New cell lines from Lymantria xylina (Lepidoptera: Lymantriidae): Characterization and susceptibility to baculoviruses

Establishment and characterization of a new embryonic cell line from Helicoverpa armigera (Hübner)

Here, a new cell line, Ha168, was established from Helicoverpa armigera eggs and has been stably subcultured for over 30 passages in TNM-FH medium supplemented with 10% fetal bovine serum. The cell line consists of round and spindle-shaped cells and several giant cells. The round cells, with a cell diameter of 14.30 ± 2.804 μm, account for 77% of the cells. DNA amplification fingerprinting, random amplified polymorphic DNA analysis, and analysis of the mitochondrial cytochrome c oxidase subunit I gene confirmed that the Ha168 cells were derived from H. armigera. Karyotype analysis revealed the average chromosome number of Ha168 cells to be 71. Growth curves at passage 25 were determined and demonstrated that the cell population doubling time is 56.8 h. No mycoplasma contamination was detected in the cell line. Ha168 cells can be infected by recombinant baculovirus AcMNPV-EGFP, and exogenous protein expression level in this cell line is 70% of that in the Sf9 cell line.

A Newly Designed EGFP-2A Peptide Monocistronic Baculoviral Vector for Concatenating the Expression of Recombinant Proteins in Insect Cells

Recombinant proteins produced by the baculovirus expression vector system (BVES) have been widely applied in the agricultural and medical fields. However, the procedure for protein expression is inefficient and needs to be improved. Herein, we propose a simple construct that incorporates a selectable marker (enhanced green fluorescent protein, EGFP) and a picorna viral-derived “self-cleaving” 2A-like peptide to separate the EGFP and target proteins in a monocistronic baculovirus vector to facilitate isolation of the recombinant baculovirus in the BVES. In this study, porcine adiponectin (ADN), a secreted, multimeric protein with insulin-sensitizing properties, was used to demonstrate its utility in our EGFP-2A-based expression system. EGFP and ADN were simultaneously expressed by a recombinant alphabaculovirus. Co-expression of EGFP facilitates the manipulation of the following processes, such as determining expression kinetics and harvesting ADN. The results showed that the 2A “self-cleaving” process does not interfere with EGFP activity or with signal peptide removal and the secretion of recombinant ADN. Posttranslational modifications, including glycosylation, of the recombinant ADN occurred in insect cells, and the formation of various multimers was further verified. Most importantly, the insect-produced ADN showed a similar bioactivity to that of mammalian cells. This concept provides a practical and economic approach that utilizes a new combination of alphabaculovirus/insect cell expression systems for future applications.

Characterization and functional assay of apsup (Lyxy105) from Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV)

The baculoviral anti-apoptotic genes, p35 and iap (inhibitor of apoptosis), play important roles in the initiation of viral infection. Recently, a new anti-apoptotic gene (apoptosis suppressor, apsup) was identified in Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV). An apsup homolog gene, Lyxy105 (ly-apsup), was also predicted in the Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV) genome. In this study, we attempt to perform a gene expression analysis and a functional assay of ly-apsup to demonstrate its anti-apoptotic activity and identify the functional domain of this protein. The transcription of the ly-apsup gene region was detected from 12 h post-infection (hpi) and increased significantly after 24-72 hpi. Comparison of the putative amino acid sequences to those of 18 baculoviral homolog proteins showed high amino acid identity to the LdMNPV sequences. Moreover, five conserved protein domains (named as domains I-V) were found. Therefore, protein functional assays were conducted on full-length proteins and different truncation clones. The overexpression of each clone was confirmed by western blot analysis, and the data revealed that a cleavage of ~ 5 kDa at the N-terminal region of the full-length, domains I-IV (1-241) and I-III (1-178), proteins occurred. The results of the functional analysis showed that full-length Ly-apsup and Ly-apsup with domain I (1-70) could inhibit Drosophila-RPR protein (D-RPR)-induced and actinomycin D (ActD)-induced apoptoses. In addition, the domains I and I-II (1-126) regions showed higher anti-apoptotic activity than the other domains in both D-RPR-induced and ActD-induced cell apoptoses. In conclusion, domain I of Ly-apsup may play an important role in the anti-apoptotic activity of this protein; cleavage of the Ly-apsup N-terminus may lead to decreased anti-apoptotic activity.

A new cell line derived from embryonic tissues of Holotrichia parallela (Coleoptera:Scarabaeidae)

Holotrichia parallela is an important agricultural underground insect pest and also an edible and medicinal insect. Establishing a new cell line of H. parallela will provide a rapid and convenient tool for the studies on its physiology, pathology, and gene functions. In this study, by using the embryonic tissue of H. parallela as the material, we established a new cell line named Hp-E-1. The microscopic observation of its morphological characteristics revealed that its cellular morphology was mainly in the spherical morphology with a mean cellular diameter of 17.71 ± 2.34 μm, accounting for 67% of the total cells. The spindle-shaped cells accounted for 33% of the total cells with a mean size of 23.51 ± 4.37 × 13.98 ± 2.05 μm. The chromosomal number varied from 7 to 40, with about 50% of the cells having a diploid chromosome number of 2n = 20. Random amplified polymorphic DNA (RAPD) analysis indicated that the profiles of PCR-amplified fragments of this cell line were basically similar to those of the embryonic tissues of H. parallela but were obviously different from those of cell line BTI-Tn5B1-4 of Trichoplusia ni and cell line Sf-9 of Spodoptera frugiperda. The DNA fragment encoding mitochondrial cytochrome C oxidase subunit I (COI) gene of this cell line shared 99.7% homology with that of the embryonic tissue of H. parallela, confirming that this cell line is indeed derived from H. parallela. The results of growth curve measurement indicated that the population doubling time of this cell line was 136.7 h. Cell line Hp-E-1 could not be infected by three viruses Autographa californica multiple nucleopolyhedrovirus (AcMNPV), Bombyx mori nucleopolyhedrovirus (BmNPV), and Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV).

Available Lepidopteran Insect Cell Lines

This chapter lists the known cell lines from Lepidoptera, largely based on previous compilations of insect cell lines published by W. Fred Hink. More than 320 lines from 65 species are listed. The official designation is given for each cell line as well as the species, tissue source, and, when known, the susceptibilities to baculoviruses.

Establishment and characterization of three embryonic cell lines of beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

Three cell lines (QAU-Se-E-1, -2 and -3, or Se-1, -2 and -3 for short) were established from eggs of beet armyworm (Spodoptera exigua) that have been passaged stably for more than 60 times in TNM-FH medium supplemented with 10 % fetal bovine serum. The cell lines consisted of round and spindle-shaped cells. The round cells accounted for 96.82, 84.34 and 83.16 % of the cells in the three cell lines, respectively, with cell diameters of 16.21 ± 0.72, 15.63 ± 0.58 and 13.06 ± 0.44 μm. Random amplified polymorphic DNA and analysis of the CO I gene showed that the three cell lines were all derived from S. exigua. Growth curves at passage 30 were determined and the results showed that the cell population doubling times were 59.03, 49.08 and 49.91 h, respectively. The three cell lines can be infected by S. exigua multiple nucleopolyhedrovirus (SeMNPV). Se-3 was extremely susceptible to the virus with an infection rate of 97.52 % 4 days after the inoculation and produced 2.02 × 10(6) OBs per mL of culture. Flow cytometry analysis showed that some of Se-1 and Se-2 cells had apoptosis after infection, whereas Se-3 cells did not. Bioassays showed that the virulence of the SeMNPV proliferated from Se-3 was similar to that from the insect with LC50 of 5.55 × 10(5) and 2.64 × 10(5) OBs/mL. Therefore, the cell lines can be used to study the SeMNPV-host interactions and mechanisms underlying the interactions.

Establishment and characterization of three new cell lines from the embryonic tissue of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae)

The establishment of new insect cell lines plays important roles in the researches of insect pathology, insect toxicology, insecticide screening and activity assay, etc. Using embryos of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae) as materials, this study describes the establishment of three cell lines designated as QAU-Ho-E-3 (Ho-3), QAU-Ho-E-4 (Ho-4), and QAU-Ho-E-6 (Ho-6), respectively. Currently, the three cell lines have been passaged more than 50 times in the TNM-FH insect cell medium containing 10% fetal bovine serum (FBS). All of them showed adherent growth. The majority of Ho-3 cells are spindle-shaped, with a size of 24.35 ± 5.29 × 11.56 ± 1.67 μm. The Ho-4 cells were either spindle-shaped or oblong, with a size of 38.07 ± 8.57 × 17.62 ± 2.48 μm. The Ho-6 cells were primarily round in shape with a diameter of 14.54 ± 1.96 μm. The Ho-3 and Ho-4 cell lines contained 20 chromosomes (i.e., diploid, 2n = 20) at passages 14 and 45. The Ho-6 cell line contained 20 chromosomes (i.e., diploid, 2n = 20) at passage 14 but 40 chromosomes (i.e., polyploidy, 4n = 40) at passage 45. The results of random amplified polymorphic DNA (RAPD) analysis showed that the RAPD fingerprint of the three cell lines was consistent with that of H. oblita eggs, but clearly different from that of BTI-Tn5B1-4 and Sf-9 cells, demonstrating that the three cell lines Ho-3, Ho-4, and Ho-6 are H. oblita cell lines. The results of the growth curve test showed that the population doubling times of Ho-3, Ho-4, and Ho-6 were 101.1, 105.2, and 83.6 h, respectively. The viral infection assay indicated that these H. oblita cell lines were not permissive to infection by Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or Bombyx mori nucleopolyhedrovirus (BmNPV).

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.

Genomic sequencing and analyses of Lymantria xylina multiple nucleopolyhedrovirus

BACKGROUND

Outbreaks of the casuarina moth, Lymantria xylina Swinehoe (Lepidoptera: Lymantriidae), which is a very important forest pest in Taiwan, have occurred every five to 10 years. This moth has expanded its range of host plants to include more than 65 species of broadleaf trees. LyxyMNPV (L. xylina multiple nucleopolyhedrovirus) is highly virulent to the casuarina moth and has been investigated as a possible biopesticide for controlling this moth. LdMNPV-like virus has also been isolated from Lymantria xylina larvae but LyxyMNPV was more virulent than LdMNPV-like virus both in NTU-LY and IPLB-LD-652Y cell lines. To better understand LyxyMNPV, the nucleotide sequence of the LyxyMNPV DNA genome was determined and analysed.

RESULTS

The genome of LyxyMNPV consists of 156,344 bases, has a G+C content of 53.4% and contains 157 putative open reading frames (ORFs). The gene content and gene order of LyxyMNPV were similar to those of LdMNPV, with 151 ORFs identified as homologous to those reported in the LdMNPV genome. Two genes (Lyxy49 and Lyxy123) were homologous to other baculoviruses, and four unique LyxyMNPV ORFs (Lyxy11, Lyxy19, Lyxy130 and Lyxy131) were identified in the LyxyMNPV genome, including a gag-like gene that was not reported in baculoviruses. LdMNPV contains 23 ORFs that are absent in LyxyMNPV. Readily identifiable homologues of the gene host range factor-1 (hrf-1), which appears to be involved in the susceptibility of L. dispar to NPV infection, were not present in LyxyMNPV. Additionally, two putative odv-e27 homologues were identified in LyxyMNPV. The LyxyMNPV genome encoded 14 bro genes compared with 16 in LdMNPV, which occupied more than 8% of the LyxyMNPV genome. Thirteen homologous regions (hrs) were identified containing 48 repeated sequences composed of 30-bp imperfect palindromes. However, they differed in the relative positions, number of repeats and orientation in the genome compared to LdMNPV.

CONCLUSION

The gene parity plot analysis, percent identity of the gene homologues and a phylogenetic analysis suggested that LyxyMNPV is a Group II NPV that is most closely related to LdMNPV but with a highly distinct genomic organisation.

Characterization of a new insect cell line (NTU-YB) derived from the common grass yellow butterfly, Eurema hecabe (Linnaeus) (Pieridae: Lepidoptera) and its susceptibility to microsporidia

A new lepidopteran cell line, NTU-YB, was derived from pupal tissue of Eurema hecabe (Linnaeus) (Pieridae: Lepidoptera). The doubling time of YB cells in TNM-FH medium supplemented with 8% FBS at 28 degrees C was 26.87h. The chromosome numbers of YB cells varied widely from 21 to 196 with a mean of 86. Compared to other insect cell lines, the YB cells produced distinct esterase, malate dehydrogenase, and lactate dehydrogenase isozyme patterns. Identity of the internal transcribed spacer region-I (ITS-I) of YB cells to E. hecabe larvae was 96% and to Eurema blanda larvae (tissue isolated from head) was 81%. The YB cells were permissive to Nosema sp. isolated from E. blanda and the infected YB cells showed obvious cytopathic effects after 3weeks post inoculation. The highest level of spore production was at 4weeks post inoculation when cells were infected with the Nosema isolate, and spore production was 1.34+/-0.9x10(6)spore/ml. Ultrastructrual studies showed that YB cells can host in vitro propagation of the E. blanda Nosema isolate, and developing stages were observed in the host cell nuclei as observed in the natural host, E. blanda. The NTU-YB cell line is also susceptible to Nosema bombycis.

A new nucleopolyhedrovirus strain (LdMNPV-like virus) with a defective fp25 gene from Lymantria xylina (Lepidoptera: Lymantriidae) in Taiwan

A new multiple nucleopolyhedrovirus strain was isolated from casuarina moth, Lymantria xylina Swinhoe, (Lepidoptera: Lymantriidae) in Taiwan. This Lymantria-derived virus can be propagated in IPLB-LD-652Y and NTU-LY cell lines and showed a few polyhedra (occlusion bodies) CPE in the infected cells. The restriction fragment length polymorphism (RFLP) profiles of whole genome indicated that this virus is distinct from LyxyMNPV and the virus genome size was approximately 139 kbps, which was smaller than that of LyxyMNPV. The molecular phylogenetic analyses of three important genes (polyhedrin, lef-8 and lef-9) were performed. Polyhedrin, LEF-8 and LEF-9 putative amino acid analyses of this virus revealed that this virus belongs to Group II NPV and closely related to LdMNPV than to LyxyMNPV. The phylogenetic distance analysis was further clarified the relationship to LdMNPV and this virus provisionally named LdMNPV-like virus. A significant deletion of a 44bp sequence found in LdMNPV-like virus was noted in the fp25k sequences of LdMNPV and LyxyMNPV and may play an important role in the few polyhedra CPE. In ultrastructural observations, the nuclei of the infected LD host cells contained large occlusion bodies (OBs), and few OBs, which presented as one or two OBs in a nucleus that was otherwise filled with free nuclocapsids and virions. We concluded that this LdMNPV-like virus is a new LdMNPV strain from L. xylina.

Morphological and molecular studies of a microsporidium (Nosema sp.) isolated from the thee spot grass yellow butterfly, Eurema blanda arsakia (Lepidoptera: Pieridae)

A microsporidium possessing molecular and morphological characteristics of the genus Nosema was isolated from larvae of the thee-spot grass yellow butterfly, Eurema blanda arsakia. The complete rRNA gene sequences of the E. blanda isolate contained 4,428 base pairs (GenBank Accession No. EU338534). The organization of the rRNA genes is LSU rRNA-ITS-SSU rRNA-IGS-5S, which corresponds with that of Nosema species closely related to Nosema bombycis. Phylogenetic analysis based on rRNA gene sequences show that this isolate is closely related to Nosema bombycis, Nosema plutellae, Nosema spodopterae, and Nosema antheraeae. The ultrastructure of all developmental stages of this microsporidium confirmed its placement in the genus Nosema. The isolate was successfully propagated in cell lines IPLB-LD652Y (Lymantria dispar) and NTU-LY (Lymantria xylina) and, in the in vitro system, it was frequently found to develop in the nuclei of the host cells, a circumstance that seldom occurs in other Nosema species. An extra-cellular vegetative stage of this microsporidium was also observed in the culture medium after 14 days of infection. The ECMDFs might be released from disrupted host cells.

Genomic and host range studies of Maruca vitrata nucleopolyhedrovirus

The complete genome of the Maruca vitrata nucleopolyhedrovirus (MaviNPV) isolated from the legume pod borer, Maruca vitrata (Lepidoptera: Pyralidae), was sequenced. It was found to be 111 953 bp in length, with an overall 39 % G+C content, and contained 126 open reading frames (ORFs) encoding predicted proteins of over 50 aa. The gene content and gene order of MaviNPV have the highest similarity to those of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and their shared homologous genes are 100 % collinear. In fact, MaviNPV seems to be a mini-AcMNPV that is native to Taiwan and possesses a smaller genome with fewer auxiliary genes than the AcMNPV type species. Except for one ORF (Mv74), all of the MaviNPV ORFs have homologues in the AcMNPV genome. MaviNPV is the first lepidopteran-specific baculovirus to lack homologues of vfgf and odv-e66. In addition, MaviNPV lacks the baculovirus repeat ORF (bro) gene that corresponds to AcMNPV ORF2. Five homologous regions (hrs) were located within the MaviNPV genome, and these contained a total of 44 imperfect palindromes. Phylogenetic analysis of the whole genome revealed that MaviNPV was separated from the common ancestor of AcMNPV and Bombyx mori nucleopolyhedrovirus before these two viral species diverged from each other. Moreover, replication of MaviNPV in several cell lines and an egfp-MaviNPV infection assay revealed that IPLB-LD-652Y cells are only partially permissive to MaviNPV, which supports our conclusion that MaviNPV is a distinct species of the group I lepidopteran NPVs.

A cell line (NTU-MV) established from Maruca vitrata (Lepidoptera: Pyralidae): Characterization, viral susceptibility, and polyhedra production

Here we describe the establishment of a new cell line, NTU-MV, derived from pupal tissues of an economically important pest, the legume pod borer Maruca vitrata. This cell line contained four major cell types: polymorphic cells, round cells, spindle-shaped cells, and comma cells. The doubling time of MV cells in TNM-FH medium supplemented with 8% FBS at 28 degrees C was 27h. The chromosome numbers of MV cells varied widely from 16 to 268. Compared to other insect cell lines, the MV cell line produced distinct isozyme patterns with esterase, malate dehydrogenase (MDH), and lactate dehydrogenase (LDH). Confirmation that NTU-MV was derived from M. vitrata was demonstrated by showing that the sequence of the internal transcribed spacer regions (ITS) of the MV cells was 98% identical to that of M. vitrata larvae. Two NTU-MV cell strains, NTU-MV1 and NTU-MV56, were selected based on susceptibility to MaviMNPV (M. vitrata multiple nucleopolyhedrovirus). NTU-MV, MV1, and MV56 cells showed a high susceptibility to MaviMNPV and produced high yields of polyhedra (47-50OBs/cell, 4x10(7)-5.96x10(7)OBs/ml) after 2 weeks of MaviMNPV infection. We conclude that the NTU-MV cell line will be a useful tool for studying MaviMNPV as well as for the mass production of MaviMNPV polyhedra for the biocontrol of M. vitrata.