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In JoVE (1)
Other Publications (11)
- Insect Biochemistry and Molecular Biology
- Journal of Virology
- Virus Research
- Proceedings of the National Academy of Sciences of the United States of America
- Proceedings of the National Academy of Sciences of the United States of America
- BMC Microbiology
- Journal of Virology
- PLoS Pathogens
- BMC Genomics
- BMC Microbiology
- Journal of Medical Entomology
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Articles by Irma Sanchez-Vargas in JoVE
JoVE Immunology and Infection
Alfaviruset Transducing System: Verktyg för att visualisera Infektion i Mosquito Vektorer
Microbiology, Immunology, and Pathology, Colorado State University
Metoder för att använda alfaviruset transducing att uttrycka fluorescerande reportrar in vitro och hos vuxna myggor beskrivs. Denna teknik kan anpassas för att uttrycka något protein av intresse i stället för eller som tillägg till en reporter.
Other articles by Irma Sanchez-Vargas on PubMed
Developing Arbovirus Resistance in Mosquitoes
Diseases caused by arthropod-borne viruses are increasingly significant public health problems, and novel methods are needed to control pathogen transmission. The hypothesis underlying the research described here is that genetic manipulation of Aedes aegypti mosquitoes can profoundly and permanently reduce their competence to transmit dengue viruses to human hosts. Recent key findings now allow us to test the genetic control hypothesis. We have identified viral genome-derived RNA segments that can be expressed in mosquito midguts and salivary glands to ablate homologous virus replication and transmission. We have demonstrated that both transient and heritable expression of virus-derived effector RNAs in cultured mosquito cells can silence virus replication, and have characterized the mechanism of RNA-mediated resistance. We are now developing virus-resistant mosquito lines by transformation with transposable elements that express effector RNAs from mosquito-active promoters.
RNA Silencing of Dengue Virus Type 2 Replication in Transformed C6/36 Mosquito Cells Transcribing an Inverted-repeat RNA Derived from the Virus Genome
Double-stranded RNA (dsRNA) initiates cellular posttranscriptional responses that are collectively called RNA silencing in a number of different organisms, including plants, nematodes, and fruit flies. In plants, RNA silencing has been associated with protection from virus infection. In this study, we demonstrate that dsRNA-mediated interference also can act as a viral defense mechanism in mosquito cells. C6/36 (Aedes albopictus) cells were stably transformed with a plasmid designed to transcribe an inverted-repeat RNA (irRNA) derived from the genome of dengue virus type 2 (DEN-2) capable of forming dsRNA. Clonal cell lines were selected with an antibiotic resistance marker and challenged with DEN-2. The cell lines were classified as either susceptible or resistant to virus replication, based on the percentage of cells expressing DEN-2 envelope (E) antigen 7 days after challenge. Eight out of 18 (44%) cell lines designed to express irRNA were resistant to DEN-2 challenge, with more than 95% of the cells showing no DEN-2 antigen accumulation. One of the DEN-2-resistant cell lines, FB 9.1, was further characterized. DEN-2 genome RNA failed to accumulate in FB 9.1 cells after challenge. Northern blot hybridization detected transcripts containing transgene sequences of both sense and antisense polarity, suggesting that DEN-2-specific dsRNA was present in the cells. In addition, a class of small RNAs 21 to 25 nucleotides in length was detected that specifically hybridized to labeled sense or antisense DEN-2 RNA derived from the target region of the genome. These observations were consistent with RNA silencing as the mechanism of resistance to DEN-2 in transformed mosquito cells.
RNA Interference, Arthropod-borne Viruses, and Mosquitoes
RNA interference (RNAi) probably functions as an antiviral mechanism in most eukaryotic organisms. Variations in the activity of this antiviral pathway in mosquitoes could explain, in part, why some mosquitoes are competent vectors of medically important, arthropod-borne viruses (arboviruses) and others are not. There are three lines of evidence that show the RNAi pathway exists in Aedes species that transmit arboviruses. The first is that recombinant Sindbis viruses expressing a RNA fragment from a genetically unrelated dengue-2 virus (DENV-2) interfere with DENV-2 replication in Aedes aegypti mosquitoes by a mechanism similar to virus-induced gene silencing described in plants. The second is that transfection of C6/36 (Aedes albopictus) cells with either double-stranded RNA or synthetic small interfering RNAs derived from an arbovirus genome interferes with replication of the homologous virus. The third is that a hairpin DENV-2-specific RNA transcribed from a plasmid can generate virus-resistant C6/36 cells. We hypothesize that genetically modified mosquitoes can be generated that transcribe a flavivirus-specific dsRNA, triggering the RNAi response soon after ingestion of a blood meal. This could induce the RNAi pathway in the midgut prior to establishment of virus infection and profoundly change vector competence. Towards this goal, we are developing transgenic A. aegypti lines that are refractory to DENV by exploiting the RNAi pathway.
RNA Interference Acts As a Natural Antiviral Response to O'nyong-nyong Virus (Alphavirus; Togaviridae) Infection of Anopheles Gambiae
RNA interference (RNAi) is triggered in eukaryotic organisms by double-stranded RNA (dsRNA), and it destroys any mRNA that has sequence identity with the dsRNA trigger. The RNAi pathway in Anopheles gambiae can be silenced by transfecting cells with dsRNA derived from exon sequence of the A. gambiae Argonaute2 (AgAgo2) gene. We hypothesized that RNAi may also act as an antagonist to alphavirus replication in A. gambiae because RNA viruses form dsRNA during replication. Silencing AgAgo2 expression would make A. gambiae mosquitoes more permissive to virus infection. To determine whether RNAi conditions the vector competence of A. gambiae for O'nyong-nyong virus (ONNV), we engineered a genetically modified ONNV that expresses enhanced GFP (eGFP) as a marker. After intrathoracic injection, ONNV-eGFP slowly spread to other A. gambiae tissues over a 9-day incubation period. Mosquitoes were then coinjected with virus and either control beta-galactosidase dsRNA (dsbetagal; note that "ds" is used as a prefix to indicate the dsRNA derived from a given gene throughout) or ONNV dsnsP3. Treatment with dsnsP3 inhibited virus spread significantly, as determined by eGFP expression patterns. ONNV-eGFP titers from mosquitoes coinjected with dsnsP3 were significantly lower at 3 and 6 days after injection than in mosquitoes coinjected with dsbetagal. Mosquitoes were then coinjected with ONNV-eGFP and dsAgAgo2. Mosquitoes coinjected with virus and AgAgo2 dsRNA displayed widespread eGFP expression and virus titers 16-fold higher than dsbetagal controls after 3 or 6 days after injection. These observations provide direct evidence that RNAi is an antagonist of ONNV replication in A. gambiae, and they suggest that the innate immune response conditions vector competence.
Engineering RNA Interference-based Resistance to Dengue Virus Type 2 in Genetically Modified Aedes Aegypti
Mosquitoes (Aedes aegypti) were genetically modified to exhibit impaired vector competence for dengue type 2 viruses (DENV-2). We exploited the natural antiviral RNA interference (RNAi) pathway in the mosquito midgut by constructing an effector gene that expresses an inverted-repeat (IR) RNA derived from the premembrane protein coding region of the DENV-2 RNA genome. The A. aegypti carboxypeptidase A promoter was used to express the IR RNA in midgut epithelial cells after ingestion of a bloodmeal. The promoter and effector gene were inserted into the genome of a white-eye Puerto Rico Rexville D (Higgs' white eye) strain by using the nonautonomous mariner MosI transformation system. A transgenic family, Carb77, expressed IR RNA in the midgut after a bloodmeal. Carb77 mosquitoes ingesting an artificial bloodmeal containing DENV-2 exhibited marked reduction of viral envelope antigen in midguts and salivary glands after infection. DENV-2 titration of individual mosquitoes showed that most Carb77 mosquitoes poorly supported virus replication. Transmission in vitro of virus from the Carb77 line was significantly diminished when compared to control mosquitoes. The presence of DENV-2-derived siRNAs in RNA extracts from midguts of Carb77 and the loss of the resistance phenotype when the RNAi pathway was interrupted proved that DENV-2 resistance was caused by a RNAi response. Engineering of transgenic A. aegypti that show a high level of resistance against DENV-2 provides a powerful tool for developing population replacement strategies to control transmission of dengue viruses.
Dengue Virus Type 2: Replication and Tropisms in Orally Infected Aedes Aegypti Mosquitoes
To be transmitted by its mosquito vector, dengue virus (DENV) must infect midgut epithelial cells, replicate and disseminate into the hemocoel, and finally infect the salivary glands, which is essential for transmission. The extrinsic incubation period (EIP) is very relevant epidemiologically and is the time required from the ingestion of virus until it can be transmitted to the next vertebrate host. The EIP is conditioned by the kinetics and tropisms of virus replication in its vector. Here we document the virogenesis of DENV-2 in newly-colonized Aedes aegypti mosquitoes from Chetumal, Mexico in order to understand better the effect of vector-virus interactions on dengue transmission.
La Crosse Bunyavirus Nonstructural Protein NSs Serves to Suppress the Type I Interferon System of Mammalian Hosts
La Crosse virus (LACV) is a mosquito-transmitted member of the Bunyaviridae family that causes severe encephalitis in children. For the LACV nonstructural protein NSs, previous overexpression studies with mammalian cells had suggested two different functions, namely induction of apoptosis and inhibition of RNA interference (RNAi). Here, we demonstrate that mosquito cells persistently infected with LACV do not undergo apoptosis and mount a specific RNAi response. Recombinant viruses that either express (rLACV) or lack (rLACVdelNSs) the NSs gene similarly persisted and were prone to the RNAi-mediated resistance to superinfection. Furthermore, in mosquito cells overexpressed LACV NSs was unable to inhibit RNAi against Semliki Forest virus. In mammalian cells, however, the rLACVdelNSs mutant virus strongly activated the antiviral type I interferon (IFN) system, whereas rLACV as well as overexpressed NSs suppressed IFN induction. Consequently, rLACVdelNSs was attenuated in IFN-competent mouse embryo fibroblasts and animals but not in systems lacking the type I IFN receptor. In situ analyses of mouse brains demonstrated that wild-type and mutant LACV mainly infect neuronal cells and that NSs is able to suppress IFN induction in the central nervous system. Thus, our data suggest little relevance of the NSs-induced apoptosis or RNAi inhibition for growth or pathogenesis of LACV in the mammalian host and indicate that NSs has no function in the insect vector. Since deletion of the viral NSs gene can be fully complemented by inactivation of the host's IFN system, we propose that the major biological function of NSs is suppression of the mammalian innate immune response.
Dengue Virus Type 2 Infections of Aedes Aegypti Are Modulated by the Mosquito's RNA Interference Pathway
A number of studies have shown that both innate and adaptive immune defense mechanisms greatly influence the course of human dengue virus (DENV) infections, but little is known about the innate immune response of the mosquito vector Aedes aegypti to arbovirus infection. We present evidence here that a major component of the mosquito innate immune response, RNA interference (RNAi), is an important modulator of mosquito infections. The RNAi response is triggered by double-stranded RNA (dsRNA), which occurs in the cytoplasm as a result of positive-sense RNA virus infection, leading to production of small interfering RNAs (siRNAs). These siRNAs are instrumental in degradation of viral mRNA with sequence homology to the dsRNA trigger and thereby inhibition of virus replication. We show that although dengue virus type 2 (DENV2) infection of Ae. aegypti cultured cells and oral infection of adult mosquitoes generated dsRNA and production of DENV2-specific siRNAs, virus replication and release of infectious virus persisted, suggesting viral circumvention of RNAi. We also show that DENV2 does not completely evade RNAi, since impairing the pathway by silencing expression of dcr2, r2d2, or ago2, genes encoding important sensor and effector proteins in the RNAi pathway, increased virus replication in the vector and decreased the extrinsic incubation period required for virus transmission. Our findings indicate a major role for RNAi as a determinant of DENV transmission by Ae. aegypti.
An Insight into the Sialotranscriptome of the West Nile Mosquito Vector, Culex Tarsalis
Saliva of adult female mosquitoes help sugar and blood feeding by providing enzymes and polypeptides that help sugar digestion, control microbial growth and counteract their vertebrate host hemostasis and inflammation. Mosquito saliva also potentiates the transmission of vector borne pathogens, including arboviruses. Culex tarsalis is a bird feeding mosquito vector of West Nile Virus closely related to C. quinquefasciatus, a mosquito relatively recently adapted to feed on humans, and the only mosquito of the genus Culex to have its sialotranscriptome so far described.
The RNA Interference Pathway Affects Midgut Infection- and Escape Barriers for Sindbis Virus in Aedes Aegypti
The RNA interference (RNAi) pathway acts as an innate antiviral immune response in Aedes aegypti, modulating arbovirus infection of mosquitoes. Sindbis virus (SINV; family: Togaviridae, genus: Alphavirus) is an arbovirus that infects Ae. aegypti in the laboratory. SINV strain TR339 encounters a midgut escape barrier (MEB) during infection of Ae. aegypti. The nature of this barrier is not well understood. To investigate the role of the midgut as the central organ determining vector competence for arboviruses, we generated transgenic mosquitoes in which the RNAi pathway was impaired in midgut tissue of bloodfed females. We used these mosquitoes to reveal effects of RNAi impairment in the midgut on SINV replication, midgut infection and dissemination efficiencies, and mosquito longevity.
The Salivary Gland Transcriptome of the Eastern Tree Hole Mosquito, Ochlerotatus Triseriatus
Saliva of blood-sucking arthropods contains a complex mixture of peptides that affect their host's hemostasis, inflammation, and immunity. These activities can also modify the site of pathogen delivery and increase disease transmission. Saliva also induces hosts to mount an antisaliva immune response that can lead to skin allergies or even anaphylaxis. Accordingly, knowledge of the salivary repertoire, or sialome, of a mosquito is useful to provide a knowledge platform to mine for novel pharmacological activities, to develop novel vaccine targets for vector-borne diseases, and to develop epidemiological markers of vector exposure and candidate desensitization vaccines. The mosquito Ochlerotatus triseriatus is a vector of La Crosse virus and produces allergy in humans. In this work, a total of 1,575 clones randomly selected from an adult female O. triseriatus salivary gland cDNA library was sequenced and used to assemble a database that yielded 731 clusters of related sequences, 560 of which were singletons. Primer extension experiments were performed in selected clones to further extend sequence coverage, allowing for the identification of 159 protein sequences, 66 of which code for putative secreted proteins. Supplemental spreadsheets containing these data are available at http://exon.niaid.nih.gov/transcriptome/Ochlerotatus_triseriatus/S1/Ot-S1.xls and http://exon.niaid. nih.gov/transcriptome/Ochlerotatus_triseriatus/S2/Ot-S2.xls.
