BgFas1: A fatty acid synthase gene required for both hydrocarbon and cuticular fatty acid biosynthesis in the German cockroach, Blattella germanica (L.)

Insect cuticular hydrocarbons (CHCs), the evolutionary products of aquatic hexapod ancestors expanding to terrestrial environment, are deposited on the surface of insect integument and originally functioned primarily as waterproofing agents. CHCs are derived from the conserved fatty acid synthesis pathway in insects. However, the pivotal fatty acid synthase (FAS) involved in hydrocarbon (HC) biosynthesis remains unknown in many insect orders including the primitive Blattodea. Here, we investigated functional FAS genes that modulate cuticular lipid biogenesis in the German cockroach, Blattella germanica (L.). Based on our full-length transcriptomic data and the available genomic data, seven FAS genes (BgFas1-7) were identified from B. germanica. Tissue-specific expression analysis revealed that BgFas1, BgFas3, BgFas4 and BgFas7 were highly expressed in the integument, whereas BgFas2 was dominantly expressed in the fat body. BgFas5/6 mRNA was almost negligible in the tested tissues. Systemic RNAi screen was performed against BgFas1-7, we found that only RNAi knockdown of BgFas1 caused a dramatic reduction of methyl-branched HCs (mbHCs) and a slight decrease of straight-chain HCs (scHCs) for both internal and external HCs. Significant reduction of cuticular free fatty acids (cFFAs) was also detected within BgFas1-repressed cockroaches, while repression of CYP4G19 resulted in dramatic increase of cFFAs. Moreover, we found that BgFas1 mRNA levels were correlated with insect molting cycles, and could be induced by long-term mild dryness treatment. Furthermore, desiccation assay revealed that BgFas1 suppression accelerated water loss and led to early death of cockroaches under desiccation. Our results indicate that BgFas1 is necessary for both HC and cFFA biosynthesis in B. germanica. In addition, our study also confirms that cuticular lipids, particularly mbCHCs, are critical for desiccation resistance in B. germanica.

Insecticidal and acetylcholine esterase inhibition activity of Asteraceae plant essential oils and their constituents against adults of the German cockroach (Blattella germanica)

The fumigant and contact toxicities of 16 Asteraceae plant essential oils and their constituents against adult male and female Blattella germanica were examined. In a fumigant toxicity test, tarragon oil exhibited 100% and 90% fumigant toxicity against adult male German cockroaches at 5 and 2.5 mg/filter paper, respectively. Fumigant toxicities of Artemisia arborescens and santolina oils against adult male German cockroaches were 100% at 20 mg/filter paper, but were reduced to 60% and 22.5% at 10 mg/filter paper, respectively. In contact toxicity tests, tarragon and santolina oils showed potent insecticidal activity against adult male German cockroaches. Components of active oils were analyzed using gas chromatography, gas chromatography-mass spectrometry, or nuclear magnetic resonance spectrometer. Among the identified compounds from active essential oils, estragole demonstrated potent fumigant and contact toxicity against adult German cockroaches. β-Phellandrene exhibited inhibition of male and female German cockroach acetylcholinesterase activity with IC50 values of 0.30 and 0.28 mg/mL, respectively.

Differential expression of hemolymph proteins between susceptible and insecticide-resistant Blattella germanica (Blattodea: Blattellidae)

A proteomic approach combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry was used to compare hemolymph expression profiles of a beta-cypermethrin-resistant Blattella germanica L. strain and a beta-cypermethrin-susceptible strain. Twenty-eight hemolymph proteins were differentially expressed in the resistant cockroach strain; 19 proteins were upregulated and 9 proteins were downregulated compared with the susceptible strain. Protein identification indicated that expression of putative cuticular protein, nitric oxide synthase, triosephosphate isomerase, alpha-amylase, ABC transporter, and Per a 3 allergen was elevated, and expression of arginine kinase and glycosidase was reduced. The differential expression of these proteins reflects the overall change in cellular structure and metabolism related to the resistance of pyrethroid insecticides.

Insulin receptor-mediated nutritional signalling regulates juvenile hormone biosynthesis and vitellogenin production in the German cockroach

Female reproductive processes, which comprise, amongst others, the synthesis of yolk proteins and the endocrine mechanisms which regulate this synthesis, need a considerable amount of energy and resources. The role of communicating that the required nutritional status has been attained is carried out by nutritional signalling pathways and, in particular, by the insulin receptor (InR) pathway. In the present study, using the German cockroach, Blattella germanica, as a model, we analysed the role of InR in different processes, but mainly those related to juvenile hormone (JH) synthesis and vitellogenin production. We first cloned the InR cDNA from B. germanica (BgInR) and then determined that its expression levels were constant in corpora allata and fat body during the first female gonadotrophic cycle. Results showed that the observed increase in BgInR mRNA in fat body from starved compared to fed females was abolished in those females treated with systemic RNAi in vivo against the transcription factor BgFoxO. RNAi-mediated BgInR knockdown during the final two nymphal stages produced significant delays in the moults, together with smaller adult females which could not spread the fore- and hindwings properly. In addition, BgInR knockdown led to a severe inhibition of juvenile hormone synthesis in adult female corpora allata, with a concomitant reduction of mRNA levels corresponding to 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase-1, HMG-CoA synthase-2, HMG-CoA reductase and methyl farnesoate epoxidase. BgInR RNAi treatment also reduced fat body vitellogenin mRNA and oocyte growth. Our results show that BgInR knockdown produces similar phenotypes to those obtained in starved females in terms of corpora allata activity and vitellogenin synthesis, and indicate that the InR pathway mediates the activation of JH biosynthesis and vitellogenin production elicited by nutrition signalling.

Alveolar macrophages play a key role in cockroach-induced allergic inflammation via TNF-α pathway

The activity of the serine protease in the German cockroach allergen is important to the development of allergic disease. The protease-activated receptor (PAR)-2, which is expressed in numerous cell types in lung tissue, is known to mediate the cellular events caused by inhaled serine protease. Alveolar macrophages express PAR-2 and produce considerable amounts of tumor necrosis factor (TNF)-α. We determined whether the serine protease in German cockroach extract (GCE) enhances TNF-α production by alveolar macrophages through the PAR-2 pathway and whether the TNF-α production affects GCE-induced pulmonary inflammation. Effects of GCE on alveolar macrophages and TNF-α production were evaluated using in vitro MH-S and RAW264.6 cells and in vivo GCE-induced asthma models of BALB/c mice. GCE contained a large amount of serine protease. In the MH-S and RAW264.7 cells, GCE activated PAR-2 and thereby produced TNF-α. In the GCE-induced asthma model, intranasal administration of GCE increased airway hyperresponsiveness (AHR), inflammatory cell infiltration, productions of serum immunoglobulin E, interleukin (IL)-5, IL-13 and TNF-α production in alveolar macrophages. Blockade of serine proteases prevented the development of GCE induced allergic pathologies. TNF-α blockade also prevented the development of such asthma-like lesions. Depletion of alveolar macrophages reduced AHR and intracellular TNF-α level in pulmonary cell populations in the GCE-induced asthma model. These results suggest that serine protease from GCE affects asthma through an alveolar macrophage and TNF-α dependent manner, reflecting the close relation of innate and adaptive immune response in allergic asthma model.

[Cloning, expression and purification of arginine kinase from Blattella germanica and its immune activity]

OBJECTIVE

To clone and express the arginine kinase (AK) gene of Blattella germanica and analyze its immune activity.

METHODS

The cDNA of AK was cloned using specific primers from the total RNA of Blattella germanica The open reading frame (ORF) of AK was cloned into pET-28A vector, and expressed in Escherichia coli BL21(DE3) with IPTG induction. The recombinant protein was purified by Ni2+ chelating affinity chromatography. The recombinant protein was detected by SDS-PAGE, and its immune activity was analyzed by Western blotting.

RESULTS

The cloned cDNA ORF sequence (GenBank accession No. FJ514482) contained 1071bp and encoded 356 amino acids. Its sequence homology with the published one (GenBank accession No. EU429466) was 97.2% at nucleotide level. The recombinant containing recombinant plasmid pET-28a-AK expressed a soluble protein of AK (Mr 45 000) after being induced with IPTG. The recombinant AK protein was recognized by sera of allergic patients, indicating that the recombinant AK protein has an adequate response activity.

CONCLUSION

The AK gene of Blattella germanica has been cloned and the recombinant AK protein has been confirmed with immune activity.

RNAi of ace1 and ace2 in Blattella germanica reveals their differential contribution to acetylcholinesterase activity and sensitivity to insecticides

Cyclorrhapha insect genomes contain a single acetylcholinesterase (AChE) gene while other insects contain at least two ace genes (ace1 and ace2). In this study we tested the hypothesis that the two ace paralogous from Blattella germanica have different contributions to AChE activity, using RNA interference (RNAi) to knockdown each one individually. Paralogous-specific depletion of Bgace transcripts was evident in ganglia of injected cockroaches, although the effects at the protein level were less pronounced. Using spectrophotometric and zymogram measurements, we obtained evidence that BgAChE1 represents 65-75% of the total AChE activity in nerve tissue demonstrating that ace1 encodes a predominant AChE. A significant increase in sensitivity of Bgace1-interfered cockroaches was observed after 48 h of exposure to chlorpyrifos. In contrast, Bgace2 knockdown had a negligible effect on mortality to this organophosphate. These results point out a key role, qualitative and/or quantitative, of AChE1 as target of organophosphate insecticides in this species. Silencing the expression of Bgace1 but not Bgace2 also produced an increased mortality in insects when synergized with lambda-cyhalothrin, a situation which resembles the synergistic effects observed between organophosphates and pyrethroids. Gene silencing of ace genes by RNAi offers an exciting approach for examining a possible functional differentiation in ace paralogous.

[Determination of insecticide-resistance and resistance mechanisms of Blattella germanica (Dictyoptera: Blattellidae)]

In this paper, the level of resistance to four insecticides of 3 Blatella germanica strains collected from various places in the City of Havana province was evaluated. These strains were resistant to two pyrethroids (cypermethrin and lambda-cyalothrine) and to organophosphorate malathion but susceptible to carbamate propoxur. The values of alpha and beta esterases, acetylcholinesterase and gluthatione-S-transferase were estimated in three strains involved in the study. The results of the study showed high esterase activity in all the strains, mainly beta esterases and two of the three strains presented with high gluthation-S-transferase enzyme. No changes in acetylcholinesterase were demonstrated in relation to the reference strain. The association of levels of resistance to insecticides, the possible resistance mechanisms in each strain and the results of the enzymatic activity were also analyzed.

Purification and cloning of a Delta class glutathione S-transferase displaying high peroxidase activity isolated from the German cockroach Blattella germanica

A highly active glutathione S-transferase was purified from adult German cockroaches, Blattella germanica. The purified enzyme appeared as a single band of 24 kDa by SDS/PAGE, and had a different electrophoretic mobility than, a previously identified Sigma class glutathione S-transferase (Bla g 5). Kinetic study of 1-chloro-2,4-dinitrobenzene conjugation revealed a high catalytic rate but common substrate-binding and cosubstrate-binding affinities, with V(max), k(cat), K(m) for 1-chloro-2,4-dinitrobenzene and K(m) for glutathione estimated to be 664 micromol x mg(-1) x min(-1), 545 s(-1), 0.33 mm and 0.76 mm, respectively. Interestingly, this enzyme possessed the highest activity for cumene hydroperoxide among insect glutathione S-transferases reported to date. Along with the ability to metabolize 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane and 4-hydroxynonenal, this glutathione S-transferase may play a role in defense against insecticides as well as oxidative stress. On the basis of the amino acid sequences obtained from Edman degradation and MS analyses, a 987-nucleotide cDNA clone encoding a glutathione S-transferase (BggstD1) was isolated. The longest ORF encoded a 24 614 Da protein consisting of 216 amino acid residues. The sequence had close similarities ( approximately 45-60%) to that of Delta class glutathione S-transferases, but had only 14% identity to Bla g 5. The putative amino acid sequence contained matching peptide fragments of the purified glutathione S-transferase. ELISA showed that BgGSTD1 bound to serum IgE obtained from patients with cockroach allergy, indicating that the protein may be a cockroach allergen.

[Adaptation of methods for quantification of the effect of esterase, acetylcholinesterase and glutathione-S-transferase in Blattella germanica (Dictyoptera: Blattellidae)]

The resistance mechanisms of Blatella germanica, one of the most important urban plagues worldwide since it is a mechanical vector that houses a number of highly harmful viruses, fungi, helmints and bacteria were studied. There are different control methods used against Blattella germnanica, with insecticides playing the leading role. Their uncontrolled application has caused the development of insecticice resistance in this species. This paper adapted biochemical methods to detect the enzymes esterase, acetylcholinesterase and glutathine-S-transferase as posible resistance mechanisms. To this end, all the parameters that allow finding out if a strain is susceptible or resistant to each mechanism were set.

Molecular, biochemical and histochemical characterization of two acetylcholinesterase cDNAs from the German cockroach Blattella germanica

Full length cDNAs encoding two acetylcholinesterases (AChEs; Bgace1 and Bgace2) were cloned and characterized from the German cockroach, Blattella germanica. Sequence analyses showed that both genes possess all the typical features of ace, and that Bgace1 is orthologous to the insect ace1 whereas Bgace2 is to the insect ace2. Transcript level of Bgace1 was significantly higher (c. 10 fold) than that of Bgace2 in all 11 tissues examined, suggesting that Bgace1 likely encodes a predominant AChE. Multiple AChE bands were identified by native polyacrylamide gel electrophoresis and isoelectricfocusing from various tissue preparations, among which ganglia produced distinct two major and two minor AChE bands, indicative of the presence of at least two active AChEs. B. germanica AChEs appeared to be mainly localized in the central nervous system as demonstrated by histochemical activity staining, together with quantitative analysis of Bgace transcripts. Fluorescence in situ hybridization of the 1st thoracic ganglion confirmed that Bgace1 is predominantly transcribed and further showed that its transcript is found in almost entire region of inter or motor neurones including the cell bodies and axonal/dendritic branches. Bgace2 transcript is found only in the subset of neurones, particularly in the cell body. In addition, certain neurones were observed to express Bgace1 only.

Characterization of BGTG-1, a tergal gland-secreted alpha-amylase, from the German cockroach, Blattella germanica (L.)

The protein fraction of the German cockroach, Blattella germanica (L.), tergal gland secretion was examined. SDS-PAGE separation of proteins present in B. germanica tergal gland secretion revealed a tergal gland-secreted protein, BGTG-1, at approximately 63 kDa. BGTG-1 first appeared in tergal gland secretion at 2 days postimaginal moult and the amount of protein observed increased through day 5. A 2051 bp cDNA sequence, bgtg-1, was obtained by RACE polymerase chain reaction and contains a 1494 bp ORF encoding a predicted protein of 498 amino acids. In a Northern hybridization experiment using total RNA from B. germanica tergal gland tissue, a (32)P-labelled bgtg-1 probe hybridized to an RNA approximately 2000 bp and confirmed the 2051 bp cDNA size obtained by RACE PCR. Using the BLASTx sequence similarity search tool, the top match to the bgtg-1 ORF was found to be an alpha-amylase from Drosophila kikkawai (e-value = 1 x 10(-178)). Alignment of the bgtg-1 deduced protein sequence with alpha-amylases from fruit fly, Drosophila melanogaster, honey bee, Apis mellifera (L.) and yellow mealworm, Tenebrio molitor (L.), revealed conserved residues throughout the ORF and sequence identities ranging from 58.4 to 58.2%. Using a gel-based assay, degradation of starch by native BGTG-1 was demonstrated in vitro and we propose that BGTG-1 may be involved in processing phagostimulatory sugars present in B. germanica tergal gland secretion.

German cockroach proteases regulate interleukin-8 expression via nuclear factor for interleukin-6 in human bronchial epithelial cells

German cockroach extract synergistically regulates tumor necrosis factor-alpha (TNF-alpha)-induced interleukin (IL)-8 expression in human airway epithelial cells. The IL-8 promoter contains nuclear factor (NF)-kappaB, activating protein (AP)-1, and NF for IL-6 (NF-IL6) transcription factor binding regions. Because cockroach extract activates extracellular regulated kinase (ERK), a known activator of AP-1 and NF-IL6, we focused on the regulation of these transcription factors. Although TNF-alpha and cockroach extract both increased AP-1 translocation, mutation of the AP-1 site in the context of the wild-type promoter had no effect on cockroach extract-induced synergy. Mutation of the NF-IL6 site in the context of the wild-type IL-8 promoter, or overexpression of a dominant-negative NF-IL6 mutant, each abolished cockroach extract-induced synergy. Cockroach extract induced NF-IL6 translocation and DNA binding, an effect that was further increased in the presence of TNF-alpha. Cockroach extract-induced regulation of NF-IL6 was due to active serine proteases in the extract as well as activation of protease activated receptor (PAR)-2, but not PAR-1. Chemical inhibition of ERK also attenuated cockroach extract-induced NF-IL6-DNA binding. We conclude that proteases in German cockroach extract regulate PAR-2 and ERK to increase NF-IL6 activity and synergistically regulate TNF-alpha-induced IL-8 promoter activity in human airway epithelium.

Overexpression of CYP4G19 associated with a pyrethroid-resistant strain of the German cockroach, Blattella germanica (L.)

A new cytochrome P450 gene, CYP4G19, was identified and isolated as a differentially expressed gene between insecticide susceptible ACY and resistant Apyr-R German cockroach strains using PCR-selected subtractive hybridization and cDNA array techniques. The cDNA sequence of CYP4G19 has an open ready frame of 1638 nucleotides encoding a putative protein of 546 amino acid residues. Sequence analysis shows that CYP4G19 putative protein contains (1) a highly hydrophobic N terminus, (2) a P450 protein signature motif, FXXGXRXCXG, known to be an important ligand for heme binding, and (3) an important characteristic motif, EVDTFMFEGHDTT, for the family 4. Northern blot analysis indicated that levels of CYP4G19 expression were low in eggs, nymphs, and adults of the susceptible ACY strain with a similar expression pattern. The expression of CYP4G19 in the resistant Apyr-R strain was developmentally regulated, with very low expression in eggs, increasing in nymphs, and reaching a maximum in both female and male adults. Comparison of CYP4G19 expression between ACY and Apyr-R strains indicated that there was no difference in their eggs, but expression was higher ( approximately 1.7-fold) in the nymphs and much higher ( approximately 5-fold) in the male and female adults of the Apyr-R strain. Levels of CYP4G19 mRNA were readily detectable in head+thorax tissues and increased ( approximately 5-fold) in the abdomens of the ACY strain. In the Apyr-R strain, however, levels of CYP4G19 mRNA were relatively low in head+thorax tissues and were about 7-fold increase in the abdomen. Although expression patterns of CYP4G19 in head+thorax and abdomen tissues were similar (i.e. lower in head+thorax tissues and higher in abdomen tissues) in both the ACY and Apyr-R strains, the overexpression was more evident in the Apyr-R strain in both head+thorax and abdomen tissues than in the ACY strain.

Inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase lower fecundity in the German cockroach: correlation between the effects on fecundity in vivo with the inhibition of enzymatic activity in embryo cells

The enzyme 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase is crucial to insect development and reproduction, as revealed by the sterilising properties of some specific inhibitors of it. In the present paper, we study the sterilising effects of a number of HMG-CoA reductase inhibitors on the German cockroach, Blattella germanica (L). The inhibitors tested were naringenin, lovastatin, mevastatin, simvastatin, atorvastatin and fluvastatin. The first two compounds were ineffective or scarcely effective as HMG-CoA reductase inhibitors. The most active compounds in vivo were fluvastatin and atorvastatin, followed by simvastatin and mevastatin. They were equally ranked when tested as HMG-CoA reductase inhibitors in the B germanica embryonic derived cell line UM-BGE-1. This suggests that this cell line may be an appropriate tool for testing HMG-CoA reductase inhibitors and so to predict their properties as insect sterilising agents with insecticide potential.

Induction of P450 monooxygenases in the German cockroach, Blattella germanica L

The cytochrome P450 monooxygenases are an important metabolic system whose level of activity can be influenced by several dietary constituents. We examined the effects of six known P450 inducers on the levels of total cytochromes P450, cytochrome b(5), and six monooxygenase activities in adult German cockroaches. In addition, the levels of CYP6L1 and CYP9E2 mRNA were also investigated. Phenobarbital treatment resulted in increases in total cytochromes P450 and metabolism of three resorufin analogues, but not CYP6L1 nor CYP9E2 mRNA. There was no significant effect of the other five inducers on any of the monooxygenase parameters we measured. In comparison with other insects, the German cockroach seems unusually refractory to most inducing agents.

Hydrocarbon synthesis by enzymatically dissociated oenocytes of the abdominal integument of the German Cockroach, Blattella germanica

In insects, hydrocarbons waterproof the cuticle, protect the insect from the external environment, and serve as semiochemicals or their metabolic precursors. In the German cockroach, Blattella germanica, hydrocarbons are synthesized by the abdominal integument, but the precise site of biosynthesis is not known. We developed a method for separation of oenocytes from other cells in the abdominal integument using enzymatic dissociation followed by Percoll gradient centrifugation. Radiolabeled propionate was then used to monitor de novo synthesis of hydrocarbons by dissociated cells. Oenocyte-enriched cell suspensions of abdominal sternites synthesized hydrocarbons, whereas suspensions enriched with epidermal cells did not. Our results show conclusively that hydrocarbons are produced by oenocytes not only in insects whose oenocytes are localized within the hemocoel, but also in those insects whose oenocytes are within the abdominal integument. Furthermore, these data support a hemolymph pathway for transport and delivery of hydrocarbons to both external and internal tissues, including the epicuticle, fat body, and ovaries.

CYP9E2, CYP4C21 and related pseudogenes from German cockroaches, Blattella germanica: implications for molecular evolution, expression studies and nomenclature of P450s

The cDNAs of two novel P450s (CYP9E2 and CYP4C21) were isolated from German cockroaches, Blattella germanica. Both CYP9E2 and CYP4C21 are typical microsomal P450s and their deduced amino acid sequences share a number of common characteristics with other members of the P450 superfamily. Northern blot analyses using a CYP9E2 or CYP4C21 probe showed that 'CYP9E2' and 'CYP4C21' were expressed at all life stages. Two pseudogenes related to CYP9E2 and three pseudogenes related to CYP4C21 were also isolated. These represent the first P450 pseudogenes from an insect other than Drosophila melanogaster. The relative number of P450 pseudogenes in B. germanica is apparently higher than in D. melanogaster. The implications of these results for the molecular evolution, expression studies and nomenclature of P450s are discussed.

Cysteine proprotease colocalizes with vitellogenin in compound granules of the cockroach fat body

A cysteine proprotease has been identified in developing embryos of the cockroach Blattella germanica and found to be a maternally encoded gene product that is transferred endocytically to the oocyte. The present study aims at establishing how this maternally derived proprotease is synthesized, packaged, and secreted during vitellogenesis. To this end, proprotease was localized immunocytochemically in the fat body of postmating females and its localization compared with that of vitellogenin over the same developmental periods. Fat bodies in cockroaches are comprised of two different cell types: trophocytes and bacteriocytes. Data show that proprotease and vitellogenin come to colocalize in compound granules of the fat body trophocytes. While synthesis of vitellogenin can be traced back to granules resulting from the coalescence of Golgi-derived vesicles in the trophocyte cytoplasm, proprotease appears to be localized predominantly on the cytolysosomes of both trophocytes and bacteriocytes. When probed with an anti-proprotease antiserum, bacteria are also positively labeled, regardless of whether they are segregated inside the cytolysosomes or free in the bacteriocyte cytoplasm. Since vitellogenin and proprotease colocalize within the same cell organelle, it is assumed that Golgi-derived vesicles, which contain vitellogenin, may fuse with cytolysosomes bearing proprotease to yield compound secretory granules. To account for the present observations, the origin and role of proprotease are discussed in relation to the turnover of bacteria in the fat body and to the requirements of endosymbiosis.

Decapitation impacting effect of topically applied chlorpyrifos on acetylcholinesterase and general esterases in susceptible and resistant German cockroaches (Dictyoptera: Blattellidae)

The effect of topically applied chlorpyrifos on acetylcholinesterase and other esterases in heads and decapitated bodies of CSMA and Crawford German cockroaches was examined with spectrophotometric enzyme assay and native polyacrylamide gel electrophoresis. The toxicity of chlorpyrifos was greatly reduced in decapitated CSMA male cockroaches with LD50 value 17.1-fold higher than that of normal CSMA cockroaches. Acetylcholinesterase activity from heads was significantly higher in the Crawford compared with the CSMA strain and did not change until 24 h after chlorpyrifos in vivo treatment in both strains. The p-nitrophenyl butyrate (NPB) esterase activities from both heads and decapitated bodies of the resistant Crawford strain were significantly greater than the susceptible CSMA strain. The p-NPB esterase activity was significantly inhibited by chlorpyrifos in vivo treatment, and total p-NPB esterase activity was significantly reduced in decapitated bodies compared with heads of both strains. Native polyacrylamide gel electrophoresis (PAGE) analysis of extracts solubilized with Triton X-100 from heads and decapitated bodies revealed five major esterase bands and an acetylcholinesterase (AChE) band with a high capability of hydrolyzing alpha-naphthyl butyrate and acetylthiocholine, respectively. In the heads of susceptible CSMA male cockroaches, the activity of mobile isozymes d1 and d2 was completely inhibited at 24 h after chlorpyrifos application, and isozyme e was partially inhibited. In contrast, isozymes c1 and c2 from the decapitated bodies of CSMA cockroaches were mostly affected at 24 h after the topical application of chlorpyrifos. The activities of acetylcholinesterase and esterase isozymes a and b from the decapitated body remained uninhibited in both strains. Inhibition of isozymes d1 and d2 seems to be more important in chlorpyrifos intoxication than acetylcholinesterase.

Cloning of two novel P450 cDNAs from German cockroaches, Blattella germanica (L.): CYP6K1 and CYP6J1

Two novel P450 cDNAs, CYP6K1 and CYP6J1, were isolated from German cockroaches, Blattella germanica (L). Both CYP6K1 and CYP6J1 are typical microsomal P450s and their deduced amino acid sequences share a number of common characteristics with other members of the P450 superfamily. Both CYP6K1 and CYP6J1 showed the highest per cent identity (based on the deduced amino acid sequence) to CYP6L1 from B. germanica and CYP6H1, a putative ecdysone 20-hydroxylase from Locusta migratoria. Using a CYP6K1 probe, two mRNA signals (~2.5 and ~2.1 kb) were detected in all life stages. Both signals were just detectable in the eggs and became stronger in later instars. The strongest signals were detected in the fifth and sixth instars as well as in adults. These two bands were also detected in the abdomens and in the remainder of bodies of both male and female adults. Southern blots suggest the two mRNA bands detected in the Northern blot might be a result of alternative splicing. No signal could be detected at any life stage using the CYP6J1 probe, suggesting that CYP6J1 was expressed at a low level.

Cytochrome P450 CYP6L1 is specifically expressed in the reproductive tissues of adult male German cockroaches, Blattella germanica (L.)

A full-length cDNA encoding a new cytochrome P450, CYP6L1, was cloned from German cockroaches, Blattella germanica. CYP6L1 has an open reading frame of 1509 nucleotides with a deduced protein of 503 amino acids and molecular mass of 57 Kd. CYP6L1 is most similar to CYP6H1, a putative ecdysone 20-hydroxylase from Locusta migratoria. CYP6L1 mRNA was not detected in embryos nor nymphs, nor in adult females. CYP6L1 mRNA was detected only in the testes and accessory glands of male adult German cockroaches. Given that the testes and accessory glands are the most important components of the reproductive system in male insects, the expression of CYP6L1 mRNA exclusively in these tissues strongly suggests that CYP6L1 has a role in reproduction. Possible substrates for CYP6L1 are discussed.

Biochemical characterization of insecticide resistance in the German cockroach, Blattella germanica, from Malaysia

The possible insecticide resistance mechanisms of four Malaysian field-collected strains of the German cockroach, Blattella germanica (Linnaeus) (Dictyoptera: Blattellidae), were characterized with biochemical assays and native polyacrylamide gel electrophoresis (PAGE). Elevated esterase activity (at low to moderate frequency) and altered acetylcholinesterase (low frequency) were detected in all field strains, while elevated glutathione S-transferase levels were present in only two strains. Seven esterase bands were separated by native PAGE; a greater intensity occurred in three bands in the resistant strains compared to the susceptible strain. Inhibition studies using specific inhibitors on polyacrylamide gels suggested that the slowest of these three esterases is a cholinesterase, while the other two are carboxylesterases with a preference for beta- over alpha-naphthyl acetate.

Cytochrome P450 MA expression in insecticide-resistant German cockroaches (Dictyoptera: Blattellidae)

Cytochrome P450 monooxygenases are detoxification enzymes commonly involved in insecticide resistance by insects. Recently, an overexpressed form of this enzyme, P450 MA, was purified from an insecticide-resistant strain of German cockroach, Blattella germanica (L.), and polyclonal antisera (anti-P450 MA) was produced. To test hypotheses that the overexpressed condition of P450 MA has evolved in > 1 geographic location and that P450 MA might be involved in insecticide resistance to specific insecticides, investigations were conducted using 4 insecticide-resistant and 1 susceptible German cockroach strains. In western blots that used anti-P450 MA antiserum as a probe, substantial differences in expression of P450 MA were observed. Strains showing the highest P450 MA expression had both the highest tolerance to the organophosphate insecticide chlorpyrifos and cytochrome P450-mediated demethylation activity. Results support the hypothesis that cytochrome P450 MA is potentially overexpressed in insecticide-resistant populations on a global scale.

Comparison of esterases between life stages and sexes of resistant and susceptible strains of German cockroach (Dictyoptera: Blattellidae)

Esterase activity between the resistant Crawford and susceptible CSMA strains of German cockroach, Blattella germanica (L.), was compared with the substrates alpha- and beta-naphthyl acetate across sex and nymphal age classes. Esterase isozyme analysis with native polyacrylamide gel electrophoresis also was conducted to identify quantitative and qualitative differences between strains, sexes, and age classes. The Crawford strain was highly resistant to cypermethrin, propoxur, and permethrin with a resistant ratio (RR) of 17.26, 15.75, and 13.53, respectively, and mildly resistant to chlorpyrifos (RR 5.62). The alpha-NA and beta-NA esterase activities in the Crawford strain were significantly higher than those activities in the CSMA strain in both nymphal and adult stages. In the Crawford strain, the enzyme activity in nymphs was significantly higher than that in adults, but such differences were not observed in the CSMA strain. The mobile isozymes a and c stained more intensely than others in every developmental stage and sex of both strains but showed greater intensity in the Crawford strain. Another intensely stained isozyme b was observed only in the homogenates from the Crawford strain. The combination of isozyme b and the overproduced isozyme a and c in the Crawford strain seems to be responsible for the difference in total esterase activity between the CSMA and Crawford strains.