A Baculovirus immediate-early gene, ie1, promoter drives efficient expression of a transgene in both Drosophila melanogaster and Bombyx mori

Evolution of temperature preference in flies of the genus Drosophila

The preference for a particular thermal range is a key determinant of the distribution of animal species. However, we know little on how temperature preference behaviour evolves during the colonization of new environments. Here we show that at least two distinct neurobiological mechanisms drive the evolution of temperature preference in flies of the genus Drosophila. Fly species from mild climates (D. melanogaster and D. persimilis) avoid both innocuous and noxious heat, and we show that the thermal activation threshold of the molecular heat receptor Gr28b.d precisely matches species-specific thresholds of behavioural heat avoidance. We find that desert-dwelling D. mojavensis are instead actively attracted to innocuous heat. Notably, heat attraction is also mediated by Gr28b.d (and by the antennal neurons that express it) and matches its threshold of heat activation. Rather, the switch in valence from heat aversion to attraction correlates with specific changes in thermosensory input to the lateral horn, the main target of central thermosensory pathways and a region of the fly brain implicated in the processing of innate valence1-5. Together, our results demonstrate that, in Drosophila, the adaptation to different thermal niches involves changes in thermal preference behaviour, and that this can be accomplished using distinct neurobiological solutions, ranging from shifts in the activation threshold of peripheral thermosensory receptor proteins to a substantial change in the way temperature valence is processed in the brain.

Subunit vaccine of PCV3 capsid protein produced by sf9 cells with double knockout of Caspase-1 and Dronc induces strong immune response in mice

Porcine circovirus type 3 (PCV3) associated with multisystemic clinicopathological diseases in swine herds has caused economic losses and there is no available commercial vaccine. Production of PCV3 capsid protein (Cap) by Spodoptera frugiperda 9 (sf9) cells using baculovirus expression vector system (BEVS) is a valid strategy to develop vaccines. Here, we report that subunit vaccine of PCV3 produced by sf9 cells with double knockout of Caspase-1 and Dronc genes induces strong immune response in mice. Three kinds of knockout sf9 cells aimed at Caspase-1 gene, Dronc gene and both genes were successfully generated by clustered regularly interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) system, and sequence analysis confirmed this. The anti-apoptosis ability of three kinds of knockout sf9 cells was assessed, and double knockout sf9 cells are the best. The expression of PCV3 Cap was enhanced in double knockout sf9 cells compared to wild type sf9 cells, and subunit vaccines were produced by PCV3 Cap expressed from double knockout sf9 cells and wild type cells, respectively. Results of immunological experiment in mice showed subunit vaccine of PCV3 Cap from double knockout sf9 cells induces higher level of serum antibody, stimulates lymphocyte proliferation and enhances expression of IL-2, IFN-γ, IL-4 and IL-10 compared to wild type cells. These results present knockout sf9 cells to enhance the expression of protein in BEVS, and provide a technical platform for vaccine development of PCV3.

Transgenic overexpression of UDP glycosyltransferase gene UGT41A3 induces resistance to nucleopolyhedrovirus in Bombyx mori

Bombyx mori nuclear polyhedrosis, caused by B. mori nucleopolyhedrovirus (BmNPV), threatens sericulture seriously. To explore strategies for controlling it, the UDP glycosyltransferase gene UGT41A3 (BmUGT41A3) was targeted. UGT is involved in exogenous substances detoxification and endogenous biomass regulation in insects. Early embryos of the BmNPV-sensitive variety 'HYB' were used to obtain the transgenic line HYB-UGT41A3, overexpressing BmUGT41A3 under the IE1 promoter. qPCR results revealed that, compared with the wild-type control 'HYB', BmUGT41A3 was upregulated during the individual developmental stages of HYB-UGT41A3 from silkworm eggs to fifth-instar larvae; peak expression was observed in the third-instar larvae, which presented the most significantly upregulated expression. Individual-tissues qPCR results revealed that BmUGT41A3 expression was highest in the hemocytes of HYB-UGT41A3, followed by the midgut, whereas expression in HYB was very low. Gradient feeding of BmNPV on HYB-UGT41A3 and control 'HYB' larvae on the first day of the second-instar stage. The results revealed that the LC50 of HYB-UGT41A3 reached 4.040 × 107 particles/mL, which was 20-fold greater than that of HYB. The decrease in the BmNPV load was more significant in HYB-UGT41A3 than in HYB at 48 h after viral inoculation. These results indicate BmUGT41A3 overexpression inhibits BmNPV proliferation and improve resistance to BmNPV in B. mori.

Establishing a dominant early larval sex-selection strain in the Asian malaria vector Anopheles stephensi

BACKGROUND

Genetic biocontrol interventions targeting mosquito-borne diseases require the release of male mosquitoes exclusively, as only females consume blood and transmit pathogens. Releasing only males eliminates the risk of increasing mosquito bites and spreading pathogens while enabling effective population control. The aim of this study is to develop robust sex-sorting methods for early larval stages in mosquitoes, enabling scalable male-only releases for genetic biocontrol interventions.

METHODS

To address the challenge of sex-sorting in the Asian malaria vector Anopheles stephensi, we engineer Sexing Element Produced by Alternative RNA-splicing of a Transgenic Observable Reporter (SEPARATOR). This dominant fluorescent-based method, previously proven effective in Aedes aegypti, exploits sex-specific alternative splicing of a reporter to ensure exclusive male-specific expression early in development. The sex-specific alternative RNA splicing of the doublesex gene was selected as a target for engineering SEPARATOR due to its evolutionary conservation in insects. To expand SEPARATOR's applicability for genetic sexing, we assessed the cross-species sex-specific RNA splicing activity of the An. gambiae doublesex (AngDsx) splicing module in An. stephensi. Male-specific enhanced green fluorescent protein (EGFP) expression was verified throughout the mosquito life cycle using a fluorescent stereomicroscope.

RESULTS

Our results confirm that SEPARATOR regulates male-specific EGFP expression in An. stephensi and enables reliable positive male selection from the first instar larval stages. Molecular analysis demonstrates that male-specific EGFP expression is dependent on doublesex sex-specific splicing events. Additionally, the splicing module from An. gambiae operates effectively in An. stephensi, demonstrating evolutionary conservation in sex-specific splicing events between these species.

CONCLUSIONS

SEPARATOR's independence from sex-chromosome linkage provides resistance to breakage that could be mediated by meiotic recombination and chromosomal rearrangements, making it highly suitable for mass male releases. By enabling precise male selection from the first instar larval stages, SEPARATOR represents a significant advancement that will aid in the genetic biocontrol for Anopheles mosquitoes.

Establishing a Male-Positive Genetic Sexing Strain in the Asian Malaria Vector Anopheles stephensi

Genetic biocontrol interventions targeting mosquito-borne diseases require the release of male mosquitoes exclusively, as only females consume blood and transmit human pathogens. This reduces the risk of spreading pathogens while enabling effective population control. Robust sex sorting methods to enable early larval sorting in mosquitoes need to be developed to allow for scalable sex sorting for genetic biocontrol interventions. This study applies the SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) system, previously developed for Aedes aegypti, to the Asian malaria vector Anopheles stephensi. We hypothesized that the intron from the doublesex gene in Anopheles gambiae would function in An. stephensi due to evolutionary conservation. Our results confirm that the splicing module from An. gambiae operates effectively in An. stephensi, demonstrating evolutionary conservation in sex-specific splicing events between these species. This system enables reliable positive male selection from first instar larval to pupal stages. RT-PCR analysis demonstrates that male-specific EGFP expression is dependent on doublesex sex-specific splicing events. The SEPARATOR system's independence from sex-chromosome linkage confers resistance to meiotic recombination and chromosomal rearrangements. This approach may facilitate the mass release of males, and the cross-species portability of SEPARATOR establishes it as a valuable tool for genetic biocontrol interventions across various pest species.

Arthropod promoters for genetic control of disease vectors

Vector-borne diseases (VBDs) impose devastating effects on human health and a heavy financial burden. Malaria, Lyme disease, and dengue fever are just a few examples of VBDs that cause severe illnesses. The current strategies to control VBDs consist mainly of environmental modification and chemical use, and to a small extent, genetic approaches. The genetic approaches, including transgenesis/genome modification and gene-drive technologies, provide the basis for developing new tools for VBD prevention by suppressing vector populations or reducing their capacity to transmit pathogens. The regulatory elements such as promoters are required for a robust sex-, tissue-, and stage-specific transgene expression. As discussed in this review, information on the regulatory elements is available for mosquito vectors but is scant for other vectors.

Transgenic black soldier flies for production of carotenoids

The black soldier fly (BSF), Hermetia illucens, has gained traction recently as a means to achieve closed-loop production cycles. BSF can subsist off mammalian waste products and their consumption of such waste in turn generates compost that can be used in agricultural operations. Their environmental impact is minimal and BSF larvae are edible, with a nutritional profile high in protein and other essential vitamins. Therefore, it is conceivable to use BSF as a mechanism for both reducing organic waste and maintaining a low-impact food source for animal livestock or humans. The main drawback to BSF as a potential human food source is they are deficient in fat-soluble vitamins such as Vitamins A, D, and E. While loading BSF with essential vitamins may be achieved via diet-based interventions, this undercuts the goal of a closed-loop as specialized diets would require additional supply chains. An alternative is to genetically engineer BSF that can synthesize these essential vitamins. Here we describe a BSF line that has been engineered with the two main carotenoid biosynthetic genes, CarRA and CarB for production of provitamin carotenoids within the Vitamin A family. Our data describe the manipulation of the BSF genome to insert transgenes for expression of functional protein products.

A Fluorescent Sex-Sorting Technique for Insects with the Demonstration in Drosophila melanogaster

Recent advances in insect genetic engineering offer alternative genetic biocontrol solutions to control populations of pests and disease vectors. While success has been achieved, sex-sorting remains problematic for scaling many genetic biocontrol interventions. Here, we describe the development of a genetically stable sex-sorting technique for female and male selection with a proof of concept in Drosophila melanogaster termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter). This elegant approach utilizes dominantly expressed fluorescent proteins and differentially spliced introns to ensure sex-specific expression. The system has the potential for adaptability to various insect species and application for high-throughput insect sex-sorting.

Efficient sex separation by exploiting differential alternative splicing of a dominant marker in Aedes aegypti

Only female mosquitoes consume blood giving them the opportunity to transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from early larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

A DNA Plasmid-Based Approach for Efficient Synthesis of Sacbrood Virus Infectious Clones within Host Cells

RNA viruses are often cited as a significant factor affecting the populations of both domestic honey bees and wild pollinators. To expedite the development of effective countermeasures against these viruses, a more comprehensive understanding of virus biology necessitates extensive collaboration among scientists from diverse research fields. While the infectious virus clone is a robust tool for studying virus diseases, the current methods for synthesizing infectious clones of bee-infecting RNA viruses entail the in vitro transcription of the viral genome RNA in 8-10 kb, presenting challenges in reproducibility and distribution. This article reports on the synthesis of an infectious clone of the Chinese variant sacbrood virus (SBV) using a DNA plasmid containing an Autographa californica multiple nucleopolyhedrovirus (AcMNPV) immediate-early protein (IE1) promoter to trigger transcription of the downstream viral genome within hosts. The results demonstrate that the IE1-SBV plasmid can synthesize SBV clones in a widely used lepidopteran immortal cell line (Sf9) and honey bee pupae. Furthermore, the negative strand of the clone was detected in both Sf9 cells and honey bee pupae, indicating active infection and replication. However, the transfection of Sf9 cells was observed in only a limited proportion (less than 10%) of the cells, and the infection did not appear to spread to adjacent cells or form infective virions. The injection of honey bee pupae with 2500 ng of the IE1-SBV plasmid resulted in high infection rates in Apis cerana pupae but low rates in A. mellifera pupae, although the dosage was comparatively high compared with other studies using in vitro transcribed viral RNA. Our findings suggest that the synthesis of bee-infecting RNA viruses using DNA plasmids is feasible, albeit requiring additional optimization. However, this method holds substantial potential for facilitating the production of clones with various sequence modifications, enabling the exploration of viral gene functions and biology. The ease of distributing infectious clones in DNA plasmid form may foster collaboration among scientists in applying the clone to bee biology, ecology, and behavior, ultimately offering a comprehensive approach to managing virus diseases in the future.

A fluorescent sex-sorting technique for insects with the demonstration in Drosophila melanogaster

Recent advances in insect genetic engineering offer alternative genetic biocontrol solutions to control populations of pests and disease vectors. While success has been achieved, sex-sorting remains problematic for scaling many genetic biocontrol interventions. Here we describe the development of a sex-sorting technique for female and male selection with a proof-of-concept in D. melanogaster termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter). This approach utilizes dominant fluorescent proteins and differentially spliced introns to ensure sex-specific expression. The system has the potential for adaptability to various insect species and application for high-throughput insect sex-sorting.

Efficient Sex Separation by Exploiting Differential Alternative Splicing of a Dominant Marker in Aedes aegypti

Only female mosquitoes consume blood and transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS®) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed in males. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Application of Baculovirus Expression Vector System (BEVS) in Vaccine Development

Vaccination is one of the most effective strategies to control epidemics. With the deepening of people's awareness of vaccination, there is a high demand for vaccination. Hence, a flexible, rapid, and cost-effective vaccine platform is urgently needed. The baculovirus expression vector system (BEVS) has emerged as a promising technology for vaccine production due to its high safety, rapid production, flexible product design, and scalability. In this review, we introduced the development history of BEVS and the procedures for preparing recombinant protein vaccines using the BEVS platform and summarized the features and limitations of this platform. Furthermore, we highlighted the progress of the BEVS platform-related research, especially in the field of vaccine. Finally, we provided a new prospect for BEVS in future vaccine manufacturing, which may pave the way for future BEVS-derived vaccine development.

Sparse and stereotyped encoding implicates a core glomerulus for ant alarm behavior

Ants communicate via large arrays of pheromones and possess expanded, highly complex olfactory systems, with antennal lobes in the brain comprising up to ∼500 glomeruli. This expansion implies that odors could activate hundreds of glomeruli, which would pose challenges for higher-order processing. To study this problem, we generated transgenic ants expressing the genetically encoded calcium indicator GCaMP in olfactory sensory neurons. Using two-photon imaging, we mapped complete glomerular responses to four ant alarm pheromones. Alarm pheromones robustly activated ≤6 glomeruli, and activity maps for the three pheromones inducing panic alarm in our study species converged on a single glomerulus. These results demonstrate that, rather than using broadly tuned combinatorial encoding, ants employ precise, narrowly tuned, and stereotyped representations of alarm pheromones. The identification of a central sensory hub glomerulus for alarm behavior suggests that a simple neural architecture is sufficient to translate pheromone perception into behavioral outputs.

Sex separation by body color via a W-chromosome-linked transgene

Sex separation processes are important for commercial insect production and sterile insect techniques. Here, we describe the transgenic insertion of a DsRed expression cassette driven by the enhancer HR3 and strong promoter IE1 into the silkworm W chromosome as a dominant visible marker of sex separation. The obtained transgenic lines showed female-specific body color visible to the naked eye at the second- to fifth-instar larval, pupal and adult stages, and their performance traits were comparable to those of a nontransgenic practical silkworm variety. This strategy can greatly facilitate the sex separation of silkworms for male-only rearing and to obtain hybrids while avoiding sibling mating, and it can also be applied to the sex separation of other light-colored insects.

Genome Editing of Silkworms

Silkworm is a lepidopteran insect that has been used as a model for a wide variety of biological studies. The microinjection technique is available, and it is possible to cause transgenesis as well as target gene disruption via the genome editing technique. TALEN-mediated knockout is especially effective in this species. We also succeeded in the precise and efficient integration of a donor vector using the precise integration into target chromosome (PITCh) method. Here we describe protocols for ZFN (zinc finger nuclease)-, TALEN (transcription activator-like effector nuclease)-, and CRISPR/Cas9-mediated genome editing as well as the PITCh technique in the silkworm. We consider that all of these techniques can contribute to the further promotion of various biological studies in the silkworm and other insect species.

Gene expression in Verson's glands of the fall armyworm suggests their role in molting and immunity

Verson's glands are segmental pairs of dermal glands attached to the epidermis in lepidopteran larvae. They produce macromolecules during intermolt period and empty them during each molt. Morphological, histochemical, developmental, and protein analysis studies have been conducted to determine the functions of Verson's glands. However, the exact role of Verson's glands remains unclear. In our previous study, a strain of transgenic fall armyworm, Spdoptera frugiperda expressing green fluorescence protein (GFP) and Systemic RNA interference defective protein 1 (SID1) from Caenorhabditis elegans was established to improve RNA interference (RNAi) efficiency. Unexpectedly, we found that GFP fluorescence was significantly brighter in Verson's glands than in other tissues. Also, RNAi efficiency improved more in Verson's glands than in other tissues. We took advantage of improved RNAi efficiency to explore the function of Verson's glands. RNA-seq analysis revealed that genes highly expressed in Verson's glands code for cuticular proteins, molting fluid proteins, hemolymph proteins, and antimicrobial peptides. Injection of dsRNA targeting essential genes, inhibitor of apoptosis (IAP), Actin, and vacuolar-type ATPase (VATPase) interfered with Verson's glands growth. These results revealed that Verson's glands may contribute to hemolymph, cuticle, molting fluid, and immune response during molting. This study also provide useful tools for future research in identifying the physiological role of Verson's glands in lepidopteran insects.

Genetic engineering of baculovirus-insect cell system to improve protein production

The Baculovirus Expression Vector System (BEVS), a mature foreign protein expression platform, has been available for decades, and has been effectively used in vaccine production, gene therapy, and a host of other applications. To date, eleven BEVS-derived products have been approved for use, including four human vaccines [Cervarix against cervical cancer caused by human papillomavirus (HPV), Flublok and Flublok Quadrivalent against seasonal influenza, Nuvaxovid/Covovax against COVID-19], two human therapeutics [Provenge against prostate cancer and Glybera against hereditary lipoprotein lipase deficiency (LPLD)] and five veterinary vaccines (Porcilis Pesti, BAYOVAC CSF E2, Circumvent PCV, Ingelvac CircoFLEX and Porcilis PCV). The BEVS has many advantages, including high safety, ease of operation and adaptable for serum-free culture. It also produces properly folded proteins with correct post-translational modifications, and can accommodate multi-gene- or large gene insertions. However, there remain some challenges with this system, including unstable expression and reduced levels of protein glycosylation. As the demand for biotechnology increases, there has been a concomitant effort into optimizing yield, stability and protein glycosylation through genetic engineering and the manipulation of baculovirus vector and host cells. In this review, we summarize the strategies and technological advances of BEVS in recent years and explore how this will be used to inform the further development and application of this system.

Intron-derived small RNAs for silencing viral RNAs in mosquito cells

Aedes aegypti and Ae. albopictus are the main vectors of mosquito-borne viruses of medical and veterinary significance. Many of these viruses have RNA genomes. Exogenously provided, e.g. transgene encoded, small RNAs could be used to inhibit virus replication, breaking the transmission cycle. We tested, in Ae. aegypti and Ae. albopictus cell lines, reporter-based strategies for assessing the ability of two types of small RNAs to inhibit a chikungunya virus (CHIKV) derived target. Both types of small RNAs use a Drosophila melanogaster pre-miRNA-1 based hairpin for their expression, either with perfect base-pairing in the stem region (shRNA-like) or containing two mismatches (miRNA-like). The pre-miRNA-1 stem loop structure was encoded within an intron; this allows co-expression of one or more proteins, e.g. a fluorescent protein marker tracking the temporal and spatial expression of the small RNAs in vivo. Three reporter-based systems were used to assess the relative silencing efficiency of ten shRNA-like siRNAs and corresponding miRNA-like designs. Two systems used a luciferase reporter RNA with CHIKV RNA inserted either in the coding sequence or within the 3’ UTR. A third reporter used a CHIKV derived split replication system. All three reporters demonstrated that while silencing could be achieved with both miRNA-like and shRNA-like designs, the latter were substantially more effective. Dcr-2 was required for the shRNA-like siRNAs as demonstrated by loss of inhibition of the reporters in Dcr-2 deficient cell lines. These positive results in cell culture are encouraging for the potential use of this pre-miRNA-1-based system in transgenic mosquitoes.

Mosquitoes are important globally, spreading viral diseases worldwide. Chikungunya virus causes epidemics of disease in people. Here we have investigated using two types of small RNAs and pathways inherent in Aedes aegypti mosquitoes to target a piece of the chikungunya virus’s genome, potentially preventing viral replication. We express these small RNAs using a pre-miRNA-1 based system, inserted into the intron within a commonly used promoter. We have used reporter systems in cell lines which can give preliminary indications of how these systems might work in mosquitoes. Our results indicate that short-hairpin-like designs are more effective than micro-RNA-like designs at knocking down expression of their targets. This knock-down requires Dcr-2 indicating that the short-hairpin-like RNAs are likely using the endo-siRNA pathway to degrade mRNA which contains their complementary RNA.

Transgenic tools for targeted chromosome rearrangements allow construction of balancer chromosomes in non-melanogaster Drosophila species

Perhaps the most valuable single set of resources for genetic studies of Drosophila melanogaster is the collection of multiply inverted chromosomes commonly known as balancer chromosomes. Balancers prevent the recovery of recombination exchange products within genomic regions included in inversions and allow perpetual maintenance of deleterious alleles in living stocks and the execution of complex genetic crosses. Balancer chromosomes have been generated traditionally by exposing animals to ionizing radiation and screening for altered chromosome structure or for unusual marker segregation patterns. These approaches are tedious and unpredictable, and have failed to produce the desired products in some species. Here, I describe transgenic tools that allow targeted chromosome rearrangements in Drosophila species. The key new resources are engineered reporter genes containing introns with yeast recombination sites and enhancers that drive fluorescent reporter genes in multiple body regions. These tools were used to generate a doubly inverted chromosome 3R in Drosophila simulans that serves as an effective balancer chromosome.

Identification of Helicoverpa armigera promoters for biotechnological applications

Helicoverpa armigera and Helicoverpa zea are highly polyphagous major agricultural pests with a global distribution. Their control is based on insecticides, however, new, effective, and environmentally friendly control tools are required to be developed and validated. In an effort to facilitate the development of advanced biotechnological tools in these species that will take advantage of new powerful molecular biology techniques like CRISPR/Cas9, we used available transcriptomic data and literature resources, in order to identify RNA polymerase II and III promoters active in RP-HzGUT-AW1(MG), a midgut derived cell line from Helicoverpa zea. Following functional analysis in insect cell lines, four RNA polymerase II promoters from the genes HaLabial, HaTsp-2A, HaPtx-I and HaCaudal were found to exhibit high transcriptional activity in vitro. The HaTsp-2A promoter did not exhibit any activity in the non-midgut derived cell lines Sf-9 and Hi-5 despite high sequence conservation among Lepidoptera, suggesting that it may function in a gut specific manner. Furthermore, considering the utility of RNA polymerase III U6 promoters in methodologies such as RNAi and CRISPR/Cas9, we identified and evaluated four different U6 promoters of H. armigera. In vitro experiments based on luciferase and GFP reporter assays, as well as in vivo experiments targeting an essential gene of Helicoverpa, indicate that these U6 promoters are functional and can be used to experimentally silence or knockout target genes through the expression of shRNAs and sgRNAs respectively. Taking our findings together, we provide a set of promoters useful for the genetic manipulation of Helicoverpa species, that can be used in various applications in the context of agricultural biotechnology.

RNAi-based immunity in insects against baculoviruses and the strategies of baculoviruses involved in siRNA and miRNA pathways to weaken the defense

Protection against viral infection in hosts concerns diverse cellular and molecular mechanisms, among which RNA interference (RNAi) response is a vital one. Small interfering RNAs (siRNAs), microRNAs (miRNAs) and PIWI interacting RNAs (piRNAs) are primary categories of small RNAs involved in RNAi response, playing significant roles in restraining viral invasion. However, during a long-term coevolution, viruses have gained the ability to evade, avoid, or suppress antiviral immunity to ensure efficient replication and transmission. Baculoviruses are enveloped, insect-pathogenic viruses with double-stranded circular DNA genomes, which encode suppressors of siRNA pathway and miRNAs targeting immune-related genes to mask the antiviral activity of their hosts. This review summarized recent findings for the RNAi-based antiviral immunity in insects as well as the strategies that baculoviruses exploit to break the shield of host siRNA pathway, and hijack cellular miRNAs or encode their own miRNAs that regulate both viral and cellular gene expression to create a favorable environment for viral infection.

A molecular toolkit for superorganisms

Social insects, such as ants, bees, wasps, and termites, draw biologists' attention due to their distinctive lifestyles. As experimental systems, they provide unique opportunities to study organismal differentiation, division of labor, longevity, and the evolution of development. Ants are particularly attractive because several ant species can be propagated in the laboratory. However, the same lifestyle that makes social insects interesting also hampers the use of molecular genetic techniques. Here, we summarize the efforts of the ant research community to surmount these hurdles and obtain novel mechanistic insight into the biology of social insects. We review current approaches and propose novel ones involving genomics, transcriptomics, chromatin and DNA methylation profiling, RNA interference (RNAi), and genome editing in ants and discuss future experimental strategies.

Cas13b-dependent and Cas13b-independent RNA knockdown of viral sequences in mosquito cells following guide RNA expression

Aedes aegypti and Aedes albopictus mosquitoes are vectors of the RNA viruses chikungunya (CHIKV) and dengue that currently have no specific therapeutic treatments. The development of new methods to generate virus-refractory mosquitoes would be beneficial. Cas13b is an enzyme that uses RNA guides to target and cleave RNA molecules and has been reported to suppress RNA viruses in mammalian and plant cells. We investigated the potential use of the Prevotella sp. P5-125 Cas13b system to provide viral refractoriness in mosquito cells, using a virus-derived reporter and a CHIKV split replication system. Cas13b in combination with suitable guide RNAs could induce strong suppression of virus-derived reporter RNAs in insect cells. Surprisingly, the RNA guides alone (without Cas13b) also gave substantial suppression. Our study provides support for the potential use of Cas13b in mosquitoes, but also caution in interpreting CRISPR/Cas data as we show that guide RNAs can have Cas-independent effects.

A drug-inducible sex-separation technique for insects

Here, we describe a drug-inducible genetic system for insect sex-separation that demonstrates proof-of-principle for positive sex selection in D. melanogaster. The system exploits the toxicity of commonly used broad-spectrum antibiotics geneticin and puromycin to kill the non-rescued sex. Sex-specific rescue is achieved by inserting sex-specific introns into the coding sequences of antibiotic-resistance genes. When raised on geneticin-supplemented food, the sex-sorter line establishes 100% positive selection for female progeny, while the food supplemented with puromycin positively selects 100% male progeny. Since the described system exploits conserved sex-specific splicing mechanisms and reagents, it has the potential to be adaptable to other insect species of medical and agricultural importance.

Identification of a germline-expression promoter for genome editing in Bombyx mori

Identification of stage- and tissue-specific cis-regulatory elements will enable more precise genomic editing. In previous studies of the silkworm Bombyx mori, we identified and characterized several tissue- and sex-specific cis-regulatory elements using transgenic technology, including a female- and fat body-specific promoter, vitellogenin, testis-specific promoters, Radial spoke head 1 (BmR1) and beta-tubulin 4 (Bmβ4). Here we report a cis-regulatory element specific for a somatic and germ cell-expressed promoter, nanos (Bmnos). We investigated activities of three truncated promoter sequences upstream of the transcriptional initiation site sequences of Bmnos in vitro (nos-0.6kb, nos-1kb and nos-2kb) and in vivo (nos-2kb). In BmN cultured cells, all three lengths drove expression of the gene encoding enhanced green fluorescence protein (EGFP), although nos-2kb had the highest fluorescence activity. In transgenic silkworms, nos-2kb drove EGFP expression at the early embryonic stage, and fluorescence was concentrated in the gonads at later embryonic stages. In addition, this cis-regulatory element was not sex differentiated. The fluorescence intensity gradually weakened following the larval developmental stage in the gonads and were broadly expressed in the whole body. The nos-2kb promoter drove the Cas9 system with efficiency comparable to that of the broad-spectrum strong IE1 promoter. These results indicate that Bmnos is an effective endogenous cis-regulatory element in the early embryo and in the gonad that can be used in applications involving the clustered, regularly interspaced, short palindromic repeats (CRISPR)/Cas9 system.

Increased antiviral capacity of transgenic silkworm via knockdown of multiple genes on Bombyx mori bidensovirus

Bombyx mori bidensovirus (BmBDV) causes fatal flacherie disease leading to severe economic losses in sericultures. The BmDNV-Z genome contains two single-stranded DNA molecules, VD1 and VD2. For generating silkworm lines with antiviral properties, two transgenic RNA interference (RNAi) vectors were constructed. Open reading frames (ORFs) 1-4 of VD1 were knockdown by vector pb-BDV1 while ORF1a, ORF1b, and ORF3 of VD2 were knockdown by vector pb-BDV2. Transgenic silkworm lines BDV1-I and BDV2-I were generated via RNAi microinjection. Mortality rates of BDV1-I and BDV2-I were reduced by 45% and 39%, respectively, and quantitative PCR showed that VD1 and VD2 contents in BDV1-I and BDV2-I were significantly lower than in the non-transgenic line. However, economic traits showed no obvious differences. Thus, knockdown of multiple BmDNV-Z genes provides strong resistance to BDV1-I and BDV2-I lines, and these can be used in sericulture without hampering silk production.

Functional characterization of the transcriptional regulatory elements of three highly expressed constitutive genes in the jewel wasp, Nasonia vitripennis

The jewel wasp, Nasonia vitripennis Ashmead (Hymenoptera: Pteromalidae), is an easily reared parasitoid that is providing an ever increasingly malleable model for examining the biology and genetics of Hymenoptera. Utilizing genomic and transcriptome resources, 5' upstream transcriptional regulatory sequences (TREs) from three highly expressed genes were identified and cloned. Criteria for TRE selection included the presence of an adjacent gene 5' of the translation initiation site. One gene was methylated whereas the other two were nonmethylated. Each TRE, heat-shock protein 70 (hsp70), activator of 90 kDa hsp ATPase protein 1 (hsp90A), and lipid storage droplet surface-binding protein 1 (lsdp) was linked with enhanced green fluorescent protein (EGFP) coding sequence and cloned into both pDP9e somatic and piggyBac germline transformation vectors. EGFP expression patterns under control of each TRE were compared with patterns of DsRed fluorescence produced from the transformation vector cassette. Functional activity of each TRE was observed in cultured Spodoptera frugiperda 9 (Sf9) cells and Drosophila melanogaster as well as in N. vitripennis embryos demonstrating that all three sequences had functional transcriptional regulatory activity in three different insect orders. Identification and functional characterization of these three TREs will provide critical and necessary resources for further genetic analyses of N. vitripennis, Hymenoptera and other insects.

Enhancement of larval RNAi efficiency by over-expressing Argonaute2 in Bombyx mori

RNA interference has been described as a powerful genetic tool for gene functional analysis and a promising approach for pest management. However, RNAi efficiency varies significantly among insect species due to distinct RNAi machineries. Lepidopteran insects include a large number of pests as well as model insects, such as the silkworm, Bombyx mori. However, only limited success of in vivo RNAi has been reported in lepidoptera, particularly during the larval stages when the worms feed the most and do the most harm to the host plant. Enhancing the efficiency of larval RNAi in lepidoptera is urgently needed to develop RNAi-based pest management strategies. In the present study, we investigate the function of the conserved RNAi core factor, Argonaute2 (Ago2), in mediating B. mori RNAi efficiency. We demonstrate that introducing BmAgo2 dsRNA inhibits the RNAi response in both BmN cells and embryos. Furthermore, we establish several transgenic silkworm lines to assess the roles of BmAgo2 in larval RNAi. Over-expressing BmAgo2 significantly facilitated both dsRNA-mediated larval RNAi when targeting DsRed using dsRNA injection and shRNA-mediated larval RNAi when targeting BmBlos2 using transgenic shRNA expression. Our results show that BmAgo2 is involved in RNAi in B. mori and provides a promising approach for improving larval RNAi efficiency in B. mori and in lepidopteran insects in general.

Cloning of cDNA encoding a Bombyx mori homolog of human oxidation resistance 1 (OXR1) protein from diapause eggs, and analyses of its expression and function

To better understand the molecular mechanisms of diapause initiation, we used the sensitive cDNA subtraction (selective amplification via biotin- and restriction-mediated enrichment) method and isolated a novel gene expressed abundantly in diapause eggs of the silkworm, Bombyx mori, which encodes a homolog of the human oxidation resistance 1 (OXR1) protein. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analyses confirmed that BmOXR1 mRNA and its 140-kDa protein were differentially expressed in diapause eggs compared to non-diapause eggs. OXR1 double-stranded RNA (dsRNA) was injected into diapause-destined eggs before the cellular blastoderm stage, and 4days later, when untreated eggs reached the diapause stage, the OXR1 protein disappeared; however, these eggs remained in diapause, suggesting that BmOXR1 is not essential for diapause initiation and/or maintenance. To further investigate the in vivo function of BmOXR1 apart from its role in diapause, we overexpressed BmOXR1 in Drosophila melanogaster. The fruit fly male adult life-span was significantly extended in the 50%-survival time when adults were reared on diets both with and without H2O2 solution under 25°C incubation. These results suggest that BmOXR1 functions in D. melanogaster via a possible antioxidant effect. As BmOXR1 was expressed mainly in the nuclei of D. melanogaster cells, the mechanism underlying its antioxidation effect appears to be different from that in humans where it is expressed mainly in the mitochondria. Taken together, these results suggest that BmOXR1 might serve as an antioxidant regulator during the early diapause stage.

Establishment of transgenic lines for jumpstarter method using a composite transposon vector in the ladybird beetle, Harmonia axyridis

In this post-genomic era, genome-wide functional analysis is indispensable. The recent development of RNA interference techniques has enabled researchers to easily analyze gene function even in non-model organisms. On the other hand, little progress has been made in the identification and functional analyses of cis-regulatory elements in non-model organisms. In order to develop experimental platform for identification and analyses of cis-regulatory elements in a non-model organism, in this case, the ladybird beetle, Harmonia axyridis, we established transgenic transposon-tagged lines using a novel composite vector. This vector enables the generation of two types of insertion products (jumpstarter and mutator). The jumpstarter portion carries a transposase gene, while the mutator segment carries a reporter gene for detecting enhancers. The full-composite element is flanked by functional termini (required for movement); however, the mutator region has an extra terminus making it possible for the mutator to remobilize on its own, thus leaving an immobile jumpstarter element behind. Each insertion type is stable on its own, but once crossed, jumpstarters can remobilize mutators. After crossing a jumpstarter and mutator line, all tested G2 females gave rise to at least one new insertion line in the next generation. This jumping rate is equivalent to the P-element-mediated jumpstarter method in Drosophila. These established transgenic lines will offer us the ideal experimental materials for the effective screening and identification of enhancers in this species. In addition, this jumpstarter method has the potential to be as effective in other non-model insect species and thus applicable to any organism.

Identification of a novel strong and ubiquitous promoter/enhancer in the silkworm Bombyx mori

Transgenic techniques offer a valuable tool for determining gene functions. Although various promoters are available for use in gene overexpression, gene knockdown, and identification of transgenic individuals, there is nevertheless a lack of versatile promoters for such studies, and this dearth acts as a bottleneck, especially with regard to nonmodel organisms. Here, we succeeded in identifying a novel strong and ubiquitous promoter/enhancer in the silkworm. We identified a unique silkworm strain whose reporter gene showed strong and ubiquitous expression during the establishment of enhancer trap strains. In this strain, the transposon was inserted into the 5'UTR of hsp90, a housekeeping gene that is abundantly expressed in a range of tissues. To determine whether the promoter/enhancer of hsp90 could be used to induce strong gene expression, a 2.9-kb upstream genomic fragment of hsp90 was isolated (hsp90(P2.9k)), and its transcriptional activation activity was examined. Strikingly, hsp90(P2.9k) induced strong gene expression in silkworm cell cultures and also strongly induced gene expression in various tissues and developmental stages of the silkworm. hsp90(P2.9k) also exhibited significant promoter/enhancer activity in Sf9, a cell culture from the armyworm, suggesting that this fragment might possibly be used as a gene expression tool in other Lepidoptera. We further found that 2.0 kb of hsp90(P2.9k) is sufficient for the induction of strong gene expression. We believe that this element will be of value for a range of studies such as targeted gene overexpression, gene knockdown and marker gene expression, not only in the silkworm but also in other insect species.