with biological activity against various insect groups of agricultural and public health importance. This study investigated the effects of a nanoformulation prototype Neem on factors linked to the vector competence of Anopheles aquasalis, a malaria vector in Latin America. Different concentrations of the nanoformulation were supplied through sugar solution and blood feeding, assessing impacts on longevity, fecundity, fertility, and transgenerational survival from larvae to adults. Additionally, the effects of the Neem nanoformulation and NeemAZAL® formulation on the sporogonic cycle of P. vivax were evaluated. Overall, significant impacts were observed at 100 ppm and 1,000 ppm concentrations on adult survival patterns and on survival of the F1 generation. A trend of reduced oviposition and hatching rates was also noted in nanoformulation-consuming groups, with fertility and fecundity declining proportionally to the concentration. Additionally, a significant decrease in the infection rate and intensity of P. vivax was observed in the 1,000 ppm group, with a mean of 3 oocysts per female compared to the control's 27 oocysts per female. In the commercial formulation, the highest tested concentration of 3 ppm yielded 5.36 oocysts per female. Concerning sporozoite numbers, there was a reduction of 52 % and 87 % at the highest concentrations compared to the control group. In conclusion, these findings suggest that the A. indica nanoformulation is a potential as a tool for malaria control through reduction in the vector longevity and reproductive capacity, possibly leading to decreased vector population densities. Moreover, the nanoformulation interfered with the sporogonic development of P. vivax. However, further basic research on Neem formulations, their effects, and mechanisms of action is imperative to gain a more specific perspective for safe field implementation.

The Set of Serine Peptidases of the Tenebrio molitor Beetle: Transcriptomic Analysis on Different Developmental Stages

Serine peptidases (SPs) of the chymotrypsin S1A subfamily are an extensive group of enzymes found in all animal organisms, including insects. Here, we provide analysis of SPs in the yellow mealworm Tenebrio molitor transcriptomes and genomes datasets and profile their expression patterns at various stages of ontogeny. A total of 269 SPs were identified, including 137 with conserved catalytic triad residues, while 125 others lacking conservation were proposed as non-active serine peptidase homologs (SPHs). Seven deduced sequences exhibit a complex domain organization with two or three peptidase units (domains), predicted both as active or non-active. The largest group of 84 SPs and 102 SPHs had no regulatory domains in the propeptide, and the majority of them were expressed only in the feeding life stages, larvae and adults, presumably playing an important role in digestion. The remaining 53 SPs and 23 SPHs had different regulatory domains, showed constitutive or upregulated expression at eggs or/and pupae stages, participating in regulation of various physiological processes. The majority of polypeptidases were mainly expressed at the pupal and adult stages. The data obtained expand our knowledge on SPs/SPHs and provide the basis for further studies of the functions of proteins from the S1A subfamily in T. molitor.

An 11-point time course midgut transcriptome across 72 h after bloodfeeding provides detailed temporal resolution of transcript expression in the arbovirus vector, Aedes aegypti

As the major vector for dengue, Zika, yellow fever, and chikungunya viruses, the mosquito Aedes aegypti is one of the most important insects in public health. These viruses are transmitted by bloodfeeding, which is also necessary for the reproduction of the mosquito. Thus, the midgut plays an essential role in mosquito physiology as the center for bloodmeal digestion and as an organ that serves as the first line of defense against viruses. Despite its importance, transcriptomic dynamics with fine temporal resolution across the entire digestion cycle have not yet been reported. To fill this gap, we conducted a transcriptomic analysis of A. aegypti female midguts across a 72-h bloodmeal digestion cycle for 11 time points, with a particular focus on the first 24 h. PCA analysis confirmed that 72 h is indeed a complete digestion cycle. Cluster and GO enrichment analysis showed the orchestrated modulation of thousands of genes to accomplish the midgut's role as the center for digestion, as well as nutrient transport with a clear progression with sequential emphasis on transcription, translation, energy production, nutrient metabolism, transport, and finally, autophagy by 24-36 h. We further determined that many serine proteases are robustly expressed as if to prepare for unexpected physiological challenges. This study provides a powerful resource for the analysis of genomic features that coordinate the rapid and complex transcriptional program induced by mosquito bloodfeeding.

Identification and expression profiling of serine protease-related genes in Tenebrio molitor

In insects, serine proteases and serine protease homologs (SPs/SPHs) are involved in a variety of physiological processes including digestion, development, and immunity. Here, we identified 112 SP and 88 SPH genes in the genome of the yellow mealworm, Tenebrio molitor. Based on the features of domain structure, they were divided into "S" group containing single Tryp-SPc or Tryp-SPHc domain, "C" group containing 1-4 CLIP domain (CLIPA-D) and "M" group containing the CBD, CUB, EGF, Fz, Gd, LDLa, PAN, SEA, SR, Sushi, and TSP domains, and have 115, 48, and 37 gene members, respectively. According to the active sites in the catalytic triad, the putative trypsin, chymotrypsin, or elastase-like enzyme specificity of the identified SPs/SPHs were predicted. Phylogenetic and genomic location analyses revealed that gene duplication exists in the large amount of SPs/SPHs. Gene expression profiling using RNA-seq data along with real time reverse transcription-polymerase chain reaction analysis showed that most SP/SPH genes display life stage specific expression patterns, indicating their important roles in development. Many SP/SPH genes are specifically or highly expressed in the gut, salivary gland, fat body, hemocyte, ovary, and testis, suggesting that they participate in digestion, immunity, and reproduction. The findings lay the foundation for further functional characterization of SPs/SPHs in T. molitor.

A blood digestion scoring method for poultry red mites, Dermanyssus gallinae

The poultry red mite (PRM), Dermanyssus gallinae, is one of the most detrimental ectoparasite on poultry farms worldwide. The blood fed on birds provides the mites with nutrition and energy for their activities, development and reproduction. In the evaluation of the efficacy of novel drugs or vaccines against PRMs, their effects on blood digestion are generally used as a key parameter. The blood digestion of haematophagous arthropods (including D. gallinae) is usually assessed by weighing; however, this method shows some limitations. The main objective of the present study was to develop a scoring method that can quickly and visually evaluate the blood digestion status of PRMs. A 0–4 point scoring criterion was established to describe the blood digestion status of D. gallinae based on the changes in appearance in the intestinal tract of PRMs during the blood digestion process. There was a good consistency between the results obtained by the blood digestion scoring and the weighing, indicating the reliability of this new method. The results obtained from volunteers were consistent with the results from researchers with low coefficient of variation, indicating that the scoring method has good practicability. The applicability of the scoring method was confirmed in an efficacy study, where it was found that doramectin could significantly inhibit the blood digestion of PRMs, lowering the blood digestion score.

Transcriptome analysis of Holotrichia oblita reveals differentially expressed unigenes related to reproduction and development under different photoperiods

Holotrichia oblita (Faldermann) (Coleoptera: Scarabaeidae) is an insect whose feeding and mating behaviors occur at night. A scotophase is necessary for H. oblita reproduction. We used RNA sequencing (RNA-seq) to compare the expression patterns of H. oblita at five photoperiods (0:24, 8:16, 12:12, 16:8, and 24:0 h) (L:D). Compared to the control (24:0) (L:D), 161-684 differentially expressed unigenes (DEUs) were found in female samples, while 698-2322 DEUs were found in male samples. For all DEUs, a total of 92-1143 DEUs were allocated to 116-662 categories of gene ontology (GO), and 81-1116 DEUs were assigned into 77-286 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The iPath diagram showed that the DEUs generated by comparing female and male samples with photoperiods of 0:24 and 24:0, respectively, involved multiple metabolic pathways, such as carbohydrate metabolism, lipid metabolism, nucleotide metabolism, purine metabolism and glutathione metabolism. Most of these DEUs were upregulated. Finally, 13 DEUs related to reproduction and development were selected to confirm the consistency of relative expression between RNA-Seq and quantitative real-time polymerase chain reaction (qRT-PCR). Most of these comparison results agreed well, except for some qRT-PCR results that were not detected in male samples due to their low expression. These results provide useful information for understanding the dark-induced reproduction of H. oblita.

A transcriptomic atlas of Aedes aegypti reveals detailed functional organization of major body parts and gut regional specializations in sugar-fed and blood-fed adult females

Mosquitoes transmit numerous pathogens, but large gaps remain in our understanding of their physiology. To facilitate explorations of mosquito biology, we have created Aegypti-Atlas (http://aegyptiatlas.buchonlab.com/), an online resource hosting RNAseq profiles of Ae. aegypti body parts (head, thorax, abdomen, gut, Malpighian tubules, ovaries), gut regions (crop, proventriculus, anterior and posterior midgut, hindgut), and a gut time course of blood meal digestion. Using Aegypti-Atlas, we provide insights into regionalization of gut function, blood feeding response, and immune defenses. We find that the anterior and posterior midgut possess digestive specializations which are preserved in the blood-fed state. Blood feeding initiates the sequential induction and repression/depletion of multiple cohorts of peptidases. With respect to defense, immune signaling components, but not recognition or effector molecules, show enrichment in ovaries. Basal expression of antimicrobial peptides is dominated by holotricin and gambicin, which are expressed in carcass and digestive tissues, respectively, in a mutually exclusive manner. In the midgut, gambicin and other effectors are almost exclusively expressed in the anterior regions, while the posterior midgut exhibits hallmarks of immune tolerance. Finally, in a cross-species comparison between Ae. aegypti and Anopheles gambiae midguts, we observe that regional digestive and immune specializations are conserved, indicating that our dataset may be broadly relevant to multiple mosquito species. We demonstrate that the expression of orthologous genes is highly correlated, with the exception of a ‘species signature’ comprising a few highly/disparately expressed genes. With this work, we show the potential of Aegypti-Atlas to unlock a more complete understanding of mosquito biology.

E93 confers steroid hormone responsiveness of digestive enzymes to promote blood meal digestion in the midgut of the mosquito Aedes aegypti

Anautogenous female mosquitoes obtain the nutrients needed for egg development from vertebrate blood, and consequently they transmit numerous pathogens of devastating human diseases. Digestion of blood proteins into amino acids that are used for energy production, egg maturation and replenishment of maternal reserves is an essential part of the female mosquito reproductive cycle. However, the regulatory mechanisms underlying this process remain largely unknown. Here, we report that the transcription factor E93 is a critical factor promoting blood meal digestion in adult females of the major arboviral vector Aedes aegypti in response to the steroid hormone 20-hydroxyecdysone (20E). E93 was upregulated in the female mosquito midgut after a blood meal, and RNA interference (RNAi)-mediated knockdown of E93 inhibited midgut blood digestion. E93 RNAi depletion repressed late trypsin (LT), serine protease I (SPI), SPVI and SPVII, and activated early trypsin (ET) expression in the female mosquito midgut after a blood meal. Injection of 20E activated E93, LT, SPI, SPVI and SPVII, and repressed ET expression, whereas RNAi knockdown of the ecdysone receptor (EcR) repressed E93, LT, SPI, SPVI and SPVII, and activated ET expression in the midgut. Furthermore, E93 depletion resulted in a complete loss of 20E responsiveness of LT, SPVI and SPVII. Our findings reveal important mechanisms regulating blood meal digestion in disease-transmitting mosquitoes.

Non-immune Traits Triggered by Blood Intake Impact Vectorial Competence

Blood-feeding arthropods are considered an enormous public health threat. They are vectors of a plethora of infectious agents that cause potentially fatal diseases like Malaria, Dengue fever, Leishmaniasis, and Lyme disease. These vectors shine due to their own physiological idiosyncrasies, but one biological aspect brings them all together: the requirement of blood intake for development and reproduction. It is through blood-feeding that they acquire pathogens and during blood digestion that they summon a collection of multisystemic events critical for vector competence. The literature is focused on how classical immune pathways (Toll, IMD, and JAK/Stat) are elicited throughout the course of vector infection. Still, they are not the sole determinants of host permissiveness. The dramatic changes that are the hallmark of the insect physiology after a blood meal intake are the landscape where a successful infection takes place. Dominant processes that occur in response to a blood meal are not canonical immunological traits yet are critical in establishing vector competence. These include hormonal circuitries and reproductive physiology, midgut permeability barriers, midgut homeostasis, energy metabolism, and proteolytic activity. On the other hand, the parasites themselves have a role in the outcome of these blood triggered physiological events, consistently using them in their favor. Here, to enlighten the knowledge on vector-pathogen interaction beyond the immune pathways, we will explore different aspects of the vector physiology, discussing how they give support to these long-dated host-parasite relationships.

Whole blood and blood components from vertebrates differentially affect egg formation in three species of anautogenous mosquitoes

Background

Most female mosquitoes are anautogenous and must blood feed on a vertebrate host to produce eggs. Prior studies show that the number of eggs females lay per clutch correlates with the volume of blood ingested and that protein is the most important macronutrient for egg formation. In contrast, how whole blood, blood fractions and specific blood proteins from different vertebrates affect egg formation is less clear. Since egg formation is best understood in Aedes aegypti, we examined how blood and blood components from different vertebrates affect this species and two others: the malaria vector Anopheles gambiae and arbovirus vector Culex quinquefasciatus.

Methods

Adult female mosquitoes were fed blood, blood fractions and purified major blood proteins from different vertebrate hosts. Markers of reproductive response including ovary ecdysteroidogenesis, yolk deposition into oocytes and number of mature eggs produced were measured.

Results

Ae. aegypti, An. gambiae and C. quinquefasciatus responded differently to meals of whole blood, plasma or blood cells from human, rat, chicken and turkey hosts. We observed more similarities between the anthropophiles Ae. aegypti and An. gambiae than the ornithophile C. quinquefasciatus. Focusing on Ae. aegypti, the major plasma-derived proteins (serum albumin, fibrinogen and globulins) differentially stimulated egg formation as a function of vertebrate host source. The major blood cell protein, hemoglobin, stimulated yolk deposition when from pigs but not humans, cows or sheep. Serum albumins from different vertebrates also variably affected egg formation. Bovine serum albumin (BSA) stimulated ovary ecdysteroidogenesis, but more weakly induced digestive enzyme activities than whole blood. In contrast, BSA-derived peptides and free amino acids had no stimulatory effects on ecdysteroidogenesis or yolk deposition into oocytes.

Conclusions

Whole blood, blood fractions and specific blood proteins supported egg formation in three species of anautogenous mosquitoes but specific responses varied with the vertebrate source of the blood components tested.

Aedes aegypti post-emergence transcriptome: Unveiling the molecular basis for the hematophagic and gonotrophic capacitation

The adult females of Aedes aegypti mosquitoes are facultative hematophagous insects but they are unable to feed on blood right after pupae emergence. The maturation process that takes place during the first post-emergence days, hereafter named hematophagic and gonotrophic capacitation, comprises a set of molecular and physiological changes that prepare the females for the first gonotrophic cycle. Notwithstanding, the molecular bases underlying mosquito hematophagic and gonotrophic capacitation remain obscure. Here, we investigated the molecular and biochemical changes in adult Ae. aegypti along the first four days post-emergence, prior to a blood meal. We performed a RNA-Seq analysis of the head and body, comparing male and female gene expression time courses. A total of 811 and 203 genes were differentially expressed, respectively in the body and head, and both body parts showed early, mid, and late female-specific expression profiles. Female-specific up-regulation of genes involved in muscle development and the oxidative phosphorylation pathway were remarkable features observed in the head. Functional assessment of mitochondrial oxygen consumption in heads showed a gradual increase in respiratory capacity and ATP-linked respiration as a consequence of induced mitochondrial biogenesis and content over time. This pattern strongly suggests that boosting oxidative phosphorylation in heads is a required step towards blood sucking habit. Several salivary gland genes, proteases, and genes involved in DNA replication and repair, ribosome biogenesis, and juvenile hormone signaling were up-regulated specifically in the female body, which may reflect the gonotrophic capacitation. This comprehensive description of molecular and biochemical mechanisms of the hematophagic and gonotrophic capacitation in mosquitoes unravels potentially new targets for vector control.

Proteases and pseudoproteases in parasitic arthropods of clinical importance

Parasitic arthropods feed on blood or skin tissue and share comparable repertoires of proteases involved in haematophagy, digestion, egg development and immunity. While proteolytically active proteases of multiple classes dominate, an increasing number of pseudoproteases have been discovered that have no proteolytic function but are pharmacologically active biomolecules, evolved to carry out alternative functions as regulatory, antihaemostatic, anti-inflammatory or immunomodulatory compounds. In this review, we provide an overview of proteases and pseudoproteases from clinically important arthropod parasites. Many of these act in central biological pathways of parasite survival and host-parasite interaction and may be potential targets for therapeutic interventions.

Transcriptomic analyses of Aedes aegypti cultured cells and ex vivo midguts in response to an excess or deficiency of heme: a quest for transcriptionally-regulated heme transporters

Background

Aedes aegypti is the principle vector of many arboviruses, including dengue virus and Zika virus, which are transmitted when an infected female mosquito takes a blood meal in order to initiate vitellogenesis. During blood digestion, ~ 10 mM heme-iron is ingested into the midgut lumen. While heme acts as both a nutrient and signaling molecule during blood digestion, it can also be highly toxic if left unchaperoned. Both signaling by, and degradation of, heme are intracellular processes, occurring in the nucleus and cytoplasm, respectively. However, the precise mechanism of heme uptake into the midgut epithelium is not currently known.

Results

We used next generation RNA sequencing with the goal to identify genes that code for membrane bound heme import protein(s) responsible for heme uptake into the midgut epithelium. Heme deprivation increased uptake of a heme fluorescent analog in cultured cells, while treatment of midguts with an excess of heme decreased uptake, confirming physiological changes were occurring in these heme-sensitive cells/tissues prior to sequencing. A list of candidate genes was assembled for each of the experimental sample sets, which included Aag2 and A20 cultured cells as well as midgut tissue, based on the results of a differential expression analysis, soft cluster analysis and number of predicted transmembrane domains. Lastly, the functions related to heme transport were examined through RNAi knockdown.

Conclusions

Despite a large number of transmembrane domain containing genes differentially expressed in response to heme, very few were highly differentially expressed in any of the datasets examined. RNAi knockdown of a subset of candidates resulted in subtle changes in heme uptake, but minimal overall disruption to blood digestion/egg production. These results could indicate that heme import in Ae. aegypti may be controlled by a redundant system of multiple distinct transport proteins. Alternatively, heme membrane bound transport in Ae. aegypti could be regulated post-translationally.

The gut anti-complement activity of Aedes aegypti: Investigating new ways to control the major human arboviruses vector in the Americas

Aedes aegypti is the main urban vector of dengue virus, chikungunya virus and Zika virus due to its great dispersal capacity and virus susceptibility. A. aegypti feed on plant-derived sugars but females need a blood meal for egg maturation. Haematophagous arthropods need to overcome host haemostasis and local immune reactions in order to take a blood meal. In this context, molecules present in the saliva and/or intestinal contents of these arthropods must contain inhibitors of the complement system (CS). CS salivary and/or intestinal inhibitors are crucial to protect gut cells of haematophagous arthropods against complement attack. The present work aimed to investigate the anti-complement activity of A. aegypti intestinal contents on the alternative, classical and lectin pathways of the human complement system. Here we show that A. aegypti gut contents inhibited the human classical and the lectin pathways but not the alternative pathway. The A. aegypti gut content has a serine protease able to specifically cleave and inactivate human C4, which is a novel mechanism for human complement inactivation in haematophagous arthropods. The gut of female A. aegypti was capable of capturing human serum factor H (a negative complement modulator), unlike males. C3 molecules in recently blood-fed female A. aegypti remain in their original state, being inactivated to iC3b soon after a blood feed. A transmission-blocking vaccine using these complement inhibitory proteins as antigens has the potential to interfere with the insect's survival, reproductive fitness and block their infection by the arboviruses they transmit to humans.

Serine hydroxymethyltransferase controls blood-meal digestion in the midgut of Aedes aegypti mosquitoes

Background

Female Aedes aegypti mosquitoes are vectors of arboviruses that cause diverse diseases of public health significance. Blood protein digestion by midgut proteases provides anautogenous mosquitoes with the nutrients essential for oocyte maturation and egg production. Midgut-specific miR-1174 affects the functions of the midgut through its target gene serine hydroxymethyltransferase (SHMT). However, less is known about SHMT-regulated processes in blood digestion by mosquitoes.

Methods

RNAi of SHMT was realized by injection of the double-stranded RNA at 16 h post-eclosion. The expression of SHMT at mRNA level and protein level was assayed by real-time PCR and Western blotting, respectively. Statistical analyses were performed with GraphPad7 using Student’s t-test.

Results

Here, we confirmed that digestion of blood was inhibited in SHMT RNAi-silenced female A. aegypti mosquitoes. Evidence is also presented that all SHMT-depleted female mosquitoes lost their flight ability and died within 48 h of a blood meal. Furthermore, most examined digestive enzymes responded differently in their transcriptional expression to RNAi depletion of SHMT, with some downregulated, some upregulated and some remaining stable. Phylogenetic analysis showed that transcriptional expression responses to SHMT silence were largely unrelated to the sequence similarity between these enzymes.

Conclusions

Overall, this research shows that SHMT was expressed at a low level in the midgut of Aedes aegypti mosquitoes, but blood-meal digestion was inhibited when SHMT was silenced. Transcriptional expressions of different digestive enzymes were affected in response to SHMT depletion, suggesting that SHMT is required for the blood-meal digestion in the midgut and targeting SHMT could provide an effective strategy for vector mosquito population control.

Mosquito adaptations to hematophagia impact pathogen transmission

Mosquito-borne diseases such as Dengue fever, Chikungunya, and Malaria are critical threats to public health in many parts of the world. Female mosquitoes have evolved multiple adaptive mechanisms to hematophagy, including the ability to efficiently draw and digest blood, as well as the ability to eliminate excess fluids and toxic by-products of blood digestion. Pathogenic agents enter the mosquito digestive tract with the blood meal and need to travel through the midgut and into the hemocele in order to reach the salivary glands and infect a new host. Pathogens need to adjust to these hostile gut, hemocele, and salivary gland environments, and when possible influence the physiology and behavior of their hosts to enhance transmission.

Characterization of the adult Aedes aegypti early midgut peritrophic matrix proteome using LC-MS

The Aedes aegypti mosquito is the principal vector of arboviruses such as dengue, chikungunya, yellow fever, and Zika virus. These arboviruses are transmitted during adult female mosquito bloodfeeding. While these viruses must transverse the midgut to replicate, the blood meal must also reach the midgut to be digested, absorbed, or excreted, as aggregation of blood meal metabolites can be toxic to the female mosquito midgut. The midgut peritrophic matrix (PM), a semipermeable extracellular layer comprised of chitin fibrils, glycoproteins, and proteoglycans, is one such mechanism of protection for the mosquito midgut. However, this structure has not been characterized for adult female Ae. aegypti. We conducted a mass spectrometry based proteomic analysis to identify proteins that comprise or are associated with the adult female Ae. aegypti early midgut PM. Altogether, 474 unique proteins were identified, with 115 predicted as secreted. GO-term enrichment analysis revealed an abundance of serine-type proteases and several known and novel intestinal mucins. In addition, approximately 10% of the peptides identified corresponded to known salivary proteins, indicating Ae. aegypti mosquitoes extensively swallow their own salivary secretions. However, the physiological relevance of this remains unclear, and further studies are needed to determine PM proteins integral for midgut protection from blood meal derived toxicity and pathogen protection. Finally, we describe substantial discordance between previously described transcriptionally changes observed in the midgut in response to a bloodmeal and the presence of the corresponding protein in the PM. Data are available via ProteomeXchange with identifier PXD007627.

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

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

An Aedes aegypti-associated fungus increases susceptibility to dengue virus by modulating gut trypsin activity

Transmission of dengue virus (DENV) requires successful completion of the infection cycle in the Aedes aegypti vector, which is initiated in the midgut tissue after ingestion of an infectious blood meal. While certain Ae. aegypti midgut-associated bacteria influence virus infection, little is known about the midgut-associated fungi (mycobiota), and how its members might influence susceptibility to DENV infection. We show that a Talaromyces (Tsp_PR) fungus, isolated from field-caught Ae. aegypti, render the mosquito more permissive to DENV infection. This modulation is attributed to a profound down-regulation of digestive enzyme genes and trypsin activity, upon exposure to Tsp_PR-secreted factors. In conclusion, we show for the first time that a natural mosquito gut-associated fungus can alter Ae. aegypti physiology in a way that facilitates pathogen infection.

The genomic and transcriptomic analyses of serine proteases and their homologs in an endoparasitoid, Pteromalus puparum

In insects, serine proteases (SPs) and serine protease homologs (SPHs) constitute a large family of proteins involved in multiple physiological processes such as digestion, development, and immunity. Here we identified 145 SPs and 38 SPHs in the genome of an endoparasitoid, Pteromalus puparum. Gene duplication and tandem repeats were observed in this large SPs/SPHs family. We then analyzed the expression profiles of SP/SPH genes in response to different microbial infections (Gram-positive bacterium Micrococcus luteus, Gram-negative bacterium Escherichia coli, and entomopathogenic fungus Beauveria bassiana), as well as in different developmental stages and tissues. Some SPs/SPHs also displayed distinct expression patterns in venom gland, suggesting their specific physiological functions as venom proteins. Our finding lays groundwork for further research of SPs and SPHs expressed in the venom glands.

Aedes aegypti Molecular Responses to Zika Virus: Modulation of Infection by the Toll and Jak/Stat Immune Pathways and Virus Host Factors

Zika (ZIKV) and dengue virus (DENV) are transmitted to humans by Aedes mosquitoes. However, the molecular interactions between the vector and ZIKV remain largely unexplored. In this work, we further investigated the tropism of ZIKV in two different Aedes aegypti strains and show that the virus infection kinetics, tissue migration, and susceptibility to infection differ between mosquito strains. We also compare the vector transcriptome changes upon ZIKV or DENV infection demonstrating that 40% of the mosquito's midgut infection-responsive transcriptome is virus-specific at 7 days after virus ingestion. Regulated genes included key factors of the mosquito's anti-viral immunity. Comparison of the ZIKV and DENV infection-responsive transcriptome data to those available for yellow fever virus and West Nile virus identified 26 genes likely to play key roles in virus infection of Aedes mosquitoes. Through reverse genetic analyses, we show that the Toll and the Jak/Stat innate immune pathways mediate increased resistance to ZIKV infection, and the conserved DENV host factors vATPase and inosine-5'-monophosphate dehydrogenase are also utilized for ZIKV infection.

Functional analysis of TcCTLP-5C2, a chymotrypsin-like serine protease needed for molting in Tribolium castaneum

In a previous study, we have characterized a gene family encoding chymotrypsin-like proteases from the red flour beetle, Tribolium castaneum (TcCTLPs). We identified 14 TcCTLP genes that were predominantly expressed in the midgut, where they presumably function in digestion. Two genes (TcCTLP-6C and TcCTLP-5C₂), however, additionally showed considerable expression in the carcass, and RNAi studies demonstrated that they are required for molting (Broehan et al., 2010; Insect Biochem. Mol. Biol 40, 274-83). Thus, the enzyme has distinct functions in different physiological environments. To study molecular adaptations that facilitate enzyme function in different environments, we performed an in-depth analysis of the molecular and enzymatic properties of TcCTLP-5C_2. We expressed different mutated versions of TcCTLP-5C₂ in form of factor Xa activatable pro-enzymes in insect cells using a baculoviral expression system, and purified the recombinant proteins by affinity chromatography. By measuring and comparing the enzyme activities, we obtained information about the significance of single amino acid residues in motifs that determine substrate specificity and pH tolerance. Further, we showed that TcCTLP-5C₂ is modified by N-glycosylation at amino acid position N137, which lies opposite to the catalytic cleft. Comparison of the enzymatic properties of non-glycosylated and glycosylated TcCTLP-5C₂ versions showed that N-glycosylation decreases V_max (maximum velocity) and k_cat (turnover) while leaving the K_m (specificity) unchanged. Thus, we provide evidence that N-glycosylation alters catalytic behavior by allosteric effects presumably due to altered structural dynamics as observed for chemically glycosylated enzymes.

The midgut transcriptome of Aedes aegypti fed with saline or protein meals containing chikungunya virus reveals genes potentially involved in viral midgut escape

BACKGROUND

The mosquito Aedes aegypti is the primary vector for medically important arthropod-borne viruses, including chikungunya virus (CHIKV). Following oral acquisition, an arbovirus has to persistently infect several organs in the mosquito before becoming transmissible to another vertebrate host. A major obstacle an arbovirus has to overcome during its infection cycle inside the mosquito is the midgut escape barrier, representing the exit mechanism arboviruses utilize when disseminating from the midgut. To understand the transcriptomic basis of midgut escape and to reveal genes involved in the process, we conducted a comparative transcriptomic analysis of midgut samples from mosquitoes which had received a saline meal (SM) or a protein meal (PM) (not) containing CHIKV.

RESULTS

CHIKV which was orally acquired by a mosquito along with a SM or PM productively infected the midgut epithelium and disseminated to secondary tissues. A total of 27 RNA-Seq libraries from midguts of mosquitoes that had received PM or SM (not) containing CHIKV at 1 and 2 days post-feeding were generated and sequenced. Fewer than 80 genes responded differentially to the presence of CHIKV in midguts of mosquitoes that had acquired the virus along with SM or PM. SM feeding induced differential expression (DE) of 479 genes at day 1 and 314 genes at day 2 when compared to midguts of sugarfed mosquitoes. By comparison, PM feeding induced 6029 DE genes at day 1 and 7368 genes at day 2. Twenty-three DE genes encoding trypsins, metalloproteinases, and serine-type endopeptidases were significantly upregulated in midguts of mosquitoes at day 1 following SM or PM ingestion. Two of these genes were Ae. aegypti late trypsin (AeLT) and serine collagenase 1 precursor (AeSP1). In vitro, recombinant AeLT showed strong matrix metalloproteinase activity whereas recombinant AeSP1 did not.

CONCLUSIONS

By substituting a bloodmeal for SM, we identified midgut-expressed genes not involved in blood or protein digestion. These included genes coding for trypsins, metalloproteinases, and serine-type endopeptidases, which could be involved in facilitating midgut escape for arboviruses in Ae. aegypti. The presence of CHIKV in any of the ingested meals had relatively minor effects on the overall gene expression profiles in midguts.

Functional analysis of five trypsin-like protease genes in the oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae)

Insect midgut proteases catalyze the release of free amino acids from dietary proteins and are essential for insect normal development. To date, digestive proteases as potential candidates have made great progress in pest control. To clarify the function of trypsin-like protease genes in the digestive system of Bactrocera dorsalis, a serious pest of a wide range of tropical and subtropical fruit and vegetable crops, five trypsin genes (BdTry1, BdTry2, BdTry3, BdTry4 and BdTry5) were identified from transcriptome dataset, and the effects of feeding condition on their expression levels were examined subsequently. RNA interference (RNAi) was applied to further explore their function on the growth of B. dorsalis. The results showed that all the BdTrys in starving midgut expressed at a minimal level but up-regulated upon feeding (except BdTry3). Besides, RNAi by feeding dsRNAs to larvae proved to be an effective method to cause gene silencing and the mixed dsRNAs of the five BdTrys slowed larvae growth of B. dorsalis. The current data suggest that trypsin genes are actively involved in digestion process of B. dorsalis larvae and thereafter play crucial roles in their development.

Proteases of haematophagous arthropod vectors are involved in blood-feeding, yolk formation and immunity - a review

Ticks, triatomines, mosquitoes and sand flies comprise a large number of haematophagous arthropods considered vectors of human infectious diseases. While consuming blood to obtain the nutrients necessary to carry on life functions, these insects can transmit pathogenic microorganisms to the vertebrate host. Among the molecules related to the blood-feeding habit, proteases play an essential role. In this review, we provide a panorama of proteases from arthropod vectors involved in haematophagy, in digestion, in egg development and in immunity. As these molecules act in central biological processes, proteases from haematophagous vectors of infectious diseases may influence vector competence to transmit pathogens to their prey, and thus could be valuable targets for vectorial control.

Transcriptome Sequencing Reveals Large-Scale Changes in Axenic Aedes aegypti Larvae

Mosquitoes host communities of microbes in their digestive tract that consist primarily of bacteria. We previously reported that Aedes aegypti larvae colonized by a native community of bacteria and gnotobiotic larvae colonized by only Escherichia coli develop very similarly into adults, whereas axenic larvae never molt and die as first instars. In this study, we extended these findings by first comparing the growth and abundance of bacteria in conventional, gnotobiotic, and axenic larvae during the first instar. Results showed that conventional and gnotobiotic larvae exhibited no differences in growth, timing of molting, or number of bacteria in their digestive tract. Axenic larvae in contrast grew minimally and never achieved the critical size associated with molting by conventional and gnotobiotic larvae. In the second part of the study we compared patterns of gene expression in conventional, gnotobiotic and axenic larvae by conducting an RNAseq analysis of gut and nongut tissues (carcass) at 22 h post-hatching. Approximately 12% of Ae. aegypti transcripts were differentially expressed in axenic versus conventional or gnotobiotic larvae. However, this profile consisted primarily of transcripts in seven categories that included the down-regulation of select peptidases in the gut and up-regulation of several genes in the gut and carcass with roles in amino acid transport, hormonal signaling, and metabolism. Overall, our results indicate that axenic larvae exhibit alterations in gene expression consistent with defects in acquisition and assimilation of nutrients required for growth.

Viral Metagenomics on Blood-Feeding Arthropods as a Tool for Human Disease Surveillance

Surveillance and monitoring of viral pathogens circulating in humans and wildlife, together with the identification of emerging infectious diseases (EIDs), are critical for the prediction of future disease outbreaks and epidemics at an early stage. It is advisable to sample a broad range of vertebrates and invertebrates at different temporospatial levels on a regular basis to detect possible candidate viruses at their natural source. However, virus surveillance systems can be expensive, costly in terms of finances and resources and inadequate for sampling sufficient numbers of different host species over space and time. Recent publications have presented the concept of a new virus surveillance system, coining the terms "flying biological syringes", "xenosurveillance" and "vector-enabled metagenomics". According to these novel and promising surveillance approaches, viral metagenomics on engorged mosquitoes might reflect the viral diversity of numerous mammals, birds and humans, combined in the mosquitoes' blood meal during feeding on the host. In this review article, we summarize the literature on vector-enabled metagenomics (VEM) techniques and its application in disease surveillance in humans. Furthermore, we highlight the combination of VEM and "invertebrate-derived DNA" (iDNA) analysis to identify the host DNA within the mosquito midgut.

Determination of juvenile hormone titers by means of LC-MS/MS/MS and a juvenile hormone-responsive Gal4/UAS system in Aedes aegypti mosquitoes

In anautogenous mosquitoes, juvenile hormone III (JH) plays an essential role in female post-eclosion (PE) development, preparing them for subsequent blood feeding and egg growth. We re-examined the JH titer during the reproductive cycle of female Aedes aegypti mosquitoes. Using liquid chromatography coupled with triple tandem mass spectrometry (LC-MS/MS/MS), we have shown that it reaches its peak at 48-54 h PE in the female hemolymph and at 72 h PE in whole body extracts. This method represents an effective assay for determination of JH titers. The 2.1-kb 5' promoter region of the Early Trypsin (ET) gene, which is specifically expressed in the female midgut under the control of JH during the PE phase, was utilized to genetically engineer the Ae. aegypti mosquito line with the ET-Gal4 activator. We then established the ET-GAL4>UAS-enhanced green fluorescent protein (EGFP) system in Ae. aegypti. In ET-Gal4>UAS-EGFP female mosquitoes, the intensity of the midgut-specific EGFP signal was observed to correspond to the ET gene transcript level and follow the JH titer during the PE phase. The EGFP signal and the EGFP transcript level were significantly diminished in midguts of transgenic female mosquitoes after RNA interference depletion of the JH receptor Methoprene-tolerant (Met), providing evidence of the control of ET gene expression by Met. Topical JH application caused premature enhancement of the EGFP signal and the EGFP transcript level in midguts of newly eclosed ET-Gal4>UAS-EGFP female mosquitoes, in which endogenous JH titer is still low. Hence, this novel ET-Gal4>UAS system permits JH-dependent gene overexpression in the midgut of Ae. aegypti female mosquitoes prior to a blood meal.

Effective disposal of nitrogen waste in blood-fed Aedes aegypti mosquitoes requires alanine aminotransferase

To better understand the mechanisms responsible for the success of female mosquitoes in their disposal of excess nitrogen, we investigated the role of alanine aminotransferase (ALAT) in blood-fed Aedes aegypti. Transcript and protein levels from the 2 ALAT genes were analyzed in sucrose- and blood-fed A. aegypti tissues. ALAT1 and ALAT2 exhibit distinct expression patterns in tissues during the first gonotrophic cycle. Injection of female mosquitoes with either double-stranded RNA (dsRNA)-ALAT1 or dsRNA ALAT2 significantly decreased mRNA and protein levels of ALAT1 or ALAT2 in fat body, thorax, and Malpighian tubules compared with dsRNA firefly luciferase-injected control mosquitoes. The silencing of either A. aegypti ALAT1 or ALAT2 caused unexpected phenotypes such as a delay in blood digestion, a massive accumulation of uric acid in the midgut posterior region, and a significant decrease of nitrogen waste excretion during the first 48 h after blood feeding. Concurrently, the expression of genes encoding xanthine dehydrogenase and ammonia transporter (Rhesus 50 glycoprotein) were significantly increased in tissues of both ALAT1- and ALAT2-deficient females. Moreover, perturbation of ALAT1 and ALAT2 in the female mosquitoes delayed oviposition and reduced egg production. These novel findings underscore the efficient mechanisms that blood-fed mosquitoes use to avoid ammonia toxicity and free radical damage.-Mazzalupo, S., Isoe, J., Belloni, V., Scaraffia, P. Y. Effective disposal of nitrogen waste in blood-fed Aedes aegypti mosquitoes requires alanine aminotransferase.

In-depth characterization of trypsin-like serine peptidases in the midgut of the sugar fed Culex quinquefasciatus

BACKGROUND

Culex quinquefasciatus is a hematophagous insect from the Culicidae family that feeds on the blood of humans, dogs, birds and livestock. This species transmits a wide variety of pathogens between humans and animals. The midgut environment is the first location of pathogen-vector interactions for blood-feeding mosquitoes and the expression of specific peptidases in the early stages of feeding could influence the outcome of the infection. Trypsin-like serine peptidases belong to a multi-gene family that can be expressed in different isoforms under distinct physiological conditions. However, the confident assignment of the trypsin genes that are expressed under each condition is still a challenge due to the large number of trypsin-coding genes in the Culicidae family and most likely because they are low abundance proteins.

METHODS

We used zymography for the biochemical characterization of the peptidase profile of the midgut from C. quinquefasciatus females fed on sugar. Protein samples were also submitted to SDS-PAGE followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for peptidase identification. The peptidases sequences were analyzed with bioinformatics tools to assess their distinct features.

RESULTS

Zymography revealed that trypsin-like serine peptidases were responsible for the proteolytic activity in the midgut of females fed on sugar diet. After denaturation in SDS-PAGE, eight trypsin-like serine peptidases were identified by LC-MS/MS. These peptidases have structural features typical of invertebrate digestive trypsin peptidases but exhibited singularities at the protein sequence level such as: the presence of different amino acids at the autocatalytic motif and substrate binding regions as well as different number of disulfide bounds. Data mining revealed a group of trypsin-like serine peptidases that are specific to C. quinquefasciatus when compared to the culicids genomes sequenced so far.

CONCLUSION

We demonstrated that proteomics approaches combined with bioinformatics tools and zymographic analysis can lead to the functional annotation of trypsin-like serine peptidases coding genes and aid in the understanding of the complexity of peptidase expression in mosquitoes.

Identification of genes associated with blood feeding in the cat flea, Ctenocephalides felis

Background

The cat flea (Ctenocephalides felis) is a blood-feeding ectoparasitic insect and particular nuisance pest of companion animals worldwide. Identification of genes that are differentially expressed in response to feeding is important for understanding flea biology and discovering targets for their control.

Methods

C. felis fleas were maintained and fed for 24 h using an artificial rearing system. The technique of suppression subtractive hybridization was employed to screen for mRNAs specifically expressed in fed fleas.

Results

We characterized nine distinct full-length flea transcripts that exhibited modulated or de novo expression during feeding. Among the predicted protein sequences were two serine proteases, a serine protease inhibitor, two mucin-like molecules, a DNA topoisomerase, an enzyme associated with GPI-mediated cell membrane attachment of proteins and a component of the insect innate immune response.

Conclusions

Our results provide a molecular insight into the physiology of flea feeding. The protein products of the genes identified may play important roles during flea feeding in terms of blood meal digestion, cellular growth/repair and protection from feeding-associated stresses.

Global transcriptional dynamics of diapause induction in non-blood-fed and blood-fed Aedes albopictus

BACKGROUND

Aedes albopictus is a vector of increasing public health concern due to its rapid global range expansion and ability to transmit Dengue virus, Chikungunya virus and a wide range of additional arboviruses. Traditional vector control strategies have been largely ineffective against Ae. albopictus and novel approaches are urgently needed. Photoperiodic diapause is a crucial ecological adaptation in a wide range of temperate insects. Therefore, targeting the molecular regulation of photoperiodic diapause or diapause-associated physiological processes could provide the basis of novel approaches to vector control.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the global transcriptional profiles of diapause induction in Ae. albopictus by performing paired-end RNA-Seq of biologically replicated libraries. We sequenced RNA from whole bodies of adult females reared under diapause-inducing and non-diapause-inducing photoperiods either with or without a blood meal. We constructed a comprehensive transcriptome assembly that incorporated previous assemblies and represents over 14,000 annotated dipteran gene models. Mapping of sequence reads to the transcriptome identified differential expression of 2,251 genes in response to diapause-inducing short-day photoperiods. In non-blood-fed females, potential regulatory elements of diapause induction were transcriptionally up-regulated, including two of the canonical circadian clock genes, timeless and cryptochrome 1. In blood-fed females, genes in metabolic pathways related to energy production and offspring provisioning were differentially expressed under diapause-inducing conditions, including the oxidative phosphorylation pathway and lipid metabolism genes.

CONCLUSIONS/SIGNIFICANCE

This study is the first to utilize powerful RNA-Seq technologies to elucidate the transcriptional basis of diapause induction in any insect. We identified candidate genes and pathways regulating diapause induction, including a conserved set of genes that are differentially expressed as part of the diapause program in a diverse group of insects. These genes provide candidates whose diapause-associated function can be further interrogated using functional genomics approaches in Ae. albopictus and other insects.

Xenosurveillance: a novel mosquito-based approach for examining the human-pathogen landscape

BACKGROUND

Globally, regions at the highest risk for emerging infectious diseases are often the ones with the fewest resources. As a result, implementing sustainable infectious disease surveillance systems in these regions is challenging. The cost of these programs and difficulties associated with collecting, storing and transporting relevant samples have hindered them in the regions where they are most needed. Therefore, we tested the sensitivity and feasibility of a novel surveillance technique called xenosurveillance. This approach utilizes the host feeding preferences and behaviors of Anopheles gambiae, which are highly anthropophilic and rest indoors after feeding, to sample viruses in human beings. We hypothesized that mosquito bloodmeals could be used to detect vertebrate viral pathogens within realistic field collection timeframes and clinically relevant concentrations.

METHODOLOGY/PRINCIPAL FINDINGS

To validate this approach, we examined variables influencing virus detection such as the duration between mosquito blood feeding and mosquito processing, the pathogen nucleic acid stability in the mosquito gut and the pathogen load present in the host's blood at the time of bloodmeal ingestion using our laboratory model. Our findings revealed that viral nucleic acids, at clinically relevant concentrations, could be detected from engorged mosquitoes for up to 24 hours post feeding by qRT-PCR. Subsequently, we tested this approach in the field by examining blood from engorged mosquitoes from two field sites in Liberia. Using next-generation sequencing and PCR we were able to detect the genetic signatures of multiple viral pathogens including Epstein-Barr virus and canine distemper virus.

CONCLUSIONS/SIGNIFICANCE

Together, these data demonstrate the feasibility of xenosurveillance and in doing so validated a simple and non-invasive surveillance tool that could be used to complement current biosurveillance efforts.

Exome and transcriptome sequencing of Aedes aegypti identifies a locus that confers resistance to Brugia malayi and alters the immune response

Many mosquito species are naturally polymorphic for their abilities to transmit parasites, a feature which is of great interest for controlling vector-borne disease. Aedes aegypti, the primary vector of dengue and yellow fever and a laboratory model for studying lymphatic filariasis, is genetically variable for its capacity to harbor the filarial nematode Brugia malayi. The genome of Ae. aegypti is large and repetitive, making genome resequencing difficult and expensive. We designed exome captures to target protein-coding regions of the genome, and used association mapping in a wild Kenyan population to identify a single, dominant, sex-linked locus underlying resistance. This falls in a region of the genome where a resistance locus was previously mapped in a line established in 1936, suggesting that this polymorphism has been maintained in the wild for the at least 80 years. We then crossed resistant and susceptible mosquitoes to place both alleles of the gene into a common genetic background, and used RNA-seq to measure the effect of this locus on gene expression. We found evidence for Toll, IMD, and JAK-STAT pathway activity in response to early stages of B. malayi infection when the parasites are beginning to die in the resistant genotype. We also found that resistant mosquitoes express anti-microbial peptides at the time of parasite-killing, and that this expression is suppressed in susceptible mosquitoes. Together, we have found that a single resistance locus leads to a higher immune response in resistant mosquitoes, and we identify genes in this region that may be responsible for this trait.

Regulation of the gut-specific carboxypeptidase: a study using the binary Gal4/UAS system in the mosquito Aedes aegypti

Pathogen transmission by mosquitoes is tightly linked to blood feeding which, in turn, is required for egg development. Studies of these processes would greatly benefit from genetic methods, such as the binary Gal4/UAS system. The latter has been well established for model organisms, but its availability is limited for mosquitoes. The objective of this study was to develop the blood-meal-activated, gut-specific Gal4/UAS system for the yellow-fever mosquito Aedes aegypti and utilize it to investigate the regulation of gut-specific gene expression. A 1.1-kb, 5(') upstream region of the carboxypeptidase A (CP) gene was used to genetically engineer the CP-Gal4 driver mosquito line. The CP-Gal4 specifically activated the Enhanced Green Fluorescent Protein (EGFP) reporter only after blood feeding in the gut of the CP-Gal4 > UAS-EGFP female Ae. aegypti. We used this system to study the regulation of CP gene expression. In vitro treatments with either amino acids (AAs) or insulin stimulated expression of the CP-Gal4 > UAS-EGFP transgene; no effect was observed with 20-hydroxyecdysone (20E) treatments. The transgene activation by AAs and insulin was blocked by rapamycin, the inhibitor of the Target-of-Rapamycin (TOR) kinase. RNA interference (RNAi) silence of the insulin receptor (IR) reduced the expression of the CP-Gal4 > UAS-EGFP transgene. Thus, in vitro and in vivo experiments have revealed that insulin and TOR pathways control expression of the digestive enzyme CP. In contrast, 20E, the major regulator of post-blood-meal vitellogenic events in female mosquitoes, has no role in regulating the expression of this gene. This novel CP-Gal4/UAS system permits functional testing of midgut-specific genes that are involved in blood digestion and interaction with pathogens in Ae. aegypti mosquitoes.

COPI-mediated blood meal digestion in vector mosquitoes is independent of midgut ARF-GEF and ARF-GAP regulatory activities

We have previously shown that defects in COPI coatomer proteins cause 80% mortality in blood fed Aedes aegypti mosquitoes by 96 h post-feeding. In this study we show that similar deficiencies in COPII and clathrin mediated vesicle transport do not disrupt blood meal digestion and are not lethal, even though both COPII and clathrin functions are required for ovarian development. Since COPI vesicle transport is controlled in mammalian cells by upstream G proteins and associated regulatory factors, we investigated the function of the orthologous ADP-ribosylation factor 1 (ARF1) and ARF4 proteins in mosquito tissues. We found that both ARF1 and ARF4 function upstream of COPI vesicle transport in blood fed mosquitoes given that an ARF1/ARF4 double deficiency is required to phenocopy the feeding-induced mortality observed in COPI coatomer deficient mosquitoes. Small molecule inhibitors of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) are often transitory, and therefore, we investigated the role of five Ae. aegypti ARF-GEF and ARF-GAP proteins in blood meal digestion using RNA interference. Surprisingly, we found that ARF-GEF and ARF-GAP functions are not required for blood meal digestion, even though both vitellogenesis and ovarian development in Ae. aegypti are dependent on GBF1 (ARF-GEF) and GAP1/GAP2 (ARF-GAPs) proteins. Moreover, deficiencies in orthologous COPI regulating genes in Anopheles stephensi mosquitoes had similar phenotypes, indicating conserved functions in these two mosquito species. We propose that based on the need for rapid initiation of protein digestion and peritrophic membrane formation, COPI vesicle transport in midgut epithelial cells is not dependent on ARF-GEF and ARF-GAP regulatory proteins to mediate vesicle recycling within the first 48 h post-feeding.

In silico cloning and annotation of genes involved in the digestion, detoxification and RNA interference mechanism in the midgut of Bactrocera dorsalis [Hendel (Diptera: Tephritidae)]

As the second largest organ in insects, the insect midgut is the major tissue involved in the digestion of food and detoxification of xenobiotics, such as insecticides, and the first barrier and target for oral RNA interference (RNAi). In this study, we performed a midgut-specific transcriptome analysis in the oriental fruit fly, Bactrocera dorsalis, an economically important worldwide pest, with many populations showing high levels of insecticide resistance. Using high-throughput sequencing, 52 838 060 short reads were generated and assembled to 25 236 unigenes with a mean length of 758 bp. Interestingly, 34 unique sequences encoding digestion enzymes were newly described and these included aminopeptidase and trypsin, genes associated with Bacillus thuringiensis resistance and fitness cost. Second, 41 transcripts were annotated to particular detoxification genes such as glutathione S-transferases, carboxylesterases and cytochrome P450s, and the subsequent phylogenetic analysis indicated homology with tissue-specific and insecticide resistance-related genes of Drosophila melanogaster. Third, we identified the genes involved in the mechanism of RNAi and the uptake of double-stranded RNA. The sequences encoding Dicer-2, R2D2, AGO2, and Eater were confirmed, but SID and SR-CI were absent in the midgut transcriptome. In conclusion, the results provide basic molecular information to better understand the mechanisms of food digestion, insecticide resistance and oral RNAi in this important pest insect in agriculture. Specific genes in these systems can be used in the future as potential targets for pest control, for instance, with RNAi technology.

Urea synthesis and excretion in Aedes aegypti mosquitoes are regulated by a unique cross-talk mechanism

Aedes aegypti mosquitoes do not have a typical functional urea cycle for ammonia disposal such as the one present in most terrestrial vertebrates. However, they can synthesize urea by two different pathways, argininolysis and uricolysis. We investigated how formation of urea by these two pathways is regulated in females of A. aegypti. The expression of arginase (AR) and urate oxidase (UO), either separately or simultaneously (ARUO) was silenced by RNAi. The amounts of several nitrogen compounds were quantified in excreta using mass spectrometry. Injection of mosquitoes with either dsRNA-AR or dsRNA-UO significantly decreased the expressions of AR or UO in the fat body (FB) and Malpighian tubules (MT). Surprisingly, the expression level of AR was increased when UO was silenced and vice versa, suggesting a cross-talk regulation between pathways. In agreement with these data, the amount of urea measured 48 h after blood feeding remained unchanged in those mosquitoes injected with dsRNA-AR or dsRNA-UO. However, allantoin significantly increased in the excreta of dsRNA-AR-injected females. The knockdown of ARUO mainly led to a decrease in urea and allantoin excretion, and an increase in arginine excretion. In addition, dsRNA-AR-injected mosquitoes treated with a specific nitric oxide synthase inhibitor showed an increase of UO expression in FB and MT and a significant increase in the excretion of nitrogen compounds. Interestingly, both a temporary delay in the digestion of a blood meal and a significant reduction in the expression of several genes involved in ammonia metabolism were observed in dsRNA-AR, UO or ARUO-injected females. These results reveal that urea synthesis and excretion in A. aegypti are tightly regulated by a unique cross-talk signaling mechanism. This process allows blood-fed mosquitoes to regulate the synthesis and/or excretion of nitrogen waste products, and avoid toxic effects that could result from a lethal concentration of ammonia in their tissues.

Trypsin-like serine peptidase profiles in the egg, larval, and pupal stages of Aedes albopictus

BACKGROUND

Aedes albopictus, a ubiquitous mosquito, is one of the main vectors of dengue and yellow fever, representing an important threat to public health worldwide. Peptidases play key roles in processes such as digestion, oogenesis, and metamorphosis of insects. However, most of the information on the proteolytic enzymes of mosquitoes is derived from insects in the adult stages and is often directed towards the understanding of blood digestion. The aim of this study was to investigate the expression of active peptidases from the preimaginal stages of Ae. albopictus.

METHODS

Ae. albopictus eggs, larvae, and pupae were analyzed using zymography with susbtrate-SDS-PAGE. The pH, temperature and peptidase inhibitor sensitivity was evaluated. In addition, the proteolytic activities of larval instars were assayed using the fluorogenic substrate Z-Phe-Arg-AMC.

RESULTS

The proteolytic profile of the larval stage was composed of 8 bands ranging from 17 to 130 kDa. These enzymes displayed activity in a broad range of pH values, from 5.5 to 10.0. The enzymatic profile of the eggs was similar to that of the larvae, although the proteolytic bands of the eggs showed lower intensities. The pupal stage showed a complex proteolytic pattern, with at least 6 bands with apparent molecular masses ranging from 30 to 150 kDa and optimal activity at pH 7.5. Peptidases from larval instars were active from 10°C to 60°C, with optimal activity at temperatures between 37°C and 50°C. The proteolytic profile of both the larval and pupal stages was inhibited by phenyl-methyl sulfonyl-fluoride (PMSF) and Nα-Tosyl L-lysine chloromethyl ketone hydrochloride (TLCK), indicating that the main peptidases expressed during these developmental stages are trypsin-like serine peptidases.

CONCLUSION

The preimaginal stages of Ae. albopictus exhibited a complex profile of trypsin-like serine peptidase activities. A comparative analysis of the active peptidase profiles revealed differential expression of trypsin-like isoforms among the preimaginal stages, suggesting that some of these enzymes are stage specific. Additionally, a comparison of the peptidase expression between larvae from eggs collected in the natural environment and larvae obtained from the eggs of female mosquitoes maintained in colonies for a long period of time demonstrated that the proteolytic profile is invariable under such conditions.

Complex modulation of the Aedes aegypti transcriptome in response to dengue virus infection

Dengue fever is the most important arboviral disease world-wide, with Aedes aegypti being the major vector. Interactions between the mosquito host and dengue viruses (DENV) are complex and vector competence varies among geographically-distinct Ae. aegypti populations. Additionally, dengue is caused by four antigenically-distinct viral serotypes (DENV1–4), each with multiple genotypes. Each virus genotype interacts differently with vertebrate and invertebrate hosts. Analyses of alterations in mosquito transcriptional profiles during DENV infection are expected to provide the basis for identifying networks of genes involved in responses to viruses and contribute to the molecular-genetic understanding of vector competence. In addition, this knowledge is anticipated to support the development of novel disease-control strategies. RNA-seq technology was used to assess genome-wide changes in transcript abundance at 1, 4 and 14 days following DENV2 infection in carcasses, midguts and salivary glands of the Ae. aegypti Chetumal strain. DENV2 affected the expression of 397 Ae. aegypti genes, most of which were down-regulated by viral infection. Differential accumulation of transcripts was mainly tissue- and time-specific. Comparisons of our data with other published reports reveal conservation of functional classes, but limited concordance of specific mosquito genes responsive to DENV2 infection. These results indicate the necessity of additional studies of mosquito-DENV interactions, specifically those focused on recently-derived mosquito strains with multiple dengue virus serotypes and genotypes.

Cloning of a trypsin-like serine protease and expression patterns during Plasmodium falciparum invasion in the mosquito, Anopheles dirus (Peyton and Harrison)

Understanding specific gene regulation during responses to malaria infection is key to dissecting the mosquito defense mechanisms and host/parasite interactions. A full-length serine protease cDNA was isolated from the fat body of female Anopheles dirus, a major malaria vector in Thailand. The predicted amino acid sequence of SERF4 identifies it as a member of the serine protease family containing a single trypsin-like protease domain. Digestive trypsins function in the female mosquito midgut and are inducible in two phases in this tissue upon blood intake. However, the gene was highly upregulated in the midgut at day 3 postinfection by Plasmodium falciparum. In situ hybridization confirmed that SERF4 transcripts were located in the midgut epithelial cells rather than hemocytes or other tissues associated with the midgut. SERF4 was also strongly downregulated in the whole insects at day 16 after infection in comparison with the blood-fed control. Changes in the expression of the SERF4 gene in response to infection with this human malaria parasite suggest a role in parasite-specific innate immunity.

In vitro activation and enzyme kinetic analysis of recombinant midgut serine proteases from the Dengue vector mosquito Aedes aegypti

Background

The major Dengue virus vector Aedes aegypti requires nutrients obtained from blood meal proteins to complete the gonotrophic cycle. Although bioinformatic analyses of Ae. aegypti midgut serine proteases have provided evolutionary insights, very little is known about the biochemical activity of these digestive enzymes.

Results

We used peptide specific antibodies to show that midgut serine proteases are expressed as zymogen precursors, which are cleaved to the mature form after blood feeding. Since midgut protein levels are insufficient to purify active proteases directly from blood fed mosquitoes, we engineered recombinant proteins encoding a heterologous enterokinase cleavage site to permit generation of the bona fide mature form of four midgut serine proteases (AaET, AaLT, AaSPVI, AaSPVII) for enzyme kinetic analysis. Cleavage of the chromogenic trypsin substrate BApNA showed that AaET has a catalytic efficiency (k_cat/K_M) that is ~30 times higher than bovine trypsin, and ~2-3 times higher than AaSPVI and AaSPVII, however, AaLT does not cleave BApNA. To measure the enzyme activities of the mosquito midgut proteases using natural substrates, we developed a quantitative cleavage assay based on cleavage of albumin and hemoglobin proteins. These studies revealed that the recombinant AaLT enzyme was indeed catalytically active, and cleaved albumin and hemoglobin with equivalent efficiency to that of AaET, AaSPVI, and AaSPVII. Structural modeling of the AaLT and AaSPVI mature forms indicated that AaLT is most similar to serine collagenases, whereas AaSPVI appears to be a classic trypsin.

Conclusions

These data show that in vitro activation of recombinant serine proteases containing a heterologous enterokinase cleavage site can be used to investigate enzyme kinetics and substrate cleavage properties of biologically important mosquito proteases.

Insulin-like peptides and the target of rapamycin pathway coordinately regulate blood digestion and egg maturation in the mosquito Aedes aegypti

Background

Mosquitoes are insects that vector many serious pathogens to humans and other vertebrates. Most mosquitoes must feed on the blood of a vertebrate host to produce eggs. In turn, multiple cycles of blood feeding promote frequent contacts with hosts and make mosquitoes ideal disease vectors. Both hormonal and nutritional factors are involved in regulating egg development in the mosquito, Aedes aegypti. However, the processes that regulate digestion of the blood meal remain unclear.

Methodology/Principal Findings

Here we report that insulin peptide 3 (ILP3) directly stimulated late phase trypsin-like gene expression in blood fed females. In vivo knockdown of the mosquito insulin receptor (MIR) by RNA interference (RNAi) delayed but did not fully inhibit trypsin-like gene expression in the midgut, ecdysteroid (ECD) production by ovaries, and vitellogenin (Vg) expression by the fat body. In contrast, in vivo treatment with double-stranded MIR RNA and rapamycin completely blocked egg production. In vitro experiments showed that amino acids did not simulate late phase trypsin-like gene expression in the midgut or ECD production by the ovaries. However, amino acids did enhance ILP3-mediated stimulation of trypsin-like gene expression and ECD production.

Conclusions/Significance

Overall, our results indicate that ILPs from the brain synchronize blood meal digestion and amino acid availability with ovarian ECD production to maximize Vg expression by the fat body. The activation of digestion by ILPs may also underlie the growth promoting effects of insulin and TOR signaling in other species.

RNA-seq analyses of blood-induced changes in gene expression in the mosquito vector species, Aedes aegypti

Background

Hematophagy is a common trait of insect vectors of disease. Extensive genome-wide transcriptional changes occur in mosquitoes after blood meals, and these are related to digestive and reproductive processes, among others. Studies of these changes are expected to reveal molecular targets for novel vector control and pathogen transmission-blocking strategies. The mosquito Aedes aegypti (Diptera, Culicidae), a vector of Dengue viruses, Yellow Fever Virus (YFV) and Chikungunya virus (CV), is the subject of this study to look at genome-wide changes in gene expression following a blood meal.

Results

Transcriptional changes that follow a blood meal in Ae. aegypti females were explored using RNA-seq technology. Over 30% of more than 18,000 investigated transcripts accumulate differentially in mosquitoes at five hours after a blood meal when compared to those fed only on sugar. Forty transcripts accumulate only in blood-fed mosquitoes. The list of regulated transcripts correlates with an enhancement of digestive activity and a suppression of environmental stimuli perception and innate immunity. The alignment of more than 65 million high-quality short reads to the Ae. aegypti reference genome permitted the refinement of the current annotation of transcript boundaries, as well as the discovery of novel transcripts, exons and splicing variants. Cis-regulatory elements (CRE) and cis-regulatory modules (CRM) enriched significantly at the 5'end flanking sequences of blood meal-regulated genes were identified.

Conclusions

This study provides the first global view of the changes in transcript accumulation elicited by a blood meal in Ae. aegypti females. This information permitted the identification of classes of potentially co-regulated genes and a description of biochemical and physiological events that occur immediately after blood feeding. The data presented here serve as a basis for novel vector control and pathogen transmission-blocking strategies including those in which the vectors are modified genetically to express anti-pathogen effector molecules.

aeGEPUCI: a database of gene expression in the dengue vector mosquito, Aedes aegypti

Background

Aedes aegypti is the principal vector of dengue and yellow fever viruses. The availability of the sequenced and annotated genome enables genome-wide analyses of gene expression in this mosquito. The large amount of data resulting from these analyses requires efficient cataloguing before it becomes useful as the basis for new insights into gene expression patterns and studies of the underlying molecular mechanisms for generating these patterns.

Findings

We provide a publicly-accessible database and data-mining tool, aeGEPUCI, that integrates 1) microarray analyses of sex- and stage-specific gene expression in Ae. aegypti, 2) functional gene annotation, 3) genomic sequence data, and 4) computational sequence analysis tools. The database can be used to identify genes expressed in particular stages and patterns of interest, and to analyze putative cis-regulatory elements (CREs) that may play a role in coordinating these patterns. The database is accessible from the address http://www.aegep.bio.uci.edu.

Conclusions

The combination of gene expression, function and sequence data coupled with integrated sequence analysis tools allows for identification of expression patterns and streamlines the development of CRE predictions and experiments to assess how patterns of expression are coordinated at the molecular level.