Role of microRNAs in insect-baculovirus interactions

MicroRNAs (miRNAs) constitute a novel class of gene expression regulators and are found to be involved in regulating a wide range of biological processes such as development, cell cycle, metabolism, apoptosis, immunity, host-pathogen interactions etc. Generally miRNAs negatively regulate the gene expression at the post-transcriptional level by binding to the complementary target mRNA sequences. These tiny molecules are abundantly found in higher eukaryotes and viruses. Most of the DNA viruses of animals and insects encode miRNAs including baculoviruses. Baculoviruses are the insect-specific viruses that cause severe infection and mortality mainly in insect larvae of the order Lepidoptera, Diptera, and Hymenoptera. These enveloped viruses have multiple applications in biotechnology and biological pest control methods. For a better understanding of baculoviruses, it is necessary to elucidate the molecular basis of insect-baculovirus interactions. Recent advancement in the technologies for studying the gene expression has accelerated the discovery of new players in the insect-baculovirus interactions. MiRNAs are the emerging and fate-determining players of host-viral interactions. The long history of host and virus co-evolution suggests that the virus keeps on evolving its arsenals to succeed in infection whereas the host continues investing in antiviral defense mechanisms. In this review, I aim to highlight the recent information and understanding of the baculovirus-encoding miRNAs and their functions in regulating viral as well as host genes. Additionally, insect-derived miRNAs response to baculovirus infection is also discussed. A detailed critical view about the regulatory roles of miRNAs in insect-baculovirus interactions will help us to understand molecular networks amid these interactions and develop a sustainable antiviral strategy.

Adaptation of the Se301 insect cell line to suspension culture. Effect of turbulence on growth and on production of nucleopolyhedrovius (SeMNPV)

As chemical pesticides are being banned as control agents for agricultural pests, the use of the highly specific, safe to non-target organisms baculoviruses has been proposed. These viruses can be produced either in vivo or in vitro. In vitro production requires appropriated host insect cell lines with the ability for growing as freely-suspended cells. In this work, the Spodoptera exigua Se301 cell line was used to produce the commercially available S. exigua nucleopolyhedrovirus (SeMNPV) in suspension. Se301 cells showed to be very sensitive to the hydrodynamic shear rates developed in bioreactors. A process of progressive adaptation to freely-suspended cultures using protective additives against shear stress and disaggregant was proposed. The best combinations were polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP) with the disaggregant dextran sulfate (DS). Both static and freely-suspended Se301 cell cultures were successfully infected with the SeMNPV baculovirus. Production of occluded baculovirus (OB) increased with the multiplicity of infection (MOI > 0.1).

Neuropeptide physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Enhancing insecticidal efficacy of baculovirus by early expressing an insect neurotoxin, LqhIT2, in infected Trichoplusia ni larvae

LqhIT(2), an insect specific neurotoxin from the venom of Leiurus quinquestriatus hebraeus, has been demonstrated to improve insecticidal efficacy of Autographa californica nuclear polyhedrosis virus (AcMNPV). A polyhedrin-positive recombinant AcMNPVvAcP(hsp70)EGFP/P(pag90)IT(2) was engineered for larvae to express the enhanced green fluorescence protein (EGFP) and LqhIT(2) under the control of P(hsp70) and P(pag90) promoters, respectively. This would allow a visual observation of the viral infection and an improvement of the insecticidal efficacy. The insecticidal activity of this recombinant baculovirus, a wild type AcMNPV and four other recombinant baculoviruses, was evaluated and compared in terms of mortality, body weight, median lethal time (LT(50)), and median lethal concentration (LC(50)). Insecticidal efficacy was unaltered when treated with vAcP(hsp70)EGFP, moderately improved when infected by vAcP(10)IT(2) (a P(10)-promoted LqhIT ( 2 ) gene), and significantly elevated when treated with vAcP(pag90)IT(2) or vAcP(hsp70)EGFP/P(pag90)IT(2). No apparent difference was observed in insecticidal efficacy when additional EGFP was expressed as a visible marker. These results suggest that recombinant AcMNPV vAcP(hsp70)EGFP/P(pag90)IT(2) may be used as an effective insecticide against Trichoplusia ni and other lepidopterous insect pests.

Genes in new environments: genetics and evolution in biological control

The availability of new genetic technologies has positioned the field of biological control as a test bed for theories in evolutionary biology and for understanding practical aspects of the release of genetically manipulated material. Purposeful introductions of pathogens, parasites, predators and herbivores, when considered as replicated semi-natural field experiments, show the unpredictable nature of biological colonization. The characteristics of organisms and their environments that determine this variation in the establishment and success of biological control can now be explored using genetic tools. Lessons from studies of classical biological control can help inform researchers and policy makers about the risks that are associated with the release of genetically modified organisms, particularly with respect to long-term evolutionary changes.

Epizootiology and transmission of a newly discovered baculovirus from the mosquitoes Culex nigripalpus and C. quinquefasciatus

Reports of mosquito baculoviruses are extremely uncommon and epizootics in field populations are rarely observed. We describe a baculovirus that was responsible for repeated and extended epizootics in field populations of Culex nigripalpus and C. quinquefasciatus over a 2 year period. These mosquito species are important vectors of St Louis and Eastern equine encephalitis in the United States. Our initial attempts to transmit this baculovirus to mosquitoes in the laboratory were unsuccessful. A salt mixture similar to that found in water supporting infection in the field was used in laboratory bioassays and indicated that certain salts were crucial to transmission of the virus. Further investigations revealed conclusively that transmission is mediated by divalent cations: magnesium is essential, whereas calcium inhibits virus transmission. These findings represent a major advancement in our understanding of the transmission of baculoviruses in mosquitoes and will allow characterization of the virus in the laboratory. In addition, they can explain, in great part, conditions that support epizootics in natural populations of mosquitoes that vector life-threatening diseases of man and animals.

Comparative effects of a genetically engineered insect virus and a growth-regulating insecticide on microbial communities in aquatic microcosms

The effects of a genetically engineered insect baculovirus on indigenous aquatic microbial communities were determined in closed, recirculating aquatic microcosms, and compared with the effects of a natural strain of the virus and of a growth-regulating insecticide, Dimilin. The recombinant virus was a nuclear polyhedrosis virus (NPV) of the spruce budworm (Choristoneura fumiferana (Cf)) with a lacZ marker gene inserted into the egt region of the CfNPV. The natural virus was Ireland strain CfNPV. Microbial measurement endpoints included decomposition activity (mass loss of organic material), respiration on two different substrates (O2 consumption), heterotrophic bacterial abundance (plate counts), and microbial community metabolic profiles (carbon source utilization patterns in Biolog GN microplates). Viral DNA of both the natural strain and the recombinant viruses, detected by polymerase chain reaction techniques, settled out of the microcosm water and accumulated on bottom substrates within 3 days of the microcosm inoculations. The viral DNA persisted in bottom substrates for the duration of the 21-day experimental period, although there was some evidence that the recombinant virus was less stable than the natural strain in particulate organic matter. No significant changes in microbial decomposition or respiration activity, bacterial abundance, or average metabolic responses were detected by a time trend analysis in microcosms inoculated with either the lacZ recombinant virus or the natural Ireland strain CfNPV. Significant effects on microbial decomposition and respiration activity were detected in microcosms treated with the growth-regulating insecticide at, and above, the expected environmental concentrations. Despite significant effects on microbial community functional attributes in Dimilin-treated microcosms, there were no detectable changes in community structure in terms of metabolic profiles or bacterial abundance.