Available lepidopteran insect cell lines

NISES-AnPe-428 cell line derived from the Chinese oak silkworm Antheraea pernyi is permissive for multiple nucleopolyhedrovirus species from insects of four different families

The cell line NISES-AnPe-428 (AnPe), derived from the Chinese oak silkworm Antheraea pernyi, was characterized for its permissiveness and productivity for six different nucleopolyhedrovirus (NPV) species. These NPVs included homologous Antheraea pernyi NPV (AnpeNPV) and heterologous Autographa californica multiple NPV (AcMNPV), Bombyx mori NPV (BmNPV), Hyphantria cunea MNPV (HycuMNPV), Spodoptera exigua MNPV (SeMNPV), and Lymantria dispar MNPV (LdMNPV), representing viruses that had been isolated from insect species belonging to five different families (Saturniidae, Noctuidae, Bombycidae, Arctiidae, and Lymantriidae). We found that AnPe cells supported productive replication of AnpeNPV, AcMNPV, BmNPV, HycuMNPV, and SeMNPV to varying degrees. Upon infection with SeMNPV, a subset of AnPe cell population in the culture underwent apoptosis, while remaining cells produced limited amounts of progeny virions and polyhedra. AnPe cells were refractory to LdMNPV infection and failed to support replication of viral DNA, indicating that viral replication was restricted at or prior to the step of viral DNA replication. These results indicated that AnPe cells have the potential to provide excellent systems for studying the molecular mechanisms underlying cellular permissiveness for NPV replication and host-range determination of NPVs.

Expressing Cloned Genes for Protein Production, Purification, and Analysis

Obtaining high quantities of a specific protein directly from native sources is often challenging, particularly when dealing with human proteins. To overcome this obstacle, many researchers take advantage of heterologous expression systems by cloning genes into artificial vectors designed to operate within easily cultured cells, such as Escherichia coli, Pichia pastoris (yeast), and several varieties of insect and mammalian cells. Heterologous expression systems also allow for easy modification of the protein to optimize expression, mutational analysis of specific sites within the protein and facilitate their purification with engineered affinity tags. Some degree of purification of the target protein is usually required for functional analysis. Purification to near homogeneity is essential for characterization of protein structure by X-ray crystallography or nuclear magnetic resonance (NMR) and characterization of the biochemical and biophysical properties of a protein, because contaminating proteins almost always adversely affect the results. Methods for producing and purifying proteins in several different expression platforms and using a variety of vectors are introduced here.

Expression of Cloned Genes Using the Baculovirus Expression System

The general strategy of the baculovirus expression system is to infect insect cells with a virus that expresses a foreign protein at a very late stage of infection. Almost all baculovirus expression systems use the procedures for insect cell transfection, baculovirus production, and protein expression given in the main portion of this protocol. This protocol also includes a method that uses molecular biology techniques to produce recombinant baculovirus DNA in E. coli before transfection of insect cells. It is important to quantify the viral titer to achieve optimal and reproducible expression of target proteins. Accordingly, the viral plaque assay is also described here.

The Cephalopod Large Brain Enigma: Are Conserved Mechanisms of Stem Cell Expansion the Key?

Within the clade of mollusks, cephalopods have developed an unusually large and complex nervous system. The increased complexity of the cephalopod centralized "brain" parallels an amazing amount of complex behaviors that culminate in one order, the octopods. The mechanisms that enable evolution of expanded brains in invertebrates remain enigmatic. While expression mapping of known molecular pathways demonstrated the conservation of major neurogenesis pathways and revealed neurogenic territories, it did not explain why cephalopods could massively increase their brain size compared to other mollusks. Such an increase is reminiscent of the expansion of the cerebral cortex in mammalians, which have enlarged their number and variety of neurogenic stem cells. We hypothesize that similar mechanisms might be at play in cephalopods and that focusing on the stem cell biology of cephalopod neurogenesis and genetic innovations might be smarter strategies to uncover the mechanism that has driven cephalopod brain expansion.

Insect Biotechnology

For the purpose of this work, insect biotechnology, which is also known as yellow biotechnology, is the use of insects as well as insect-derived cells or molecules in medical (red biotechnology), agricultural (green biotechnology), and industrial (white) biotechnology. It is based on the application of biotechnological techniques on insects or their cells to develop products or services for human use. Such products are then applied in agriculture, medicine, and industrial biotechnology. Insect biotechnology has proven to be a useful resource in diverse industries, especially for the production of industrial enzymes including chitinases and cellulases, pharmaceuticals, microbial insecticides, insect genes, and many other substances. Insect cells (ICs), and particularly lepidopteran cells, constitute a competitive strategy to mammalian cells for the manufacturing of biotechnology products. Among the wide range of methods and expression hosts available for the production of biotech products, ICs are ideal for the production of complex proteins requiring extensive posttranslational modification. The progress so far made in insect biotechnology essentially derives from scientific breakthroughs in molecular biology, especially with the advances in techniques that allow genetic manipulation of organisms and cells. Insect biotechnology has grown tremendously in the last 30 years.

Establishment of a cell line from the ash and privet borer beetle Tylonotus bimaculatus Haldeman and assessment of its sensitivity to diacylhydrazine insecticides

A novel cell line, NRCAN-Tb521, was developed from larvae of the longhorn beetle Tylonotus bimaculatus (Coleoptera: Cerambycidae), a pest of North American ash trees. The cell line has been successfully passaged more than 50 times and displayed very strong attachment to the substrate and a modal chromosomal count distribution of 19. Sequencing of a 649 bp fragment of the mitochondrial cytochrome oxidase I gene confirmed the identity of NRCAN-Tb521 as T. bimaculatus. The response of the cell line to 20-hydroxyecdysone and diacylhydrazine ecdysone agonist insecticides was also studied. At 10(-6) M, 20-hydroxyecdysone, tebufenozide, methoxyfenozide and halofenozide triggered the production of numerous filamentous cytoplasmic extensions, and the cells tended to form aggregates, indicative of a cell differentiation response. This response was followed by a strong decrease in viability after 4 d. Reverse transcription polymerase chain reaction (PCR) experiments and sequencing of PCR fragments showed that the 20E receptor gene EcR is expressed in the cells and that 20E, tebufenozide, methoxyfenozide and halofenozide also induce the expression of the nuclear hormone receptor gene HR3. This report establishes that NRCAN-Tb521 is a valuable in vitro model to study effects of ecdysone agonists in wood-boring cerambycids.

An Overview and History of Glyco-Engineering in Insect Expression Systems

Insect systems, including the baculovirus-insect cell and Drosophila S2 cell systems are widely used as recombinant protein production platforms. Historically, however, no insect-based system has been able to produce glycoproteins with human-type glycans, which often influence the clinical efficacy of therapeutic glycoproteins and the overall structures and functions of other recombinant glycoprotein products. In addition, some insect cell systems produce N-glycans with immunogenic epitopes. Over the past 20 years, these problems have been addressed by efforts to glyco-engineer insect-based expression systems. These efforts have focused on introducing the capacity to produce complex-type, terminally sialylated N-glycans and eliminating the capacity to produce immunogenic N-glycans. Various glyco-engineering approaches have included genetically engineering insect cells, baculoviral vectors, and/or insects with heterologous genes encoding the enzymes required to produce various glycosyltransferases, sugars, nucleotide sugars, and nucleotide sugar transporters, as well as an enzyme that can deplete GDP-fucose. In this chapter, we present an overview and history of glyco-engineering in insect expression systems as a prelude to subsequent chapters, which will highlight various methods used for this purpose.

A new continuous cell line from Blaps rhynchoptera Fairmaire (Coleoptera: Tenebrionidae)

The first continuous cell line from the neonate larval tissues of Blaps rhynchoptera, which has been used as a folk medicine in Yunnan Province, China, was established and designated RIRI-BR1. This cell line was serially subcultured in Schneider's medium supplemented with 15% fetal bovine serum (FBS). The cells grew adherent to culture flasks and exhibited spindle-like and polygonal shapes. The growth rate was determined at the 50th passage, and the population doubling time was calculated to be 79.5 h. The post-thaw viability of the cell line at different passages showed that the cells from higher passages could be recovered easier after cryopreservation than the cells from lower passages. The average chromosome numbers from cells of the RIRI-BR1 cell line at passages 5 to 50 ranged from 12 to 130. The rDNA internal transcribed spacer (ITS) sequence analysis indicated that the RIRI-BR1 cell line was derived from B. rhynchoptera.

Mosquito cell lines: history, isolation, availability and application to assess the threat of arboviral transmission in the United Kingdom

Mosquitoes are highly effective vectors for transmission of human and animal pathogens. Understanding the relationship between pathogen and vector is vital in developing strategies to predict and prevent transmission. Cell lines derived from appropriate mosquito hosts provide a relatively simple tool for investigating the interaction between the host and viruses transmitted by mosquitoes. This review provides a brief overview of the development of mosquito cell lines, methods of isolation, their availability and application for investigating insect-virus interactions.

Tnao38, high five and Sf9--evaluation of host-virus interactions in three different insect cell lines: baculovirus production and recombinant protein expression

PURPOSE OF WORK

A comparative analysis of new and established insect cell lines, in regard to process relevant parameters, provide data that can be exploited for designing more robust and effective protein production processes. The baculovirus-insect cell expression system has been efficiently used for the production of heterologous proteins. Three different insect cell lines Tnao38, High Five and Sf9 were compared in terms of virus susceptibility, baculovirus production and product yield of an intra-cellularly (YFP) and extra-cellularly (influenza A virus hemagglutinin)-expressed recombinant protein. The Tnao38 and High Five cell lines exhibited higher (tenfold) susceptibility to baculovirus infection than Sf9 cells, whereas Sf9 cells showed a higher (100-fold) capacity for production of infectious virus particles. Analysis of recombinant protein expression revealed considerably higher product yields in Tnao38 and High Five cells as compared to Sf9 cells, for both model proteins. Overall, the two Trichoplusia ni-derived cell lines, High Five and Tnao38, were significantly more efficient in terms of secreting proteins such as the glycoprotein hemagglutinin of influenza A virus.

Conserved microRNA miR-8 blocks activation of the Toll pathway by upregulating Serpin 27 transcripts

microRNAs (miRNAs) play significant regulatory roles in gene expression at the post-transcriptional level. This includes modulating processes such as development, immunity, cancer, and host-pathogen interactions. It was recently shown that the phylogenetically deeply conserved miRNA, miR-8, plays a role in maintaining the homeostasis of immunity by suppressing the production of anti-microbial peptides. In this study, we show that miR-8 from the insect Plutella xylostella positively regulates the transcript levels of the serine protease inhibitor Serpin 27, which has been shown to regulate activation of the Toll pathway and prophenoloxidase involved in the melanization response in insects. Interestingly, miR-8 is downregulated following parasitization by Diadegma semiclausum leading to significant declines in Serpin 27 transcript levels. This allows upregulation of antimicrobial peptides, such as gloverin, that are controlled by the Toll pathway and activation of proteolytic cascades essential for humoral immune responses to foreign invasion.

Suppression of scavenger receptors transcription by parasitoid factors

Scavenger receptors (SR) are a group of membrane proteins that play central roles in various functions, such as immune responses in insects. Members of different SR classes were identified from Plutella xylostella larval transcriptome. SR B1 and B3 were found to be differentially expressed in larvae and pupae. Expression of P. xylostella SR genes was significantly altered during immune challenge induced in P. xylostella cells (Px) and parasitized larvae. Maternal factors injected into the larvae by the endoparasitoid wasp Diadegma semiclausum at oviposition include venom and ichnovirus (DsIV) genes to suppress the host immune system. Transient expression of two DsIV genes, Vankyrin1 and Repeat element 4 (Rep4), in Px cells led to significant down-regulation of both SR B1 and B3 transcript levels, while DsIV Rep4 expression did not change the relative transcription levels of SR B3. In conclusion, it appears that the two members of the SR family play important roles in innate immune responses in P. xylostella and that each member of this group may play different roles in the host-parasitoid interaction.

A new cell line (NTU-SE) from pupal tissues of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is highly susceptible to S. exigua multiple nucleopolyhedrovirus (SeMNPV) and Autographa californica MNPV (AcMNPV)

A new continuous cell line, NTU-SE, was established from the pupal tissues of an economically important pest, the beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae). This cell line contains four major morphologic types: round, polymorphic, spindle-shaped, and comma-shaped cells. The population doubling time of this new line in TNM-FH medium supplemented with 8% fetal bovine serum (FBS) at 28°C is 35.5h. The chromosomal spread from NTU-SE cells is typical to the chromosomal morphology of lepidopteran cell lines. Confidently, NTU-SE cell line is a new cell line that exhibits distinct isozyme patterns of esterase, lactate dehydrogenase (LDH), and malate dehydrogenase (MDH) from those of the other insect cell lines. In addition, the DNA sequence of the nuclear ribosomal internal transcribed spacer (ITS) region of NTU-SE cells is above 96% identical to that sequence of S. exigua larvae, as compared to only 66% identical to that of S. litura larvae. The NTU-SE cell line is highly susceptible to S. exigua multiple nucleopolyhedrovirus (SeMNPV) and Autographa californica MNPV (AcMNPV). Therefore, a highly virulent SeMNPV strain, SeMNPV-1, had been successfully isolated and propagated in NTU-SE cells. We conclude that the NTU-SE cell line will be a useful tool for the selection and mass production of highly virulent SeMNPV strains for the S. exigua biocontrol and the baculovirus based recombinant protein expression systems.

Insect cell culture: virus replication and applications in biotechnology

Insect cell lines have been initiated since the 1930s and were used to replicate insect baculoviruses as well as arboviruses. Since the latter group of viruses cause serious diseased in man and equines, efforts were expended to characterize the viruses in the new cell lines in attempts to understand the replication cycle at the cellular and molecular levels. Soon it was realized that insect baculoviruses have a potential as viable alternatives to chemicals in the control of agricultural and forest insect pests. The cell lines provided excellent tools to understand the molecular biology of baculoviruses before wide-scale use in the field. During these investigastions, it came to light that baculoviruses can be exploited as vectors for the expression of exogenous proteins and vaccines. The amenability of the virus to genetic modifications and the increasing numbers of permissive cell lines opened new avenues in protein expression. However, not all baculoviruses were able to replicate in cell lines. Indeed, there are no cell lines permissive to viruses belonging to the genera Gammabaculvirus and Deltabaculovirus. Some entomopoxviruses have been replicated in a few cell lines and this paper reports the replication of an entomopoxvirus from the spruce budworm in a homologous cell line.

A cell line derived from the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae)

The red flour beetle, Tribolium castaneum, is a model organism for agricultural and medical research and its complete genome is sequenced. We established a continuously replicating T. castaneum cell line to complement existing physiological, genetic, and genomic research tools. We set up trial cell cultures from egg, pupa, and adult stages as tissue sources and incubated them in six separate cell culture media to determine the optimal combination of tissue source and medium for cell replication. Our most promising culture was generated by co-culturing adult (∼75 %) and pupal tissues in EX-CELL 420 medium containing 9 % FBS. Our new cell culture is designated BCIRL-TcA-CLG1 (TcA) and it has been subcultured more than 90 times. Amplification of genomic DNA with species-specific primers yielded DNA fragments of the expected sizes and with sequences identical to those from the published Tribolium genome. Additionally, we characterized this line using DNA fingerprinting (DAF-PCR) and compared it with three other coleopteran cell lines and its conspecific pupae to confirm identity. Its doubling time is 155.2 hr. Early passages consisted of attached cells and vesicles in suspension, whereas later passages consisted primarily of attached, spherical cells. Similar to other established cell lines, the ploidy of TcA cells was variable, ranging from 20 chromosomes/cell (diploid) to above 30 chromosomes/cell. TcA cells withstood incubation at 40°C for 1 h with no decrease in viability. We recorded increased levels of one heat shock protein (43 kDa) and of the hsp68a transcript following exposure to 40°C. Taken together, this represents the first report of a continuously replicating T. castaneum cell line. We expect the BCIRL-TcA-CLG1 line will become a useful tool in Tribolium research.

Baculovirus-insect cell expression systems

In the early 1980s, the first-published reports of baculovirus-mediated foreign gene expression stimulated great interest in the use of baculovirus-insect cell systems for recombinant protein production. Initially, this system appeared to be the first that would be able to provide the high production levels associated with bacterial systems and the eukaryotic protein processing capabilities associated with mammalian systems. Experience and an increased understanding of basic insect cell biology have shown that these early expectations were not completely realistic. Nevertheless, baculovirus-insect cell expression systems have the capacity to produce many recombinant proteins at high levels and they also provide significant eukaryotic protein processing capabilities. Furthermore, important technological advances over the past 20 years have improved upon the original methods developed for the isolation of baculovirus expression vectors, which were inefficient, required at least some specialized expertise and, therefore, induced some frustration among those who used the original baculovirus-insect cell expression system. Today, virtually any investigator with basic molecular biology training can relatively quickly and efficiently isolate a recombinant baculovirus vector and use it to produce their favorite protein in an insect cell culture. This chapter will begin with background information on the basic baculovirus-insect cell expression system and will then focus on recent developments that have greatly facilitated the ability of an average investigator to take advantage of its attributes.