A baculovirus superinfection system: efficient vehicle for gene transfer into Drosophila S2 cells

Nematode Extracellular Protein Interactome Expands Connections between Signaling Pathways

Multicellularity was accompanied by the emergence of new classes of cell surface and secreted proteins. The nematode C. elegans is a favorable model to study cell surface interactomes, given its well-defined and stereotyped cell types and intercellular contacts. Here we report our C. elegans extracellular interactome dataset, the largest yet for an invertebrate. Most of these interactions were unknown, despite recent datasets for flies and humans, as our collection contains a larger selection of protein families. We uncover new interactions for all four major axon guidance pathways, including ectodomain interactions between three of the pathways. We demonstrate that a protein family known to maintain axon locations are secreted receptors for insulins. We reveal novel interactions of cystine-knot proteins with putative signaling receptors, which may extend the study of neurotrophins and growth-factor-mediated functions to nematodes. Finally, our dataset provides insights into human disease mechanisms and how extracellular interactions may help establish connectomes.

Protein Production at the 100L Scale

The Baculovirus Expression Vector System (BEVS) has revolutionized the field of recombinant protein expression by enabling efficient and high yield production. The platform offers many advantages including manufacturing speed, flexible design, and scalability. In this chapter, we describe the methods including strategies and considerations to successfully optimize and scale-up using BEVS as a tool for production (Fig. 1). As an illustrative case study, we present an example focused on the production of a viral glycoprotein.

Infectivity and virulence of the infectious Macrobrachium rosenbergii nodavirus produced from Drosophila melanogaster cell using Penaeus merguiensis as an infection model

It has been established that baculovirus-insect cell line is applicable for shrimp virus replication, propagation and secretion in the in vitro culture system. We thus aimed to produce Macrobrachium rosenbergii nodavirus (MrNV) clone within S2 cell to improve viral production over the previous model using Sf9 cell. Upon the transfection of genomic RNA1 and RNA2 into S2 cells, the recognizable cellular changes including cytoplasmic swelling and clumping of cells were observed within 24 h. The culture media containing secreted MrNV particles were re-transfected into healthy S2 cells and similar cellular changes as with the first transfection were observed. Immunohistochemistry analysis of the re-infecting S2 cell revealed an intense immunoreactivity against MrNV capsid protein confirming that S2 cell was permissive cells for MrNV. In vivo infectivity test using P. merguiensis as a model animal exposed to the secreted MrNV revealed the presence of RNA2 fragment in shrimp tissue accompanied with the sign of whitish abdominal muscle at 24 h post-infection (p.i.). In addition, the number of shrimp hemocytes decreased at 6-24 h p.i. and returned to the normal level at 48 h p.i., whereas a significant up-regulation of immune-related genes including HSP70 and trypsin was noted. These data suggested that rescued MrNV produced in S2 is practically useful for MrNV infection test in which their natural virion inoculae are difficult to obtain. In addition, the molecular basis of viral pathogenesis can further be investigated which should be beneficial for any antiviral therapy developments in the future.

Entomoculture: A Preliminary Techno-Economic Assessment

Cultured meat, or the practice of growing meat from cell culture, has been experiencing rapid advances in research and technology as the field of biotechnology attempts to answer the call to fight climate change and feed a growing global population. A major hurdle for cell-based meat products entering the market in the near-future is their price. The complex production facilities required to make such products will require advanced bioreactor systems, resources such as energy and water, and a skilled labor force, among other factors. The use of insect cells in this process is hypothesized to address some of these costs due to the characteristics that make them more resilient in cell culture when compared to traditional livestock-derived cells. To address the potential for cost savings by utilizing insect cells in the cultivation of protein-enriched foods, here we utilized a techno-economic assessment model. Three different insect cell lines were used in the model. The results indicate that insect cell lines offer potential to significantly reduce the cost per kilogram of cell cultivated meat, along with further opportunities to optimize production processes through technological advances and scaling.

FAS2FURIOUS: Moderate-Throughput Secreted Expression of Difficult Recombinant Proteins in Drosophila S2 Cells

Recombinant protein expression in eukaryotic insect cells is a powerful approach for producing challenging targets. However, due to incompatibility with standard baculoviral platforms and existing low-throughput methodology, the use of the Drosophila melanogaster “S2” cell line lags behind more common insect cell lines such as Sf9 or High-Five™. Due to the advantages of S2 cells, particularly for secreted and secretable proteins, the lack of a simple and parallelizable S2-based platform represents a bottleneck, particularly for biochemical and biophysical laboratories. Therefore, we developed FAS2FURIOUS, a simple and rapid S2 expression pipeline built upon an existing low-throughput commercial platform. FAS2FURIOUS is comparable in effort to simple E. coli systems and allows users to clone and test up to 46 constructs in just 2 weeks. Given the ability of S2 cells to express challenging targets, including receptor ectodomains, secreted glycoproteins, and viral antigens, FAS2FURIOUS represents an attractive orthogonal approach for protein expression in eukaryotic cells.

A review of alternative promoters for optimal recombinant protein expression in baculovirus-infected insect cells

Generating recombinant proteins in insect cells has been made possible via the use of the Baculovirus Expression Vector System (BEVS). Despite the success of many proteins via this platform, some targets remain a challenge due to issues such as cytopathic effects, the unpredictable nature of co-infection and co-expressions, and baculovirus genome instability. Many promoters have been assayed for the purpose of expressing diverse proteins in insect cells, and yet there remains a lack of implementation of those results when reviewing the landscape of commercially available baculovirus vectors. In advancing the platform to produce a greater variety of proteins and complexes, the development of such constructs cannot be avoided. A better understanding of viral gene regulation and promoter options including viral, synthetic, and insect-derived promoters will be beneficial to researchers looking to utilize BEVS by recruiting these intricate mechanisms of gene regulation for heterologous gene expression. Here we summarize some of the developments that could be utilized to improve the expression of recombinant proteins and multi-protein complexes in insect cells.

Generating and working with Drosophila cell cultures: Current challenges and opportunities

The use of Drosophila cell cultures has positively impacted both fundamental and biomedical research. The most widely used cell lines: Schneider, Kc, the CNS and imaginal disc lines continue to be the choice for many applications. Drosophila cell lines provide a homogenous source of cells suitable for biochemical experimentations, transcriptomics, functional genomics, and biomedical applications. They are amenable to RNA interference and serve as a platform for high-throughput screens to identify relevant candidate genes or drugs for any biological process. Currently, CRISPR-based functional genomics are also being developed for Drosophila cell lines. Even though many uniquely derived cell lines exist, cell genetic techniques such the transgenic UAS-GAL4-based Ras^V12 oncogene expression, CRISPR-Cas9 editing and recombination mediated cassette exchange are likely to drive the establishment of many more lines from specific tissues, cells, or genotypes. However, the pace of creating new lines is hindered by several factors inherent to working with Drosophila cell cultures: single cell cloning, optimal media formulations and culture conditions capable of supporting lines from novel tissue sources or genotypes. Moreover, even though many Drosophila cell lines are morphologically and transcriptionally distinct it may be necessary to implement a standard for Drosophila cell line authentication, ensuring the identity and purity of each cell line. Altogether, recent advances and a standardized authentication effort should improve the utility of Drosophila cell cultures as a relevant model for fundamental and biomedical research. This article is categorized under: Technologies > Analysis of Cell, Tissue, and Animal Phenotypes.

Baculovirus as an efficient vector for gene delivery into mosquitoes

Efficient gene delivery technologies play an essential role in the gene functional analyses that are necessary for basic and applied researches. Mosquitoes are ubiquitous insects, responsible for transmitting many deadly arboviruses causing millions of human deaths every year. The lack of efficient and flexible gene delivery strategies in mosquitoes are among the major hurdles for the study of mosquito biology and mosquito-pathogen interactions. We found that Autographa californica multiple nucleopolyhedrovirus (AcMNPV), the type baculovirus species, can efficiently transduce mosquito cells without viral propagation, allowing high level gene expression upon inducement by suitable promoters without obvious negative effects on cell propagation and viability. AcMNPV transduces into several mosquito cell types, efficiently than in commonly used mammalian cell lines and classical plasmid DNA transfection approaches. We demonstrated the application of this system by expressing influenza virus neuraminidase (NA) into mosquito hosts. Moreover, AcMNPV can transduce both larvae and adults of essentially all blood-sucking mosquito genera, resulting in bright fluorescence in insect bodies with little or no tissue barriers. Our experiments establish baculovirus as a convenient and powerful gene delivery vector in vitro and in vivo that will greatly benefit research into mosquito gene regulation, development and the study of mosquito-borne viruses.

Adventitious viruses in insect cell lines used for recombinant protein expression

Insect cells are widely used for recombinant protein expression, typically as hosts for recombinant baculovirus vectors, but also for plasmid-mediated transient transfection or stable genetic transformation. Insect cells are used to express proteins for research, as well as to manufacture biologicals for human and veterinary medicine. Recently, several insect cell lines used for recombinant protein expression were found to be persistently infected with adventitious viruses. This has raised questions about how these infections might affect research performed using those cell lines. Furthermore, these findings raised serious concerns about the safety of biologicals produced using those cell lines. In response, new insect cell lines lacking adventitious viruses have been isolated for use as improved research tools and safer biological manufacturing platforms. Here, we review the scientific and patent literature on adventitious viruses found in insect cell lines, affected cell lines, and new virus-free cell lines.

Quantitative phosphoproteome on the silkworm (Bombyx mori) cells infected with baculovirus

Background

Bombyx mori has become an important model organism for many fundamental studies. Bombyx mori nucleopolyhedrovirus (BmNPV) is a significant pathogen to Bombyx mori, yet also an efficient vector for recombinant protein production. A previous study indicated that acetylation plays many vital roles in several cellular processes of Bombyx mori while global phosphorylation pattern upon BmNPV infection remains elusive.

Method

Employing tandem mass tag (TMT) labeling and phosphorylation affinity enrichment followed by high-resolution LC-MS/MS analysis and intensive bioinformatics analysis, the quantitative phosphoproteome in Bombyx mori cells infected by BmNPV at 24 hpi with an MOI of 10 was extensively examined.

Results

Totally, 6480 phosphorylation sites in 2112 protein groups were identified, among which 4764 sites in 1717 proteins were quantified. Among the quantified proteins, 81 up-regulated and 25 down-regulated sites were identified with significant criteria (the quantitative ratio above 1.3 was considered as up-regulation and below 0.77 was considered as down-regulation) and with significant p-value (p < 0.05). Some proteins of BmNPV were also hyperphosphorylated during infection, such as P6.9, 39 K, LEF-6, Ac58-like protein, Ac82-like protein and BRO-D.

Conclusion

The phosphorylated proteins were primary involved in several specific functions, out of which, we focused on the binding activity, protein synthesis, viral replication and apoptosis through kinase activity.

Comparisons of Transcriptional Profiles of Gut Genes between Cry1Ab-Resistant and Susceptible Strains of Ostrinia nubilalis Revealed Genes Possibly Related to the Adaptation of Resistant Larvae to Transgenic Cry1Ab Corn

A microarray developed on the basis of 2895 unique transcripts from larval gut was used to compare gut gene expression profiles between a laboratory-selected Cry1Ab-resistant (R) strain and its isoline susceptible (S) strain of the European corn borer (Ostrinia nubilalis) after the larvae were fed the leaves of transgenic corn (MON810) expressing Cry1Ab or its non-transgenic isoline for 6 h. We revealed 398 gut genes differentially expressed (i.e., either up- or down-regulated genes with expression ratio ≥2.0) in S-strain, but only 264 gut genes differentially expressed in R-strain after being fed transgenic corn leaves. Although the percentages of down-regulated genes among the total number of differentially expressed genes (50% in S-strain and 45% in R-strain) were similar between the R- and S-strains, the expression ratios of down-regulated genes were much higher in S-strain than in R-strain. We revealed that 17 and 9 significantly up- or down-regulated gut genes from S and R-strain, respectively, including serine proteases and aminopeptidases. These genes may be associated with Cry1Ab toxicity by degradation, binding, and cellular defense. Overall, our study suggests enhanced adaptation of Cry1Ab-resistant larvae on transgenic Cry1Ab corn as revealed by lower number and lower ratios of differentially expressed genes in R-strain than in S-strain of O. nubilalis.

Insecticide cytotoxicology in China: Current status and challenges

The insecticide cytotoxicology, as a new branch of toxicology, has rapidly developed in China. During the past twenty years, thousands of investigations have sprung up to evaluate the damages and clarify the mechanisms of insecticidal chemical substances to insect cells in vivo or in vitro. The mechanisms of necrosis, apoptosis or autophagy induced by synthetic or biogenic pesticides and virus infections have been systematically illuminated in many important models, including S2, BmN, SL-1, Sf21 and Sf9 cell lines. In addition, a variety of methods have also been applied to examine the effects of insecticides and elaborate the modes of action. As a result, many vital factors and pathways, such as cytochrome c, the Bcl-2 family and caspases, in mitochondrial signaling pathways, intracellular free calcium and lysosome signal pathways have been illuminated and drawn much attention. Benefiting from the application of insecticide cytotoxicology, natural products purifications, biological activities assessments of synthetic compounds and high throughput screening models have been accelerated in China. However, many questions remained, and there exist great challenges, especially in theory system, evaluation criterion, evaluation model, relationship between activity in vitro and effectiveness in vivo, and the toxicological mechanism. Fortunately, the generation of "omics" could bring opportunities for the development of insecticide cytotoxicology.

Transgene expression in Penaeus monodon cells: evaluation of recombinant baculoviral vectors with shrimp specific hybrid promoters

It has been realized that shrimp cell immortalization may not be accomplished without in vitro transformation by expressing immortalizing gene in cells. In this process, efficiency of transgene expression is confined to the ability of vectors to transmit gene of interests to the genome. Over the years, unavailability of such vectors has been hampering application of such a strategy in shrimp cells. We report the use of recombinant baculovirus mediated transduction using hybrid promoter system for transgene expression in lymphoid cells of Penaeus monodon. Two recombinant baculovirus vectors with shrimp viral promoters (WSSV-Ie1 and IHHNV-P2) were constructed (BacIe1-GFP and BacP2-GFP) and green fluorescent protein (GFP) used as the transgene. The GFP expression in cells under the control of hybrid promoters, PH-Ie1 or PH-P2, were analyzed and confirmed in shrimp cells. The results indicate that the recombinant baculovirus with shrimp specific viral promoters (hybrid) can be employed for delivery of foreign genes to shrimp cells for in vitro transformation.

Analysis of Genetic Variation across the Encapsidated Genome of Microplitis demolitor Bracovirus in Parasitoid Wasps

Insect parasitoids must complete part of their life cycle within or on another insect, ultimately resulting in the death of the host insect. One group of parasitoid wasps, the ‘microgastroid complex’ (Hymenoptera: Braconidae), engage in an association with beneficial symbiotic viruses that are essential for successful parasitism of hosts. These viruses, known as Bracoviruses, persist in an integrated form in the wasp genome, and activate to replicate in wasp ovaries during development to ultimately be delivered into host insects during parasitism. The lethal nature of host-parasitoid interactions, combined with the involvement of viruses in mediating these interactions, has led to the hypothesis that Bracoviruses are engaged in an arms race with hosts, resulting in recurrent adaptation in viral (and host) genes. Deep sequencing was employed to characterize sequence variation across the encapsidated Bracovirus genome within laboratory and field populations of the parasitoid wasp species Microplitis demolitor. Contrary to expectations, there was a paucity of evidence for positive directional selection among virulence genes, which generally exhibited signatures of purifying selection. These data suggest that the dynamics of host-parasite interactions may not result in recurrent rounds of adaptation, and that adaptation may be more variable in time than previously expected.

Recombinant baculovirus mediates dsRNA specific to rr2 delivery and its protective efficacy against WSSV infection

White spot syndrome virus (WSSV) is a major causative agent in shrimp farming. Consequently, RNAi technology is an effective strategy to prevent WSSV infection in shrimp especially dsRNA targeting to rr2 of WSSV. In an effort to develop dsRNA expression in shrimp for control of WSSV infection, we developed a recombinant baculovirus expressing recombinant VP28 as the gene delivery system to carry a gene encoding dsRNA specific to rr2 for triggering the RNAi process in shrimp. The results showed that the recombinant baculovirus harboring VP28 was able to express VP28 indicated by Western blot with polyclonal antibody specific to VP28. VP28 transcript was detected in shrimp hemocytes after co-culture hemocytes with the recombinant baculovirus displaying VP28. In addition, we found that shrimp injected with the recombinant baculovirus displaying VP28 and encoding dsRNA synthetic gene specific to rr2 (Bac-VP28-dsrr2) showed the lowest cumulative mortality (33%) at 14days post infection (dpi) when compared to shrimp injected with baculovirus displaying VP28 (Bac-VP28) (64% cumulative mortality) (p<0.05). According to the results, shrimp injected with Bac-VP28-dsrr2 also showed significantly lower WSSV copies than shrimp injected with Bac-VP28 (p<0.05) along with the down-regulation of rr2 expression at 1, 3 and 7dpi. In conclusion, the Bac-VP28-dsrr2 was effective in prevention of WSSV infection. Therefore, the results obtained here can be applied to the prevention of WSSV infection by mixing the recombinant baculovirus with shrimp feed in the future.

Disrupted nitric oxide signaling due to GUCY1A3 mutations increases risk for moyamoya disease, achalasia and hypertension

Moyamoya disease (MMD) is a progressive vasculopathy characterized by occlusion of the terminal portion of the internal carotid arteries and its branches, and the formation of compensatory moyamoya collateral vessels. Homozygous mutations in GUCY1A3 have been reported as a cause of MMD and achalasia. Probands (n = 96) from unrelated families underwent sequencing of GUCY1A3. Functional studies were performed to confirm the pathogenicity of identified GUCY1A3 variants. Two affected individuals from the unrelated families were found to have compound heterozygous mutations in GUCY1A3. MM041 was diagnosed with achalasia at 4 years of age, hypertension and MMD at 18 years of age. MM149 was diagnosed with MMD and hypertension at the age of 20 months. Both individuals carry one allele that is predicted to lead to haploinsufficiency and a second allele that is predicted to produce a mutated protein. Biochemical studies of one of these alleles, GUCY1A3 Cys517Tyr, showed that the mutant protein (a subunit of soluble guanylate cyclase) has a significantly blunted signaling response with exposure to nitric oxide (NO). GUCY1A3 missense and haploinsufficiency mutations disrupt NO signaling leading to MMD and hypertension, with or without achalasia.

A genome-wide CRISPR library for high-throughput genetic screening in Drosophila cells

The simplicity of the CRISPR/Cas9 system of genome engineering has opened up the possibility of performing genome-wide targeted mutagenesis in cell lines, enabling screening for cellular phenotypes resulting from genetic aberrations. Drosophila cells have proven to be highly effective in identifying genes involved in cellular processes through similar screens using partial knockdown by RNAi. This is in part due to the lower degree of redundancy between genes in this organism, whilst still maintaining highly conserved gene networks and orthologs of many human disease-causing genes. The ability of CRISPR to generate genetic loss of function mutations not only increases the magnitude of any effect over currently employed RNAi techniques, but allows analysis over longer periods of time which can be critical for certain phenotypes. In this study, we have designed and built a genome-wide CRISPR library covering 13,501 genes, among which 8989 genes are targeted by three or more independent single guide RNAs (sgRNAs). Moreover, we describe strategies to monitor the population of guide RNAs by high throughput sequencing (HTS). We hope that this library will provide an invaluable resource for the community to screen loss of function mutations for cellular phenotypes, and as a source of guide RNA designs for future studies.

Cell lines

We review the properties and uses of cell lines in Drosophila research, emphasizing the variety of lines, the large body of genomic and transcriptional data available for many of the lines, and the variety of ways the lines have been used to provide tools for and insights into the developmental, molecular, and cell biology of Drosophila and mammals.

Epstein-Barr virus BALF3 has nuclease activity and mediates mature virion production during the lytic cycle

Epstein-Barr virus (EBV) lytic replication involves complex processes, including DNA synthesis, DNA cleavage and packaging, and virion egress. These processes require many different lytic gene products, but the mechanisms of their actions remain unclear, especially for DNA cleavage and packaging. According to sequence homology analysis, EBV BALF3, encoded by the third leftward open reading frame of the BamHI-A fragment in the viral genome, is a homologue of herpes simplex virus type 1 UL28. This gene product is believed to possess the properties of a terminase, such as nucleolytic activity on newly synthesized viral DNA and translocation of unit length viral genomes into procapsids. In order to characterize EBV BALF3, the protein was produced by and purified from recombinant baculoviruses and examined in an enzymatic reaction in vitro, which determined that EBV BALF3 acts as an endonuclease and its activity is modulated by Mg(2+), Mn(2+), and ATP. Moreover, in EBV-positive epithelial cells, BALF3 was expressed and transported from the cytoplasm into the nucleus following induction of the lytic cycle, and gene silencing of BALF3 caused a reduction of DNA packaging and virion release. Interestingly, suppression of BALF3 expression also decreased the efficiency of DNA synthesis. On the basis of these results, we suggest that EBV BALF3 is involved simultaneously in DNA synthesis and packaging and is required for the production of mature virions.

IMPORTANCE

Virus lytic replication is essential to produce infectious virions, which is responsible for virus survival and spread. This work shows that an uncharacterized gene product of the human herpesvirus Epstein-Barr virus (EBV), BALF3, is expressed during the lytic cycle. In addition, BALF3 mediates an endonucleolytic reaction and is involved in viral DNA synthesis and packaging, leading to influence on the production of mature virions. According to sequence homology and physical properties, the lytic gene product BALF3 is considered a terminase in EBV. These findings identify a novel viral gene with an important role in contributing to a better understanding of the EBV life cycle.

Baculovirus superinfection: a probable restriction factor on the surface display of proteins for library screening

In addition to the expression of recombinant proteins, baculoviruses have been developed as a platform for the display of complex eukaryotic proteins on the surface of virus particles or infected insect cells. Surface display has been used extensively for antigen presentation and targeted gene delivery but is also a candidate for the display of protein libraries for molecular screening. However, although baculovirus gene libraries can be efficiently expressed and displayed on the surface of insect cells, target gene selection is inefficient probably due to super-infection which gives rise to cells expressing more than one protein. In this report baculovirus superinfection of Sf9 cells has been investigated by the use of two recombinant multiple nucleopolyhedrovirus carrying green or red fluorescent proteins under the control of both early and late promoters (vAcBacGFP and vAcBacDsRed). The reporter gene expression was detected 8 hours after the infection of vAcBacGFP and cells in early and late phases of infection could be distinguished by the fluorescence intensity of the expressed protein. Simultaneous infection with vAcBacGFP and vAcBacDsRed viruses each at 0.5 MOI resulted in 80% of infected cells co-expressing the two fluorescent proteins at 48 hours post infection (hpi), and subsequent infection with the two viruses resulted in similar co-infection rate. Most Sf9 cells were re-infectable within the first several hours post infection, but the re-infection rate then decreased to a very low level by 16 hpi. Our data demonstrate that Sf9 cells were easily super-infectable during baculovirus infection, and super-infection could occur simultaneously at the time of the primary infection or subsequently during secondary infection by progeny viruses. The efficiency of super-infection may explain the difficulties of baculovirus display library screening but would benefit the production of complex proteins requiring co-expression of multiple polypeptides.

RNA interference with special reference to combating viruses of crustacea

RNA interference has evolved from being a nuisance biological phenomenon to a valuable research tool to determine gene function and as a therapeutic agent. Since pioneering observations regarding RNA interference were first reported in the 1990s from the nematode worm, plants and Drosophila, the RNAi phenomenon has since been reported in all eukaryotic organisms investigated from protozoans, plants, arthropods, fish and mammals. The design of RNAi therapeutics has progressed rapidly to designing dsRNA that can specifically and effectively silence disease related genes. Such technology has demonstrated the effective use of short interfering as therapeutics. In the absence of a B cell lineage in arthropods, and hence no long term vaccination strategy being available, the introduction of using RNA interference in crustacea may serve as an effective control and preventative measure for viral diseases for application in aquaculture.

The screening and functional study of proteins binding with the BmNPV polyhedrin promoter

Background

The polyhedrin gene promoter has an essential role in regulating foreign gene expression in baculovirus expression vector systems (BEVS); however, the high-level transcription mechanism is still unknown. One-hybrid screening in yeast is a powerful way of identifying rapidly heterologous transcription factors that can interact with the polyhedrin promoter DNA sequence. In the current study, total RNA was extracted from the fat bodies of fifth-instar silkworm larvae that had been infected with Bombyx mori nuclear polyhedrosis virus (BmNPV) for 5 days; complementary DNA (cDNA) was then generated using reverse-transcription (RT)-PCR to construct a silkworm gene expression library. Key polyhedrin promoter bait sequences were synthesized to generate a bait yeast strain, which was used to screen the one-hybrid cDNA library.

Results

In total, 12 positive yeast colonies were obtained from the SD/-Leu/AbA plates; sequencing analysis showed that they belong to two different protein cDNA colonies. Positive colonies underwent bioinformatics analysis, which revealed one colony to be ribosomal proteins [B. mori ribosomal protein SA (BmRPSA)] and the other to be NPV DNA-binding proteins (DBP). To further verify the regulatory function of these two protein groups, transient expression vectors (pSK-IE-dbp and pSK-IE-BmRPSA) were constructed. The recombinant plasmids were then transfected into cultured B. mori N (BmN) cells, which had been infected with a recombinant bacmid containing the gene encoding luciferase (luc). The results showed that overexpression of either dbp or BmRPSA upregulated the polh promoter-driven transcription of luc in BmN cells. In addition, dbp or BmRPSA RNA interference (RNAi) resulted in the downregulation of luciferase reporter expression in BmN cells, demonstrating that DBP and BmRPSA are important for luc transcription. EMSA results further confirmed that DBP could directly bind to the conserved single-stranded polh promoter region in intro. However, EMSA assay also showed that BmRPSA did not bind to this region, precluding a direct DNA association.

Conclusions

Both DBP and BmRPSA are important for polh transcription. DBP can regulate polh promoter activity by direct binding to the conserved single-stranded polh promoter region, BmRPSA may regulate polh promoter activity by indirect binding to this region.

Drosophila melanogaster S2 cells for expression of heterologous genes: From gene cloning to bioprocess development

In the present review we discuss strategies that have been used for heterologous gene expression in Drosophila melanogaster Schneider 2 (S2) cells using plasmid vectors. Since the growth of S2 cells is not dependent on anchorage to solid substrates, these cells can be easily cultured in suspension in large volumes. The factors that most affect the growth and gene expression of S2 cells, namely cell line, cell passage, inoculum concentration, culture medium, temperature, dissolved oxygen concentration, pH, hydrodynamic forces and toxic metabolites, are discussed by comparison with other insect and mammalian cells. Gene expression, cell metabolism, culture medium formulation and parameters involved in cellular respiration are particularly emphasized. The experience of the authors with the successful expression of a biologically functional protein, the rabies virus glycoprotein (RVGP), by recombinant S2 cells is presented in the topics covered.

The COMPASS family of H3K4 methylases in Drosophila

Methylation of histone H3 lysine 4 (H3K4) in Saccharomyces cerevisiae is implemented by Set1/COMPASS, which was originally purified based on the similarity of yeast Set1 to human MLL1 and Drosophila melanogaster Trithorax (Trx). While humans have six COMPASS family members, Drosophila possesses a representative of the three subclasses within COMPASS-like complexes: dSet1 (human SET1A/SET1B), Trx (human MLL1/2), and Trr (human MLL3/4). Here, we report the biochemical purification and molecular characterization of the Drosophila COMPASS family. We observed a one-to-one similarity in subunit composition with their mammalian counterparts, with the exception of LPT (lost plant homeodomains [PHDs] of Trr), which copurifies with the Trr complex. LPT is a previously uncharacterized protein that is homologous to the multiple PHD fingers found in the N-terminal regions of mammalian MLL3/4 but not Drosophila Trr, indicating that Trr and LPT constitute a split gene of an MLL3/4 ancestor. Our study demonstrates that all three complexes in Drosophila are H3K4 methyltransferases; however, dSet1/COMPASS is the major monoubiquitination-dependent H3K4 di- and trimethylase in Drosophila. Taken together, this study provides a springboard for the functional dissection of the COMPASS family members and their role in the regulation of histone H3K4 methylation throughout development in Drosophila.

Rapid expression of recombinant proteins in modified CHO cells using the baculovirus system

Baculovirus containing the mammalianCMV promoter, in place of the insect polyhedronpromoter (BacMam), has been used to transientlytransfect COS, CHO and CHOE1a (CHO cells expressing theE1a transcriptional activator). Using this system forthe expression of a cellular adhesion factor (SAF-3) Fcfusion protein in CHOE1a, we found that levels ofexpression were highest with a MOI of 100, 20mM sodiumbutyrate, at 34 degrees C. Production increased furtherif the cells were resuspended in fresh medium, about3 x 10(6) cells ml(-1), prior to addition of the virus. These conditions were used to express 3 secretedproteins, SAF-3-Fc, CD40-hexa his and Asp 2-Fc, and, at2 to 6 days post infection, protein levels ranged from4 ug ml(-1) to 25 ug ml(-1). Based on these results, theBacMam system represents a viable technique forproducing protein at ug ml(-1) levels in a relatively shortperiod of time.

Baculovirus expression systems for production of recombinant proteins in insect and mammalian cells

Baculovirus vector systems are extensively used for the expression of foreign gene products in insect and mammalian cells. New advances increase the possibilities and applications of the baculovirus expression system, which makes it possible to express multiple genes simultaneously within a single infected insect cell and to obtain multimeric proteins functionally similar to their natural analogs. Recombinant viruses with expression cassettes active in mammalian cells are used to deliver and express genes in mammalian cells in vitro and in vivo. Further improvement of the baculovirus expression system and its adaptation to specific target cells can open up a wide variety of applications. The review considers recent achievements in the use of modified baculoviruses to express recombinant proteins in eukaryotic cells, advantages and drawbacks of the baculovirus expression system, and ways to optimize the expression of recombinant proteins in both insect and mammalian cell lines.

Drosophila S2 cells are non-permissive for vaccinia virus DNA replication following entry via low pH-dependent endocytosis and early transcription

Vaccinia virus (VACV), a member of the chordopox subfamily of the Poxviridae, abortively infects insect cells. We have investigated VACV infection of Drosophila S2 cells, which are useful for protein expression and genome-wide RNAi screening. Biochemical and electron microscopic analyses indicated that VACV entry into Drosophila S2 cells depended on the VACV multiprotein entry-fusion complex but appeared to occur exclusively by a low pH-dependent endocytic mechanism, in contrast to both neutral and low pH entry pathways used in mammalian cells. Deep RNA sequencing revealed that the entire VACV early transcriptome, comprising 118 open reading frames, was robustly expressed but neither intermediate nor late mRNAs were made. Nor was viral late protein synthesis or inhibition of host protein synthesis detected by pulse-labeling with radioactive amino acids. Some reduction in viral early proteins was noted by Western blotting. Nevertheless, synthesis of the multitude of early proteins needed for intermediate gene expression was demonstrated by transfection of a plasmid containing a reporter gene regulated by an intermediate promoter. In addition, expression of a reporter gene with a late promoter was achieved by cotransfection of intermediate genes encoding the late transcription factors. The requirement for transfection of DNA templates for intermediate and late gene expression indicated a defect in viral genome replication in VACV-infected S2 cells, which was confirmed by direct analysis. Furthermore, VACV-infected S2 cells did not support the replication of a transfected plasmid, which occurs in mammalian cells and is dependent on all known viral replication proteins, indicating a primary restriction of DNA synthesis.

Expression of membrane proteins in Drosophila Melanogaster S2 cells: Production and analysis of a EGFP-fused G protein-coupled receptor as a model

In the process of selecting an appropriate host for the heterologous expression of functional eukaryotic membrane proteins, Drosophila S2 cells, although not yet fully explored, appear as a valuable alternative to mammalian cell lines or other virus-infected insect cell systems. This nonlytic, plasmid-based system actually combines several major physiological and bioprocess advantages that make it a highly potential and scalable cellular tool for the production of membrane proteins in a variety of applications, including functional characterization, pharmacological profiling, molecular simulations, structural analyses, or generation of vaccines. We present here a series of protocols and hints that would serve the successful expression of membrane proteins in S2 cells, using an enhanced green fluorescent protein (EGFP)/G protein-coupled receptor (EGFP-GPCR) as a model.

Identification of an RNA-dependent RNA polymerase in Drosophila involved in RNAi and transposon suppression

Here, we show that recombinant Drosophila elp1 (D-elp1) produced in Sf9 cells or Escherichia coli, corresponding to the largest of the three subunits in the RNA polymerase II core elongator complex, has RNA-dependent RNA polymerase (RdRP) activity. D-elp1 is a noncanonical RdRP that can synthesize dsRNA from different ssRNA templates using either a primer-dependent or primer-independent initiation mechanism. Of the three core subunits, only D-elp1 depletion inhibits RNAi in S2 cells but does not affect micro RNA function. Furthermore, D-elp1 depletion results in increased steady state levels of representative transposon RNAs and a decrease in the corresponding transposon antisense transcripts and endo siRNAs. In contrast, although Dcr-2 depletion results in increased transposon RNA levels and a reduction in the corresponding endo siRNAs, there is no change in the transposon antisense RNA levels. In D-elp1 null third instar larvae transposon RNA levels are also increased and the corresponding transposon antisense RNAs are reduced. D-elp1 associates tightly with Dcr-2, similar to the Dicer-RdRP interaction observed in lower eukaryotes. These results identify an aspect of the RNAi pathway in Drosophila that suggest transposon derived endo siRNAs, critical for transposon suppression, are produced, in part, in a D-elp1 dependent step that converts transposon RNA into dsRNA that is subsequently processed by Dcr-2. The generality of this mechanism in genome defense and RNA silencing in higher eukaryotes is suggested.

Statistical determination of optimal baculovirus infection condition for recombinant protein production in Drosophila S2 cells

Insect Drosophila melanogaster S2 cell was developed as plasmid-based and, therefore, a nonlytic expression system for functional foreign proteins. To achieve multiple protein expressions, it was suggested that baculovirus be used on S2 cell system because baculovirus can infect S2 cells but cannot replicate inside the cells. Therefore, establishment of baculovirus infection conditions is the first important step and this should be properly optimized for production yield. We used statistical methodology to optimize the baculovirus infection conditions using green fluorescent protein (GFP) as a reporter protein. Consequently, we arrived at optimal infection conditions through a statistical regression method. The secreted GFP yield from vMT-GFP baculovirus-infected wild-type S2 cells under optimal infection conditions was >15-fold higher than that under nonoptimal conditions and comparable to that from stably transfected recombinant S2 cells.

Recombinant baculovirus-based multiple protein expression platform for Drosophila S2 cell culture

A platform for selective and controllable expression of multiple foreign protein types was developed in insect cell culture. Based on the fact that baculovirus cannot replicate in nonpermissive Drosophila melanogaster Schneider line 2 (S2) cells, S2 cells that stably express human erythropoietin (hEPO) under the control of the S2-derived inducible metallothionein (MT) promoter were infected with three types of recombinant baculoviruses, each of which expressed a different fluorescent protein gene under the control of MT promoter. Addition of copper sulfate as an inducer to infected, stably transfected S2 cells resulted in simultaneous expression of hEPO and three fluorescent proteins. Expression profiles and levels of the three induced fluorescent proteins were similar in all single infected cells. Importantly, expression profiles and levels of hEPO were similar in both non-infected and infected cells, indicating that baculovirus expressed recombinant proteins do not adversely affect expression of host cell recombinant proteins. Expressions of the three fluorescent proteins were able to be selectively regulated by altering combination ratios of the three types of recombinant baculoviruses. Collectively, these data indicate that the baculovirus/stably transfected S2 cell system can be successfully used to express multiple foreign proteins in a controlled and selective manner without the burden of additional selection markers. Such a system would be expected to be attractive as a multiple protein expression platform for engineering metabolic or glycosylation pathways.

Temporal transcription program of recombinant Autographa californica multiple nucleopolyhedrosis virus

Baculoviruses, a family of large, rod-shaped viruses that mainly infect lepidopteran insects, have been widely used to transduce various cells for exogenous gene expression. Nonetheless, how a virus controls its transcription program in cells is poorly understood. With a custom-made baculovirus DNA microarray, we investigated the recombinant Autographa californica multiple nucleopolyhedrosis virus (AcMNPV) gene expression program in lepidopteran Sf21 cells over the time course of infection. Our analysis of transcription kinetics in the cells uncovered sequential viral gene expression patterns possibly regulated by different mechanisms during different phases of infection. To gain further insight into the regulatory network, we investigated the transcription program of a mutant virus deficient in an early transactivator (pe38) and uncovered several pe38-dependent and pe38-independent genes. This study of baculovirus dynamic transcription programs in different virus genetic backgrounds provides new molecular insights into how gene expression in viruses is regulated.

Select what you need: a comparative evaluation of the advantages and limitations of frequently used expression systems for foreign genes

The expression of heterologous proteins in microorganisms using genetic recombination is still the high point in the development and exploitation of modern biotechnology. People can produce bioactive proteins from relatively cheap culture medium instead of expensive extraction. Host cell systems for the expression of heterologous genes are generally prokaryotic or eukaryotic systems, both of which have inherent advantages and drawbacks. An optimal expression system can be selected only if the productivity, bioactivity, purpose, and physicochemical characteristics of the interest protein are taken into consideration, together with the cost, convenience and safety of the system itself. Here, we concisely review the most frequently used prokaryotic, yeast, insect and mammalian expression systems, as well as expression in eukaryote individuals. The merits and demerits of these systems are discussed.

Baculovirus-mediated gene expression in chicken primary cells

A recombinant baculovirus was constructed containing an expression cassette with a reporter gene, green fluorescent protein, directed by a constitutive mammalian promoter: a human cytomegalovirus immediate early promoter/enhancer (CMV-IE). High titer virus was prepared with ultracentrifugation. Efficient gene delivery and expression were observed in the virus-treated chicken primary culture, myoblast cells, and whole embryonic fibroblast cells. It was noticed that an addition of sodium butyrate (a selective histone deacetylase inhibitor) to viral transduction medium extremely enhanced the reporter-gene expression. However, there is no effect of presence of trichostatin A observed. To maximize the reporter-gene expression, the baculoviral infection condition was optimized with both cell types. Our approaches demonstrated that recombinant baculovirus could efficiently deliver its genome DNA into chicken primary cells and that CMV-IE, a mammalian-cell-active promoter, was functional in chicken primary cells and could direct a high level of gene expression. Clearly, the recombinant baculovirus provides an alternative means for foreign gene delivery into avian cells.

Stable RNA Interference in Spodoptera frugiperda Cells by a DNA Vector-based Method

Double-stranded RNA (dsRNA)-mediated interference (RNAi) is a powerful tool for silencing of gene expression in many organisms. To establish a DNA vector-based method for stable RNAi in Spodoptera frugiperda cells (Sf9), we created a stably transfected Sf9 cell line to express large dsRNA fragment targeting to silence the firefly luciferase gene (luc). The luc dsRNA specifically and stably suppressed the baculovirus-mediated luciferase expression. Thus, gene silencing in Sf9 cells was achieved using DNA vectors similar to the facile design described in this study.

Stably Transformed Insect Cell Lines: Tools for Expression of Secreted and Membrane‐anchored Proteins and High‐throughput Screening Platforms for Drug and Insecticide Discovery

Insect cell-based expression systems are prominent amongst current expression platforms for their ability to express virtually all types of heterologous recombinant proteins. Stably transformed insect cell lines represent an attractive alternative to the baculovirus expression system, particularly for the production of secreted and membrane-anchored proteins. For this reason, transformed insect cell systems are receiving increased attention from the research community and the biotechnology industry. In this article, we review recent developments in the field of insect cell-based expression from two main perspectives, the production of secreted and membrane-anchored proteins and the establishment of novel methodological tools for the identification of bioactive compounds that can be used as research reagents and leads for new pharmaceuticals and insecticides.

The baculovirus anti-apoptotic protein Op-IAP does not inhibit Drosophila caspases or apoptosis in Drosophila S2 cells and instead sensitizes S2 cells to virus-induced apoptosis

The Op-IAP protein from the baculovirus Orgyia pseudotsugata M nucleopolyhedrovirus (OpMNPV) is highly effective at inhibiting apoptosis triggered by a variety of different stimuli in lepidopteran cells as well as in several different mammalian cell types, suggesting that it functions at a highly conserved step in the apoptotic pathway. However, the mechanism by which Op-IAP inhibits apoptosis is unclear. Since some IAP proteins can bind and inhibit caspases, we tested whether Op-IAP could inhibit the activity of caspases from Drosophila melanogaster. We found that recombinant Op-IAP protein was not able to bind or directly inhibit the activity of the Drosophila caspases DRONC, DrICE, or DCP-1 in vitro. In addition, expression of Op-IAP was unable to inhibit apoptosis triggered by either actinomycin D or UV light in D. melanogaster S2 cells. Surprisingly, Op-IAP expression in S2 cells enhanced apoptosis caused by baculovirus infection, but did not cause increased sensitivity to either actinomycin D or UV damage-induced apoptosis. The observation that Op-IAP cannot inhibit these insect caspases suggests that it functions by a mechanism that does not involve direct caspase inhibition.

Abi enhances Abl-mediated CDC2 phosphorylation and inactivation

Abelson tyrosine kinase (Abl) is a non-receptor tyrosine kinase which is frequently coupled with adaptor proteins to interact with its substrates for the regulation of cytoskeleton rearrangement, cell growth and apoptosis in response to a variety of biological stimuli. The Abl interactor (Abi) family members were first identified as adaptor proteins of Abl for regulating Abl transforming and kinase activity. In the present study, we used a yeast two-hybrid screen to identify Cdc2 as a novel Abi-binding protein. This finding led us to investigate the role of Abi in linking Abl and Cdc2. These three proteins formed a trimeric complex in Drosophila and mammalian cells. The expression of Abi in cells greatly enhanced the formation of the Abl-Cdc2 complex, suggesting that Abi functions as an adaptor protein facilitating the binding between Abl and Cdc2. We show that Abi promotes Abl-mediated phosphorylation of Cdc2 at tyrosine 15 and inactivation of Cdc2 kinase activity. Furthermore, coexpression of Abl and Abi in Drosophila S2 cells led to suppression of cell growth. These data suggest that Abl signaling may be involved in the downregulation of Cdc2 kinase in cell cycle control.

From gene to protein: a review of new and enabling technologies for multi-parallel protein expression

In the post-genomic era, increasingly greater demands and expectations are being placed on protein production laboratories to produce more proteins and in faster timelines. This has been coupled with an exponential increase in the number of requests for the production of proteins which lack structural and functional information. No longer can groups use literature available in the public domain solely to drive their expression strategy, and moreover current expression and concomitant purification strategies clearly do not meet modern-day demands for protein production. This review will therefore attempt to provide a definitive review of current 'best in class' cloning, expression and purification systems, and the adaptations and developments that have been made by laboratories, both academic and industrial, to enhance protein production throughput.

One site mutation disrupts dimer formation in human DPP-IV proteins

DPP-IV is a prolyl dipeptidase, cleaving the peptide bond after the penultimate proline residue. It is an important drug target for the treatment of type II diabetes. DPP-IV is active as a dimer, and monomeric DPP-IV has been speculated to be inactive. In this study, we have identified the C-terminal loop of DPP-IV, highly conserved among prolyl dipeptidases, as essential for dimer formation and optimal catalysis. The conserved residue His750 on the loop contributes significantly for dimer stability. We have determined the quaternary structures of the wild type, H750A, and H750E mutant enzymes by several independent methods including chemical cross-linking, gel electrophoresis, size exclusion chromatography, and analytical ultracentrifugation. Wild-type DPP-IV exists as dimers both in the intact cell and in vitro after purification from human semen or insect cells. The H750A mutation results in a mixture of DPP-IV dimer and monomer. H750A dimer has the same kinetic constants as those of the wild type, whereas the H750A monomer has a 60-fold decrease in kcat. Replacement of His750 with a negatively charged Glu (H750E) results in nearly exclusive monomers with a 300-fold decrease in catalytic activity. Interestingly, there is no dynamic equilibrium between the dimer and the monomer for all forms of DPP-IVs studied here. This is the first study of the function of the C-terminal loop as well as monomeric mutant DPP-IVs with respect to their enzymatic activities. The study has important implications for the discovery of drugs targeted to the dimer interface.

Purification and characterization of human prolyl dipeptidase DPP8 in Sf9 insect cells

DPP8 is a new member of the prolyl dipeptidases, many of which have important biological functions in vivo. DPP8 catalyzes the cleavage at the carboxyl side of the proline residue at the penultimate position. To study its structure and biochemical properties, we have overexpressed the human DPP8 protein in baculovirus infected Sf9 cells. The protein is soluble and can be purified to homogeneity. Using the chromogenic H-Gly-Pro-pNA as the substrate, a kinetic study shows that purified DPP8 is active and has a similar kcat value as that of DPP-IV, a prolyl dipeptidase that is a drug target for type II diabetes. The kinetic constants of DPP8 are also determined for other chromogenic substrates, and the results indicate that DPP8 has substrate preference at both the P1 and P2 sites. The expression system provides means of better understanding the structure, catalytic mechanism, and biological function of DPP8 protein.

Recombinant baculoviruses as mammalian cell gene-delivery vectors

The baculovirus expression system has been used extensively for the expression of recombinant proteins in insect cells. Recently, recombinant baculovirus vectors engineered to contain mammalian cell-active promoter elements, have been used successfully for transient and stable gene delivery in a broad spectrum of primary and established mammalian cells. The application of modified baculoviruses for in vivo gene delivery has also been demonstrated. In contrast to other commonly used viral vectors, baculoviruses have the unique property of replicating in insect cells while being incapable of initiating a replication cycle and producing infectious virus in mammalian cells. The viruses can be readily manipulated, accommodate large insertions of foreign DNA, initiate little to no microscopically observable cytopathic effect in mammalian cells and have a good biosafety profile. These attributes will undoubtedly lead to the increased application and continued development of this system for efficient gene delivery into mammalian cells. Who said you can't teach an old dog new tricks?