Discovery of mosquito saliva microRNAs during CHIKV infection

A glimpse into the world of microRNAs and their putative roles in hard ticks

Ticks are important blood feeding ectoparasites that transmit pathogens to wildlife, domestic animals, and humans. Hard ticks can feed for several days to weeks, nevertheless they often go undetected. This phenomenon can be explained by a tick's ability to release analgesics, immunosuppressives, anticoagulants, and vasodilators within their saliva. Several studies have identified extracellular vesicles (EVs) as carriers of some of these effector molecules. Further, EVs, and their contents, enhance pathogen transmission, modulate immune responses, and delay wound healing. EVs are double lipid-membrane vesicles that transport intracellular cargo, including microRNAs (miRNAs) to recipient cells. miRNAs are involved in regulating gene expression post-transcriptionally. Interestingly, tick-derived miRNAs have been shown to enhance pathogen transmission and affect vital biological processes such as oviposition, blood digestion, and molting. miRNAs have been found within tick salivary EVs. This review focuses on current knowledge of miRNA loading into EVs and homologies reported in ticks. We also describe findings in tick miRNA profiles, including miRNAs packed within tick salivary EVs. Although no functional studies have been done to investigate the role of EV-derived miRNAs in tick feeding, we discuss the functional characterization of miRNAs in tick biology and pathogen transmission. Lastly, we propose the possible uses of tick miRNAs to develop management tools for tick control and to prevent pathogen transmission. The identification and functional characterization of conserved and tick-specific salivary miRNAs targeting important molecular and immunological pathways within the host could lead to the discovery of new therapeutics for the treatment of tick-borne and non-tick-borne human diseases.

Analysis of Amblyomma americanum microRNAs in response to Ehrlichia chaffeensis infection and their potential role in vectorial capacity

Background

MicroRNAs (miRNAs) represent a subset of small noncoding RNAs and carry tremendous potential for regulating gene expression at the post-transcriptional level. They play pivotal roles in distinct cellular mechanisms including inhibition of bacterial, parasitic, and viral infections via immune response pathways. Intriguingly, pathogens have developed strategies to manipulate the host's miRNA profile, fostering environments conducive to successful infection. Therefore, changes in an arthropod host's miRNA profile in response to pathogen invasion could be critical in understanding host-pathogen dynamics. Additionally, this area of study could provide insights into discovering new targets for disease control and prevention. The main objective of the present study is to investigate the functional role of differentially expressed miRNAs upon Ehrlichia chaffeensis, a tick-borne pathogen, infection in tick vector, Amblyomma americanum.

Methods

Small RNA libraries from uninfected and E. chaffeensis-infected Am. americanum midgut and salivary gland tissues were prepared using the Illumina Truseq kit. Small RNA sequencing data was analyzed using miRDeep2 and sRNAtoolbox to identify novel and known miRNAs. The differentially expressed miRNAs were validated using a quantitative PCR assay. Furthermore, a miRNA inhibitor approach was used to determine the functional role of selected miRNA candidates.

Results

The sequencing of small RNA libraries generated >147 million raw reads in all four libraries and identified a total of >250 miRNAs across the four libraries. We identified 23 and 14 differentially expressed miRNAs in salivary glands, and midgut tissues infected with E. chaffeensis, respectively. Three differentially expressed miRNAs (miR-87, miR-750, and miR-275) were further characterized to determine their roles in pathogen infection. Inhibition of target miRNAs significantly decreased the E. chaffeensis load in tick tissues, which warrants more in-depth mechanistic studies.

Conclusions

The current study identified known and novel miRNAs and suggests that interfering with these miRNAs may impact the vectorial capacity of ticks to harbor Ehrlichia. This study identified several new miRNAs for future analysis of their functions in tick biology and tick-pathogen interaction studies.

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

Analysis of Amblyomma americanum microRNAs in response to Ehrlichia chaffeensis infection and their potential role in vectorial capacity

Background

MicroRNAs (miRNAs) represent a subset of small noncoding RNAs and carry tremendous potential for regulating gene expression at the post-transcriptional level. They play pivotal roles in distinct cellular mechanisms including inhibition of bacterial, parasitic, and viral infections via immune response pathways. Intriguingly, pathogens have developed strategies to manipulate the host's miRNA profile, fostering environments conducive to successful infection. Therefore, changes in an arthropod host's miRNA profile in response to pathogen invasion could be critical in understanding host-pathogen dynamics. Additionally, this area of study could provide insights into discovering new targets for disease control and prevention. The main objective of the present study is to investigate the functional role of differentially expressed miRNAs upon Ehrlichia chaffeensis, a tick-borne pathogen, infection in tick vector, Amblyomma americanum.

Methods

Small RNA libraries from uninfected and E. chaffeensis-infected Am. americanum midgut and salivary gland tissues were prepared using the Illumina Truseq kit. Small RNA sequencing data was analyzed using miRDeep2 and sRNAtoolbox to identify novel and known miRNAs. The differentially expressed miRNAs were validated using a quantitative PCR assay. Furthermore, a miRNA inhibitor approach was used to determine the functional role of selected miRNA candidates.

Results

The sequencing of small RNA libraries generated >147 million raw reads in all four libraries and identified a total of >250 miRNAs across the four libraries. We identified 23 and 14 differentially expressed miRNAs in salivary glands, and midgut tissues infected with E. chaffeensis, respectively. Three differentially expressed miRNAs (miR-87, miR-750, and miR-275) were further characterized to determine their roles in pathogen infection. Inhibition of target miRNAs significantly decreased the E. chaffeensis load in tick tissues, which warrants more in-depth mechanistic studies.

Conclusions

The current study identified known and novel miRNAs and suggests that interfering with these miRNAs may impact the vectorial capacity of ticks to harbor Ehrlichia. This study identified several new miRNAs for future analysis of their functions in tick biology and tick-pathogen interaction studies.

Insights into the microRNA landscape of Rhodnius prolixus, a vector of Chagas disease

The growing interest in microRNAs (miRNAs) over recent years has led to their characterization in numerous organisms. However, there is currently a lack of data available on miRNAs from triatomine bugs (Reduviidae: Triatominae), which are the vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. A comprehensive understanding of the molecular biology of vectors provides new insights into insect-host interactions and insect control approaches, which are key methods to prevent disease incidence in endemic areas. In this work, we describe the miRNome profiles from gut, hemolymph, and salivary gland tissues of the Rhodnius prolixus triatomine. Small RNA sequencing data revealed abundant expression of miRNAs, along with tRNA- and rRNA-derived fragments. Fifty-two mature miRNAs, previously reported in Ecdysozoa, were identified, including 39 ubiquitously expressed in the three tissues. Additionally, 112, 73, and 78 novel miRNAs were predicted in the gut, hemolymph, and salivary glands, respectively. In silico prediction showed that the top eight most highly expressed miRNAs from salivary glands potentially target human blood-expressed genes, suggesting that R. prolixus may modulate the host's gene expression at the bite site. This study provides the first characterization of miRNAs in a Triatominae species, shedding light on the role of these crucial regulatory molecules.

The Host Non-Coding RNA Response to Alphavirus Infection

Alphaviruses are important human and animal pathogens that can cause a range of debilitating symptoms and are found worldwide. These include arthralgic diseases caused by Old-World viruses and encephalitis induced by infection with New-World alphaviruses. Non-coding RNAs do not encode for proteins, but can modulate cellular response pathways in a myriad of ways. There are several classes of non-coding RNAs, some more well-studied than others. Much research has focused on the mRNA response to infection against alphaviruses, but analysis of non-coding RNA responses has been more limited until recently. This review covers what is known regarding host cell non-coding RNA responses in alphavirus infections and highlights gaps in the knowledge that future research should address.

Identification and profiling of stable microRNAs in hemolymph of young and old Locusta migratoria fifth instars

Since the discovery of the first microRNA (miRNA) in the nematode Caenorhabditis elegans, numerous novel miRNAs have been identified which can regulate presumably every biological process in a wide range of metazoan species. In accordance, several insect miRNAs have been identified and functionally characterized. While regulatory RNA pathways are traditionally described at an intracellular level, studies reporting on the presence and potential role of extracellular (small) sRNAs have been emerging in the last decade, mainly in mammalian systems. Interestingly, evidence in several species indicates the functional transfer of extracellular RNAs between donor and recipient cells, illustrating RNA-based intercellular communication. In insects, however, reports on extracellular small RNAs are emerging but the number of detailed studies is still very limited. Here, we demonstrate the presence of stable sRNAs in the hemolymph of the migratory locust, Locusta migratoria. Moreover, the levels of several extracellular miRNAs (ex-miRNAs) present in locust hemolymph differed significantly between young and old fifth nymphal instars. In addition, we performed a 'proof of principle' experiment which suggested that extracellularly delivered miRNA molecules are capable of affecting the locusts' development.

MicroRNAs and other small RNAs in Aedes aegypti saliva and salivary glands following chikungunya virus infection

Mosquito saliva facilitates blood feeding through the anti-haemostatic, anti-inflammatory and immunomodulatory properties of its proteins. However, the potential contribution of non-coding RNAs to host manipulation is still poorly understood. We analysed small RNAs from Aedes aegypti saliva and salivary glands and show here that chikungunya virus-infection triggers both the siRNA and piRNA antiviral pathways with limited effects on miRNA expression profiles. Saliva appears enriched in specific miRNA subsets and its miRNA content is well conserved among mosquitoes and ticks, clearly pointing to a non-random sorting and occurrence. Finally, we provide evidence that miRNAs from Ae. aegypti saliva may target human immune and inflammatory pathways, as indicated by prediction analysis and searching for experimentally validated targets of identical human miRNAs. Overall, we believe these observations convincingly support a scenario where both proteins and miRNAs from mosquito saliva are injected into vertebrates during blood feeding and contribute to the complex vector-host-pathogen interactions.

A Human Skin Model for Assessing Arboviral Infections

Arboviruses such as flaviviruses and alphaviruses cause a significant human healthcare burden on a global scale. Transmission of these viruses occurs during human blood feeding at the mosquito-skin interface. Not only do pathogen immune evasion strategies influence the initial infection and replication of pathogens delivered, but arthropod salivary factors also influence transmission foci. In vitro cell cultures do not provide an adequate environment to study complex interactions between viral, mosquito, and host factors. To address this need for a whole tissue system, we describe a proof of concept model for arbovirus infection using adult human skin ex vivo with Zika virus (flavivirus) and Mayaro virus (alphavirus). Replication of these viruses in human skin was observed up to 4 days after infection. Egressed viruses could be detected in the culture media as well. Antiviral and proinflammatory genes, including chemoattractant chemokines, were expressed in infected tissue. Immunohistochemical analysis showed the presence of virus in the skin tissue 4 days after infection. This model will be useful to further investigate: (i) the immediate molecular mechanisms of arbovirus infection in human skin, and (ii) the influence of arthropod salivary molecules during initial infection of arboviruses in a more physiologically relevant system.

An Insight Into the microRNA Profile of the Ectoparasitic Mite Varroa destructor (Acari: Varroidae), the Primary Vector of Honey Bee Deformed Wing Virus

The remarkably adaptive mite Varroa destructor is the most important honey bee ectoparasite. Varroa mites are competent vectors of deformed wing virus (DWV), and the Varroa-virus complex is a major determinant of annual honey bee colony mortality and collapse. MicroRNAs (miRNAs) are 22-24 nucleotide non-coding RNAs produced by all plants and animals and some viruses that influence biological processes through post-transcriptional regulation of gene expression. Knowledge of miRNAs and their function in mite biology remains limited. Here we constructed small RNA libraries from male and female V. destructor using Illumina's small RNA-Seq platform. A total of 101,913,208 and 91,904,732 small RNA reads (>18 nucleotides) from male and female mites were analyzed using the miRDeep2 algorithm. A conservative approach predicted 306 miRNAs, 18 of which were upregulated and 13 downregulated in female V. destructor compared with males. Quantitative real-time PCR validated the expression of selected differentially-expressed female Varroa miRNAs. This dataset provides a list of potential miRNA targets involved in regulating vital Varroa biological processes and paves the way for developing strategies to target Varroa and their viruses.

Transgenic refractory Aedes aegypti lines are resistant to multiple serotypes of dengue virus

The areas where dengue virus (DENV) is endemic have expanded rapidly, driven in part by the global spread of Aedes species, which act as disease vectors. DENV replicates in the mosquito midgut and is disseminated to the mosquito’s salivary glands for amplification. Thus, blocking virus infection or replication in the tissues of the mosquito may be a viable strategy for reducing the incidence of DENV transmission to humans. Here we used the mariner Mos1 transposase to create an Aedes aegypti line that expresses virus-specific miRNA hairpins capable of blocking DENV replication. These microRNA are driven by the blood-meal-inducible carboxypeptidase A promoter or by the polyubiquitin promoter. The transgenic mosquitoes exhibited significantly lower infection rates and viral titers for most DENV serotypes 7 days after receiving an infectious blood meal. The treatment was also effective at day 14 post infection after a second blood meal had been administered. In viral transmission assay, we found there was significantly reduced transmission in these lines. These transgenic mosquitoes were effective in silencing most of the DENV genome; such an approach may be employed to control a dengue fever epidemic.

Development of miRNA-Based Approaches to Explore the Interruption of Mosquito-Borne Disease Transmission

MicroRNA (miRNA or miR)-based approaches to interrupt the transmission of mosquito-borne diseases have been explored since 2005. A review of these studies and areas in which to proceed is needed. In this review, significant progress is reviewed at the level of individual miRNAs, and miRNA diversification and relevant confounders are described in detail. Current miRNA studies in mosquitoes include four steps, namely, identifying miRNAs, validating miRNA-pathogen interactions, exploring action mechanisms, and performing preapplication investigations. Notably, regarding the Plasmodium parasite, mosquito miRNAs generally bind to mosquito immunity- or development-related mRNAs, indirectly regulating Plasmodium infection; However, regarding arboviruses, mosquito miRNAs can bind to the viral genome, directly modifying viral replication. Thus, during explorations of miRNA-based approaches, researchers need select an ideal miRNA for investigation based on the mosquito species, tissue, and mosquito-borne pathogen of interest. Additionally, strategies for miRNA-based approaches differ for arboviruses and protozoan parasites.

RNAs on the Go: Extracellular Transfer in Insects with Promising Prospects for Pest Management

RNA-mediated pathways form an important regulatory layer of myriad biological processes. In the last decade, the potential of RNA molecules to contribute to the control of agricultural pests has not been disregarded, specifically via the RNA interference (RNAi) mechanism. In fact, several proofs-of-concept have been made in this scope. Furthermore, a novel research field regarding extracellular RNAs and RNA-based intercellular/interorganismal communication is booming. In this article, we review key discoveries concerning extracellular RNAs in insects, insect RNA-based cell-to-cell communication, and plant-insect transfer of RNA. In addition, we overview the molecular mechanisms implicated in this form of communication and discuss future biotechnological prospects, namely from the insect pest-control perspective.

Mosquito antiviral immune pathways

Mosquitoes are vectors of a large number of viral pathogens. In recent years, increased urbanization and climate change has expanded the range of many vector mosquitoes. The lack of effective medical interventions has made the control of mosquito-borne viral diseases very difficult. Understanding the interactions between the mosquito immune system and viruses is critical if we are to develop effective control strategies against these diseases. Mosquitoes harbor multiple conserved immune pathways that curb invading viral pathogens. Despite the conservation of these pathways, the activation and intensity of the mosquito immune response varies with the mosquito species, tissue, and the infecting virus. This article reviews major conserved antiviral immune pathways in vector mosquitoes, their interactions with invading viral pathogens, and how these interactions restrict or promote infection of these medically important viruses.

miRNA profile of extracellular vesicles isolated from saliva of Haemaphysalis longicornis tick

Extracellular vesicles (EVs) play a key role in host-parasite interactions. Previous studies have shown that parasites can release microRNA (miRNA) containing EVs, which can transfer their contents to host cells and regulate gene expression in recipient cells. However, a little is known about the secretion of EVs by the ticks. This study was therefore, carried out to examine the saliva of ticks for the presence of miRNA containing EVs. Vesicles were purified from saliva of partially engorged Haemaphysalis longicornis ticks. Transmission electron microscopy (TEM) was carried out to confirm that vesicles within saliva were EVs based on size and morphology. Total RNA was extracted from EVs and was analyzed by deep sequencing to determine miRNA profile. TEM analysis confirmed the presence of extracellular vesicle-like structures within tick saliva. RNA-seq analysis showed that tick-derived EVs contained small non-coding RNA populations including miRNAs. The analysis of tick-derived EVs identified 36 known miRNAs, 34 novel miRNAs and 842 novel Piwi-interacting RNAs (piRNA). The results of this study provide evidence that EVs containing miRNAs can be secreted by the ticks and suggest that vesicles could transfer these miRNAs to modulate host cell functions.

Role of MicroRNAs in Bone Pathology during Chikungunya Virus Infection

Chikungunya virus (CHIKV) is an alphavirus, transmitted by mosquitoes, which causes Chikungunya fever with symptoms of fever, rash, headache, and joint pain. In about 30%-40% of cases, the infection leads to polyarthritis and polyarthralgia. Presently, there are no treatment strategies or vaccine for Chikungunya fever. Moreover, the mechanism of CHIKV induced bone pathology is not fully understood. The modulation of host machinery is known to be essential in establishing viral pathogenesis. MicroRNAs (miRNAs) are small non-coding RNAs that regulate major cellular functions by modulating gene expression. Fascinatingly, recent reports have indicated the role of miRNAs in regulating bone homeostasis and altered expression of miRNAs in bone-related pathological diseases. In this review, we summarize the altered expression of miRNAs during CHIKV pathogenesis and the possible role of miRNAs during bone homeostasis in the context of CHIKV infection. A holistic understanding of the different signaling pathways targeted by miRNAs during bone remodeling and during CHIKV-induced bone pathology may lead to identification of useful biomarkers or therapeutics.

The Vector - Host - Pathogen Interface: The Next Frontier in the Battle Against Mosquito-Borne Viral Diseases?

An unprecedented spread of mosquito-borne viruses and increasing populations of mosquito vectors has led to an increase in the frequency of mosquito-borne virus disease outbreaks. Recent outbreaks of Zika virus (ZIKV) and yellow fever virus (YFV), among others have led to a concerted effort to understand the biology of mosquito-borne viruses and their interaction with their vector mosquito and vertebrate hosts. Recent studies have aimed to understand the vector-host-pathogen interface and how it influences infection, tropism and disease severity in the vertebrate host. The initial replication of the pathogen at the skin bite site is crucial in determining the progression of the infection in the vertebrate host. Delineating the role of the commensal microbes in the mosquito saliva as well as how they interact with the vertebrate host keratinocytes will improve our understanding of disease immunopathology and may lead to new therapeutics.

Aedes Mosquito Salivary Components and Their Effect on the Immune Response to Arboviruses

Vector-borne diseases are responsible for over a billion infections each year and nearly one million deaths. Mosquito-borne dengue virus, West Nile, Japanese encephalitis, Zika, Chikungunya, and Rift Valley Fever viruses constitute major public health problems in regions with high densities of arthropod vectors. During the initial step of the transmission cycle, vector, host, and virus converge at the bite site, where local immune cells interact with the vector's saliva. Hematophagous mosquito saliva is a mixture of bioactive components known to modulate vertebrate hemostasis, immunity, and inflammation during the insect's feeding process. The capacity of mosquito saliva to modulate the host immune response has been well-studied over the last few decades and has led to the consensus that the presence of saliva is linked to the enhancement of virus transmission, host susceptibility, disease progression, viremia levels, and mortality. We review some of the major aspects of the interactions between mosquito saliva and the host immune response that may be useful for future studies on the control of arboviruses.

Ross River Virus Provokes Differentially Expressed MicroRNA and RNA Interference Responses in Aedes aegypti Mosquitoes

Alphaviruses are globally distributed and predominately transmitted by mosquitoes. Aedes species are common vectors for the clinically important alphaviruses-Chikungunya, Sindbis, and Ross River (RRV) viruses-with Aedes aegypti also being a vector for the flaviviruses dengue, Yellow Fever, and Zika viruses. Ae. aegypti was putatively implicated in the large 1979-1980 South Pacific Islands outbreak of RRV-the leading cause of arboviral disease in Australia today. The RNA interference (RNAi) defense response in mosquitoes involves a number of small RNAs, with their kinetics induced by alphaviruses being poorly understood, particularly at the tissue level. We compared the small RNA profiles between RRV-infected and noninfected Ae. aegypti midgut and fat body tissues at 2, 6, and 12 days post-inoculation (dpi). RRV induced an incremental RNAi response, yielding short interfering and P-element-induced-wimpy-testis (PIWI)-interacting RNAs. Fourteen host microRNAs were differentially expressed due to RRV with the majority in the fat body at 2 dpi. The largely congruent pattern of microRNA regulation with previous reports for alphaviruses and divergence from those for flaviviruses suggests a degree of conservation, whereas patterns of microRNA expression unique to this study provide novel insights into the tissuespecific hostvirus attributes of Ae. aegypti responses to this previously unexplored oldworld alphavirus.

Ixodes scapularis salivary gland microRNAs are differentially expressed during Powassan virus transmission

Successful tick feeding is facilitated by an assortment of pharmacologically-active factors in tick saliva that create an immunologically privileged micro-environment in the host's skin. Through a process known as saliva-assisted transmission, bioactive tick salivary factors modulate the host environment, promoting transmission and establishment of a tick-borne pathogen. This phenomenon was previously demonstrated for Powassan virus (POWV), a North American tick-borne flavivirus that is the causative agent of a severe neuroinvasive disease in humans. Here, we sought to characterize the Ixodes scapularis salivary gland microRNAs (miRNAs) expressed during the earliest period of POWV transmission to a mammalian host. POWV-infected and uninfected I. scapularis females were fed on naïve mice for 1, 3, and 6 hours, and Illumina next generation sequencing was used to characterize the salivary gland miRNA expression profiles of POWV-infected versus uninfected ticks. 379 salivary miRNAs were detected, of which 338 are reported here as putative novel I. scapularis miRNAs. 35 salivary gland miRNAs were significantly up-regulated and 17 miRNAs were significantly down-regulated in response to POWV infection. To investigate the potential role of salivary gland miRNAs in POWV replication in-vitro, we transfected miRNA inhibitors into VeroE6 cells to profile temporal POWV replication in mammalian cells. Together, the small RNA sequencing data and the in vitro miRNA inhibition assay suggest that the differentially expressed tick salivary miRNAs could act in regulating POWV replication in host tissues.

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.

Arboviruses and the Challenge to Establish Systemic and Persistent Infections in Competent Mosquito Vectors: The Interaction With the RNAi Mechanism

Arboviruses are capable to establish long-term persistent infections in mosquitoes that do not affect significantly the physiology of the insect vectors. Arbovirus infections are controlled by the RNAi machinery via the production of viral siRNAs and the formation of RISC complexes targeting viral genomes and mRNAs. Engineered arboviruses that contain cellular gene sequences can therefore be transformed to "viral silencing vectors" for studies of gene function in reverse genetics approaches. More specifically, "ideal" viral silencing vectors must be competent to induce robust RNAi effects while other interactions with the host immune system should be kept at a minimum to reduce non-specific effects. Because of their inconspicuous nature, arboviruses may approach the "ideal" viral silencing vectors in insects and it is therefore worthwhile to study the mechanisms by which the interactions with the RNAi machinery occur. In this review, an analysis is presented of the antiviral RNAi response in mosquito vectors with respect to the major types of arboviruses (alphaviruses, flaviviruses, bunyaviruses, and others). With respect to antiviral defense, the exo-RNAi pathway constitutes the major mechanism while the contribution of both miRNAs and viral piRNAs remains a contentious issue. However, additional mechanisms exist in mosquitoes that are capable to enhance or restrict the efficiency of viral silencing vectors such as the amplification of RNAi effects by DNA forms, the existence of incorporated viral elements in the genome and the induction of a non-specific systemic response by Dicer-2. Of significance is the observation that no major "viral suppressors of RNAi" (VSRs) seem to be encoded by arboviral genomes, indicating that relatively tight control of the activity of the RNA-dependent RNA polymerase (RdRp) may be sufficient to maintain the persistent character of arbovirus infections. Major strategies for improvement of viral silencing vectors therefore are proposed to involve engineering of VSRs and modifying of the properties of the RdRp. Because of safety issues (pathogen status), however, arbovirus-based silencing vectors are not well suited for practical applications, such as RNAi-based mosquito control. In that case, related mosquito-specific viruses that also establish persistent infections and may cause similar RNAi responses may represent a valuable alternative solution.

Assessing the Potential Interactions between Cellular miRNA and Arboviral Genomic RNA in the Yellow Fever Mosquito, Aedes aegypti

Although the role of exogenous small interfering RNA (siRNA) and P-element induced wimpy testis (PIWI)-interacting RNA (piRNA) pathways in mosquito antiviral immunity is increasingly better understood, there is still little knowledge regarding the role of mosquito cellular microRNA (miRNA). Identifying direct interactions between the mosquito miRNAs and the RNA genome of arboviruses and choosing the relevant miRNA candidates to explore resulting antiviral mechanisms are critical. Here, we carried out genomic analyses to identify Aedes aegypti miRNAs that potentially interact with various lineages and genotypes of chikungunya, dengue, and Zika viruses. By using prediction tools with distinct algorithms, several miRNA binding sites were commonly found within different genotypes/and or lineages of each arbovirus. We further analyzed those miRNAs that could target more than one arbovirus, required a low energy threshold to form miRNA-viralRNA (vRNA) complexes, and predicted potential RNA structures using RNAhybrid software. We predicted miRNA candidates that might participate in regulating arboviral replication in Ae. aegypti. Even without any experimental validation, which should be done as a next step, this study can shed further light on the role of miRNA in mosquito innate immunity and targets for future studies.

Expanding the canon: Non-classical mosquito genes at the interface of arboviral infection

Mosquito transmitted viruses cause significant morbidity and mortality in human populations. Despite the use of insecticides and other measures of vector control, arboviral diseases are on the rise. One potential solution for limiting disease transmission to humans is to render mosquitoes refractory to viral infection through genetic modification. Substantial research effort in Drosophila, Aedes and Anopheles has helped to define the major innate immune pathways, including Toll, IMD, Jak/Stat and RNAi, however we still have an incomplete picture of the mosquito antiviral response. Transcriptional profiles of virus-infected insects reveal a much wider range of pathways activated by the process of infection. Within these lists of genes are unexplored mosquito candidates of viral defense. Wolbachia species are endosymbiotic bacteria that naturally limit arboviral infection in mosquitoes. Our understanding of the Wolbachia-mediated viral blocking mechanism is poor, but it does not appear to operate via the classical immune pathways. Herein, we reviewed the transcriptomic response of mosquitoes to multiple viral species and put forth consensus gene types/families outside the immune canon whose expression responds to infection, including cytoskeleton and cellular trafficking, the heat shock response, cytochromes P450, cell proliferation, chitin and small RNAs. We then examine emerging evidence for their functional role in viral resistance in diverse insect and mammalian hosts and their potential role in Wolbachia-mediated viral blocking. These candidate gene families offer novel avenues for research into the nature of insect viral defense.

Aedes-Chikungunya Virus Interaction: Key Role of Vector Midguts Microbiota and Its Saliva in the Host Infection

Aedes mosquitoes are important vectors for emerging diseases caused by arboviruses, such as chikungunya (CHIKV). These viruses’ main transmitting species are Aedes aegypti and Ae. albopictus, which are present in tropical and temperate climatic areas all over the globe. Knowledge of vector characteristics is fundamentally important to the understanding of virus transmission. Only female mosquitoes are able to transmit CHIKV to the vertebrate host since they are hematophagous. In addition, mosquito microbiota is fundamentally important to virus infection in the mosquito. Microorganisms are able to modulate viral transmission in the mosquito, such as bacteria of the Wolbachia genus, which are capable of preventing viral infection, or protozoans of the Ascogregarina species, which are capable of facilitating virus transmission between mosquitoes and larvae. The competence of the mosquito is also important in the transmission of the virus to the vertebrate host, since their saliva has several substances with biological effects, such as immunomodulators and anticoagulants, which are able to modulate the host’s response to the virus, interfering in its pathogenicity and virulence. Understanding the Aedes vector-chikungunya interaction is fundamentally important since it can enable the search for new methods of combating the virus’ transmission.

Over expression of bmo-miR-2819 suppresses BmNPV replication by regulating the BmNPV ie-1 gene in Bombyx mori

Bombyx mori nucleopolyhedrovirus (BmNPV) is a major pathogen that threatens the growth and sustainability of the sericulture industry. Accumulating studies in recent years suggest that insect viruses infection can change the host microRNAs (miRNAs) expression profile and both cellular and viral miRNAs play roles in host-pathogen interactions. Until now, the functional analysis of miRNA encoded by silkworm for host-virus interaction is limited. In this study, we validate the down-regulation of bmo-miR-2819 upon BmNPV infection by qRT-PCR and confirm the BmNPV immediately early 1 gene, ie-1 is one of the targets for bmo-miR-2819 based on the results of dual luciferase report assay. Overexpression of bmo-miR-2819 can significantly decline the abundance of IE-1 protein level in BmNPV-infected silkworm larvae. Further, the expression level of polyhedrin gene and VP39 protein of BmNPV in the infected larvae after applying bmo-miR-2819 mimics was significantly decreased comparing with that of larvae with mimic control. Our results suggest that overexpression of bmo-miR-2819 could suppress BmNPV replication by down-regulating the expression of BmNPV ie-1 gene, which demonstrate that cellular miRNAs could affect virus infection by regulating the expression of virus genes.

MicroRNAs from saliva of anopheline mosquitoes mimic human endogenous miRNAs and may contribute to vector-host-pathogen interactions

During blood feeding haematophagous arthropods inject into their hosts a cocktail of salivary proteins whose main role is to counteract host haemostasis, inflammation and immunity. However, animal body fluids are known to also carry miRNAs. To get insights into saliva and salivary gland miRNA repertoires of the African malaria vector Anopheles coluzzii we used small RNA-Seq and identified 214 miRNAs, including tissue-enriched, sex-biased and putative novel anopheline miRNAs. Noteworthy, miRNAs were asymmetrically distributed between saliva and salivary glands, suggesting that selected miRNAs may be preferentially directed toward mosquito saliva. The evolutionary conservation of a subset of saliva miRNAs in Anopheles and Aedes mosquitoes, and in the tick Ixodes ricinus, supports the idea of a non-random occurrence pointing to their possible physiological role in blood feeding by arthropods. Strikingly, eleven of the most abundant An. coluzzi saliva miRNAs mimicked human miRNAs. Prediction analysis and search for experimentally validated targets indicated that miRNAs from An. coluzzii saliva may act on host mRNAs involved in immune and inflammatory responses. Overall, this study raises the intriguing hypothesis that miRNAs injected into vertebrates with vector saliva may contribute to host manipulation with possible implication for vector-host interaction and pathogen transmission.

Emerging role of circulating microRNA in the diagnosis of human infectious diseases

The endogenic microRNAs (miRNA) are evolutionary, conserved, and belong to a group of small noncoding RNAs with a stretch of 19-24 nucleotides. The miRNAs play an indispensable role in gene modulation at the posttranscriptional level, inclusive of stem-cell differentiation, embryogenesis, hematopoiesis, metabolism, immune responses, or infections. The miRNAs secreted from the cells and their presence in the biological fluids signifies the regulatory role of circulating miRNAs in the pathogenesis. The phenomenal expression levels of circulating miRNAs in serum or plasma during infection makes them the potential therapeutic biomarkers for the diagnosis of assorted human infectious diseases. In this article, we have accentuated the methods for the profiling of circulating miRNA as well as the importance of miRNA as biomarkers for the diagnosis of human infectious diseases. To date, numerous biomarkers have been identified for the diagnostic or prognostic purpose; for instance, miR-182, miR-486, and miR15a in sepsis; miR-320 and miR505 in inflammatory bowel disease; miR-155 and miR-1260 in influenza; miR-12, miRVP-3p, and miR-184 in arboviruses; and miR-29b and miR-125 in hepatitis infection. Nevertheless, the noninvasive diagnostic approach, with the aid of biomarkers, currently plays a decisive role in the untimely diagnosis of human infections. So, in the near future, the exploitation of circulating miRNAs as therapeutic biomarkers for the diagnosis of human infections will help us to cure the associated diseases promptly and effectively.

Time to Micromanage the Pathogen-Host-Vector Interface: Considerations for Vaccine Development

The current increase in vector-borne disease worldwide necessitates novel approaches to vaccine development targeted to pathogens delivered by blood-feeding arthropod vectors into the host skin. A concept that is gaining traction in recent years is the contribution of the vector or vector-derived components, like salivary proteins, to host-pathogen interactions. Indeed, the triad of vector-host-pathogen interactions in the skin microenvironment can influence host innate and adaptive responses alike, providing an advantage to the pathogen to establish infection. A better understanding of this "bite site" microenvironment, along with how host and vector local microbiomes immunomodulate responses to pathogens, is required for future vaccines for vector-borne diseases. Microneedle administration of such vaccines may more closely mimic vector deposition of pathogen and saliva into the skin with the added benefit of near painless vaccine delivery. Focusing on the 'micro'⁻from microenvironments to microbiomes to microneedles⁻may yield an improved generation of vector-borne disease vaccines in today's increasingly complex world.

Saliva of hematophagous insects: a multifaceted toolkit

Transcriptomic, proteomic and genomic studies significantly improved our understanding of the complexity of blood feeding insect saliva providing unparalleled evolutionary insights. Salivary genes appeared to be under strong selective pressure with gene duplication and functional diversification being a powerful driver in the evolution of novel salivary genes/functions. The first insect salivary proteins responsible for complement inhibition were identified and a widespread mechanism of action shared by unrelated salivary protein families was recognized and named kratagonism. microRNAs were for the first time described in the saliva of a few blood feeding arthropods raising intriguing questions on their possible contribution to vertebrate host manipulation and pathogen transmission and further emphasizing how much we still have to learn on blood feeding insect saliva.

Expression Profile of Glossina pallidipes MicroRNAs During Symptomatic and Asymptomatic Infection With Glossina pallidipes Salivary Gland Hypertrophy Virus (Hytrosavirus)

The Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) infects tsetse flies predominantly asymptomatically and occasionally symptomatically. Symptomatic infections are characterized by overt salivary gland hypertrophy (SGH) in mass reared tsetse flies, which causes reproductive dysfunctions and colony collapse, thus hindering tsetse control via sterile insect technique (SIT). Asymptomatic infections have no apparent cost to the fly's fitness. Here, small RNAs were sequenced and profiles in asymptomatically and symptomatically infected G. pallidipes flies determined. Thirty-eight host-encoded microRNAs (miRNAs) were present in both the asymptomatic and symptomatic fly profiles, while nine host miRNAs were expressed specifically in asymptomatic flies versus 10 in symptomatic flies. Of the shared 38 miRNAs, 15 were differentially expressed when comparing asymptomatic with symptomatic flies. The most up-regulated host miRNAs in symptomatic flies was predicted to target immune-related mRNAs of the host. Six GpSGHV-encoded miRNAs were identified, of which five of them were only in symptomatic flies. These virus-encoded miRNAs may not only target host immune genes but may also participate in viral immune evasion. This evidence of differential host miRNA profile in Glossina in symptomatic flies advances our understanding of the GpSGHV-Glossina interactions and provides potential new avenues, for instance by utilization of particular miRNA inhibitors or mimics to better manage GpSGHV infections in tsetse mass-rearing facilities, a prerequisite for successful SIT implementation.

miRNAs in Insects Infected by Animal and Plant Viruses

Viruses vectored by insects cause severe medical and agricultural burdens. The process of virus infection of insects regulates and is regulated by a complex interplay of biomolecules including the small, non-coding microRNAs (miRNAs). Considered an anomaly upon its discovery only around 25 years ago, miRNAs as a class have challenged the molecular central dogma which essentially typifies RNAs as just intermediaries in the flow of information from DNA to protein. miRNAs are now known to be common modulators or fine-tuners of gene expression. While recent years has seen an increased emphasis on understanding the role of miRNAs in host-virus associations, existing literature on the interaction between insects and their arthropod-borne viruses (arboviruses) is largely restricted to miRNA abundance profiling. Here we analyse the commonalities and contrasts between miRNA abundance profiles with different host-arbovirus combinations and outline a suggested pipeline and criteria for functional analysis of the contribution of miRNAs to the insect vector-virus interaction. Finally, we discuss the potential use of the model organism, Drosophila melanogaster, in complementing research on the role of miRNAs in insect vector-virus interaction.

Diverse Host and Restriction Factors Regulate Mosquito-Pathogen Interactions

Mosquitoes transmit diseases that seriously impact global human health. Despite extensive knowledge of the life cycles of mosquito-borne parasites and viruses within their hosts, control strategies have proven insufficient to halt their spread. An understanding of the relationships established between such pathogens and the host tissues they inhabit is therefore paramount for the development of new strategies that specifically target these interactions, to prevent the pathogens' maturation and transmission. Here we present an updated account of the antagonists and host factors that affect the development of Plasmodium, the parasite causing malaria, and mosquito-borne viruses, such as dengue virus and Zika virus, within their mosquito vectors, and we discuss the similarities and differences between Plasmodium and viral systems, looking toward the elucidation of new targets for disease control.

microRNA profiles and functions in mosquitoes

Mosquitoes are incriminated as vectors for many crippling diseases, including malaria, West Nile fever, Dengue fever, and other neglected tropical diseases (NTDs). microRNAs (miRNAs) can interact with multiple target genes to elicit biological functions in the mosquitoes. However, characterization and function of individual miRNAs and their potential targets have not been fully determined to date. We conducted a systematic review of published literature following PRISMA guidelines. We summarize the information about miRNAs in mosquitoes to better understand their metabolism, development, and responses to microorganisms. Depending on the study, we found that miRNAs were dysregulated in a species-, sex-, stage-, and tissue/organ-specific manner. Aberrant miRNA expressions were observed in development, metabolism, host-pathogen interactions, and insecticide resistance. Of note, many miRNAs were down-regulated upon pathogen infection. The experimental studies have expanded the identification of miRNA target from the 3' untranslated regions (UTRs) of mRNAs of mosquitoes to the 5' UTRs of mRNAs of the virus. In addition, we discuss current trends in mosquito miRNA research and offer suggestions for future studies.

Aedes aegypti microRNA miR-2b regulates ubiquitin-related modifier to control chikungunya virus replication

Arboviruses that replicate in mosquitoes activate innate immune response within mosquitoes. Regulatory non-coding microRNAs (miRNA) are known to be modulated in mosquitoes during chikungunya infection. However, information about targets of these miRNAs is scant. The present study was aimed to identify and analyze targets of miRNAs that are regulated during chikungunya virus (CHIKV) replication in Aedes aegypti cells and in the mosquito. Employing next-generation sequencing technologies, we identified a total of 126 miRNAs from the Ae. aegypti cell line Aag2. Of these, 13 miRNAs were found to be regulated during CHIKV infection. Putative targets of three of the most significantly regulated miRNAs- miR-100, miR-2b and miR-989 were also analyzed using quantitative PCRs, in cell lines and in mosquitoes, to validate whether they were the targets of the miRNAs. Our study expanded the list of miRNAs known in Ae. aegypti and predicted targets for the significantly regulated miRNAs. Further analysis of some of these targets revealed that ubiquitin-related modifier is a target of miRNA miR-2b and plays a significant role in chikungunya replication.

Chikungunya vaccines in development

Chikungunya virus has become a global health threat, spreading to the industrial world of Europe and the Americas; no treatment or prophylactic vaccine is available. Since the late 1960s much effort has been put into the development of a vaccine, and several heterogeneous strategies have already been explored. Only two candidates have recently qualified to enter clinical phase II trials, a chikungunya virus-like particle-based vaccine and a recombinant live attenuated measles virus-vectored vaccine.

This review focuses on the current status of vaccine development against chikungunya virus in humans and discusses the diversity of immunization strategies, results of recent human trials and promising vaccine candidates.

Understanding the role of microRNAs in the interaction of Aedes aegypti mosquitoes with an insect-specific flavivirus

The Flavivirus genus contains some of the most prevalent vector-borne viruses, such as the dengue, Zika and yellow fever viruses that cause devastating diseases in humans. However, the insect-specific clade of flaviviruses is restricted to mosquito hosts, albeit they have retained the general features of the genus, such as genome structure and replication. The interactions between insect-specific flaviviruses (ISFs) and their mosquito hosts are largely unknown. Pathogenic flaviviruses are known to modulate host-derived microRNAs (miRNAs), a class of non-coding RNAs that are important in controlling gene expression. Alterations in miRNAs may represent changes in host gene expression and promote understanding of virus-host interactions. The role of miRNAs in ISF-mosquito interactions is largely unknown. A recently discovered Australian ISF, Palm Creek virus (PCV), has the ability to suppress medically relevant flaviviruses. Here, we investigated the potential involvement of miRNAs in PCV infection using the model mosquito Aedes aegypti. By combining small-RNA sequencing and bioinformatics analysis, differentially expressed miRNAs were determined. Our results indicated that PCV infection hardly affects host miRNAs. Out of 101 reported miRNAs of Ae. aegypti, only aae-miR-2940-5p had a significantly altered expression over the course of infection. However, further analysis of aae-miR-2940-5p revealed that this miRNA does not have any direct impact on PCV replication in vitro. Thus, overall the results suggest that PCV infection has a limited effect on the mosquito miRNA profile and therefore miRNAs may not play a significant role in the PCV-Ae. aegypti interaction.

The role of miR-2∼13∼71 cluster in resistance to deltamethrin in Culex pipiens pallens

Excessive and continuous application of deltamethrin has resulted in the development of deltamethrin resistance among mosquitoes, which becomes a major obstacle for mosquito control. In a previous study, differentially expressed miRNAs between deltamethrin-susceptible (DS) strain and deltamethrin-resistant (DR) strain using illumina sequencing in Culex pipiens pallens were identified. In this study, we applied RNAi and the Centers for Disease Control and Prevention (CDC) bottle bioassay to investigate the relationship between miR-2∼13∼71 cluster (miR-2, miR-13 and miR-71) and deltamethrin resistance. We used quantitative real-time PCR (qRT-PCR) to measure expression levels of miR-2∼13∼71 clusters. MiR-2∼13∼71 cluster was down regulated in adult female mosquitoes from the DR strain and played important roles in deltamethrin resistance through regulating target genes, CYP9J35 and CYP325BG3. Knocking down CYP9J35 and CYP325BG3 resulted in decreased mortality of DR mosquitoes. This study provides the first evidence that miRNA clusters are associated with deltamethrin resistance in mosquitoes. Moreover, we investigated the regulatory networks formed between miR-2∼13∼71 cluster and its target genes, which provide a better understanding of the mechanism involved in deltamethrin resistance.

Chikungunya virus: an update on the biology and pathogenesis of this emerging pathogen

Re-emergence of chikungunya virus, a mosquito-transmitted pathogen, is of serious public health concern. In the past 15 years, after decades of infrequent, sporadic outbreaks, the virus has caused major epidemic outbreaks in Africa, Asia, the Indian Ocean, and more recently the Caribbean and the Americas. Chikungunya virus is mainly transmitted by Aedes aegypti mosquitoes in tropical and subtropical regions, but the potential exists for further spread because of genetic adaptation of the virus to Aedes albopictus, a species that thrives in temperate regions. Chikungunya virus represents a substantial health burden to affected populations, with symptoms that include severe joint and muscle pain, rashes, and fever, as well as prolonged periods of disability in some patients. The inflammatory response coincides with raised levels of immune mediators and infiltration of immune cells into infected joints and surrounding tissues. Animal models have provided insights into disease pathology and immune responses. Although host innate and adaptive responses have a role in viral clearance and protection, they can also contribute to virus-induced immune pathology. Understanding the mechanisms of host immune responses is essential for the development of treatments and vaccines. Inhibitory compounds targeting key inflammatory pathways, as well as attenuated virus vaccines, have shown some success in animal models, including an attenuated vaccine strain based on an isolate from La Reunion incorporating an internal ribosome entry sequence that prevents the virus from infecting mosquitoes and a vaccine based on virus-like particles expressing envelope proteins. However, immune correlates of protection, as well as the safety of prophylactic and therapeutic candidates, are important to consider for their application in chikungunya infections. In this Review, we provide an update on chikungunya virus with regard to its epidemiology, molecular virology, virus-host interactions, immunological responses, animal models, and potential antiviral therapies and vaccines.

Mosquito-specific microRNA-1890 targets the juvenile hormone-regulated serine protease JHA15 in the female mosquito gut

Females of the hematophagous mosquito species require a vertebrate blood meal to supply amino acids and other nutrients necessary for egg development, serving as the driving force for the spread of many vector-borne diseases in humans. Blood digestion utilizes both early and late phase serine proteases (SPs) that are differentially regulated at the transcriptional and post-transcriptional level. To uncover the regulatory complexity of SPs in the female mosquito midgut, we investigated involvement of miRNAs in regulating the juvenile hormone (JH)-controlled chymotrypsin-like SP, JHA15. We identified regulatory regions complementary to the mosquito-specific miRNA, miR-1890, within the 3' UTR of JHA15 mRNA. The level of the JHA15 transcript is highest post eclosion and drastically declines post blood meal (PBM), exhibiting an opposite trend to miR-1890 that peaks at 24 h PBM. Depletion of miR-1890 results in defects in blood digestion, ovary development and egg deposition. JHA15 mRNA and protein levels are elevated in female mosquitoes with miR-1890 inhibition. JHA15 RNA interference in the miR-1890 depletion background alleviates miR-1890 depletion phenotypes. The miR-1890 gene is activated by the 20-hydroxyecdysone pathway that involves the ecdysone receptor and the early genes, E74B and Broad Z2. Our study suggests that miR-1890 controls JHA15 mRNA stability in a stage- and tissue- specific manner.

Differential expression of microRNAs in plasma of patients with prediabetes and newly diagnosed type 2 diabetes

AIMS

MicroRNAs (miRNAs) are present in plasma and have emerged as critical regulators of gene expression at posttranscriptional level, and thus are involved in various human diseases, including diabetes. The objective of this study was to screen and validate differentially expressed plasma miRNAs in prediabetes and newly diagnosed type 2 diabetes (T2D).

METHODS

In this study, we screened differentially expressed plasma miRNAs in prediabetes and newly diagnosed T2D by miRNA microarray analysis, and validated the expression of candidate miRNAs using quantitative reverse transcription polymerase chain reaction assays. Furthermore, we performed gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analyses to disclose functional enrichment of genes predicted to be regulated by the differentially expressed miRNAs.

RESULTS

Notably, our results revealed that hsa-miR-1249, hsa-miR-320b, and hsa-miR-572 (P < 0.05) were differentially expressed among the three groups, which yielded an area under the receiver operator characteristics curve (AUC) of 0.784 [95 % confidence interval (CI) 0.685-0.883], 0.946 (95 % CI 0.906-0.985), and 0.843 (95 % CI 0.766-0.920) discriminating T2D patients from NGT control groups, respectively, while the AUC was 0.887 (95 % CI 0.818-0.957), 0.635 (95 % CI 0.525-0.744), and 0.69 (95 % CI 0.580-0.793) discriminating prediabetes patients from NGT control groups, respectively. In addition, GO and KEGG pathway analyses showed that genes predicted to be regulated by differentially expressed miRNAs were significantly enriched in several related biological processes and pathways, including the development of multicellular organisms, signal transduction, cell differentiation, apoptosis, cell metabolism, ion transport regulation, and other biological functions.

CONCLUSIONS

Taken together, our results showed differentially expressed miRNAs in T2D and prediabetes. Plasma hsa-miR-1249, hsa-miR-320b, and hsa-miR-572 may serve as novel biomarkers for diagnosis and potential targets for the treatment for prediabetes and T2D.

Small RNAs from Bemisia tabaci Are Transferred to Solanum lycopersicum Phloem during Feeding

The phloem-feeding whitefly Bemisia tabaci is a serious pest to a broad range of host plants, including many economically important crops such as tomato. These insects serve as a vector for various devastating plant viruses. It is known that whiteflies are capable of manipulating host-defense responses, potentially mediated by effector molecules in the whitefly saliva. We hypothesized that, beside putative effector proteins, small RNAs (sRNA) are delivered by B. tabaci into the phloem, where they may play a role in manipulating host plant defenses. There is already evidence to suggest that sRNAs can mediate the host-pathogen dialogue. It has been shown that Botrytis cinerea, the causal agent of gray mold disease, takes advantage of the plant sRNA machinery to selectively silence host genes involved in defense signaling. Here we identified sRNAs originating from B. tabaci in the phloem of tomato plants on which they are feeding. sRNAs were isolated and sequenced from tomato phloem of whitefly-infested and control plants as well as from the nymphs themselves, control leaflets, and from the infested leaflets. Using stem-loop RT-PCR, three whitefly sRNAs have been verified to be present in whitefly-infested leaflets that were also present in the whitefly-infested phloem sample. Our results show that whitefly sRNAs are indeed present in tomato tissues upon feeding, and they appear to be mobile in the phloem. Their role in the host-insect interaction can now be investigated.

Regulation of physiological processes by microRNAs in insects

MicroRNAs (miRNAs) are small non-coding RNAs that function in gene regulatory processes in plants and animals by targeting sites within messenger RNA. In insects, miRNAs have been shown to regulate a variety of physiological processes throughout insect development, including molting, metamorphosis, oogenesis, embryogenesis, behavior and host-pathogen interactions. The roles of miRNAs in the model organism, Drosophila melanogaster, have been studied extensively due to the conserved nature of miRNA function among highly divergent species. However, seeking to understand miRNA function in non-drosophilid insect species has become a growing trend in insect science. Here, we highlight the recent discoveries regarding miRNA function in insect physiology and development.