Caister Academic Press

Insect Molecular Virology: Advances and Emerging Trends | Book

Publisher: Caister Academic Press
Edited by: Bryony C. Bonning
Department of Entomology and Nematology, University of Florida
Pages: c. 258
Publication date: June 2019
ISBN: 978-1-912530-08-3
Price: GB £159 or US $319Buy book
Publication date: June 2019
ISBN: 978-1-912530-09-0
Price: GB £159 or US $319

The substantial costs of insect-associated viruses, ranging from honey bee decline to human, animal and plant disease, have driven investment in molecular research toward mitigation. Interest in insect viruses extends beyond these negative impacts however with biotechnological insect virus-based tools used to produce recombinant proteins, for gene therapy, vaccine production, and virus-induced gene silencing.

The volume opens with a description of the insect virome and the explosion in discovery of new viral taxa. The following four chapters focus on anti-viral immunity including endogenous viral elements some of which may provide the molecular basis for long-term anti-viral immunity, the discovery of new viral suppressors of RNA interference, the role of new classes of small RNA molecules in dictating infection outcomes, and the Drosophila-dicistrovirus model as a powerful resource for insect molecular virology. The application of omics tools to insect-vectored plant viral disease, recent advances in tetravirus, polydnavirus, and baculovirus research are then described. The final chapters review progress in baculovirus expression vector and surface display technologies for use in laboratory and therapeutic applications.

Written by leading experts, this work is essential reading for students and scholars of insect virology and immunology and provides a valuable resource for users of baculovirus-derived tools.

Table of contents
1. The Insect Virome: Opportunities and Challenges
Bryony C. Bonning
The insect virome is composed of a myriad of viruses. Both field populations and laboratory colonies of insects harbour diverse viruses, including viruses that infect the insect itself, viruses of microbes associated with the insect, and viruses associated with ingested materials. Metagenomics analysis for identification of virus-derived sequences has allowed for new appreciation of the extent and diversity of the insect virome. The complex interactions between insect viruses and host antiviral immune pathways (RNA interference and apoptosis), and between viruses and other members of the microbiome (e.g. Wolbachia) are becoming apparent. In this chapter, an overview of the diversity of viruses in insects and recent virus discovery research for specific insects and insect-derived cell lines is provided. The opportunities and challenges associated with the insect virome, including the potential impacts of viruses on both research and insect management programs are also addressed.
2. The Widespread Occurrence and Potential Biological Roles of Endogenous Viral Elements in Insect Genomes
Carol D. Blair, Ken E. Olson and Mariangela Bonizzoni
Modern genomic sequencing and bioinformatics approaches have detected numerous examples of DNA sequences derived from DNA and RNA virus genomes integrated into both vertebrate and insect genomes. Retroviruses encode RNA-dependent DNA polymerases (reverse transcriptases) and integrases that convert their RNA viral genomes into DNA proviruses and facilitate proviral DNA integration into the host genome. Surprisingly, DNA sequences derived from RNA viruses that do not encode these enzymes also occur in host genomes. Non-retroviral integrated RNA virus sequences (NIRVS) occur at relatively high frequency in the genomes of the arboviral vectors Aedes aegypti and Aedes albopictus, are not distributed randomly and possibly contribute to mosquito antiviral immunity, suggesting these mosquitoes could serve as a model system for unravelling the function of NIRVS. Here we address the following questions: What drives DNA synthesis from the genomes of non-retroviral RNA viruses? How does integration of virus cDNA into host DNA occur, and what is its biological function (if any)? We review current knowledge of viral integrations in insect genomes, hypothesize mechanisms of NIRVS formation and their potential impact on insect biology, particularly antiviral immunity, and suggest directions for future research.
3. Sensing Viral Infections in Insects: A Dearth of Pathway Receptors
Loïc Talide and Jean-Luc Imler and Carine Meignin
Insects, the most diverse group of animals, can be infected by an extraordinary diversity of viruses. Among them, arthropod-borne viruses can be transmitted to humans, while bee and silkworm viruses cause important economic losses. Like all invertebrates, insects rely solely on innate immunity to counter viral infections. Protein-based mechanisms, involving restriction factors and evolutionarily conserved signaling pathways regulating transcription factors of the NF-kB and STAT families, participate in the control of viral infections in insects. In addition, RNA-based responses play a major role in the silencing of viral RNAs. We review here our current state of knowledge on insect antiviral defense mechanisms, which include conserved as well as adaptive, insect-specific strategies. Identification of the innate immunity receptors that sense viral infection in insects remains a major challenge for the field.
4. miRNA Modulation of Insect Virus Replication
Verna Monsanto-Hearne and Karyn N. Johnson
The outcome of virus infection in insects is impacted by regulation of both host and virus gene expression. A class of small RNAs called microRNAs (miRNA) have emerged as important regulators of gene expression that can influence the outcome of virus infection. miRNA regulation occurs at a comparatively late stage of gene expression, allowing for rapid control and fine-tuning of gene expression levels. Here we discuss the biogenesis of miRNAs from both host and virus genomes, the interactions that lead to regulation of gene expression, and the miRNA-mRNA interactions that lead to either antivirus or provirus consequences in the course of virus infection in insects.
5. Dicistrovirus-Host Molecular Interactions
Reid Warsaba, Jibin Sadasivan and Eric Jan
Members of the family Dicistroviridae are small RNA viruses containing a monopartite positive-sense RNA genome. Dicistroviruses mainly infect arthropods, causing diseases that impact agriculture and the economy. In this chapter, we provide an overview of current and past research on dicistroviruses including the viral life cycle, viral translational control mechanisms, virus structure, and the use of dicistrovirus infection in Drosophila as a model to identify insect antiviral responses. We then delve into how research on dicistrovirus mechanisms has yielded insights into ribosome dynamics, RNA structure/function and insect innate immunity signaling. Finally, we highlight the diseases caused by dicistroviruses, their impacts on agriculture including the shrimp and honey bee industries, and the potential use of dicistroviruses as biopesticides. Although knowledge of the mechanisms underlying dicistrovirus virus-host interactions is limited, the establishment of the first infectious clone should accelerate the discovery of new mechanistic insights into dicistrovirus infections and pathogenesis.
6. Looking Through the Lens of 'Omics Technologies: Insights Into the Transmission of Insect Vector-borne Plant Viruses
Jennifer R. Wilson, Stacy L. DeBlasio, Mariko M. Alexander and Michelle Heck
Insects in the orders Hemiptera and Thysanoptera transmit viruses and other pathogens associated with the most serious diseases of plants. Plant viruses transmitted by these insects target similar tissues, genes, and proteins within the insect to facilitate plant-to-plant transmission with some degree of specificity at the molecular level. 'Omics experiments are becoming increasingly important and practical for vector biologists to use towards better understanding the molecular mechanisms and biochemistry underlying transmission of these insect-borne diseases. These discoveries are being used to develop novel means to obstruct virus transmission into and between plants. In this chapter, we summarize 'omics technologies commonly applied in vector biology and the important discoveries that have been made using these methods, including virus and insect proteins involved in transmission, as well as the tri-trophic interactions involved in host and vector manipulation. Finally, we critically examine the limitations and new horizons in this area of research, including the role of endosymbionts and insect viruses in virus-vector interactions, and the development of novel control strategies.
7. Advances in Tetravirus Research: New Insight Into the Infectious Virus Lifecycle and an Expanding Host Range
Rosemary Ann Dorrington, Meesbah Jiwaji, Janet Awino Awando and Mart-Mari de Bruyn
Tetraviruses are a group of relatively unknown small RNA viruses with particles that display a characteristic T=4 capsid architecture. Tetraviruses are classified into three families, the Alphatetraviridae, Permutotetraviridae and Carmotetraviridae, according to the divergent characteristics of their respective viral replicases. Tetraviruses generally infect the larvae of lepidopteran insect species, many of which are important agricultural pests and, until recently, were thought to have an unusually narrow host range and tissue tropism. The development of experimental systems for studying the viral infectious life cycle in tissue culture has permitted the extension of the virus host range to mammalian cells and plants. This chapter will review recent advances in the understanding of the biology of tetraviruses, highlighting new information on the expression and functional characterisation of viral proteins and the development of biological systems for elucidating the molecular mechanisms of infection, viral replication and host range.
8. Polydnaviruses: Evolution and Function
Michael R. Strand and Gaelen R. Burke
Polydnaviruses (PDVs) were originally viewed as large DNA viruses that are beneficial symbionts of parasitoid wasps. Two groups of PDVs were also recognized: bracoviruses (BVs), which are associated with wasps in the family Braconidae, and ichnoviruses (IVs), which are associated with wasps in the family Ichneumonidae. Results to date indicate that BVs are endogenous virus elements (EVEs) that evolved from an ancient betanudivirus. IVs are also likely EVEs but are unrelated to BVs. BVs and IVs are very unusual relative to most known EVEs because they retain many viral functions that benefit wasps in parasitizing hosts. However, BVs and IVs cannot be considered beneficial symbionts because all components of their genomes are fixed in wasps. Recent studies indicate that other nudiviruses have endogenized in insects. Each exhibits a different functional fate from BVs but shares certain architectural features. We discuss options for classifying BVs and other endogenized nudiviruses. We also discuss future directions.
9. Advances in Molecular Biology of Baculoviruses
Manli Wang and Zhihong Hu
Baculoviridae constitutes a family of insect-specific, large DNA viruses with a unique life cycle characterized by the production of two morphologically distinct virions, the budded virus (BV) and the occlusion-derived virus (ODV). ODV and BV, with different tissue tropisms, have been widely applied in the areas of biological control and biotechnology, respectively. In nature, baculovirus infection of susceptible host larvae is initiated by ODV-mediated primary infection, followed by the production of BV for spreading infection within larval body. Across millions of years of co-evolution with their hosts, baculoviruses have developed dedicated mechanisms for efficient entry/egress, genome replication/transcription, and virion assembly by employing either their own proteins or host machineries. They have also adopted versatile strategies to precisely regulate the immunity, behaviors and physiology of hosts to facilitate their own replication and dispersal. In this chapter, research advances relating to key aspects of the baculovirus life cycle are reviewed, and the application of a newly-developed baculovirus synthetic biology technology is introduced. Finally, future avenues for baculovirus research are discussed.
10. Recent Developments in the Use of Baculovirus Expression Vectors
Robert D. Possee, Adam C. Chambers, Leo P. Graves, Mine Aksular and Linda A. King
Over 35 years since it was established to make recombinant proteins, the baculovirus expression vector system continues to develop and improve. Early systems for recombinant virus selection were laborious, but better methods were rapidly devised that enabled non-virologists to use baculovirus vectors successfully in a wide range of applications. These applications include multiple gene expression for complex molecules, production of adeno-associated virus-like particles for gene therapy, the use of baculovirus budded virus for the same purpose, numerous potential human and animal vaccines, and for other therapeutic proteins. A number of products for human and veterinary use are now on the market, which attests to the utility of the systems. Despite these successes, baculovirus vectors essentially remain in a relatively primitive state of development. Many proteins, particularly membrane-bound or secreted products, continue to be difficult to produce. Various research groups are working to identify potential areas of improvement, which if combined into an ideal vector might offer considerable advances to the system. This chapter will review some of the most recent reports and highlight those that might have generic application for recombinant protein synthesis in insect cells. We also summarize parallel developments in host cells used for baculovirus expression and how culture conditions can influence protein production.
11. Baculovirus as Versatile Vectors for Protein Display and Biotechnological Applications
Chih-Hsuan Tsai, Sung-Chan Wei, Huei-Ru Lo and Yu-Chan Chao
The baculovirus-insect cell system has long been deployed for a variety of applications including for use as biopesticides, for recombinant protein production, transient transgene expression, tissue therapy, and for vaccine production. Apart from the advantage of large-scale heterologous protein production with appropriate eukaryotic post-translational modification, foreign proteins can also be displayed on the viral envelope. This surface-display technology preserves the native multimeric structure of the protein, thereby expanding the clinical and pharmaceutical utility of the baculovirus system. Recombinant baculoviruses displaying major antigens for human or animal viruses can serve as appropriate vaccines. They can also serve as effective diagnostic platforms and various cell-based assay systems. In this review, we discuss progress in applying baculovirus surface-display, including protein display on the envelope, capsid, and occlusion bodies of baculoviruses, as well as on cells. We will also describe strategies for improvement of this biotechnological approach.

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(EAN: 9781912530083 9781912530090 Subjects: [microbiology] [plant science] [virology] )