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Weingartl HM, Zhang S, Marszal P, McGreevy A, Burton L, Wilson WC. Rift Valley fever virus incorporates the 78 kDa glycoprotein into virions matured in mosquito C6/36 cells. PLoS One 2014; 9:e87385. [PMID: 24489907 PMCID: PMC3905018 DOI: 10.1371/journal.pone.0087385] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Accepted: 12/20/2013] [Indexed: 12/04/2022] Open
Abstract
Rift Valley fever virus (RVFV), genus Phlebovirus, family Bunyaviridae is a zoonotic arthropod-borne virus able to transition between distant host species, causing potentially severe disease in humans and ruminants. Viral proteins are encoded by three genomic segments, with the medium M segment coding for four proteins: nonstructural NSm protein, two glycoproteins Gn and Gc and large 78 kDa glycoprotein (LGp) of unknown function. Goat anti-RVFV polyclonal antibody and mouse monoclonal antibody, generated against a polypeptide unique to the LGp within the RVFV proteome, detected this protein in gradient purified RVFV ZH501 virions harvested from mosquito C6/36 cells but not in virions harvested from the mammalian Vero E6 cells. The incorporation of LGp into the mosquito cell line - matured virions was confirmed by immune-electron microscopy. The LGp was incorporated into the virions immediately during the first passage in C6/36 cells of Vero E6 derived virus. Our data indicate that LGp is a structural protein in C6/36 mosquito cell generated virions. The protein may aid the transmission from the mosquitoes to the ruminant host, with a possible role in replication of RVFV in the mosquito host. To our knowledge, this is a first report of different protein composition between virions formed in insect C6/36 versus mammalian Vero E6 cells.
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Affiliation(s)
- Hana M. Weingartl
- National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada
- Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada
- * E-mail:
| | - Shunzhen Zhang
- National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada
| | - Peter Marszal
- National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada
| | - Alan McGreevy
- Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Lynn Burton
- National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada
| | - William C. Wilson
- Arthropod-Borne Animal Disease Research Unit, United States Department of Agriculture, Manhattan, Kansas, United States of America
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Paweska JT. Rift Valley Fever. Emerg Infect Dis 2014. [DOI: 10.1016/b978-0-12-416975-3.00006-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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Lihoradova O, Ikegami T. Countermeasure development for Rift Valley fever: deletion, modification or targeting of major virulence factor NSs.. Future Virol 2014; 9:27-39. [PMID: 24910709 DOI: 10.2217/fvl.13.117] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Rift Valley fever (RVF) is a mosquito-borne zoonotic disease characterized by a high rate of abortion in ruminants, and febrile illness, hemorrhagic fever, retinitis and encephalitis in humans. RVF is caused by the RVF virus (RVFV), belonging to the genus Phlebovirus of the family Bunyaviridae. RVFV encodes a major virulence factor, NSs, which is dispensable for viral replication, yet required for evasion of host innate immune responses. RVFV NSs inhibits host gene upregulation at the transcriptional level, while promoting viral translation in the cytoplasm. In this article, we summarize the virology and pathology of RVF, and countermeasure development for RVF, with emphasis on NSs function and applications.
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Affiliation(s)
- Olga Lihoradova
- Department of Pathology, University of Texas Medical Branch, MMNP3.206D, 301 University Blvd. Galveston, TX 77555-0436, USA
| | - Tetsuro Ikegami
- Department of Pathology, University of Texas Medical Branch, MMNP3.206D, 301 University Blvd. Galveston, TX 77555-0436, USA ; Sealy Center for Vaccine Development, The University of Texas Medical Branch, Galveston, TX, USA ; Center for Biodefense & Emerging Infectious Diseases, The University of Texas Medical Branch, Galveston, TX, USA
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Mweya CN, Kimera SI, Kija JB, Mboera LEG. Predicting distribution of Aedes aegypti and Culex pipiens complex, potential vectors of Rift Valley fever virus in relation to disease epidemics in East Africa. Infect Ecol Epidemiol 2013; 3:21748. [PMID: 24137533 PMCID: PMC3797365 DOI: 10.3402/iee.v3i0.21748] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2013] [Revised: 09/08/2013] [Accepted: 09/12/2013] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND The East African region has experienced several Rift Valley fever (RVF) outbreaks since the 1930s. The objective of this study was to identify distributions of potential disease vectors in relation to disease epidemics. Understanding disease vector potential distributions is a major concern for disease transmission dynamics. METHODS DIVERSE ECOLOGICAL NICHE MODELLING TECHNIQUES HAVE BEEN DEVELOPED FOR THIS PURPOSE: we present a maximum entropy (Maxent) approach for estimating distributions of potential RVF vectors in un-sampled areas in East Africa. We modelled the distribution of two species of mosquitoes (Aedes aegypti and Culex pipiens complex) responsible for potential maintenance and amplification of the virus, respectively. Predicted distributions of environmentally suitable areas in East Africa were based on the presence-only occurrence data derived from our entomological study in Ngorongoro District in northern Tanzania. RESULTS Our model predicted potential suitable areas with high success rates of 90.9% for A. aegypti and 91.6% for C. pipiens complex. Model performance was statistically significantly better than random for both species. Most suitable sites for the two vectors were predicted in central and northwestern Tanzania with previous disease epidemics. Other important risk areas include western Lake Victoria, northern parts of Lake Malawi, and the Rift Valley region of Kenya. CONCLUSION Findings from this study show distributions of vectors had biological and epidemiological significance in relation to disease outbreak hotspots, and hence provide guidance for the selection of sampling areas for RVF vectors during inter-epidemic periods.
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Affiliation(s)
- Clement Nyamunura Mweya
- National Institute for Medical Research, Tukuyu Research Centre, Tukuyu, Tanzania
- Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Morogoro, Tanzania
| | - Sharadhuli Iddi Kimera
- Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Morogoro, Tanzania
| | - John Bukombe Kija
- Serengeti Biodiversity Programme, Tanzania Wildlife Research Institute, Arusha, Tanzania
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Non-structural proteins of arthropod-borne bunyaviruses: roles and functions. Viruses 2013; 5:2447-68. [PMID: 24100888 PMCID: PMC3814597 DOI: 10.3390/v5102447] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 09/20/2013] [Accepted: 09/25/2013] [Indexed: 12/24/2022] Open
Abstract
Viruses within the Bunyaviridae family are tri-segmented, negative-stranded RNA viruses. The family includes several emerging and re-emerging viruses of humans, animals and plants, such as Rift Valley fever virus, Crimean-Congo hemorrhagic fever virus, La Crosse virus, Schmallenberg virus and tomato spotted wilt virus. Many bunyaviruses are arthropod-borne, so-called arboviruses. Depending on the genus, bunyaviruses encode, in addition to the RNA-dependent RNA polymerase and the different structural proteins, one or several non-structural proteins. These non-structural proteins are not always essential for virus growth and replication but can play an important role in viral pathogenesis through their interaction with the host innate immune system. In this review, we will summarize current knowledge and understanding of insect-borne bunyavirus non-structural protein function(s) in vertebrate, plant and arthropod.
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Abstract
Bunyaviruses are the largest known family of RNA viruses, infecting vertebrates, insects, and plants. Here we isolated three novel bunyaviruses from mosquitoes sampled in Côte d'Ivoire, Ghana, and Uganda. The viruses define a highly diversified monophyletic sister clade to all members of the genus Orthobunyavirus and are virtually equidistant to orthobunyaviruses and tospoviruses. Maximal amino acid identities between homologous putative proteins of the novel group and orthobunyaviruses ranged between 12 and 25%. The type isolates, tentatively named Herbert virus (HEBV), Taï virus (TAIV), and Kibale virus (KIBV), comprised genomes with L, M, and S segments of about 7.4 kb, 2.7 kb, and 1.1 kb, respectively. HEBV, TAIV, and KIBV encode the shortest bunyavirus M segments known and did not seem to encode NSs and NSm proteins but contained an elongated L segment with an ∼500-nucleotide (nt) insertion that shows no identity to other bunyaviruses. The viruses replicated to high titers in insect cells but did not replicate in vertebrate cells. The enveloped virions were 90 to 110 nm in diameter and budded at cellular membranes with morphological features typical of the Golgi complex. Viral RNA recovered from infected cells showed 5'-terminal nontemplated sequences of 9 to 22 nt, suggestive of cap snatching during mRNA synthesis, as described for other bunyaviruses. Northern blotting identified RNA species of full and reduced lengths, suggested upon analogy with other bunyaviruses to constitute antigenomic-sense cRNA and transcript mRNAs, respectively. Functional studies will be necessary to determine if this group of viruses constitutes a novel genus in the bunyavirus family.
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Nuclear relocalization of polyadenylate binding protein during rift valley fever virus infection involves expression of the NSs gene. J Virol 2013; 87:11659-69. [PMID: 23966414 DOI: 10.1128/jvi.01434-13] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Rift Valley fever virus (RVFV), an ambisense member of the family Bunyaviridae, genus Phlebovirus, is the causative agent of Rift Valley fever, an important zoonotic infection in Africa and the Middle East. Phlebovirus proteins are translated from virally transcribed mRNAs that, like host mRNA, are capped but, unlike host mRNAs, are not polyadenylated. Here, we investigated the role of PABP1 during RVFV infection of HeLa cells. Immunofluorescence studies of infected cells demonstrated a gross relocalization of PABP1 to the nucleus late in infection. Immunofluorescence microscopy studies of nuclear proteins revealed costaining between PABP1 and markers of nuclear speckles. PABP1 relocalization was sharply decreased in cells infected with a strain of RVFV lacking the gene encoding the RVFV nonstructural protein S (NSs). To determine whether PABP1 was required for RVFV infection, we measured the production of nucleocapsid protein (N) in cells transfected with small interfering RNAs (siRNAs) targeting PABP1. We found that the overall percentage of RVFV N-positive cells was not changed by siRNA treatment, indicating that PABP1 was not required for RVFV infection. However, when we analyzed populations of cells producing high versus low levels of PABP1, we found that the percentage of RVFV N-positive cells was decreased in cell populations producing physiologic levels of PABP1 and increased in cells with reduced levels of PABP1. Together, these results suggest that production of the NSs protein during RVFV infection leads to sequestration of PABP1 in the nuclear speckles, creating a state within the cell that favors viral protein production.
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Le Coupanec A, Babin D, Fiette L, Jouvion G, Ave P, Misse D, Bouloy M, Choumet V. Aedes mosquito saliva modulates Rift Valley fever virus pathogenicity. PLoS Negl Trop Dis 2013; 7:e2237. [PMID: 23785528 PMCID: PMC3681724 DOI: 10.1371/journal.pntd.0002237] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 04/15/2013] [Indexed: 01/10/2023] Open
Abstract
Background Rift Valley fever (RVF) is a severe mosquito-borne disease affecting humans and domestic ruminants. Mosquito saliva contains compounds that counteract the hemostatic, inflammatory, and immune responses of the host. Modulation of these defensive responses may facilitate virus infection. Indeed, Aedes mosquito saliva played a crucial role in the vector's capacity to effectively transfer arboviruses such as the Cache Valley and West Nile viruses. The role of mosquito saliva in the transmission of Rift Valley fever virus (RVFV) has not been investigated. Objective Using a murine model, we explored the potential for mosquitoes to impact the course of RVF disease by determining whether differences in pathogenesis occurred in the presence or absence of mosquito saliva and salivary gland extract. Methods C57BL/6NRJ male mice were infected with the ZH548 strain of RVFV via intraperitoneal or intradermal route, or via bites from RVFV-exposed mosquitoes. The virus titers in mosquitoes and mouse organs were determined by plaque assays. Findings After intraperitoneal injection, RVFV infection primarily resulted in liver damage. In contrast, RVFV infection via intradermal injection caused both liver and neurological symptoms and this route best mimicked the natural infection by mosquitoes. Co-injections of RVFV with salivary gland extract or saliva via intradermal route increased the mortality rates of mice, as well as the virus titers measured in several organs and in the blood. Furthermore, the blood cell counts of infected mice were altered compared to those of uninfected mice. Interpretation Different routes of infection determine the pattern in which the virus spreads and the organs it targets. Aedes saliva significantly increases the pathogenicity of RVFV. Rift Valley fever is an endemic and epidemic zoonosis in Africa and the Arabic Peninsula. In humans, in the most severe cases the viral infection causes fulminant hepatitis associated with haemorrhagic fever, permanent blindness or severe encephalitis. Despite the importance of vector transmission in the spread of arboviruses, few studies on the physiopathology of viral infection have considered the role of the arthropod in the efficiency of viral infection. Moreover, the route of virus inoculation and the presence of the vector's saliva can potentially affect virus pathogenicity. Our results show that saliva from Aedes mosquitoes increases Rift Valley fever pathogenicity. Importantly, our study also revealed that RVFV transmitted via mosquito bites spread differently than virus inoculated by other routes. These observations may have interesting repercussions given the role mosquitoes were shown to play in the transmission of RVFV in humans during the last outbreak of the disease in Saudi Arabia. Identification of salivary proteins able to increase RVFV virulence may pave the way to new approaches to prevent or cure the disease.
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Affiliation(s)
- Alain Le Coupanec
- Unité de Génétique Moléculaire des Bunyavirus, Institut Pasteur, Paris, France
| | - Divya Babin
- Unité de Génétique Moléculaire des Bunyavirus, Institut Pasteur, Paris, France
| | - Laurence Fiette
- Unité d'Histopathologie humaine et modèles animaux, Institut Pasteur, Paris, France
| | - Grégory Jouvion
- Unité d'Histopathologie humaine et modèles animaux, Institut Pasteur, Paris, France
| | - Patrick Ave
- Unité d'Histopathologie humaine et modèles animaux, Institut Pasteur, Paris, France
| | - Dorothee Misse
- MIVEGEC (IRD 224 CNRS 5290-UM1-UM2) Maladies infectieuses et vecteurs: écologie, génétique, évolution et contrôle, Centre IRD de Montpellier, Montpellier, France
| | - Michèle Bouloy
- Unité de Génétique Moléculaire des Bunyavirus, Institut Pasteur, Paris, France
| | - Valerie Choumet
- Unité de Génétique Moléculaire des Bunyavirus, Institut Pasteur, Paris, France
- * E-mail:
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Lihoradova O, Ikegami T. Modifying the NSs gene to improve live-attenuated vaccine for Rift Valley fever. Expert Rev Vaccines 2013; 11:1283-5. [PMID: 23249225 DOI: 10.1586/erv.12.106] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Rift Valley fever virus clearance and protection from neurologic disease are dependent on CD4+ T cell and virus-specific antibody responses. J Virol 2013; 87:6161-71. [PMID: 23536675 DOI: 10.1128/jvi.00337-13] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rift Valley fever virus (RVFV) causes outbreaks of severe disease in people and livestock throughout Africa and the Arabian Peninsula. Human RVFV infections generally manifest as a self-limiting febrile illness, but in some individuals, the disease can progress to a fatal encephalitis or hemorrhagic syndrome. Little is known about the host characteristics that predispose development of more severe disease. Early in infection, interferon-mediated antiviral responses are critical for controlling RVFV replication, but the roles of downstream adaptive immune responses in determining clinical outcome have not been examined. Here, using a C57BL/6 mouse disease model, we evaluated the roles of B cells and T cells in RVFV pathogenesis. Given the profound inhibition of the innate response by the viral NSs protein and rapid course of wild-type infection, we utilized an attenuated RVFV lacking NSs to examine host responses following primary infection. Experiments utilizing B-cell-deficient mice or targeted T cell depletions of wild-type mice demonstrated that B cells and CD4(+) T cells, but not CD8(+) T cells, were critical for mediating viral clearance, even in the presence of a functional innate response. One-third of CD4-depleted mice developed severe neurologic disease following infection, in contrast to virus-infected mock-depleted mice that showed no clinical signs. CD4(+) T cells were required for robust IgG and neutralizing antibody responses that correlated with RVFV clearance from peripheral tissues. Furthermore, CD4-depleted mice demonstrated significantly stronger proinflammatory responses relative to controls, suggesting CD4(+) T cells regulate immune responses to RVFV infection. Together, these results indicate CD4(+) T cells are critical determinants of RVFV pathogenesis and play an important role in preventing onset of neurologic disease.
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Xue L, Scoglio C. The network level reproduction number for infectious diseases with both vertical and horizontal transmission. Math Biosci 2013; 243:67-80. [PMID: 23454228 DOI: 10.1016/j.mbs.2013.02.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Revised: 01/30/2013] [Accepted: 02/06/2013] [Indexed: 10/27/2022]
Abstract
A wide range of infectious diseases are both vertically and horizontally transmitted. Such diseases are spatially transmitted via multiple species in heterogeneous environments, typically described by complex meta-population models. The reproduction number, R0, is a critical metric predicting whether the disease can invade the meta-population system. This paper presents the reproduction number for a generic disease vertically and horizontally transmitted among multiple species in heterogeneous networks, where nodes are locations, and links reflect outgoing or incoming movement flows. The metapopulation model for vertically and horizontally transmitted diseases is gradually formulated from two species, two-node network models. We derived an explicit expression of R0, which is the spectral radius of a matrix reduced in size with respect to the original next generation matrix. The reproduction number is shown to be a function of vertical and horizontal transmission parameters, and the lower bound is the reproduction number for horizontal transmission. As an application, the reproduction number and its bounds for the Rift Valley fever zoonosis, where livestock, mosquitoes, and humans are the involved species are derived. By computing the reproduction number for different scenarios through numerical simulations, we found the reproduction number is affected by livestock movement rates only when parameters are heterogeneous across nodes. To summarize, our study contributes the reproduction number for vertically and horizontally transmitted diseases in heterogeneous networks. This explicit expression is easily adaptable to specific infectious diseases, affording insights into disease evolution.
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Affiliation(s)
- Ling Xue
- Department of Electrical & Computer Engineering, Kansas State University, KS 66506, USA.
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Kading R, Crabtree M, Miller B. Inactivation of infectious virus and serological detection of virus antigen in Rift Valley fever virus-exposed mosquitoes fixed with paraformaldehyde. J Virol Methods 2013; 189:184-8. [PMID: 23391826 DOI: 10.1016/j.jviromet.2013.01.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 01/11/2013] [Accepted: 01/28/2013] [Indexed: 10/27/2022]
Abstract
Formaldehyde is routinely used to fix tissues in preparation for pathology studies, however concerns remain that treatment of tissues with cellular fixatives may not entirely inactivate infectious virus particles. This concern is of particular regulatory importance for research involving viruses that are classified as select agents such as Rift Valley fever virus (RVFV). Therefore, the specific aims of this study were to (1) assay RVFV-exposed Aedes aegypti mosquitoes fixed in 4% paraformaldehyde for the presence of infectious RVFV particles at various time points following infection and (2) demonstrate the utility of immunofluorescence assay (IFA) for the detection of RVFV antigen in various tissues of paraformaldehyde-fixed mosquitoes. Mosquitoes were administered an infectious blood meal containing one of two strains of RVFV, harvested at various time points following infection, intrathoracically inoculated with 4% paraformaldehyde, and fixed overnight at 4°C. The infection status of a subset of mosquitoes was verified by IFA on leg tissues prior to fixation, and infectivity of RVFV in fixed mosquito carcasses was determined by Vero cell plaque assay. Paraformaldehyde-fixed mosquitoes harvested 14 days post infection were also paraffin-embedded and sectioned for detection of RVFV antigen to particular tissues by IFA. None of the RVFV-exposed mosquitoes tested by Vero cell plaque assay contained infectious RVFV after fixation. Furthermore, incubation of mosquito sections with trypsin prior to antibody staining is recommended for optimal visualization of RVFV antigen in infected mosquito tissues by IFA.
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Affiliation(s)
- Rebekah Kading
- Centers for Disease Control and Prevention, Division of Vector-borne Diseases, Arbovirus Diseases Branch, 3156 Rampart Road, Mail Stop P02, Fort Collins, CO 80521, USA.
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Terasaki K, Won S, Makino S. The C-terminal region of Rift Valley fever virus NSm protein targets the protein to the mitochondrial outer membrane and exerts antiapoptotic function. J Virol 2013; 87:676-82. [PMID: 23097454 PMCID: PMC3536385 DOI: 10.1128/jvi.02192-12] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 10/18/2012] [Indexed: 11/20/2022] Open
Abstract
The NSm nonstructural protein of Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus) has an antiapoptotic function and affects viral pathogenesis. We found that NSm integrates into the mitochondrial outer membrane and that the protein's N terminus is exposed to the cytoplasm. The C-terminal region of NSm, which contains a basic amino acid cluster and a putative transmembrane domain, targeted the protein to the mitochondrial outer membrane and exerted antiapoptotic function.
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Affiliation(s)
| | | | - Shinji Makino
- Department of Microbiology and Immunology
- Center for Biodefense and Emerging Infectious Diseases
- UTMB Center for Tropical Diseases
- Sealy Center for Vaccine Development, The University of Texas Medical Branch, Galveston, Texas, USA
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Dicer-2- and Piwi-mediated RNA interference in Rift Valley fever virus-infected mosquito cells. J Virol 2012; 87:1631-48. [PMID: 23175368 DOI: 10.1128/jvi.02795-12] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rift Valley fever virus (RVFV) is a Phlebovirus (Bunyaviridae family) transmitted by mosquitoes. It infects humans and ruminants, causing dramatic epidemics and epizootics in Africa, Yemen, and Saudi Arabia. While recent studies demonstrated the importance of the nonstructural protein NSs as a major component of virulence in vertebrates, little is known about infection of mosquito vectors. Here we studied RVFV infection in three different mosquito cell lines, Aag2 cells from Aedes aegypti and U4.4 and C6/36 cells from Aedes albopictus. In contrast with mammalian cells, where NSs forms nuclear filaments, U4.4 and Aag2 cells downregulated NSs expression such that NSs filaments were never formed in nuclei of U4.4 cells and disappeared at an early time postinfection in the case of Aag2 cells. On the contrary, in C6/36 cells, NSs nuclear filaments were visible during the entire time course of infection. Analysis of virus-derived small interfering RNAs (viRNAs) by deep sequencing indicated that production of viRNAs was very low in C6/36 cells, which are known to be Dicer-2 deficient but expressed some viRNAs presenting a Piwi signature. In contrast, Aag2 and U4.4 cells produced large amounts of viRNAs predominantly matching the S segment and displaying Dicer-2 and Piwi signatures. Whereas 21-nucleotide (nt) Dicer-2 viRNAs were prominent during early infection, the population of 24- to 27-nt Piwi RNAs (piRNAs) increased progressively and became predominant later during the acute infection and during persistence. In Aag2 and U4.4 cells, the combined actions of the Dicer-2 and Piwi pathways triggered an efficient antiviral response permitting, among other actions, suppression of NSs filament formation and allowing establishment of persistence. In C6/36 cells, Piwi-mediated RNA interference (RNAi) appeared to be sufficient to mount an antiviral response against a secondary infection with a superinfecting virus. This study provides new insights into the role of Dicer and Piwi in mosquito antiviral defense and the development of the antiviral response in mosquitoes.
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Genetic subpopulations of Rift Valley fever virus strains ZH548 and MP-12 and recombinant MP-12 strains. J Virol 2012; 86:13566-75. [PMID: 23035230 DOI: 10.1128/jvi.02081-12] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rift Valley fever virus strain MP-12 was generated by serial plaque passages of parental strain ZH548 12 times in MRC-5 cells in the presence of a chemical mutagen, 5-fluorouracil. As a result, MP-12 encoded 4, 9, and 10 mutations in the S, M, and L segments, respectively. Among them, mutations in the M and L segments were responsible for attenuation, while the MP-12 S segment still encoded a virulent phenotype. We performed high-throughput sequencing of MP-12 vaccine, ZH548, and recombinant MP-12 (rMP-12) viruses. We found that rMP-12 contains very low numbers of viral subpopulations, while MP-12 and ZH548 contain 2 to 4 times more viral genetic subpopulations than rMP-12. MP-12 genetic subpopulations did not encode the ZH548 sequence at the 23 MP-12 consensus mutations. On the other hand, 4 and 2 mutations in M and L segments of MP-12 were found in ZH548 subpopulations. Thus, those 6 mutations were no longer MP-12-specific mutations. ZH548 encoded several unique mutations compared to other Egyptian strains, i.e., strains ZH501, ZH1776, and ZS6365. ZH548 subpopulations shared nucleotides at the mutation site common with those in the Egyptian strains, while MP-12 subpopulations did not share those nucleotides. Thus, MP-12 retains unique genetic subpopulations and has no evidence of reversion to the ZH548 sequence in the subpopulations. This study provides the first information regarding the genetic subpopulations of RVFV and shows the genetic stability of the MP-12 vaccine manufactured in MRC-5 cells.
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Szemiel AM, Failloux AB, Elliott RM. Role of Bunyamwera Orthobunyavirus NSs protein in infection of mosquito cells. PLoS Negl Trop Dis 2012; 6:e1823. [PMID: 23029584 PMCID: PMC3459826 DOI: 10.1371/journal.pntd.0001823] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Accepted: 08/06/2012] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Bunyamwera orthobunyavirus is both the prototype and study model of the Bunyaviridae family. The viral NSs protein seems to contribute to the different outcomes of infection in mammalian and mosquito cell lines. However, only limited information is available on the growth of Bunyamwera virus in cultured mosquito cells other than the Aedes albopictus C6/36 line. METHODOLOGY AND PRINCIPAL FINDINGS To determine potential functions of the NSs protein in mosquito cells, replication of wild-type virus and a recombinant NSs deletion mutant was compared in Ae. albopictus C6/36, C7-10 and U4.4 cells, and in Ae. aegypti Ae cells by monitoring N protein production and virus yields at various times post infection. Both viruses established persistent infections, with the exception of NSs deletion mutant in U4.4 cells. The NSs protein was nonessential for growth in C6/36 and C7-10 cells, but was important for productive replication in U4.4 and Ae cells. Fluorescence microscopy studies using recombinant viruses expressing green fluorescent protein allowed observation of three stages of infection, early, acute and late, during which infected cells underwent morphological changes. In the absence of NSs, these changes were less pronounced. An RNAi response efficiently reduced virus replication in U4.4 cells transfected with virus specific dsRNA, but not in C6/36 or C7/10 cells. Lastly, Ae. aegypti mosquitoes were exposed to blood-meal containing either wild-type or NSs deletion virus, and at various times post-feeding, infection and disseminated infection rates were measured. Compared to wild-type virus, infection rates by the mutant virus were lower and more variable. If the NSs deletion virus was able to establish infection, it was detected in salivary glands at 6 days post-infection, 3 days later than wild-type virus. CONCLUSIONS/SIGNIFICANCE Bunyamwera virus NSs is required for efficient replication in certain mosquito cell lines and in Ae. aegypti mosquitoes.
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Affiliation(s)
- Agnieszka M. Szemiel
- Biomedical Sciences Research Complex, School of Biology, University of St. Andrews, North Haugh, St. Andrews, Scotland, United Kingdom
| | | | - Richard M. Elliott
- Biomedical Sciences Research Complex, School of Biology, University of St. Andrews, North Haugh, St. Andrews, Scotland, United Kingdom
- * E-mail:
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