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Maringer K. Re-evaluating the mosquito RNAi pathway's influence on arbovirus transmission. Trends Parasitol 2023; 39:898-899. [PMID: 37758630 DOI: 10.1016/j.pt.2023.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Accepted: 09/11/2023] [Indexed: 09/29/2023]
Abstract
With new RNA interference (RNAi) pathway-deficient mosquitoes, Merkling et al. invite a shift in our view of this pathway's role in regulating arthropod-borne virus (arbovirus) transmission. While loss of RNAi function enhanced early viral replication, little impact on transmission was observed, inviting renewed exploration of molecular barriers to arbovirus transmission.
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Affiliation(s)
- Kevin Maringer
- The Pirbright Institute, Ash Road, Pirbright, Surrey GU24 0NF, UK.
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Agboli E, Schulze J, Jansen S, Cadar D, Sreenu VB, Leggewie M, Altinli M, Badusche M, Jöst H, Börstler J, Schmidt-Chanasit J, Schnettler E. Interaction of Mesonivirus and Negevirus with arboviruses and the RNAi response in Culex tarsalis-derived cells. Parasit Vectors 2023; 16:361. [PMID: 37833743 PMCID: PMC10576325 DOI: 10.1186/s13071-023-05985-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 09/26/2023] [Indexed: 10/15/2023] Open
Abstract
BACKGROUND Mosquito-specific viruses (MSVs) comprise a variety of different virus families, some of which are known to interfere with infections of medically important arboviruses. Viruses belonging to the family Mesoniviridae or taxon Negevirus harbor several insect-specific viruses, including MSVs, which are known for their wide geographical distribution and extensive host ranges. Although these viruses are regularly identified in mosquitoes all over the world, their presence in mosquitoes in Germany had not yet been reported. METHODS A mix of three MSVs (Yichang virus [Mesoniviridae] and two negeviruses [Daeseongdong virus and Dezidougou virus]) in a sample that contained a pool of Coquillettidia richiardii mosquitoes collected in Germany was used to investigate the interaction of these viruses with different arboviruses in Culex-derived cells. In addition, small RNA sequencing and analysis of different mosquito-derived cells infected with this MSV mix were performed. RESULTS A strain of Yichang virus (Mesoniviridae) and two negeviruses (Daeseongdong virus and Dezidougou virus) were identified in the Cq. richiardii mosquitoes sampled in Germany, expanding current knowledge of their circulation in central Europe. Infection of mosquito-derived cells with these three viruses revealed that they are targeted by the small interfering RNA (siRNA) pathway. In Culex-derived cells, co-infection by these three viruses had varying effects on the representative arboviruses from different virus families (Togaviridae: Semliki forest virus [SFV]; Bunyavirales: Bunyamwera orthobunyavirus [BUNV]; or Flaviviridae: Usutu virus [USUV]). Specifically, persistent MSV co-infection inhibited BUNV infection, as well as USUV infection (but the latter only at specific time points). However, the impact on SFV infection was only noticeable at low multiplicity of infection (MOI 0.1) and at specific time points in combination with the infection status. CONCLUSIONS Taken together, these results are important findings that will lead to a better understanding of the complex interactions of MSVs, mosquitoes and arboviruses.
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Affiliation(s)
- Eric Agboli
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
- School of Basic and Biomedical Sciences, Department of Biomedical Sciences, University of Health and Allied Sciences, PMB 31, Ho, Ghana
| | - Jonny Schulze
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Stephanie Jansen
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
- Faculty of Mathematics, Informatics and Natural Sciences, University of Hamburg, 20148, Hamburg, Germany
| | - Daniel Cadar
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | | | - Mayke Leggewie
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Mine Altinli
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Marlis Badusche
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Hanna Jöst
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Jessica Börstler
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
| | - Jonas Schmidt-Chanasit
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany
- Faculty of Mathematics, Informatics and Natural Sciences, University of Hamburg, 20148, Hamburg, Germany
| | - Esther Schnettler
- Bernhard-Nocht-Institute for Tropical Medicine, 20359, Hamburg, Germany.
- Faculty of Mathematics, Informatics and Natural Sciences, University of Hamburg, 20148, Hamburg, Germany.
- German Center for Infection Research (DZIF), Partner Site Hamburg-Luebeck-Borstel-Riems, Hamburg, Germany.
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Leggewie M, Scherer C, Altinli M, Gestuveo RJ, Sreenu VB, Fuss J, Vazeille M, Mousson L, Badusche M, Kohl A, Failloux AB, Schnettler E. The Aedes aegypti RNA interference response against Zika virus in the context of co-infection with dengue and chikungunya viruses. PLoS Negl Trop Dis 2023; 17:e0011456. [PMID: 37440582 DOI: 10.1371/journal.pntd.0011456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Accepted: 06/12/2023] [Indexed: 07/15/2023] Open
Abstract
Since its detection in 2015 in Brazil, Zika virus (ZIKV) has remained in the spotlight of international public health and research as an emerging arboviral pathogen. In addition to single infection, ZIKV may occur in co-infection with dengue (DENV) and chikungunya (CHIKV) viruses, with whom ZIKV shares geographic distribution and the mosquito Aedes aegypti as a vector. The main mosquito immune response against arboviruses is RNA interference (RNAi). It is unknown whether or not the dynamics of the RNAi response differ between single arboviral infections and co-infections. In this study, we investigated the interaction of ZIKV and DENV, as well as ZIKV and CHIKV co-infections with the RNAi response in Ae. aegypti. Using small RNA sequencing, we found that the efficiency of small RNA production against ZIKV -a hallmark of antiviral RNAi-was mostly similar when comparing single and co-infections with either DENV or CHIKV. Silencing of key antiviral RNAi proteins, showed no change in effect on ZIKV replication when the cell is co-infected with ZIKV and DENV or CHIKV. Interestingly, we observed a negative effect on ZIKV replication during CHIKV co-infection in the context of Ago2-knockout cells, though his effect was absent during DENV co-infection. Overall, this study provides evidence that ZIKV single or co-infections with CHIKV or DENV are equally controlled by RNAi responses. Thus, Ae. aegypti mosquitoes and derived cells support co-infections of ZIKV with either CHIKV or DENV to a similar level than single infections, as long as the RNAi response is functional.
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Affiliation(s)
- Mayke Leggewie
- Bernhard-Nocht Institute for Tropical Medicine, Hamburg, Germany
- German Center for Infection; Research (DZIF), partner site Hamburg-Luebeck-Borstel-Riems, Germany
| | - Christina Scherer
- Bernhard-Nocht Institute for Tropical Medicine, Hamburg, Germany
- German Center for Infection; Research (DZIF), partner site Hamburg-Luebeck-Borstel-Riems, Germany
| | - Mine Altinli
- Bernhard-Nocht Institute for Tropical Medicine, Hamburg, Germany
- German Center for Infection; Research (DZIF), partner site Hamburg-Luebeck-Borstel-Riems, Germany
| | - Rommel J Gestuveo
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
- Division of Biological Sciences, University of the Philippines Visayas, Miagao, Iloilo, Philippines
| | - Vattipally B Sreenu
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
| | - Janina Fuss
- Institute of Clinical Molecular Biology (IKMB), Kiel University, Kiel, Germany
| | - Marie Vazeille
- Institut Pasteur, Université Paris Cité, Arboviruses and Insect Vectors, Paris, France
| | - Laurence Mousson
- Institut Pasteur, Université Paris Cité, Arboviruses and Insect Vectors, Paris, France
| | - Marlis Badusche
- Bernhard-Nocht Institute for Tropical Medicine, Hamburg, Germany
| | - Alain Kohl
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
| | - Anna-Bella Failloux
- Institut Pasteur, Université Paris Cité, Arboviruses and Insect Vectors, Paris, France
| | - Esther Schnettler
- Bernhard-Nocht Institute for Tropical Medicine, Hamburg, Germany
- German Center for Infection; Research (DZIF), partner site Hamburg-Luebeck-Borstel-Riems, Germany
- University Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Hamburg, Germany
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Jagtap SV, Brink J, Frank SC, Badusche M, Leggewie M, Sreenu VB, Fuss J, Schnettler E, Altinli M. Agua Salud Alphavirus Infection, Dissemination and Transmission in Aedes aegypti Mosquitoes. Viruses 2023; 15:1113. [PMID: 37243199 PMCID: PMC10223791 DOI: 10.3390/v15051113] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 04/25/2023] [Accepted: 04/28/2023] [Indexed: 05/28/2023] Open
Abstract
Mosquitoes are competent vectors for many important arthropod-borne viruses (arboviruses). In addition to arboviruses, insect-specific viruses (ISV) have also been discovered in mosquitoes. ISVs are viruses that replicate in insect hosts but are unable to infect and replicate in vertebrates. They have been shown to interfere with arbovirus replication in some cases. Despite the increase in studies on ISV-arbovirus interactions, ISV interactions with their hosts and how they are maintained in nature are still not well understood. In the present study, we investigated the infection and dissemination of the Agua Salud alphavirus (ASALV) in the important mosquito vector Aedes aegypti through different infection routes (per oral infection, intrathoracic injection) and its transmission. We show here that ASALV infects the female Ae. aegypti and replicates when mosquitoes are infected intrathoracically or orally. ASALV disseminated to different tissues, including the midgut, salivary glands and ovaries. However, we observed a higher virus load in the brain than in the salivary glands and carcasses, suggesting a tropism towards brain tissues. Our results show that ASALV is transmitted horizontally during adult and larval stages, although we did not observe vertical transmission. Understanding ISV infection and dissemination dynamics in Ae. aegypti and their transmission routes could help the use of ISVs as an arbovirus control strategy in the future.
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Affiliation(s)
- Swati V. Jagtap
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
- German Center for Infection Research, Partner Site Hamburg-Lübeck-Borstel-Riems, 20359 Hamburg, Germany
| | - Jorn Brink
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
| | - Svea C. Frank
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
| | - Marlis Badusche
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
| | - Mayke Leggewie
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
| | | | - Janina Fuss
- Institute of Clinical Molecular Biology (IKMB), Kiel University, 24105 Kiel, Germany
| | - Esther Schnettler
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
- German Center for Infection Research, Partner Site Hamburg-Lübeck-Borstel-Riems, 20359 Hamburg, Germany
- Faculty of Mathematics, Informatics and Natural Sciences, University Hamburg, 20148 Hamburg, Germany
| | - Mine Altinli
- Bernhard-Nocht-Institute for Tropical Medicine, 20359 Hamburg, Germany; (S.V.J.)
- German Center for Infection Research, Partner Site Hamburg-Lübeck-Borstel-Riems, 20359 Hamburg, Germany
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Bruner-Montero G, Luque CM, Cesar CS, Ding SD, Day JP, Jiggins FM. Hunting Drosophila viruses from wild populations: A novel isolation approach and characterisation of viruses. PLoS Pathog 2023; 19:e1010883. [PMID: 36996192 PMCID: PMC10109509 DOI: 10.1371/journal.ppat.1010883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 04/17/2023] [Accepted: 03/08/2023] [Indexed: 04/01/2023] Open
Abstract
Metagenomic studies have demonstrated that viruses are extremely diverse and abundant in insects, but the difficulty of isolating them means little is known about the biology of these newly discovered viruses. To overcome this challenge in Drosophila, we created a cell line that was more permissive to infection and detected novel viruses by the presence of double-stranded RNA. We demonstrate the utility of these tools by isolating La Jolla virus (LJV) and Newfield virus (NFV) from several wild Drosophila populations. These viruses have different potential host ranges, with distinct abilities to replicate in five Drosophila species. Similarly, in some species they cause high mortality and in others they are comparatively benign. In three species, NFV but not LJV caused large declines in female fecundity. This sterilization effect was associated with differences in tissue tropism, as NFV but not LJV was able to infect Drosophila melanogaster ovaries. We saw a similar effect in the invasive pest of fruit crops Drosophila suzukii, where oral infection with NFV caused reductions in the fecundity, suggesting it has potential as a biocontrol agent. In conclusion, a simple protocol allowed us to isolate new viruses and demonstrate that viruses identified by metagenomics have a large effect on the fitness of the model organism D. melanogaster and related species.
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Affiliation(s)
- Gaspar Bruner-Montero
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Coiba Scientific Station, City of Knowledge, Clayton, Panama
| | - Carlos M Luque
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
| | - Cássia Siqueira Cesar
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Ecology Department, Universidade de São Paulo, São Paulo, Brazil
| | | | - Jonathan P Day
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
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Antiviral RNAi Response in Culex quinquefasciatus-Derived HSU Cells. Viruses 2023; 15:v15020436. [PMID: 36851650 PMCID: PMC9968050 DOI: 10.3390/v15020436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 01/20/2023] [Accepted: 01/31/2023] [Indexed: 02/09/2023] Open
Abstract
Culex spp. mosquitoes are important vectors of viruses, such as West Nile virus, Eastern equine encephalitis virus and Rift valley fever virus. However, their interactions with innate antiviral immunity, especially RNA interference (RNAi), are not well known. Most research on RNAi pathways in mosquitoes is focused on the tropical vector mosquito Aedes aegypti. Here, we investigated the production of arbovirus-specific small RNAs in Cx. quinquefasciatus-derived HSU cells. Furthermore, by silencing RNAi-related proteins, we investigated the antiviral role of these proteins for two different arboviruses: Semliki Forest virus (SFV) and Bunyamwera orthobunyavirus (BUNV). Our results showed an expansion of Ago2 and Piwi6 in Cx. quinquefasciatus compared to Ae. aegypti. While silencing Ago2a and Ago2b increased BUNV replication, only Ago2b showed antiviral activity against SFV. Our results suggest differences in the function of Cx. quinquefasciatus and Ae. aegypti RNAi proteins and highlight the virus-specific function of these proteins in Cx. quinquefasciatus.
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Torres TZB, Prince BC, Robison A, Rückert C. Optimized In Vitro CRISPR/Cas9 Gene Editing Tool in the West Nile Virus Mosquito Vector, Culex quinquefasciatus. INSECTS 2022; 13:856. [PMID: 36135557 PMCID: PMC9502113 DOI: 10.3390/insects13090856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 09/13/2022] [Accepted: 09/16/2022] [Indexed: 06/16/2023]
Abstract
Culex quinquefasciatus mosquitoes are a globally widespread vector of multiple human and animal pathogens, including West Nile virus, Saint Louis encephalitis virus, and lymphatic filariasis. Since the introduction of West Nile virus to the United States in 1999, a cumulative 52,532 cases have been reported to the CDC, including 25,849 (49.2%) neuroinvasive cases and 2456 (5%) deaths. Viral infections elicit immune responses in their mosquito vectors, including the RNA interference (RNAi) pathway considered to be the cornerstone antiviral response in insects. To investigate mosquito host genes involved in pathogen interactions, CRISPR/Cas9-mediated gene-editing can be used for functional studies of mosquito-derived cell lines. Yet, the tools available for the study of Cx. quinquefasciatus-derived (Hsu) cell lines remain largely underdeveloped compared to other mosquito species. In this study, we constructed and characterized a Culex-optimized CRISPR/Cas9 plasmid for use in Hsu cell cultures. By comparing it to the original Drosophila melanogaster CRISPR/Cas9 plasmid, we showed that the Culex-optimized plasmid demonstrated highly efficient editing of the genomic loci of the RNAi proteins Dicer-2 and PIWI4 in Hsu cells. These new tools support our ability to investigate gene targets involved in mosquito antiviral response, and thus the future development of gene-based vector control strategies.
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Zhao Z, Lin S, Wu W, Zhang Z, Wu P, Shen M, Qian H, Guo X. A cypovirus encoded microRNA negatively regulates the NF-κB pathway to enhance viral multiplication in Silkworm, Bombyx mori. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2022; 131:104382. [PMID: 35245604 DOI: 10.1016/j.dci.2022.104382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Revised: 02/25/2022] [Accepted: 02/27/2022] [Indexed: 06/14/2023]
Abstract
MicroRNAs (miRNAs) are small non-coding RNAs that function as novel gene expression regulators at the post-transcriptional level. Not with standing that the biogenesis and function of miRNAs are well-understood in eukaryotes, little is known about RNA virus-encoded miRNAs. Bombyx mori cypovirus (BmCPV) is a double-stranded RNA virus with a segmented genome that causes cytoplasmic polyhedrosis disease in silkworm larvae. To date, the interaction between BmCPV and silkworm remains largely unclear. 22 candidate BmCPV-encoded miRNAs were identified in this study through small RNA sequencing, stem-loop RT-PCR and qRT-PCR. Then, generation and function analyses were conducted on one of the candidate miRNAs, BmCPV-miR-1, in the BmN cells and the silkworm larvae by RNA interference, quantitative PCR, dual-luciferase assay. Our results revealed that BmCPV-miR-1 was encoded by BmCPV genome RNA rather than the degraded fragments of the viral genome. Its generation depended on Dicer-1 and might also be correlated with Dicer-2, Argonaute-1 and Argonaute-2. Moreover, BmCPV-miR-1 could suppress the expression of the target gene, B. mori inhibitor of nuclear factor kappa-B kinase subunit beta (BmIKKβ), via binding to the target mRNA 3'-untranslated region, which fine-tuned the host NF-κB signaling pathway and consequently enhanced viral replication. Our results provide new evidence supporting the hypothesis that RNA viruses could generate miRNAs to modulate antiviral host defense.
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Affiliation(s)
- Ze Zhao
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Su Lin
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Wanming Wu
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Zhendong Zhang
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Ping Wu
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Manman Shen
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Heying Qian
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China
| | - Xijie Guo
- School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, 212000, China; Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, 212000, China.
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Antiviral RNAi Response against the Insect-Specific Agua Salud Alphavirus. mSphere 2022; 7:e0100321. [PMID: 35171691 PMCID: PMC8849343 DOI: 10.1128/msphere.01003-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Arboviruses transmitted by mosquitoes are responsible for the death of millions of people each year. In addition to arboviruses, many insect-specific viruses (ISVs) have been discovered in mosquitoes in the last decade. ISVs, in contrast to arboviruses transmitted by mosquitoes to vertebrates, cannot replicate in vertebrate cells even when they are evolutionarily closely related to arboviruses. The alphavirus genus includes many arboviruses, although only a few ISVs have been discovered from this genus so far. Here, we investigate the interactions of a recently isolated insect-specific alphavirus, Agua Salud alphavirus (ASALV), with its mosquito host. RNA interference (RNAi) is one of the essential antiviral responses against arboviruses, although there is little knowledge on the interactions of RNAi with ISVs. Through the knockdown of transcripts of the different key RNAi pathway (small interfering RNA [siRNA], microRNA [miRNA], and P-element-induced wimpy testis [PIWI]-interacting RNA [piRNA]) proteins, we show the antiviral role of Ago2 (siRNA), Ago1 (miRNA), and Piwi4 proteins against ASALV in Aedes aegypti-derived cells. ASALV replication was increased in Dicer2 and Ago2 knockout cells, confirming the antiviral role of the siRNA pathway. In infected cells, mainly ASALV-specific siRNAs are produced, while piRNA-like small RNAs, with the characteristic nucleotide bias resulting from ping-pong amplification, are produced only in Dicer2 knockout cells. Taken together, ASALV interactions with the mosquito RNAi response differ from those of arthropod-borne alphaviruses in some aspects, although they also share some commonalities. Further research is needed to understand whether the identified differences can be generalized to other insect-specific alphaviruses. IMPORTANCE Mosquitoes are efficient vectors for many arboviruses that cause emergent infectious diseases in humans. Many insect-specific viruses (ISVs) that can infect mosquitoes but cannot infect vertebrates have been discovered in the last decade. ISVs have attracted great attention due to their potential use in mosquito or arbovirus control, by either decreasing mosquito fitness or restricting arbovirus replication and transmission to humans. However, ISV-mosquito interactions are not well understood. RNA interference (RNAi) is the most important innate immune response against many arboviruses, while it is unknown if it is antiviral against ISVs. Here, we investigate in detail the antiviral effect of the RNAi response in mosquitoes against an ISV for the first time. Using a recently isolated insect-specific alphavirus, we show that the regulation of virus replication was different from that for arthropod-borne alphaviruses despite some similarities. The differences in mosquito-virus interactions could drive the different transmission modes, which could eventually drive the evolution of arboviruses. Hence, an understanding of mosquito-ISV interactions can shed light on the ecology and evolution of both ISVs and the medically important arboviruses.
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Gestuveo RJ, Parry R, Dickson LB, Lequime S, Sreenu VB, Arnold MJ, Khromykh AA, Schnettler E, Lambrechts L, Varjak M, Kohl A. Mutational analysis of Aedes aegypti Dicer 2 provides insights into the biogenesis of antiviral exogenous small interfering RNAs. PLoS Pathog 2022; 18:e1010202. [PMID: 34990484 PMCID: PMC8769306 DOI: 10.1371/journal.ppat.1010202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 01/19/2022] [Accepted: 12/15/2021] [Indexed: 12/13/2022] Open
Abstract
The exogenous small interfering RNA (exo-siRNA) pathway is a key antiviral mechanism in the Aedes aegypti mosquito, a widely distributed vector of human-pathogenic arboviruses. This pathway is induced by virus-derived double-stranded RNAs (dsRNA) that are cleaved by the ribonuclease Dicer 2 (Dcr2) into predominantly 21 nucleotide (nt) virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs are used by the effector protein Argonaute 2 within the RNA-induced silencing complex to cleave target viral RNA. Dcr2 contains several domains crucial for its activities, including helicase and RNase III domains. In Drosophila melanogaster Dcr2, the helicase domain has been associated with binding to dsRNA with blunt-ended termini and a processive siRNA production mechanism, while the platform-PAZ domains bind dsRNA with 3’ overhangs and subsequent distributive siRNA production. Here we analyzed the contributions of the helicase and RNase III domains in Ae. aegypti Dcr2 to antiviral activity and to the exo-siRNA pathway. Conserved amino acids in the helicase and RNase III domains were identified to investigate Dcr2 antiviral activity in an Ae. aegypti-derived Dcr2 knockout cell line by reporter assays and infection with mosquito-borne Semliki Forest virus (Togaviridae, Alphavirus). Functionally relevant amino acids were found to be conserved in haplotype Dcr2 sequences from field-derived Ae. aegypti across different continents. The helicase and RNase III domains were critical for silencing activity and 21 nt vsiRNA production, with RNase III domain activity alone determined to be insufficient for antiviral activity. Analysis of 21 nt vsiRNA sequences (produced by functional Dcr2) to assess the distribution and phasing along the viral genome revealed diverse yet highly consistent vsiRNA pools, with predominantly short or long sequence overlaps including 19 nt overlaps (the latter representing most likely true Dcr2 cleavage products). Combined with the importance of the Dcr2 helicase domain, this suggests that the majority of 21 nt vsiRNAs originate by processive cleavage. This study sheds new light on Ae. aegypti Dcr2 functions and properties in this important arbovirus vector species. Aedes aegypti mosquitoes that transmit human-pathogenic viruses rely on the exogenous small interfering RNA (exo-siRNA) pathway as part of antiviral responses. This pathway is triggered by virus-derived double-stranded RNA (dsRNA) produced during viral replication that is then cleaved by Dicer 2 (Dcr2) into virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs target viral RNA, leading to suppression of viral replication. The importance of Dcr2 in this pathway has been intensely studied in the Drosophila melanogaster model but is largely lacking in mosquitoes. Here, we have identified conserved and functionally relevant amino acids in the helicase and RNase III domains of Ae. aegypti Dcr2 that are important in its silencing activity and antiviral responses against Semliki Forest virus (SFV). Small RNA sequencing of SFV-infected mosquito cells with functional or mutated Dcr2 gave new insights into the nature and origin of vsiRNAs. The findings of this study, together with the different molecular tools we have previously developed to investigate the exo-siRNA pathway of mosquito cells, have started to uncover important properties of Dcr2 that could be valuable in understanding mosquito-arbovirus interactions and potentially in developing or assisting vector control strategies.
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Affiliation(s)
- Rommel J. Gestuveo
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
- Division of Biological Sciences, University of the Philippines Visayas, Miagao, Iloilo, Philippines
- * E-mail: (R.J.G.); (M.V.); (A.K.)
| | - Rhys Parry
- School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Australia
| | - Laura B. Dickson
- Insect-Virus Interactions Unit, Institut Pasteur, UMR2000, CNRS, Paris, France
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, United States of America
- Institute for Human Infection and Immunity, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Sebastian Lequime
- Insect-Virus Interactions Unit, Institut Pasteur, UMR2000, CNRS, Paris, France
- Cluster of Microbial Ecology, Groningen Institute for Evolutionary Life Sciences, Groningen, The Netherlands
| | | | - Matthew J. Arnold
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
| | - Alexander A. Khromykh
- School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Australia
- Australian Infectious Diseases Research Centre, Global Virus Network Centre of Excellence, Brisbane, Queensland, Australia
| | - Esther Schnettler
- Bernhard-Nocht-Institute for Tropical Medicine, Hamburg, Germany
- German Centre for Infection Research (DZIF), Partner Site Hamburg-Luebeck-Borstel-Riems, Hamburg, Germany
- Faculty of Mathematics, Informatics and Natural Sciences, University Hamburg, Hamburg, Germany
| | - Louis Lambrechts
- Insect-Virus Interactions Unit, Institut Pasteur, UMR2000, CNRS, Paris, France
| | - Margus Varjak
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
- Institute of Technology, University of Tartu, Tartu, Estonia
- * E-mail: (R.J.G.); (M.V.); (A.K.)
| | - Alain Kohl
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
- * E-mail: (R.J.G.); (M.V.); (A.K.)
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