Shizuo G. Kamita

Sequencing of the putative DNA helicase-encoding gene of the Bombyx mori nuclear polyhedrosis virus and fine-mapping of a region involved in host range expansion

The complete sequence of a 3666-nucleotide (nt) open reading frame (ORF) and its flanking regions (58.1-62.1 map units (m.u.) from Bombyx mori nuclear polyhedrosis virus (BmNPV)) was determined. This ORF, BmNPV dnahel, encoded a predicted protein of 143623 Da which possessed seven consensus motifs found in proteins which unwind duplex DNAs, indicating that it is a DNA helicase. A 572-bp SacI-HindIII fragment, BmScH, that was previously shown to expand the host range of Autographa californica NPV (AcNPV) following homologous recombination [Maeda et al. (1993) J. Virol. 67, 6234-6238], was localized within BmNPV dnahel. By cotransfection experiments, two adjacent nt (A and T) that appeared to be the minimal essential sequence necessary to expand the host range of AcNPV, were mapped within BmScH. These adjacent nt encoded a single amino acid difference between BmNPV (Asp) and AcNPV (Ser).

The Baculovirus Uses a Captured Host Phosphatase to Induce Enhanced Locomotory Activity in Host Caterpillars

The baculovirus is a classic example of a parasite that alters the behavior or physiology of its host so that progeny transmission is maximized. Baculoviruses do this by inducing enhanced locomotory activity (ELA) that causes the host caterpillars to climb to the upper foliage of plants. We previously reported that this behavior is not induced in silkworms that are infected with a mutant baculovirus lacking its protein tyrosine phosphatase (ptp) gene, a gene likely captured from an ancestral host. Here we show that the product of the ptp gene, PTP, associates with baculovirus ORF1629 as a virion structural protein, but surprisingly phosphatase activity associated with PTP was not required for the induction of ELA. Interestingly, the ptp knockout baculovirus showed significantly reduced infectivity of larval brain tissues. Collectively, we show that the modern baculovirus uses the host-derived phosphatase to establish adequate infection for ELA as a virion-associated structural protein rather than as an enzyme.

6.9 – Genetically Modified Baculoviruses for Pest Insect Control

Abstract Baculoviruses are insect pathogenic viruses that are used for pest insect control and as tools to produce recombinant proteins. Numerous studies show that both natural baculoviruses and genetically modified (GM) baculoviruses hold clear and substantial benefits for crop protection. Natural baculoviruses and potentially GM baculoviruses are particularly valuable under conditions where traditional chemical insecticides, have become ineffective, are economically prohibitive or have lost favor with the general public. The increased use of natural baculoviruses for pest insect control as well as GM baculoviruses for the production of pharmaceuticals may open doors to the use of GM baculoviruses for pest insect control. We review here the major approaches that are used to modify the baculovirus genome for improved efficacy as a biopesticide. The most common and successful of these approaches involve the insertion of a gene into the baculovirus genome that disrupts host insect feeding or is toxic to the host. GM baculoviruses remain a viable alternative to synthetic chemical pesticides and GM crops, we believe that baculoviruses should be utilized when alternative methods of pest insect control are required due to resistance, high cost of traditional insecticides, or changes in the regulatory environment and public opinion.

Immunochemical determination of dioxins in sediment and serum samples

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO-Triton X-100 and ELISA measurement. The gas chromatography-high resolution mass spectrometry (GC-HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100pgg(-1) dry sediment with a precision of 13-33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC-HRMS. Dioxins were determined in serum samples after a simple liquid-liquid extraction and solvent exchange into DMSO-Triton X-100 without further dilution. The current method (approximate method LOQ of 200pgml(-1) serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit.

The basic DNA-binding protein of Bombyx mori nuclear polyhedrosis virus : the existence of an additional arginine repeat

The basic DNA-binding protein of the Bombyx mori nuclear polyhedrosis virus (BmNPV) was purified by HPLC and a sequence of 45 amino acids from the N-terminus was determined. There were no detectable modifications such as N-terminal blockage, glycosylation, or phosphorylation. The amino acid sequence showed high homology to the predicted amino acid sequences of the basic proteins of Autographa californica NPV (AcNPV) and Orgyia pseudotsugata NPV (OpNPV) (90 and 76%, respectively), however, the BmNPV basic protein possessed an additional sequence of 10 amino acids. A DNA fragment encoding the basic protein was identified in a BmNPV DNA library by screening for possible DNA sequences coding for the basic proteins amino acid sequence. The nucleotide sequence of the basic protein of BmNPV was more similar to that of AcNPV (97%) than to that of OpNPV (62%). Homology plot analysis of the nucleotide sequence indicates that the BmNPV basic protein internal repeat evolved very recently.

Pharmacokinetic studies of the recombinant juvenile hormone esterase in Manduca sexta

Abstract Catalytically active juvenile hormone esterase (JHE) was expressed at a high level by Spodoptera frugiperda cells infected with recombinant Autographa californica nuclear polyhedrosis virus carrying the JHE gene cloned from the tobacco budworm, Heliothis virescens . JHE was partially purified from the culture medium by DEAE ion-exchange chromatography to a specific activity of 3000–5200 nmol juvenile hormone III metabolized per minute per milligram of protein after viral particles were inactivated by Triton X-100 following ultracentrifugation. Pharmacokinetic studies showed that catalytic activity was cleared with first-order kinetics after the purified enzyme was injected into larval hemolymph of the tobacco hornworm, Manduca sexta and H. virescens . The half-life of JHE was approximately 1.2 hr in both species. Experiments were undertaken to elucidate the mechanism of clearance from M. sexta larvae. Persistence of catalytic activity in hemolymph in vitro and Western blot analysis suggested an uptake process of JHE by tissue(s), rather than degradation in the plasma. Injection of a high dose of JHE resulted in an increased half-life and showed that the clearance process was saturable. The clearance rate was decreased by coinjection of a high dose of JHE inactivated by an irreversible inhibitor, paraoxon. Coinjection of an equal amount of bovine serum albumin did not influence the clearance rate of JHE. These results suggest that a specific process is involved in JHE clearance from hemolymph. N-linked oligosaccharides of JHE apparently were not important in the clearance of JHE from hemolymph.

Cloning and characterization of two glutathione S-transferases from pyrethroid-resistant Culex pipiens.

BACKGROUND The Marin strain of Culex pipiens Say is a pyrethroid-resistant population that was collected in Marin County, California, in 2001 and subsequently maintained in the laboratory under regular permethrin exposure. RESULTS In this study, two cDNAs, CpGSTd1 and CpGSTd2, encoding glutathione S-transferase (GST) were cloned from Cx. pipiens Marin. Phylogenetic analysis of the deduced amino acid sequences, CpGSTD1 and CpGSTD2, of these genes indicated that they belong to the Delta class of insect GSTs. The nucleotide and deduced amino acid sequences of CpGSTd1 and CpGSTd2 were 59 and 48% identical respectively. CpGSTD1 and CpGSTD2 were expressed in Escherichia coli and purified by affinity chromatography. The recombinant GSTs exhibited unique selectivity towards the general GST substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB), and also differed in their sensitivity to known inhibitors of GSTs. CpGSTD1 exhibited peroxidase activity with cumene hydroperoxide, while CpGSTD2 appeared to lack this activity. CpGSTD1 was able to metabolize 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), while DDT metabolism by CpGSTD2 was not detectable. CpGSTD1 and CpGSTD2 showed no detectable metabolism of permethrin. Gene expression of CpGSTd1 and CpGSTd2 in Marin mosquitoes was elevated about twofold in comparison with that found in a pyrethroid-sensitive mosquito strain. CONCLUSION The results indicate that CpGSTD1 and CpGSTD2 have unique biochemical characteristics, but they do not appear to play major roles in permethrin resistance in Marin mosquitoes.

RNA interference is induced in the glassy winged sharpshooter Homalodisca vitripennis by actin dsRNA

BACKGROUND The glassy winged sharpshooter, Homalodisca vitripennis, is an unusually robust and efficient leafhopper vector of Xylella fastidiosa. X. fastidiosa is the causative agent of Pierces disease, almond scorch, citrus variegated chlorosis and other serious plant diseases. The present study was conducted to establish whether RNA interference (RNAi) was induced in nymphal H. vitripennis that were injected with actin dsRNAs and other dsRNAs. RESULTS A dramatic reduction in target H. vitripennis actin mRNAs and the formation of small interfering RNAs (siRNAs), hallmarks of RNAi, were found following the injection of actin dsRNAs. Quantitative reverse transcription PCR indicated an 80% reduction in actin mRNA levels by 5 days post-injection. Western blot analysis showed a dramatic drop in actin protein levels by 3 days post-injection. Biological effects such as incomplete nymphal-adult ecdysis and > 95% mortality were also found following the injection of fifth-instar nymphs with actin dsRNA. Dramatic reductions in target mRNA levels were also found following the injection of other dsRNAs into fifth-instar H. vitripennis. CONCLUSION The findings indicate that RNAi is induced in post-embryonic leafhoppers by dsRNA. The present system can be used to screen potential gene-silencing targets that can be used for reducing the vector competence of H. vitripennis and other leafhoppers.

Juvenile Hormone (JH) Esterase of the Mosquito Culex quinquefasciatus Is Not a Target of the JH Analog Insecticide Methoprene

Juvenile hormones (JHs) are essential sesquiterpenes that control insect development and reproduction. JH analog (JHA) insecticides such as methoprene are compounds that mimic the structure and/or biological activity of JH. In this study we obtained a full-length cDNA, cqjhe, from the southern house mosquito Culex quinquefasciatus that encodes CqJHE, an esterase that selectively metabolizes JH. Unlike other recombinant esterases that have been identified from dipteran insects, CqJHE hydrolyzed JH with specificity constant (k cat/K M ratio) and V max values that are common among JH esterases (JHEs). CqJHE showed picomolar sensitivity to OTFP, a JHE-selective inhibitor, but more than 1000-fold lower sensitivity to DFP, a general esterase inhibitor. To our surprise, CqJHE did not metabolize the isopropyl ester of methoprene even when 25 pmol of methoprene was incubated with an amount of CqJHE that was sufficient to hydrolyze 7,200 pmol of JH to JH acid under the same assay conditions. In competition assays in which both JH and methoprene were available to CqJHE, methoprene did not show any inhibitory effects on the JH hydrolysis rate even when methoprene was present in the assay at a 10-fold higher concentration relative to JH. Our findings indicated that JHE is not a molecular target of methoprene. Our findings also do not support the hypothesis that methoprene functions in part by inhibiting the action of JHE.

CHARACTERIZATION OF CELL LINES DEVELOPED FROM THE GLASSY-WINGED SHARPSHOOTER, HOMALODISCA COAGULATA (HEMIPTERA: CICADELLIDAE)

SummaryFour continuous cell lines were established from the embryos of the glassy-winged sharpshooter, Homalodisca coagulata (Say), an economically important insect vector of bacterial pathogens of grape, almond citrus, oleander, and other agricultural and ornamental plantings. The cell lines were designated GWSS-Z10, GWSS-Z15, GWSS-G3, and GWSS-LH. The GWSS-Z10, GWSS-Z15, and GWSS-G3 lines were cultured in Ex-Cell 401 medium supplemented with 10% fetal bovine serum (FBS), whereas the GWSS-LH line was cultured in LH medium supplemented with 20% FBS. The cell lines were characterized in terms of their morphology, growth, protein composition, and polymerase chain reactionamplification patterns of their chromosomal deoxyribonucleic acid. The population doubling times of GWSS-Z10, GWSS-Z15, GWSS-G3, and GWSS-LH were 46.2, 90.9, 100.3 and 60.2 h, respectively. These lines should be useful for the study of insect-pathogenic viruses of leafhoppers, aphids, treehoppers, and other related insects as well as plant-pathogenic viruses that are transmitted by these insects.