Transcriptional regulation of the mosquito vitellogenin gene via a blood meal-triggered cascade

Tyrosine transfer RNA levels and modifications during blood-feeding and vitellogenesis in the mosquito, Aedes aegypti

Mosquitoes such as Aedes aegypti must consume a blood meal for the nutrients necessary for egg production. Several transcriptome and proteome changes occur post-blood meal that likely corresponds with codon usage alterations. Transfer RNA (tRNA) is the adapter molecule that reads messenger RNA codons to add the appropriate amino acid during protein synthesis. Chemical modifications to tRNA enhance codon decoding, improving the accuracy and efficiency of protein synthesis. Here, we examined tRNA modifications and transcripts associated with the blood meal and subsequent periods of vitellogenesis in A. aegypti. More specifically, we assessed tRNA transcript abundance and modification levels in the fat body at critical times post blood-feeding. Based on a combination of alternative codon usage and identification of particular modifications, we discovered that increased transcription of tyrosine tRNAs is likely critical during the synthesis of egg yolk proteins in the fat body following a blood meal. Altogether, changes in both the abundance and modification of tRNA are essential factors in the process of vitellogenin production after blood-feeding in mosquitoes.

Transcription factor E93 regulates vitellogenesis via the vitelline membrane protein 26Ab gene in Chilo Suppressalis

BACKGROUND

Ecdysone-induced protein 93 F (E93, also known as Eip93F) plays a crucial role in the reproductive process of numerous insects. This study aims to delineate the function of E93 in Chilo suppressalis and elucidated the regulatory mechanism by which E93 influences the reproduction of C. suppressalis METHODS AND RESULTS: The results of the bioinformatics analysis indicate that C. suppressalis E93 shows the highest homology with E93 from Bombyx mori. We used qPCR to evaluate the expression profile of CsE93 from different developmental stages and tissues, revealed that CsE93 had the highest expression levels in the head, which peaked during the prepupal stage. Silencing CsE93 resulted in a significant reduction in yolk deposition and abnormal ovarian development. Moreover, the transcriptional levels of vitellogenin (Vg) and E74A, which are related to vitellogenesis and the 20E pathway, were significantly down-regulated in dsE93-treated female pupae. In addition, we identified Vitelline membrane protein 26Ab (VMP26Ab), a downstream gene associated with the integrity of the inner eggshell. The knockdown of VMP26Ab resulted in a significant reduction in the number of eggs and abnormal ovarian development, similar to RNAi E93. Finally, we identified an active promoter fragment (containing GAGA-containing motif) of CsVMP26Ab and demonstrated that CsE93 can bind to it.

RESULTS

Our results indicate that CsE93 plays an important role in C. suppressalis reproduction. CsE93 modulates the CsVMP26Ab expression by acting on its promoter involve in the reproduction of C. suppressalis finally.

Tyrosine transfer RNA levels and modifications during blood-feeding and vitellogenesis in the mosquito, Aedes aegypti

Mosquitoes such as Aedes aegypti must consume a blood meal for the nutrients necessary for egg production. Several transcriptome and proteome changes occur post blood meal that likely corresponds with codon usage alterations. Transfer RNA (tRNA) is the adapter molecule that reads messenger RNA (mRNA) codons to add the appropriate amino acid during protein synthesis. Chemical modifications to tRNA enhance codons' decoding, improving the accuracy and efficiency of protein synthesis. Here, we examined tRNA modifications and transcripts associated with the blood meal and subsequent periods of vitellogenesis in A. aegypti. More specifically, we assessed tRNA transcript abundance and modification levels in the fat body at critical times post blood-feeding. Based on a combination of alternative codon usage and identification of particular modifications, we identified that increased transcription of tyrosine tRNAs is likely critical during the synthesis of egg yolk proteins in the fat body following a blood meal. Altogether, changes in both the abundance and modification of tRNA are essential factors in the process of vitellogenin production after blood-feeding in mosquitoes.

RNAi-Mediated Functional Analysis Reveals the Regulation of Oocyte Vitellogenesis by Ecdysone Signaling in Two Coleoptera Species

Coleoptera is the largest taxa of animals by far. The robust reproductive capacity is one of the main reasons for such domination. Successful female reproduction partially relies on effective vitellogenesis. However, the hormone regulation of vitellogenesis remains to be explored. In the present paper, in vitro culture of Leptinotarsa decemlineata 1-day-old adult fat bodies in the 20E-contained median did not activate juvenile hormone production and insulin-like peptide pathways, but significantly stimulated the expression of two LdVg genes, in a cycloheximide-dependent pattern. In vivo RNA interference (RNAi) of either ecdysone receptor (LdEcR) or ultraspiracle (Ldusp) by injection of corresponding dsRNA into 1-day-old female adults inhibited oocyte development, dramatically repressed the transcription of LdVg genes in fat bodies and of LdVgR in ovaries; application of JH into the LdEcR or Ldusp RNAi L. decemlineata females did not restore the oocyte development, partially rescued the decreased LdVg mRNA levels but over-compensated LdVgR expression levels. The same RNAi experiments were performed in another Coleoptera species, Henosepilachna vigintioctopunctata. Little yolk substances were seen in the misshapen oocytes in the HvEcR or Hvusp RNAi ovaries, in contrast to larger amounts of yolk granules in the normal oocytes. Correspondingly, the transcript levels of HvVg in the fat bodies and ovaries decreased significantly in the HvEcR and Hvusp RNAi samples. Our results here show that 20E signaling is indispensable in the activation of vitellogenesis in the developing oocytes of the two beetle species.

Vitellogenin genes are transcribed in Culex quinquefasciatus ovary

BACKGROUND

Culex quinquefasciatus, a cosmopolitan, domestic, and highly anthropophilic mosquito, is a vector of pathogenic arboviruses such as West Nile virus and Rift Valley virus, as well as lymphatic filariasis. The current knowledge on its reproductive physiology regarding vitellogenin expression in different tissues is still limited.

OBJECTIVES

In this study, we analysed the transcriptional profiles of vitellogenin genes in the fat body and ovaries of C. quinquefasciatus females during the first gonotrophic cycle.

METHODS

C. quinquefasciatus ovaries and/or fat bodies were dissected in different times during the first gonotrophic cycle and total RNA was extracted and used for reverse transcription polymerase chain reaction, quantitative real time-PCR, and in situ hybridisation.

FINDINGS

We confirmed the classical descriptions of the vitellogenic process in mosquitoes by verifying that vitellogenin genes are transcribed in the fat bodies of C. quinquefasciatus females. Using RNA in situ hybridisation approach, we showed that vitellogenin genes are also transcribed in developing ovaries, specifically by the follicle cells.

MAIN CONCLUSIONS

This is the first time that vitellogenin transcripts are observed in mosquito ovaries. Studies to determine if Vg transcripts are translated into proteins and their contribution to the reproductive success of the mosquito need to be further investigated.

Proteasome β3 subunit (PSMB3) controls female reproduction by promoting ecdysteroidogenesis during sexual maturation in Bactrocera dorsalis

Steroid hormone 20-hydroxyecdysone (20E) plays critical roles in reproductive development in dipterans and several other insect species. Ecdysteroidogenesis in the glands of larval or nymphal insects and other arthropods has been extensively studied, but that in the adult gonads remains largely unknown. Here we identified a proteasome β3 subunit (PSMB3) from a highly invasive pest Bactrocera dorsalis, and found that this gene was crucial for ecdysone production during female reproduction. PSMB3 was enriched in the ovary, and it was upregulated during sexual maturation. RNAi-mediated depletion of PSMB3 resulted in retarded ovarian development and decreased fecundity. Additionally, knockdown of PSMB3 reduced 20E titer in hemolymph of B. dorsalis. Molecularly, RNA sequencing and qPCR validation revealed that PSMB3 depletion suppressed the expression of 20E biosynthetic genes in the ovary and 20E responsive genes in the ovary and fat body. Furthermore, exogenous 20E rescued the inhibition of the ovarian development caused by PSMB3 depletion. Taken together, this study provides new insights into the adult reproductive development-related biological processes controlled by PSMB3, and proposed a potential eco-friendly control strategy against this notorious agricultural pest.

The Aedes aegypti peritrophic matrix controls arbovirus vector competence through HPx1, a heme-induced peroxidase

Aedes aegypti mosquitoes are the main vectors of arboviruses. The peritrophic matrix (PM) is an extracellular layer that surrounds the blood bolus. It acts as an immune barrier that prevents direct contact of bacteria with midgut epithelial cells during blood digestion. Here, we describe a heme-dependent peroxidase, hereafter referred to as heme peroxidase 1 (HPx1). HPx1 promotes PM assembly and antioxidant ability, modulating vector competence. Mechanistically, the heme presence in a blood meal induces HPx1 transcriptional activation mediated by the E75 transcription factor. HPx1 knockdown increases midgut reactive oxygen species (ROS) production by the DUOX NADPH oxidase. Elevated ROS levels reduce microbiota growth while enhancing epithelial mitosis, a response to tissue damage. However, simultaneous HPx1 and DUOX silencing was not able to rescue bacterial population growth, as explained by increased expression of antimicrobial peptides (AMPs), which occurred only after double knockdown. This result revealed hierarchical activation of ROS and AMPs to control microbiota. HPx1 knockdown produced a 100-fold decrease in Zika and dengue 2 midgut infection, demonstrating the essential role of the mosquito PM in the modulation of arbovirus vector competence. Our data show that the PM connects blood digestion to midgut immunological sensing of the microbiota and viral infections.

A critical role for ecdysone response genes in regulating egg production in adult female Rhodnius prolixus

Ecdysteroids control ovary growth and egg production through a complex gene hierarchy. In the female Rhodnius prolixus, a blood-gorging triatomine and the vector of Chagas disease, we have identified the ecdysone response genes in the ovary using transcriptomic data. We then quantified the expression of the ecdysone response gene transcripts (E75, E74, BR-C, HR3, HR4, and FTZ-F1) in several tissues, including the ovary, following a blood meal. These results confirm the presence of these transcripts in several tissues in R. prolixus and show that the ecdysone response genes in the ovary are mostly upregulated during the first three days post blood meal (PBM). Knockdown of E75, E74, or FTZ-F1 transcripts using RNA interference (RNAi) was used to understand the role of the ecdysone response genes in vitellogenesis and egg production. Knockdown significantly decreases the expression of the transcripts for the ecdysone receptor and Halloween genes in the fat body and the ovaries and reduces the titer of ecdysteroid in the hemolymph. Knockdown of each of these transcription factors typically alters the expression of the other transcription factors. Knockdown also significantly decreases the expression of vitellogenin transcripts, Vg1 and Vg2, in the fat body and ovaries and reduces the number of eggs produced and laid. Some of the laid eggs have an irregular shape and smaller volume, and their hatching rate is decreased. Knockdown also influences the expression of the chorion gene transcripts Rp30 and Rp45. The overall effect of knockdown is a decrease in number of eggs produced and a severe reduction in number of eggs laid and their hatching rate. Clearly, ecdysteroids and ecdysone response genes play a significant role in reproduction in R. prolixus.

Senescence of the immune defences and reproductive trade-offs in females of the mealworm beetle, Tenebrio molitor

In the theory of ageing, it has been assumed that ageing is associated with a decline in somatic defences, including the immune system, as a consequence of a trade-off with reproduction. While overall immunity suffers from age-related deterioration (immune senescence), the different components of the immune response appear to age differently. It is also likely that investment among the many arms of the immune system and reproduction with age is finely adjusted to the organisms' reproductive strategy. We investigated this possibility in females of Tenebrio molitor, a species of long-lived insect with reproductive strategies similar to those of long-lived mammals. We specifically tested the effects of immunological challenges imposed early or late in adult life on immune pathway activation as well as fertility early and late in life. We found complex patterns of changes in immune defences with age and age-specific immune challenges with contrasted relationships with female reproduction. While cellular and enzymatic defences showed signs of ageing, they did not trade-off with reproduction. By contrast, the induced antibacterial immune response was found to be unaffected by age and to be highly connected to female fecundity. These findings suggest that these immunological pathways have different functions with regard to female ageing in this insect species.

Transcription factors CncC and Maf connect the molecular network between pesticide resistance and resurgence of pest mites

Pesticide resistance and resurgence are serious problems often occurring simultaneously in the field. In our long-term study of a fenpropathrin-resistant strain of Tetranychus cinnabaribus, enhancement of detoxification and modified fecundity mechanisms were both observed. Here we investigate the network across these two mechanisms and find a key node between resistance and resurgence. We show that the ecdysone pathway is involved in regulating the fecundity of T. cinnabaribus. The concentration change of ecdysone is consistent with the fecundity curve; the concentration of ecdysone is higher in the fenpropathrin-resistant strain which has stronger fecundity. The enhancement of ecdysone is due to overexpression of two P450 genes (CYP314A1 and CYP315A1) in the ecdysone synthesis pathway. Silencing expression of these CYP genes resulted in lower concentration of ecdysone, reduced expression of vitellogenin, and reduced fecundity of T. cinnabaribus. The expression of CYP315A1 is regulated by transcription factors Cap-n-collar isoform C (CncC) and Musculoaponeurotic fibrosarcoma protein (Maf), which are involved in regulating other P450 genes functioning in detoxification of fenpropathrin in T. cinnabaribus. A similar regulation is established in citrus pest mite Panonychus citri showing that the CncC pathway regulates expression of PcCYP315A1, which affects mite fecundity. Transcription factors are activated to upregulate detoxification genes facilitating pesticide resistance, while the "one to multiple" regulation mode of transcription factors simultaneously increases expression of metabolic enzyme genes in hormone pathways and alters the physiology of pests. This is an important response of arthropods to pesticides which leads to resistance and population resurgence.

Kr-h1, a Cornerstone Gene in Insect Life History

Insect life cycle is coordinated by hormones and their downstream effectors. Krüppel homolog1 (Kr-h1) is one of the crucial effectors which mediates the actions of the two critical hormones of insects, the juvenile hormone (JH) and 20-hydroxyecdysone (20E). It is a transcription factor with a DNA-binding motif of eight C₂H₂ zinc fingers which is found to be conserved among insect orders. The expression of Kr-h1 is fluctuant during insect development with high abundance in juvenile instars and lower levels in the final instar and pupal stage, and reappearance in adults, which is governed by the coordination of JH, 20E, and miRNAs. The dynamic expression pattern of Kr-h1 is closely linked to its function in the entire life of insects. Over the past several years, accumulating studies have advanced our understanding of the role of Kr-h1 during insect development. It acts as a universal antimetamorphic factor in both hemimetabolous and holometabolous species by directly inhibiting the transcription of 20E signaling genes Broad-Complex (Br-C) and Ecdysone induced protein 93F (E93), and steroidogenic enzyme genes involved in ecdysone biosynthesis. Meanwhile, it promotes vitellogenesis and ovarian development in the majority of studied insects. In addition, Kr-h1 regulates insect behavioral plasticity and caste identity, neuronal morphogenesis, maturation of sexual behavior, as well as embryogenesis and metabolic homeostasis. Hence, Kr-h1 acts as a cornerstone regulator in insect life.

The ecdysone receptor regulates several key physiological factors in Anopheles funestus

Background

Malaria is a devastating disease, transmitted by female Anopheles mosquitoes infected with Plasmodium parasites. Current insecticide-based strategies exist to control the spread of malaria by targeting vectors. However, the increase in insecticide resistance in vector populations hinder the efficacy of these methods. It is, therefore, essential to develop novel vector control methods that efficiently target transmission reducing factors such as vector density and competence. A possible vector control candidate gene, the ecdysone receptor, regulates longevity, reproduction, immunity and other physiological processes in several insects, including malaria vectors. Anopheles funestus is a prominent vector in sub-Saharan Africa, however, the function of the ecdysone receptor in this mosquito has not previously been studied. This study aimed to determine if the ecdysone receptor depletion impacts An. funestus longevity, reproduction and susceptibility to Plasmodium falciparum infection.

Methods

RNA interference was used to reduce ecdysone receptor expression levels in An. funestus females and investigate how the above-mentioned phenotypes are influenced. Additionally, the expression levels of the ecdysone receptor, and reproduction genes lipophorin and vitellogenin receptor as well as the immune gene, leucine rich immune molecule 9 were determined in ecdysone receptor-depleted mosquitoes using quantitative polymerase chain reaction.

Results

Ecdysone receptor-depleted mosquitoes had a shorter lifespan, impaired oogenesis, were less fertile, and had reduced P. falciparum infection intensity.

Conclusions

Overall, this study provides the first experimental evidence that supports ecdysone receptor as a potential target in the development of vector control measures targeting An. funestus.

Novel synthetic 3'-untranslated regions for controlling transgene expression in transgenic Aedes aegypti mosquitoes

Transgenic technology for mosquitoes is now more than two decades old, and a wide array of control sequences have been described for regulating gene expression in various life stages or specific tissues. Despite this, comparatively little attention has been paid to the development and validation of other transgene-regulating elements, especially 3'-untranslated regions (3'UTRs). As a consequence, the same regulatory sequences are often used multiple times in a single transgene array, potentially leading to instability of transgenic effector genes. To increase the repertoire of characterized 3'UTRs available for genetics-based mosquito control, we generated fifteen synthetic sequences based on the base composition of the widely used SV40 3'UTR sequence, and tested their ability to contribute to the expression of reporter genes EGFP or luciferase. Transient transfection in mosquito cells identified nine candidate 3'UTRs that conferred moderate to strong gene expression. Two of these were engineered into the mosquito genome through CRISPR/Cas9-mediated site-specific insertion and compared to the original SV40 3'UTR. Both synthetic 3'UTRs were shown to successfully promote transgene expression in all mosquito life stages (larva, pupa and adults), similar to the SV40 3'UTR, albeit with differences in intensity. Thus, the synthetic 3'UTR elements described here are suitable for regulating transgene expression in Ae. aegypti, and provide valuable alternatives in the design of multi-gene cassettes. Additionally, the synthetic-scramble approach we validate here could be used to generate additional functional 3'UTR elements in this or other organisms.

Phospholipase C gamma (PLCγ) regulates soluble trehalase in the 20E-induced fecundity of Apolygus lucorum

Apolygus lucorum is the dominant pathogenic insect attacking Bacillus thuringiensis (Bt) cotton in China. Additionally, 20-hydroxyecdysone (20E) has important functions in many biological processes, including insect reproduction. Phospholipase C (PLC), which is an essential enzyme for phosphoinositide metabolism, is involved in 20E signal transduction, but its function in 20E-mediated reproduction in A. lucorum remains unclear. In this study, 20E increased AlPLCγ transcription as well as the abundance and activity of the encoded protein during molting and metamorphosis. The 20E treatment also induced the considerable accumulation of two second messengers, inositol triphosphate and diacylglycerol. The expression levels of genes encoding vitellogenin (AlVg) and soluble trehalase (AlTre-1) were similar to those of AlPLCγ, and were upregulated in response to 20E. The silencing of AlPLCγ resulted in downregulated expression of AlTre-1 and AlVg. However, the silencing of AlTre-1 and AlVg did not affect AlPLCγ expression. Moreover, the silencing of AlVg did not alter AlTre-1 expression. Furthermore, an examination of the insect specimens indicated that AlPLCγ is required for female adult reproduction, and that downregulated expression of this gene is associated with decreases in fecundity, adult longevity, and egg hatching rate as well as delayed oocyte maturation. We propose that 20E regulates AlTre-1 expression via AlPLCγ and affects Vg expression as well as ovary development to facilitate the reproductive activities of A. lucorum females.

Genetic changes of Plasmodium vivax tempers host tissue-specific responses in Anopheles stephensi

Recently, we showed how an early restriction of gut flora proliferation by Plasmodium vivax favors immune-suppression and Plasmodium survival in the gut lumen (Sharma et al., 2020). Here, we asked post gut invasion how P. vivax interacts with individual tissues such as the midgut, hemocyte, and salivary glands, and manages its survival in the mosquito host. Our data from tissue-specific comparative RNA-Seq analysis and extensive temporal/spatial expression profiling of selected mosquito transcripts in the uninfected and P. vivax infected mosquito's tissues indicated that (i) a transient suppression of gut metabolic machinery by early oocysts; (ii) enriched expression of nutritional responsive proteins and immune proteins against late oocysts, together may ensure optimal parasite development and gut homeostasis restoration; (iii) pre-immune activation of hemocyte by early gut-oocysts infection via REL induction (p ​< ​0.003); and altered expression of hemocyte-encoded immune proteins may cause rapid removal of free circulating sporozoites from hemolymph; (iv) while a strong suppression of salivary metabolic activities, and elevated expression of salivary specific secretory, as well as immune proteins together, may favor the long-term storage and survival of invaded sporozoites. Finally, our RNA-Seq-based discovery of 4449 transcripts of Plasmodium vivax origin, and their developmental stage-specific expression modulation in the corresponding infected mosquito tissues, predicts a possible mechanism of mosquito responses evasion by P. vivax. Conclusively, our system-wide RNA-Seq analysis provides the first genetic evidence of direct mosquito-Plasmodium interaction and establishes a functional correlation.

Lead stress affects the reproduction of Spodoptera litura but not by regulating the vitellogenin gene promoter

Lead (Pb) stress affects hormone-mediated responses (e.g., reproduction) in insects. In this study, the effects of Pb stress (12.5-50 mg Pb/kg in larval artificial diets) on the reproduction of the common cutworm Spodoptera litura (Lepidoptera: Noctuidae) were investigated after 7 generations. The results showed that Pb stress did not reduce the longevity of adult females, but 50 mg Pb/kg significantly reduced the longevity of adult males, regardless of the generation. After 50 mg Pb/kg stress for one or 7 generations, the peak time of egg-laying was delayed, and egg production and hatchability were decreased significantly. The vitellin content in eggs was significantly inhibited by Pb stress. The S. litura vitellogenin (Vg) gene promoter was cloned and analyzed. Multiple putative transcription factors were predicted for the 2321 bp Vg promoter region, including the TATA box, GATA, basic helix-loop-helix (bHLH) transcription factor, Broad-Complex (BR-C) binding sites, etc. The fragment from -2222 to -211 bp of the Vg promoter was the activation domain for Vg, whereas the region from -211 to -55 bp repressed the activity of the Vg promoter. The construct promoter (-782/+76) in Trichoplusia ni (Hi5) cells significantly improved Vg expression, which was not affected by Pb stress (1 or 10 mg/ml). Therefore, Pb stress significantly inhibited the reproduction of S. litura but not by regulating the Vg promoter.

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.

20-Hydroxyecdysone Primes Innate Immune Responses That Limit Bacterial and Malarial Parasite Survival in Anopheles gambiae

Blood feeding is an integral behavior of mosquitoes to acquire nutritional resources needed for reproduction. This requirement also enables mosquitoes to serve as efficient vectors to acquire and potentially transmit a multitude of mosquito-borne diseases, most notably malaria. Recent studies suggest that mosquito immunity is stimulated following a blood meal, independent of infection status. Since blood feeding promotes production of the hormone 20-hydroxyecdysone (20E), we hypothesized that 20E plays an important role in priming the immune response for pathogen challenge. Here, we examine the immunological effects of priming Anopheles gambiae with 20E prior to pathogen infection, demonstrating a significant reduction in bacteria and Plasmodium berghei survival in the mosquito host. Transcriptome sequencing (RNA-seq) analysis following 20E treatment identifies several known 20E-regulated genes, as well as several immune genes with previously reported function in antipathogen defense. Together, these data demonstrate that 20E influences cellular immune function and antipathogen immunity following mosquito blood feeding, arguing the importance of hormones in the regulation of mosquito innate immune function.IMPORTANCE Blood feeding is required to provide nutrients for mosquito egg production and serves as a mechanism to acquire and transmit pathogens. Shortly after a blood meal is taken, there is a peak in the production of 20-hydroxyecdysone (20E), a mosquito hormone that initiates physiological changes, including yolk protein production and mating refractoriness. Here, we examine additional roles of 20E in the regulation of mosquito immunity, demonstrating that priming the immune system with 20E increases mosquito resistance to pathogens. We identify differentially expressed genes in response to 20E treatment, including several involved in innate immune function as well as lipid metabolism and transport. Together, these data argue that 20E stimulates mosquito cellular immune function and innate immunity shortly after blood feeding.

The Developmental Transcriptome of Aedes albopictus, a Major Worldwide Human Disease Vector

Aedes albopictus mosquitoes are important vectors for a number of human pathogens including the Zika, dengue, and chikungunya viruses. Capable of displacing Aedes aegypti populations, this mosquito adapts to cooler environments which increases its geographical range and transmission potential. There are limited control strategies for Aedes albopictus mosquitoes which is likely attributed to the lack of comprehensive biological studies on this emerging vector. To fill this void, here using RNAseq we characterized Aedes albopictus mRNA expression profiles at 34 distinct time points throughout development providing the first high-resolution comprehensive view of the developmental transcriptome of this worldwide human disease vector. This enabled us to identify several patterns of shared gene expression among tissues as well as sex-specific expression patterns. To illuminate the similarities and differences with Aedes aegypti, a related human disease vector, we also performed a comparative analysis between the two developmental transcriptomes, identifying life stages where the two species exhibit similar and distinct gene expression patterns. These findings provide insights into the similarities and differences between Aedes albopictus and Aedes aegypti mosquito biology. In summary, the results generated from this study should form the basis for future investigations on the biology of Aedes albopictus and provide a gold mine resource for the development of transgene-based vector control strategies.

Regulation of adult female germline stem cells by nutrient-responsive signaling

Insect oogenesis is greatly affected by nutrient availability. When nutrients are abundant, oocytes are rapidly generated, but the process is slowed to conserve energy under nutrient-deficient conditions. To properly allocate limited resources toward oogenesis, systemic factors coordinate the behavioral response of ovarian germline stem cells (GSCs) to nutritional inputs by acting on the GSC itself, GSC supporting cells (the niche), or the adipose tissue surrounding the ovary. In this review, we describe current knowledge of the Drosophila ovarian GSC-niche-adipocyte system and major nutrient sensing pathways (insulin/IGF signaling, TOR signaling, and GCN2-dependent amino acid sensing) that intrinsically or extrinsically regulate GSC responses to nutrient signals.

Disruption of mosGILT in Anopheles gambiae impairs ovarian development and Plasmodium infection

Plasmodium infection in Anopheles is influenced by mosquito-derived factors. We previously showed that a protein in saliva from infected Anopheles, mosquito gamma-interferon-inducible lysosomal thiol reductase (mosGILT), inhibits the ability of sporozoites to traverse cells and readily establish infection of the vertebrate host. To determine whether mosGILT influences Plasmodium within the mosquito, we generated Anopheles gambiae mosquitoes carrying mosaic mutations in the mosGILT gene using CRISPR/CRISPR associated protein 9 (Cas9). Here, we show that female mosaic mosGILT mutant mosquitoes display defects in ovarian development and refractoriness to Plasmodium. Following infection by either Plasmodium berghei or Plasmodium falciparum, mutant mosquitoes have significantly reduced oocyst numbers as a result of increased thioester-containing protein 1 (TEP1)-dependent parasite killing. Expression of vitellogenin (Vg), the major yolk protein that can reduce the parasite-killing efficiency of TEP1, is severely impaired in mutant mosquitoes. MosGILT is a mosquito factor that is essential for ovarian development and indirectly protects both human and rodent Plasmodium species from mosquito immunity.

Identification of COP9 Signalosome Subunit Genes in Bactrocera dorsalis and Functional Analysis of csn3 in Female Fecundity

The COP9 signalosome (CSN) is an evolutionarily conserved multi-subunit complex that plays crucial roles in regulating various biological processes in plants, mammals, and the model insect Drosophila. However, it is poorly studied in non-model insects, whereas its role in fecundity remains unclear. In this study, all nine CSN subunits were identified and characterized in Bactrocera dorsalis, a major invasive agricultural tephritid pest. Each subunit gene, except for csn9x1, encoded a protein containing a PCI/PINT or MPN domain. Phylogenetic analysis revealed that all CSN subunits were individually clustered into a specific branch with their counterparts from other species. All CSN subunit genes were expressed in all detected developmental stages and tissues. Most subunits, except for csn8 and csn9x1, showed the highest expression level in the eggs. Notably, csn3 and csn5 were significantly enriched in mature female adults. Further analysis of csn3 revealed that it was enriched in the ovary and that its ovarian expression level gradually increased with the reproductive development process. RNAi-based knockdown of csn3 in female adults significantly reduced the number of laid eggs. The expression level of EcRB1 and USP, which encode the heterodimer receptors of 20E, and vitellogenin transcripts (Vg1 and Vg2) was suppressed in the fat body of female adults injected with csn3dsRNA. Decreased level of Vg1 protein was confirmed by means of Western blots. These data indicate that csn3 is involved in female reproduction by regulating 20E signaling and Vg synthesis. Overall, our study may facilitate the development of new strategies for controlling B. dorsalis since it provides insights into the evolution and expression patterns of all CSN subunit genes as well as the critical roles of csn3 in female fecundity.

Regulation of NlE74A on vitellogenin may be mediated by angiotensin converting enzyme through a fecundity-related SNP in the brown planthopper, Nilaparvata lugens

The major yolk protein precursors (YPP) gene, vitellogenin (Vg), usually considered as a reproductive indicator and molecular marker for evaluating insect fecundity, is controlled by insect hormone (mainly ecdysteroids and juvenile hormone), transcription factors and many other fecundity-related genes. To better understand the underlying molecular regulation mechanisms of the NlVg in the brown planthopper Nilaparvata lugens (N. lugens), the correlation between one early ecdysone response gene E74 and one important fecundity-related gene angiotensin converting enzyme (ACE) on the regulation of Vg gene expression, was investigated. We first showed that the mRNA expression level of NlACE were significantly higher in a high-fecundity population (HFP) than a low-fecundity population (LFP) at different development stages, and knockdown of NlACE expression by RNA interference (RNAi) results in a reduced level of NlVg expression and N. lugens fecundity. Subsequently, we analyzed the promoter of NlACE and found an E74A binding site, which was also differentially expressed in HFP and LFP. Then a gene putatively encoding E74A, namely NlE74A, predominant in the ovary and fat body was cloned and characterized. Furthermore, the developmental profile during female adult and the tissue-specific expression pattern of NlACE and NlE74A were similar to the expression pattern of NlVg gene, implying that both NlACE and NlE74A may be involved in regulating the expression of NlVg. Finally, after injecting the dsRNA of NlE74A, the NlACE expression levels were significantly reduced simultaneously at 24 h and 48 h post-injection, and the NlVg expression level was significant reduced at 24 h post-injection and the downswing was more significant at 48 h post-injection. These results imply that regulation of NlE74A on NlVg transcription might be mediated by NlACE through the E74 binding site at the NlACE promoter region in N. lugens.

Transcriptional regulation of the vitellogenin gene through a fecundity-related single nucleotide polymorphism within a GATA-1 binding motif in the brown planthopper, Nilaparvata lugens

Identifying the Single Nucleotide Polymorphisms (SNPs) with functions in insect fecundity promises to provide novel insight into genetic mechanisms of adaptation and to aid in effective control of insect populations. We previously identified several SNPs within the vitellogenin (Vg) promoter region between a high-fecundity population (HFP) and a low-fecundity population (LFP) of the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae). Here, we found that an A-to-T (HFP allele to LFP allele) transversion at nucleotide -953 upstream of Vg in a Nilaparvata lugens GATA-1 (NlGATA-1) binding motif is associated with the level of Vg transcription. We also characterized NlGATA-1, containing a double CX₂ CX₁₇ CX₂ C zinc finger, which has been implicated in the activation of Vg gene expression. Knockdown of the NlGATA-1 gene results in a reduced basal level of expression of the Vg gene and fewer offspring of N. lugens in vivo, whereas overexpression of NlGATA-1 in cells increased Vg promoter activity. Moreover, upon cotransfection with NlGATA-1 expression vector, the luciferase activities of Vg reporter vectors with the A allele were significantly higher than those with the T allele. These findings support a mechanism in which a SNP within the promoter of Vg is associated with the level of Vg transcription by altering the binding activity of NlGATA-1 and subsequently affecting fecundity in N. lugens.

The nuclear hormone receptor E75A regulates vitellogenin gene (Al-Vg) expression in the mirid bug Apolygus lucorum

Apolygus lucorum is the predominant pest of Bacillus thuringiensis (Bt) cotton in China. 20-hydroxyecdysone (20E) plays a key role in the reproduction of this insect. To better understand the mechanism underlying 20E-regulated reproduction, the nuclear hormone receptor E75 isoform-A of Ap. lucorum (Al-E75A) was cloned and its expression analysed. A 2241-bp sequence of Al-E75A cDNA encoded an open reading frame of a polypeptide with a predicted molecular mass of 69.04 kDa. Al-E75A mRNA was detected in female adult stages of Ap. lucorum with peak expression in 7-day-old animals. Al-E75A was also expressed in several tissues, particularly in the fat body and ovary. A 3.2 kb Al-E75A mRNA was detected in all tissues by Northern blot. The fecundity and longevity were significantly decreased in female adults treated with Al-E75A small interfering RNA. The rates of egg incubation rates were considerably lower in the RNA interference-treated animals compared to the untreated controls. In order to investigate the molecular mechanism underlying the effects described above, vitellogenin (Al-Vg) was selected for further investigation. The expression pattern of Al-Vg was similar to that of Al-E75A and was up-regulated by 20E. After knockdown of Al-E75A, the expression profile of Al-Vg and the protein levels were down-regulated. These findings suggest that Al-E75A plays a crucial role in the regulation of Al-Vg expression in Ap. lucorum.

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.

Regulatory Pathways Controlling Female Insect Reproduction

The synthesis of vitellogenin and its uptake by maturing oocytes during egg maturation are essential for successful female reproduction. These events are regulated by the juvenile hormones and ecdysteroids and by the nutritional signaling pathway regulated by neuropeptides. Juvenile hormones act as gonadotropins, regulating vitellogenesis in most insects, but ecdysteroids control this process in Diptera and some Hymenoptera and Lepidoptera. The complex crosstalk between the juvenile hormones, ecdysteroids, and nutritional signaling pathways differs distinctly depending on the reproductive strategies adopted by various insects. Molecular studies within the past decade have revealed much about the relationships among, and the role of, these pathways with respect to regulation of insect reproduction. Here, we review the role of juvenile hormones, ecdysteroids, and nutritional signaling, along with that of microRNAs, in regulating female insect reproduction at the molecular level.

Conserved Transcription Factors Steer Growth-Related Genomic Programs in Daphnia

Ecological genomics aims to understand the functional association between environmental gradients and the genes underlying adaptive traits. Many genes that are identified by genome-wide screening in ecologically relevant species lack functional annotations. Although gene functions can be inferred from sequence homology, such approaches have limited power. Here, we introduce ecological regulatory genomics by presenting an ontology-free gene prioritization method. Specifically, our method combines transcriptome profiling with high-throughput cis-regulatory sequence analysis in the water fleas Daphnia pulex and Daphnia magna. It screens coexpressed genes for overrepresented DNA motifs that serve as transcription factor binding sites, thereby providing insight into conserved transcription factors and gene regulatory networks shaping the expression profile. We first validated our method, called Daphnia-cisTarget, on a D. pulex heat shock data set, which revealed a network driven by the heat shock factor. Next, we performed RNA-Seq in D. magna exposed to the cyanobacterium Microcystis aeruginosa. Daphnia-cisTarget identified coregulated gene networks that associate with the moulting cycle and potentially regulate life history changes in growth rate and age at maturity. These networks are predicted to be regulated by evolutionary conserved transcription factors such as the homologues of Drosophila Shavenbaby and Grainyhead, nuclear receptors, and a GATA family member. In conclusion, our approach allows prioritising candidate genes in Daphnia without bias towards prior knowledge about functional gene annotation and represents an important step towards exploring the molecular mechanisms of ecological responses in organisms with poorly annotated genomes.

Artificial Diets for Mosquitoes

Mosquito-borne diseases are responsible for more than a million human deaths every year. Modern mosquito control strategies such as sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), population replacement strategies (PR), and Wolbachia-based strategies require the rearing of large numbers of mosquitoes in culture for continuous release over an extended period of time. Anautogenous mosquitoes require essential nutrients for egg production, which they obtain through the acquisition and digestion of a protein-rich blood meal. Therefore, mosquito mass production in laboratories and other facilities relies on vertebrate blood from live animal hosts. However, vertebrate blood is expensive to acquire and hard to store for longer times especially under field conditions. This review discusses older and recent studies that were aimed at the development of artificial diets for mosquitoes in order to replace vertebrate blood.

Molecular Profiling of Phagocytic Immune Cells in Anopheles gambiae Reveals Integral Roles for Hemocytes in Mosquito Innate Immunity

The innate immune response is highly conserved across all eukaryotes and has been studied in great detail in several model organisms. Hemocytes, the primary immune cell population in mosquitoes, are important components of the mosquito innate immune response, yet critical aspects of their biology have remained uncharacterized. Using a novel method of enrichment, we isolated phagocytic granulocytes and quantified their proteomes by mass spectrometry. The data demonstrate that phagocytosis, blood-feeding, and Plasmodium falciparum infection promote dramatic shifts in the proteomic profiles of An. gambiae granulocyte populations. Of interest, large numbers of immune proteins were induced in response to blood feeding alone, suggesting that granulocytes have an integral role in priming the mosquito immune system for pathogen challenge. In addition, we identify several granulocyte proteins with putative roles as membrane receptors, cell signaling, or immune components that when silenced, have either positive or negative effects on malaria parasite survival. Integrating existing hemocyte transcriptional profiles, we also compare differences in hemocyte transcript and protein expression to provide new insight into hemocyte gene regulation and discuss the potential that post-transcriptional regulation may be an important component of hemocyte gene expression. These data represent a significant advancement in mosquito hemocyte biology, providing the first comprehensive proteomic profiling of mosquito phagocytic granulocytes during homeostasis blood-feeding, and pathogen challenge. Together, these findings extend current knowledge to further illustrate the importance of hemocytes in shaping mosquito innate immunity and their principal role in defining malaria parasite survival in the mosquito host.

DsRNA-mediated targeting of ribosomal transcripts RPS6 and RPL26 induces long-lasting and significant reductions in fecundity of the vector Aedes aegypti

Ribosomal transcripts produce critical proteins that are involved in most cellular production processes. Targeting ribosomal transcripts has produced mortality in mites and ticks but the effect of ribosomal transcript knockdown has not been thoroughly examined in mosquitoes. We examine the effects of triggers targeting four ribosomal proteins (RP) transcripts. Although no significant mortality was observed after dsRNA microinjection and subsequent blood feeding, significant contrasts were observed on fecundity. Triggers targeting RPS6 and RPL26 effectively reduced gene expression but more importantly, reduced reproductive output by more than 96% and 91% at the first oviposition while triggers targeting RPL1 and RPS2 did not cause a reduction although gene expression was reduced. Significantly reduced fecundity continued through a second oviposition cycle in dsRPS6 and dsRPL26 cohorts, although the effect was not as strong. Relative gene expression levels confirmed specific transcript knockdown up to 20days post-injection in mosquitoes that did not oviposit or produced reduced clutch sizes. Dissections at 36h post-blood meal indicated defects in oocyte provisioning. The strong phenotype produced by dsRPS6 allowed us to examine the effects in various tissues as well as the dose response, trigger format, delivery method and trigger specificity in Aedes aegypti. Strong knockdown was observed in the abdomen and the ovaries. Greater than 50ng of dsRPS6 significantly reduced fecundity but not when delivered in a sugar meal or as an siRNA. Similar bioassays with mutated dsRPS6 triggers indicates that up to three mismatches per possible siRNA are still effective in reducing fecundity. These studies indicate that while active and effective triggers can be developed for vector species, the lack of an efficient delivery method is the biggest barrier to use as a potential control method.

Reproduction-Immunity Trade-Offs in Insects

Immune defense and reproduction are physiologically and energetically demanding processes and have been observed to trade off in a diversity of female insects. Increased reproductive effort results in reduced immunity, and reciprocally, infection and activation of the immune system reduce reproductive output. This trade-off can manifest at the physiological level (within an individual) and at the evolutionary level (genetic distinction among individuals in a population). The resource allocation model posits that the trade-off arises because of competition for one or more limiting resources, and we hypothesize that pleiotropic signaling mechanisms regulate allocation of that resource between reproductive and immune processes. We examine the role of juvenile hormone, 20-hydroxyecdysone, and insulin/insulin-like growth factor-like signaling in regulating both oogenesis and immune system activity, and propose a signaling network that may mechanistically regulate the trade-off. Finally, we discuss implications of the trade-off in an ecological and evolutionary context.

Substrate specificity and transport mechanism of amino-acid transceptor Slimfast from Aedes aegypti

Anautogenous mosquitoes depend on vertebrate blood as nutrient source for their eggs. A highly efficient set of membrane transporters mediates the massive movement of nutrient amino acids between mosquito tissues after a blood meal. Here we report the characterization of the amino-acid transporter Slimfast (Slif) from the yellow-fever mosquito Aedes aegypti using codon-optimized heterologous expression. Slif is a well-known component of the target-of-rapamycin signalling pathway and fat body nutrient sensor, but its substrate specificity and transport mechanism were unknown. We found that Slif transports essential cationic and neutral amino acids with preference for arginine. It has an unusual dual-affinity mechanism with only the high affinity being Na⁺ dependent. Tissue-specific expression and blood meal-dependent regulation of Slif are consistent with conveyance of essential amino acids from gut to fat body. Slif represents a novel transport system and type of transceptor for sensing and transporting essential amino acids during mosquito reproduction.

Anautogenous mosquitoes need to obtain essential amino acids from a blood meal for reproduction. Here, the authors examine the amino acid transporter Slimfast from the yellow-fever mosquito and describe both its specificity and mechanism of action.

Nutritional Control of Insect Reproduction

The amino acid-Target of Rapamycin (AA/TOR) and insulin pathways play a pivotal role in reproduction of female insects, serving as regulatory checkpoints that guarantee the sufficiency of nutrients for developing eggs. Being evolutionary older, the AA/TOR pathway functions as an initial nutritional sensor that not only activates nutritional responses in a tissue-specific manner, but is also involved in the control of insect insulin-like peptides (ILPs) secretion. Insulin and AA/TOR pathways also assert their nutritionally linked influence on reproductive events by contributing to the control of biosynthesis and secretion of juvenile hormone and ecdysone. This review covers the present status of our understanding of the contributions of AA/TOR and insulin pathways in insect reproduction.

Genetic technologies for disease vectors

The first genetic technologies for insect vectors of disease were introduced 20 years ago. As of today there are 12 classes of genetic technologies used as functional genomic tools for insect vectors of important diseases. Although the applications of genetic technologies in insect disease vectors have been conducted primarily in mosquitoes, other insect systems could benefit from current technologies. While the various technological platforms are likely to function in diverse arthropods, the delivery of these technologies to cells and tissues of interest is the major technical constraint that limits their widespread adoption. Increased community resources of various types would enhance the adoption of these technologies and potentially eliminate technical limitations.

Unravelling the Evolution of the Allatostatin-Type A, KISS and Galanin Peptide-Receptor Gene Families in Bilaterians: Insights from Anopheles Mosquitoes

Allatostatin type A receptors (AST-ARs) are a group of G-protein coupled receptors activated by members of the FGL-amide (AST-A) peptide family that inhibit food intake and development in arthropods. Despite their physiological importance the evolution of the AST-A system is poorly described and relatively few receptors have been isolated and functionally characterised in insects. The present study provides a comprehensive analysis of the origin and comparative evolution of the AST-A system. To determine how evolution and feeding modified the function of AST-AR the duplicate receptors in Anopheles mosquitoes, were characterised. Phylogeny and gene synteny suggested that invertebrate AST-A receptors and peptide genes shared a common evolutionary origin with KISS/GAL receptors and ligands. AST-ARs and KISSR emerged from a common gene ancestor after the divergence of GALRs in the bilaterian genome. In arthropods, the AST-A system evolved through lineage-specific events and the maintenance of two receptors in the flies and mosquitoes (Diptera) was the result of a gene duplication event. Speciation of Anopheles mosquitoes affected receptor gene organisation and characterisation of AST-AR duplicates (GPRALS1 and 2) revealed that in common with other insects, the mosquito receptors were activated by insect AST-A peptides and the iCa²⁺-signalling pathway was stimulated. GPRALS1 and 2 were expressed mainly in mosquito midgut and ovaries and transcript abundance of both receptors was modified by feeding. A blood meal strongly up-regulated expression of both GPRALS in the midgut (p < 0.05) compared to glucose fed females. Based on the results we hypothesise that the AST-A system in insects shared a common origin with the vertebrate KISS system and may also share a common function as an integrator of metabolism and reproduction. Highlights: AST-A and KISS/GAL receptors and ligands shared common ancestry prior to the protostome-deuterostome divergence. Phylogeny and gene synteny revealed that AST-AR and KISSR emerged after GALR gene divergence. AST-AR genes were present in the hemichordates but were lost from the chordates. In protostomes, AST-ARs persisted and evolved through lineage-specific events and duplicated in the arthropod radiation. Diptera acquired and maintained functionally divergent duplicate AST-AR genes.

Characterization of a novel RXR receptor in the salmon louse (Lepeophtheirus salmonis, Copepoda) regulating growth and female reproduction

BACKGROUND

Nuclear receptors have crucial roles in all metazoan animals as regulators of gene transcription. A wide range of studies have elucidated molecular and biological significance of nuclear receptors but there are still a large number of animals where the knowledge is very limited. In the present study we have identified an RXR type of nuclear receptor in the salmon louse (Lepeophtheirus salmonis) (i.e. LsRXR). RXR is one of the two partners of the Ecdysteroid receptor in arthropods, the receptor for the main molting hormone 20-hydroxyecdysone (E20) with a wide array of effects in arthropods.

RESULTS

Five different LsRXR transcripts were identified by RACE showing large differences in domain structure. The largest isoforms contained complete DNA binding domain (DBD) and ligand binding domain (LBD), whereas some variants had incomplete or no DBD. LsRXR is transcribed in several tissues in the salmon louse including ovary, subcuticular tissue, intestine and glands. By using Q-PCR it is evident that the LsRXR mRNA levels vary throughout the L. salmonis life cycle. We also show that the truncated LsRXR transcript comprise about 50% in all examined samples. We used RNAi to knock-down the transcription in adult reproducing female lice. This resulted in close to zero viable offspring. We also assessed the LsRXR RNAi effects using a L. salmonis microarray and saw significant effects on transcription in the female lice. Transcription of the major yolk proteins was strongly reduced by knock-down of LsRXR. Genes involved in lipid metabolism and transport were also down regulated. Furthermore, different types of growth processes were up regulated and many cuticle proteins were present in this group.

CONCLUSIONS

The present study demonstrates the significance of LsRXR in adult female L. salmonis and discusses the functional aspects in relation to other arthropods. LsRXR has a unique structure that should be elucidated in the future.

Vector competence of Aedes aegypti mosquitoes for filarial nematodes is affected by age and nutrient limitation

Mosquitoes are one of the most important vectors of human disease. The ability of mosquitoes to transmit disease is dependent on the age structure of the population, as mosquitoes must survive long enough for the parasites to complete their development and infect another human. Age could have additional effects due to mortality rates and vector competence changing as mosquitoes senesce, but these are comparatively poorly understood. We have investigated these factors using the mosquito Aedes aegypti and the filarial nematode Brugia malayi. Rather than observing any effects of immune senescence, we found that older mosquitoes were more resistant, but this only occurred if they had previously been maintained on a nutrient-poor diet of fructose. Constant blood feeding reversed this decline in vector competence, meaning that the number of parasites remained relatively unchanged as mosquitoes aged. Old females that had been maintained on fructose also experienced a sharp spike in mortality after an infected blood meal ("refeeding syndrome") and few survived long enough for the parasite to develop. Again, this effect was prevented by frequent blood meals. Our results indicate that old mosquitoes may be inefficient vectors due to low vector competence and high mortality, but that frequent blood meals can prevent these effects of age.

Role of microRNAs in arbovirus/vector interactions

The role of microRNAs (miRNAs) as small non-coding RNAs in regulation of gene expression has been recognized. They appear to be involved in regulation of a wide range of cellular pathways that affect several biological processes such as development, the immune system, survival, metabolism and host-pathogen interactions. Arthropod-borne viruses impose great economic and health risks around the world. Recent advances in miRNA biology have shed some light on the role of these small RNAs in vector-virus interactions. In this review, I will reflect on our current knowledge on the role of miRNAs in arbovirus-vector interactions and the potential avenues for their utilization in limiting virus replication and/or transmission.

Culex tarsalis vitellogenin gene promoters investigated in silico and in vivo using transgenic Drosophila melanogaster

INTRODUCTION

Genetic modification, or transgenesis, is a powerful technique to investigate the molecular interactions between vector-borne pathogens and their arthropod hosts, as well as a potential novel approach for vector-borne disease control. Transgenesis requires the use of specific regulatory regions, or promoters, to drive expression of genes of interest in desired target tissues. In mosquitoes, the vast majority of described promoters are from Anopheles and Aedes mosquitoes.

RESULTS

Culex tarsalis is one of the most important vectors of arboviruses (including West Nile virus) in North America, yet it has not been the subject of molecular genetic study. In order to facilitate molecular genetic work in this important vector species, we isolated four fat body-specific promoter sequences located upstream of the Cx. tarsalis vitellogenin genes (Vg1a, Vg1b, Vg2a and Vg2b). Sequences were analyzed in silico to identify requisite cis-acting elements. The ability for promoter sequences to drive expression of green fluorescent protein (GFP) in vivo was investigated using transgenic Drosophila melanogaster. All four promoters were able to drive GFP expression but there was dramatic variation between promoters and between individual Drosophila lines, indicating significant position effects. The highest expression was observed in line Vg2bL3, which was >300-fold higher than the lowest line Vg1aL2.

CONCLUSIONS

These new promoters will be useful for driving expression of genes of interest in transgenic Cx. tarsalis and perhaps other insects.

Novel Genetic and Molecular Tools for the Investigation and Control of Dengue Virus Transmission by Mosquitoes

Aedes aegypti is the principal vector of dengue virus (DENV) throughout the tropical world. This anthropophilic mosquito species needs to be persistently infected with DENV before it can transmit the virus through its saliva to a new vertebrate host. In the mosquito, DENV is confronted with several innate immune pathways, among which RNA interference is considered the most important. The Ae. aegypti genome project opened the doors for advanced molecular studies on pathogen-vector interactions including genetic manipulation of the vector for basic research and vector control purposes. Thus, Ae. aegypti has become the primary model for studying vector competence for arboviruses at the molecular level. Here, we present recent findings regarding DENV-mosquito interactions, emphasizing how innate immune responses modulate DENV infections in Ae. aegypti. We also describe the latest advancements in genetic manipulation of Ae. aegypti and discuss how this technology can be used to investigate vector transmission of DENV at the molecular level and to control transmission of the virus in the field.

Studying Culicoides vectors of BTV in the post-genomic era: resources, bottlenecks to progress and future directions

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Culicoides sonorensis is the only colonized species of bluetongue virus vector.

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The development of a fully annotated genome for this species is in progress.

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Transcriptomic analyses are being employed to investigate functional elements of the genome, particularly genes involved in hematophagy, reproduction, development and vector competence.

Culicoides biting midges (Diptera: Ceratopogonidae) are a major vector group responsible for the biological transmission of a wide variety of globally significant arboviruses, including bluetongue virus (BTV). In this review we examine current biological resources for the study of this genus, with an emphasis on detailing the history of extant colonies and cell lines derived from C. sonorensis, the major vector of BTV in the USA. We then discuss the rapidly developing area of genomic and transcriptomic analyses of biological processes in vectors and introduce the newly formed Culicoides Genomics and Transcriptomics Alliance. Preliminary results from these fields are detailed and finally likely areas of future research are discussed from an entomological perspective describing limitations in our understanding of Culicoides biology that may impede progress in these areas.

The interaction between a sexually transferred steroid hormone and a female protein regulates oogenesis in the malaria mosquito Anopheles gambiae

Molecular interactions between male and female factors during mating profoundly affect the reproductive behavior and physiology of female insects. In natural populations of the malaria mosquito Anopheles gambiae, blood-fed females direct nutritional resources towards oogenesis only when inseminated. Here we show that the mating-dependent pathway of egg development in these mosquitoes is regulated by the interaction between the steroid hormone 20-hydroxy-ecdysone (20E) transferred by males during copulation and a female Mating-Induced Stimulator of Oogenesis (MISO) protein. RNAi silencing of MISO abolishes the increase in oogenesis caused by mating in blood-fed females, causes a delay in oocyte development, and impairs the function of male-transferred 20E. Co-immunoprecipitation experiments show that MISO and 20E interact in the female reproductive tract. Moreover MISO expression after mating is induced by 20E via the Ecdysone Receptor, demonstrating a close cooperation between the two factors. Male-transferred 20E therefore acts as a mating signal that females translate into an increased investment in egg development via a MISO-dependent pathway. The identification of this male-female reproductive interaction offers novel opportunities for the control of mosquito populations that transmit malaria.

A critical role of the nuclear receptor HR3 in regulation of gonadotrophic cycles of the mosquito Aedes aegypti

The orphan nuclear receptor HR3 is essential for developmental switches during insect development and metamorphosis regulated by 20-hydroxyecdysone (20E). Reproduction of female mosquitoes of the major vector of Dengue fever, Aedes aegypti, is cyclic because of its dependence on blood feeding. 20E is an important hormone regulating vitellogenic events in this mosquito; however, any role for HR3 in 20E-driven reproductive events has not been known. Using RNA interference (RNAi) approach, we demonstrated that Aedes HR3 plays a critical role in a timely termination of expression of the vitellogenin (Vg) gene encoding the major yolk protein precursor. It is also important for downregulation of the Target-of-Rapamycin pathway and activation of programmed autophagy in the Aedes fat body at the end of vitellogenesis. HR3 is critical in activating betaFTZ-F1, EcRB and USPA, the expressions of which are highly elevated at the end of vitellogenesis. RNAi depletion of HR3 (iHR3) prior to the first gonadotrophic cycle affects a normal progression of the second gonadotrophic cycle. Most of ovaries 24 h post second blood meal from iHR3 females in the second cycle were small with follicles that were only slightly different in length from of those of resting stage. In addition, these iHR3 females laid a significantly reduced number of eggs per mosquito as compared to those of iMal and the wild type. Our results indicate an important role of HR3 in regulation of 20E-regulated developmental switches during reproductive cycles of A. aegypti females.

West Nile virus encodes a microRNA-like small RNA in the 3' untranslated region which up-regulates GATA4 mRNA and facilitates virus replication in mosquito cells

West Nile virus (WNV) belongs to a group of medically important single-stranded, positive-sense RNA viruses causing deadly disease outbreaks around the world. The 3' untranslated region (3'-UTR) of the flavivirus genome, in particular the terminal 3' stem-loop (3'SL) fulfils multiple functions in virus replication and virus-host interactions. Using the Kunjin strain of WNV (WNV(KUN)), we detected a virally encoded small RNA, named KUN-miR-1, derived from 3'SL. Transcription of WNV(KUN) pre-miRNA (3'SL) in mosquito cells either from plasmid or Semliki Forest virus (SFV) RNA replicon resulted in the production of mature KUN-miR-1. Silencing of Dicer-1 but not Dicer-2 led to a reduction in the miRNA levels. Further, when a synthetic inhibitor of KUN-miR-1 was transfected into mosquito cells, replication of viral RNA was significantly reduced. Using cloning and bioinformatics approaches, we identified the cellular GATA4 mRNA as a target for KUN-miR-1. KUN-miR-1 produced in mosquito cells during virus infection or from plasmid DNA, SFV RNA replicon or mature miRNA duplex increased accumulation of GATA4 mRNA. Depletion of GATA4 mRNA by RNA silencing led to a significant reduction in virus RNA replication while a KUN-miR-1 RNA mimic enhanced replication of a mutant WNV(KUN) virus producing reduced amounts of KUN-miR-1, suggesting that GATA4-induction via KUN-miR-1 plays an important role in virus replication.

Distinct roles of isoforms of the heme-liganded nuclear receptor E75, an insect ortholog of the vertebrate Rev-erb, in mosquito reproduction

Mosquitoes are adapted to using vertebrate blood as a nutrient source to promote egg development and as a consequence serve as disease vectors. Blood-meal activated reproductive events in female mosquitoes are hormonally and nutritionally controlled with an insect steroid hormone 20-hydroxyecdysone (20E) playing a central role. The nuclear receptor E75 is an essential factor in the 20E genetic hierarchy, however functions of its three isoforms - E75A, E75B, and E75C - in mosquito reproduction are unclear. By means of specific RNA interference depletion of E75 isoforms, we identified their distinct roles in regulating the level and timing of expression of key genes involved in vitellogenesis in the fat body (an insect analog of vertebrate liver and adipose tissue) of the mosquito Aedes aegypti. Heme is required in a high level of expression of 20E-controlled genes in the fat body, and this heme action depends on E75. Thus, in mosquitoes, heme is an important signaling molecule, serving as a sensor of the availability of a protein meal for egg development. Disruption of this signaling pathway could be explored in the design of mosquito control approaches.