cDNA cloning and characterization of Bombyx mori juvenile hormone esterase: an inducible gene by the imidazole insect growth regulator KK-42

Identification and Functions of JHE 6 Specifically Expressed in Bombyx mori Silk Gland

Juvenile hormone esterase (JHE) is the specific enzyme that degrades juvenile hormone (JH) and regulates the JH titer in insects. JH also regulates the development of the silk gland and the synthesis and secretion of silk proteins in Bombyx mori. Here, we identified nine possible JHE family members, Bmjhe1-9. Notably, Bmjhe6 is specifically expressed in the silk gland. Using semi-quantitative, quantitative real-time RT-PCR and Western blot, it was confirmed that Bmjhe6 was specifically expressed in the middle silk gland (MSG) with high levels in the anterior region of the MSG (A-MSG). The immunofluorescence localization analysis revealed that Bmjhe6 is produced within cells, secreted into the gland lumen, and co-transported with silk proteins into the anterior silk gland (ASG). In vitro hormone induction experiments demonstrated that Bmjhe6 responds to a JH analog, increasing its expression after 12-24 h, whereas 20-hydroxyecdysone inhibited it. In addition, Bmjhe6 knockdown using dsBmjhe6 injections accelerated larval development, resulting in increased larval body and silk gland weight. This induced disordered sericin genes (Ser2, Ser3) expression, and key genes in the JH synthesis pathway (BmKr-h1 and BmMet1) were significantly upregulated along with the transcription factors (SGF-1 and Sage). These results indicate that Bmjhe6 plays an important role in silk gland growth and silk protein synthesis by modulating JH signal.

Hormonal gatekeeping via the blood-brain barrier governs caste-specific behavior in ants

Here, we reveal an unanticipated role of the blood-brain barrier (BBB) in regulating complex social behavior in ants. Using scRNA-seq, we find localization in the BBB of a key hormone-degrading enzyme called juvenile hormone esterase (Jhe), and we show that this localization governs the level of juvenile hormone (JH3) entering the brain. Manipulation of the Jhe level reprograms the brain transcriptome between ant castes. Although ant Jhe is retained and functions intracellularly within the BBB, we show that Drosophila Jhe is naturally extracellular. Heterologous expression of ant Jhe into the Drosophila BBB alters behavior in fly to mimic what is seen in ants. Most strikingly, manipulation of Jhe levels in ants reprograms complex behavior between worker castes. Our study thus uncovers a remarkable, potentially conserved role of the BBB serving as a molecular gatekeeper for a neurohormonal pathway that regulates social behavior.

Insect growth-regulating activity of 1-benzyl-2-methylbenzimidazole derivatives on silkworms

Derivatives of 1-benzyl-2-methylbenzimidazoles (BMBIs) were synthesized to evaluate their biological activities against Bombyx mori, a lepidopteran model insect. Synthesized BMBIs exhibited two different biological activities: inhibition of development and acute lethality. From a structural perspective, the activity varied with the position of the substitutions on the 1-benzyl moiety; BMBIs with substitutions on the 2 and/or 4 positions had comparatively high activity in comparison with those with substitutions on the 3-position. There was more activity for the inhibition of development with low doses, and more for acute lethality with high doses. The activity was also affected by the applied stage, that is, application in the 4th instar mostly interfered the larval molting or pupation, whereas that in the 3rd instar caused more acute mortality. Taken together, these results suggest that BMBIs have multiple modes of action.

Cloning and characterization of Aedes aegypti juvenile hormone epoxide hydrolases (JHEHs)

Juvenile hormone epoxide hydrolase (JHEH) plays an important role in the metabolism of juvenile hormone III (JH III) in insects. To study the role that JHEH plays in female Aedes aegypti JHEH 1, 2, and 3 complementary DNA (cDNAs) were cloned and sequenced. Northern blot analyses show that the three transcripts are expressed in the head thorax, the gut, the ovaries, and the fat body of females. Molecular modeling shows that the enzyme is a homodimer that binds JH III acid (JH IIIA) at the catalytic groove better than JH III. The cDNA of JHEH 1 and 2 are very similar indicating close relationship. Knocking down of jheh 1, 2, and 3 in adult female and larval Ae. aegypti using double-stranded RNA (dsRNA) did not affect egg development or caused adult mortality. Larvae that were fed bacterial cells expressing dsRNA against jheh 1, 2, and 3 grew normally. Treating blood-fed female Ae. aegypti with [12-³ H](10R) JH III and analyzing the metabolites by C₁₈ reversed phase chromatography showed that JHEH preferred substrate is not JH III but JH IIIA. Genomic analysis of jheh 1, 2, and 3 indicate that jheh 1 and 2 are transcribed from a 1.53 kb DNA whereas jheh 3 is transcribed from a 10.9 kb DNA. All three genes are found on chromosome two at distinct locations. JHEH 2 was expressed in bacterial cells and purified by Ni affinity chromatography. Sequencing of the recombinant protein by MS/MS identified JHEH 2 as the expressed recombinant protein.

Cloning and Characterization of Drosophila melanogaster Juvenile Hormone Epoxide Hydrolases (JHEH) and Their Promoters

Juvenile hormone epoxide hydrolase (JHEH) plays an important role in the metabolism of JH III in insects. To study the control of JHEH in female Drosophila melanogaster, JHEH 1, 2 and 3 cDNAs were cloned and sequenced. Northern blot analyses showed that the three transcripts are expressed in the head thorax, the gut, the ovaries and the fat body of females. Molecular modeling shows that the enzyme is a homodimer that binds juvenile hormone III acid (JH IIIA) at the catalytic groove better than JH III. Analyses of the three JHEH promoters and expressing short promoter sequences behind a reporter gene (lacZ) in D. melanogaster cell culture identified a JHEH 3 promoter sequence (626 bp) that is 10- and 25-fold more active than the most active promoter sequences of JHEH 2 and JHEH 1, respectively. A transcription factor (TF) Sp1 that is involved in the activation of JHEH 3 promoter sequence was identified. Knocking down Sp1 using dsRNA inhibited the transcriptional activity of this promoter in transfected D. melanogaster cells and JH III and 20HE downregulated the JHEH 3 promoter. On the other hand, JH IIIA and farnesoic acid did not affect the promoter, indicating that JH IIIA is JHEH's preferred substrate. A transgenic D. melanogaster expressing a highly activated JHEH 3 promoter behind a lacZ reporter gene showed promoter transcriptional activity in many D. melanogaster tissues.

Structural characterization and functional analysis of juvenile hormone diol kinase from the silkworm, Bombyx mori

Juvenile hormone diol kinase (JHDK) is an important enzyme involved in the juvenile hormone metabolism pathway, which catalyzes the phosphorylation of juvenile hormone diol to form the polar metabolite JH diol phosphate. Here, we reported the first crystal structure of insect JHDK from Bombyx mori, BmJHDK-L2, determined at a resolution of 1.22 Å. The structure of BmJHDK-L2 mainly comprises of eight α-helical segments linked with loops, forming four helix-loop-helix motifs. In these four helix-loop-helix motifs with only one calcium ion bound in the first motif. Circular dichroism spectra indicated that BmJHDK-L2 has strong thermal stability, which is independent of the divalent cation. The structure of BmJHDK-L2 further allowed us to define an ATP-binding site using computational simulation and binding assays, providing a structural basis for development of inhibitor of JHDK. Moreover, the expression profile of BmJHDK-L2 indicated a predominant role in juvenile hormone metabolism in the Malpighian tubules of silkworm. Collectively, these findings expand our knowledge regarding the structural and biochemical features of insect JHDK proteins.

Genomic Characterization and Expression of Juvenile Hormone Esterase-Like Carboxylesterase Genes in Pacific White Shrimp, Litopenaeus vannamei

The sesquiterpenoid methyl farnesoate (MF), a juvenile hormone (JH) analog, plays important roles in many physiological processes of crustaceans, such as morphogenesis, molting and reproduction. Juvenile hormone esterase-like (JHE-like) carboxylesterase (CXE) is a key enzyme in MF degradation, playing a significant role in regulating MF titer. However, its function is barely known in shrimp. In this study, a total of 21 JHE-like CXEs (LvCXEs) were characterized in Pacific white shrimp Litopenaeus vannamei, based on the full genome and multi-transcriptomic data. LvCXE has a conserved triplet catalytic site (Ser-Glu-His) and a characteristic GxSxG motif. Most LvCXEs were highly expressed in the hepatopancreas, which was the main site for MF degradation. LvCXEs containing a GESAG motif showed a specific expansion in the L. vannamei genome. Those GESAG-containing LvCXEs presented differential expressions at different larvae stages and different molting stages of L. vannamei, which suggested their potential functions in development and molting. Additionally, when the transcription level of CXEs was inhibited, it could lead to failed molt and death of L. vannamei. When we further detected the expression levels of the key ecdysone responsive transcription factors including LvE75, LvBr-C, LvHr3 and LvFtz-f1 after the CXE inhibitor was injected into L. vannamei, they all showed apparent down-regulation. These results suggested that the expansion of LvCXEs in the L. vannamei genome should contribute to the regulation of metamorphosis at larvae stages and frequent molting during the growth of L. vannamei.

Reconstruction of insect hormone pathways in an aquatic firefly, Sclerotia aquatilis (Coleoptera: Lampyridae), using RNA-seq

Insect hormones: ecdysteroids and juvenile hormones have crucial functions during the regulation of different developmental pathways in insects. Insect metamorphosis is one of the primary pathways regulated by these hormones. The insect hormone biosynthetic pathway is conserved among arthropods, including insects, with some variations in the form of hormones used among each group of insects. In this study, the candidate genes involved in the insect hormone pathways and their functional roles were assessed in an aquatic firefly, Sclerotia aquatilis using a high-throughput RNA sequencing technique. Illumina next-generation sequencing (NGS) was used to generate transcriptome data for the different developmental stages (i.e., larva, pupa, and adult) of S. aquatilis. A total of 82,022 unigenes were generated across all different developmental stages. Functional annotation was performed for each gene, based on multiple biological databases, generating 46,230 unigenes. These unigenes were subsequently mapped using KEGG pathways. Accordingly, 221 protein-encoding genes involved in the insect hormone pathways were identified, including, JHAMT, CYP15A1, JHE, and Halloween family genes. Twenty potential gene candidates associated with the biosynthetic and degradation pathways for insect hormones were subjected to real-time PCR, reverse transcriptase PCR (RT-PCR) and sequencing analyses. The real-time PCR results showed similar expression patterns as those observed for transcriptome expression profiles for most of the examined genes. RT-PCR and Sanger sequencing confirmed the expressed coding sequences of these gene candidates. This study is the first to examine firefly insect hormone pathways, facilitating a better understanding of firefly growth and development.

Latrophilin mediates insecticides susceptibility and fecundity through two carboxylesterases, esterase4 and esterase6, in Tribolium castaneum

Latrophilin (LPH) is known as an adhesion G-protein-coupled receptor which involved in multiple physiological processes in organisms. Previous studies showed that lph not only involved the susceptibility to anticholinesterase insecticides but also affected fecundity in Tribolium castaneum. However, its regulatory mechanisms in these biological processes are still not clear. Here, we identified two potential downstream carboxylesterase (cce) genes of Tclph, esterase4 and esterase6, and further characterized their interactions with Tclph. After treatment of T. castaneum larvae with carbofuran or dichlorvos insecticides, the transcript levels of Tcest4 and Tcest6 were significantly induced from 12 to 72 h. RNAi against Tcest4 or Tcest6 led to the higher mortality compared with the controls after the insecticides treatment, suggesting that these two genes play a vital role in detoxification of insecticides in T. castaneum. Furthermore, with insecticides exposure to Tclph knockdown beetles, the expression of Tcest4 was upregulated but Tcest6 was downregulated, indicating that beetles existed a compensatory response against the insecticides. Additionally, RNAi of Tcest6 resulted in 43% reductions in female egg laying and completely inhibited egg hatching, which showed the similar phenotype as that of Tclph knockdown. These results indicated that Tclph affected fecundity by positively regulating Tcest6 expression. Our findings will provide a new insight into the molecular mechanisms of Tclph involved in physiological functions in T. castaneum.

Improved strength of silk fibers in Bombyx mori trimolters induced by an anti-juvenile hormone compound

BACKGROUND

Bombyx mori silk fibers with thin diameters have advantages of lightness and crease-resistance. Many studies have used anti-juvenile hormones to induce trimolters in order to generate thin silk; however, there has been comparatively little analysis of the morphology, structure and mechanical properties of trimolter silk.

METHODS

This study induced two kinds of trimolters by appling topically anti-juvenile hormones and obtained thin diameter silk. Scanning electron microscope (SEM), FTIR analysis, tensile mechanical testing, chitin staining were used to reveal that the morphology, conformation and mechanical property of the trimolter silk.

RESULTS

Cocoon of trimolters were highly densely packed by thinner fibers and thus had small apertures. We found that the conformation of trimolter silk fibroin changed and formed more β-sheet structures. In addition, analysis of mechanical parameters yielded a higher Young's modulus and strength in trimolter silk than in the control. By chitin staining of silk gland, we postulated that the mechanical properties of trimolters' silk was enhanced greatly during to the structural changes of silk gland.

CONCLUSION

We induced trimolters by anti-juvenile hormones and the resulting cocoons were more closely packed and had smaller silk fiber diameters. We found that the conformation of trimolters silk fibroin had a higher content of β-sheet structures and better mechanical properties.

GENERAL SIGNIFICANCE

Our study revealed the structures and mechanical properties of trimolter silk, and provided a valuable reference to improve silk quality by influencing molting in silkworms.

Characterization and Expression Profiles of Juvenile Hormone Epoxide Hydrolase From Lymantria dispar (Lepidoptera: Lymantridae) and RNA Interference by Ingestion

Juvenile hormone epoxide hydrolase (JHEH) is an important enzyme in the degradation pathways of juvenile hormone (JH) in insects. It converts JH to JH diol and hydrolyses JH acid to JH acid diol. JHEH titers regulate the entire process of insect development. In this study, full length ldjheh cDNA (2101 bp) was cloned from the Asian gypsy moth Lymantria dispar (L.; Lepidoptera: Lymantridae), and provisionally designated ldjheh1. LdJHEH1 was characterized by predicted molecular weight of 52.64 kDa, theoretical isoelectric points of 6.87 and contains a transmembrane domain at the N-terminus. The transcriptional profiles of ldjheh1 were detected by qRT-PCR. The ldjheh1 was found to be expressed throughout all developmental stages with maximum expression levels occurring in fourth instar larvae. The ldjheh1 mRNA was detected in the heads, thoraces, and abdomens of gypsy moth larvae on day 2 of the third instar. The ldjheh1 was also detected in bodies of third instar larvae stage, with the highest peaks occurring at 24 h after ecdysis. The ldjheh1 gene was successfully knocked down by oral delivery dsRNA in the third instar larvae of L. dispar. The dsRNA targeting ldjheh1 was produced in vitro. Ingesting dsRNA for ldjheh1 only slightly delayed larval development.

Depletion of juvenile hormone esterase extends larval growth in Bombyx mori

Two major hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E), regulate insect growth and development according to their precisely coordinated titres, which are controlled by both biosynthesis and degradation pathways. Juvenile hormone esterase (JHE) is the primary JH-specific degradation enzyme that plays a key role in regulating JH titers, along with JH epoxide hydrolase (JHEH) and JH diol kinase (JHDK). In the current study, a loss-of-function analysis of JHE in the silkworm, Bombyx mori, was performed by targeted gene disruption using the transgenic CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/RNA-guided Cas9 nucleases) system. Depletion of B. mori JHE (BmJHE) resulted in the extension of larval stages, especially the penultimate and ultimate larval stages, without deleterious effects to silkworm physiology. The expression of JHEH and JHDK was upregulated in mutant animals, indicating the existence of complementary routes in the JH metabolism pathway in which inactivation of one enzyme will activate other enzymes. RNA-Seq analysis of mutant animals revealed that genes involved in protein processing in the endoplasmic reticulum and in amino acid metabolism were affected by BmJHE depletion. Depletion of JHE and subsequent delayed JH metabolism activated genes in the TOR pathway, which are ultimately responsible for extending larval growth. The transgenic Cas9 system used in the current study provides a promising approach for analysing the actions of JH, especially in nondrosophilid insects. Furthermore, prolonging larval stages produced larger larvae and cocoons, which is greatly beneficial to silk production.

Modulation of Juvenile Hormone Esterase Gene Expression Against Development of Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a widespread and destructive pest of cruciferous crops. Owing to its increasing resistance to conventional pesticides, new strategies need to be developed for diamondback moth control. Here, we investigated factors that modulate juvenile hormone esterase (JHE) activity and jhe (Px004817) transcription, and determined the effects of these factors on subsequent growth and development in diamondback moth. Starvation inhibited JHE activity and jhe transcription, increased mortality, and decreased the rate of molting from the third- to the fourth-instar stages. Larvae kept at 32°C molted earlier and showed increased JHE activity and jhe transcription after 24-h treatment. Exposure to 1,325 mg/liter OTFP (3-octylthio-1,1,1-trifluoro-2-propanone) delayed molting and pupation, increased pupal weight, and decreased JHE activity and jhe transcription at both 24 and 48 h. Treatment with 500 mg/liter pyriproxyfen delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. A combination of OTFP (1,325 mg/liter) and pyriproxyfen (500 mg/liter) induced the highest mortality, delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. These effects on JHE activity and jhe transcription were similar to those in insects treated only with pyriproxyfen. The results demonstrated that JHE and jhe (Px004817) were involved in the responses of diamondback moth to external modulators and caused changes in growth and development. The combination of OTFP and pyriproxyfen increased the effectiveness of action against diamondback moth.

CHARACTERIZATION AND FUNCTIONAL STUDY OF A PUTATIVE JUVENILE HORMONE DIOL KINASE IN THE COLORADO POTATO BEETLE Leptinotarsa decemlineata (Say)

Juvenile hormone diol kinase (JHDK) is an enzyme involved in JH degradation. In the present article, a putative JHDK cDNA (LdJHDK) was cloned from the Colorado potato beetle Leptinotarsa decemlineata. The cDNA consists of 814 bp, containing a 555 bp open reading frame encoding a 184 amino acid protein. LdJHDK reveals a high degree of identity to the previously reported insect JHDKs. It possesses three conserved purine nucleotide-binding elements, and contains three EF-hand motifs (helix-loop-helix structural domains). LdJHDK mRNA was mainly detected in hindgut and Malpighian tubules. Besides, a trace amount of LdJHDK mRNA was also found in thoracic muscles, brain-corpora cardiaca-corpora allata complex, foregut, midgut, ventral ganglia, fat body, epidermis, and hemocytes. Moreover, LdJHDK was expressed throughout all developmental stages. Within the first, second, and third larval instar, the expression levels of LdJHDK were higher just before and right after the molt, and were lower in the intermediate instar. In the fourth larval instar, the highest peak of LdJHDK occurred 56 h after ecdysis. Ingestion of double-stranded RNA (dsRNA) against LdJHDK successfully knocked down the target gene, increased JH titer, and significantly upregulated LdKr-h1 mRNA level. Knockdown of LdJHDK significantly impaired adult emergence. Thus, we provide a line of experimental evidence in L. decemlineata to support that LdJHDK encodes function protein involved in JH degradation.

A whole genome screening and RNA interference identify a juvenile hormone esterase-like gene of the diamondback moth, Plutella xylostella

Juvenile hormone (JH) plays a crucial role in preventing precocious metamorphosis and stimulating reproduction. Thus, its hemolymph titer should be under a tight control. As a negative controller, juvenile hormone esterase (JHE) performs a rapid breakdown of residual JH in the hemolymph during last instar to induce a larval-to-pupal metamorphosis. A whole genome of the diamondback moth (DBM), Plutella xylostella, has been annotated and proposed 11 JHE candidates. Sequence analysis using conserved motifs commonly found in other JHEs proposed a putative JHE (Px004817). Px004817 (64.61 kDa, pI=5.28) exhibited a characteristic JHE expression pattern by showing high peak at the early last instar, at which JHE enzyme activity was also at a maximal level. RNA interference of Px004817 reduced JHE activity and interrupted pupal development with a significant increase of larval period. This study identifies Px004817 as a JHE-like gene of P. xylostella.

Juvenile hormone (JH) esterase activity but not JH epoxide hydrolase activity is downregulated in larval Adoxophyes honmai following nucleopolyhedroviruses infection

Juvenile hormones (JHs) and ecdysteroids are critical insect developmental hormones. JH esterase (JHE) and JH epoxide hydrolase (JHEH) are JH-selective enzymes that metabolize JH and thus regulate the titer of JH. Baculoviruses are known to alter host endocrine regulation. The nucleopolyhedroviruses, AdhoNPV and AdorNPV, are known to have slow and fast killing activity against Adoxophyes honmai (Lepidoptera: Tortricidae), respectively. Here we found that when penultimate (4th) instar A. honmai are inoculated with AdhoNPV or AdorNPV, the mean survival time is 9.7 and 8.2 days, respectively. The larvae molted once but did not pupate. The AdhoNPV- or AdorNPV-infected larvae did not show a dramatic increase in JHE activity as was found in mock-infected larvae, instead they showed a marked decrease in JHE activity. In contrast, both viral infections had no effect on JHEH activity. In order to further characterize the JHE activity, the JHE-coding sequence of A. honmai (ahjhe) was cloned and confirmed to encode a biologically active JHE. Quantitative real-time PCR analysis of ahjhe expression in 4th and 5th instar A. honmai revealed that AdhoNPV and AdorNPV are able to reduce ahjhe expression levels.

Imidazole derivative KK-42 boosts pupal diapause incidence and delays diapause termination in several insect species

The imidazole derivative KK-42 is a synthetic insect growth regulator known previously to be capable of averting embryonic diapause in several Lepidoptera, but whether it also affects diapauses occurring in other developmental stages remains unknown. In the present study, we examined the effect of KK-42 on pupal diapause in two species of Lepidoptera, the Chinese oak silkworm Antheraea pernyi and the corn earworm Helicoverpa zea, and in one species of Diptera, the flesh fly Sarcophaga crassipalpis. In A. pernyi, KK-42 delayed pupal diapause termination under the long day conditions that normally break diapause in this species. Likewise, in H. zea, KK-42 delayed termination of pupal diapause, a diapause that, in this species, is normally broken by high temperature. KK-42-treated pupae of these two species eventually terminated diapause and successfully emerged as adults, but the timing of diapause termination was significantly delayed. KK-42 also significantly increased the incidence of pupal diapause in H. zea and S. crassipalpis when administered to larvae that were environmentally programmed for diapause, but it was not capable of inducing pupal diapause in H. zea if larvae were reared under environmental conditions that do not normally evoke the diapause response. Experiments with H. zea showed that the effect of KK-42 on pupal diapause was dose- and stage-dependent, but not temperature-dependent. Results presented here are consistent with a link between KK-42 and the ecdysteroid signaling pathway that regulates pupal diapause.

Genome-wide comparison of genes involved in the biosynthesis, metabolism, and signaling of juvenile hormone between silkworm and other insects

Juvenile hormone (JH) contributes to the regulation of larval molting and metamorphosis in insects. Herein, we comprehensively identified 55 genes involved in JH biosynthesis, metabolism and signaling in the silkworm (Bombyx mori) as well as 35 in Drosophila melanogaster, 35 in Anopheles gambiae, 36 in Apis mellifera, 47 in Tribolium castaneum, and 44 in Danaus plexippus. Comparative analysis showed that each gene involved in the early steps of the mevalonate (MVA) pathway, in the neuropeptide regulation of JH biosynthesis, or in JH signaling is a single copy in B. mori and other surveyed insects, indicating that these JH-related pathways or steps are likely conserved in all surveyed insects. However, each gene participating in the isoprenoid branch of JH biosynthesis and JH metabolism, together with the FPPS genes for catalyzing the final step of the MVA pathway of JH biosynthesis, exhibited an obvious duplication in Lepidoptera, including B. mori and D. plexippus. Microarray and real-time RT-PCR analysis revealed that different copies of several JH-related genes presented expression changes that correlated with the dynamics of JH titer during larval growth and metamorphosis. Taken together, the findings suggest that duplication-derived copy variation of JH-related genes might be evolutionarily associated with the variation of JH types between Lepidoptera and other insect orders. In conclusion, our results provide useful clues for further functional analysis of JH-related genes in B. mori and other insects.

Molecular and functional characterization of cDNAs putatively encoding carboxylesterases from the migratory locust, Locusta migratoria

Carboxylesterases (CarEs) belong to a superfamily of metabolic enzymes encoded by a number of genes and are widely distributed in microbes, plants and animals including insects. These enzymes play important roles in detoxification of insecticides and other xenobiotics, degradation of pheromones, regulation of neurodevelopment, and control of animal development. In this study, we characterized a total of 39 full-length cDNAs putatively encoding different CarEs from the migratory locust, Locusta migratoria, one of the most severe insect pests in many regions of the world, and evaluated the role of four CarE genes in insecticide detoxification. Our phylogenetic analysis grouped the 39 CarEs into five different clades including 20 CarEs in clade A, 3 in D, 13 in E, 1 in F and 2 in I. Four CarE genes (LmCesA3, LmCesA20, LmCesD1, LmCesE1), representing three different clades (A, D and E), were selected for further analyses. The transcripts of the four genes were detectable in all the developmental stages and tissues examined. LmCesA3 and LmCesE1 were mainly expressed in the fat bodies and Malpighian tubules, whereas LmCesA20 and LmCesD1 were predominately expressed in the muscles and hemolymph, respectively. The injection of double-stranded RNA (dsRNA) synthesized from each of the four CarE genes followed by the bioassay with each of four insecticides (chlorpyrifos, malathion, carbaryl and deltamethrin) increased the nymphal mortalities by 37.2 and 28.4% in response to malathion after LmCesA20 and LmCesE1 were silenced, respectively. Thus, we proposed that both LmCesA20 and LmCesE1 played an important role in detoxification of malathion in the locust. These results are expected to help researchers reveal the characteristics of diverse CarEs and assess the risk of insecticide resistance conferred by CarEs in the locust and other insect species.

Functional characterization of a juvenile hormone esterase related gene in the moth Sesamia nonagrioides through RNA interference

Juvenile hormone esterase (JHE) is a carboxylesterase that has attracted great interest because of its critical role in regulating larval to adult transition in insects and other arthropods. Previously, we characterized an ecdysteroid sensitive and juvenile hormone non-susceptible juvenile hormone esterase related gene (SnJHER) in the corn stalk borer, Sesamia nonagrioides. SnJHER was rhythmically up-regulated close to each molt during the corn stalk borer's larval development. In this paper we attempted to functionally characterize SnJHER using several reverse genetics techniques. To functionally characterize SnJHER, we experimented with different dsRNA administration methods, including hemolymph, bacterial or baculovirus-mediated RNA interference, (RNAi). Our findings indicate the potential implication of SnJHER in the developmental programming of Sesamia nonagrioides. It is still unclear whether SnJHER is closely related to the authentic JHE gene, with different or similar biological functions.

Identification of a juvenile hormone esterase binding protein gene and its developmental and hormone regulation in the silkworm, Bombyx mori

The regulation of the juvenile hormone (JH) titer is critical for insect development. Consequently, both regulators of JH such as juvenile hormone esterase (JHE; EC 3.1.1.1) and the appropriate regulation of these regulators are also critically important for development. To better characterize and understand JHE regulation, we identified a putative JHE binding protein gene named BmJHEBP in Bombyx mori. The full-length cDNA of BmJHEBP is 963 bp and encodes a 243 amino acid polypeptide. Its molecular weight is ∼29 kDa, as confirmed by Western blotting, and transcripts of BmJHEBP were found to be expressed in all tissues. The mRNA level of BmJHEBP in the fat body was high on day 1 of the fifth instar, followed by a decrease from day 2 to day 5; thereafter, the mRNA level increased simultaneously with an increase in the hemolymph ecdysteroid titer. This temporary expression pattern was similar to that of BmJHE in the fat body and of the JHE enzyme activity in the hemolymph. The BmJHEBP level in the fat body of male larvae was slightly higher than that of the fat body in female larvae. Moreover, this protein expression pattern is consistent with the qRT-PCR results. The in vitro fat body culture results indicate that the high titer JH III induced BmJHEBP mRNA expression, while the lower titer exhibited no significant difference at the mRNA level to the group cultivated with DMSO. These studies demonstrate that BmJHEBP might function in JHE transportation and degradation when the JH III titer is high. BmJHEBP was upregulated by 20E cultivation, but this cultivation induced less upregulation and later responses to the JH pulse. Thus, BmJHEBP is regulated by both JH and ecdysone in a balanced manner.

A novel effect of imidazole derivative KK-42 on increasing survival of Aeromonas hydrophila challenged prawn Macrobrachium nipponense

Imidazole derivative KK-42 is well known as the insect growth regulator. Here we find that KK-42 pretreatment could promote the survival of Macrobrachium nipponense infected with Aeromonas hydrophila, which is considered to be possibly related to the prophenoloxidase (proPO), a conserved copper-containing enzyme that plays an important role in defense against pathogens. In this study, a full-length of proPO gene from M. nipponense haemocytes, designated as MnproPO, was firstly cloned and characterized. The full-length cDNA contained 2428 bp with a 2013 bp open reading frame encoding a putative proPO protein of 671 amino acids with a predicted molecular mass of 76.5 kDa and pI of 7.31. It was predicted to possess all the expected features of proPO members, including two putative copper-binding sites with six histidine residues and a thiol ester-like motif. Sequence analysis showed that MnproPO exhibited the highest amino acid sequence similarity (93%) to a proPO of Macrobrachium rosenbergii. The gene was expressed highly in haemocytes and weakly in hepatopancreas. Real-time PCR analysis revealed that the MnproPO expression increased significantly at 3, 12 and 24 h after KK-42 treatment, the PO activity also importantly rose from 6 to 48 h in KK-42-treated prawns and reached the maximum at 24 h with a 2.3-fold higher than that in control group. Injection of A. hydrophila could stimulate the MnproPO transcription and PO activity whether or not the prawns were pretreated by KK-42, the mRNA level increased obviously only at 3 h and 6 h after the bacterium injection (challenged control), but increased constantly during the phase of experiment except at 6 h under the condition of KK-42 pretreatment (challenged treatment group). The change trend of PO activity was basically similar to that of MnproPO expression. Our present results demonstrate that the MnproPO expression as well as PO activity may be induced by KK-42, which is likely one of the molecular mechanisms of KK-42 acts for increasing survival of the prawn infected with A. hydrophila.

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.

Molecular characterization of an ecdysteroid inducible carboxylesterase with GQSCG motif in the corn borer, Sesamia nonagrioides

We obtained a full-length cDNA encoding a carboxylesterase in Sesamia nonagrioides. The complete cDNA sequence is comprised of 1838 bp with an open reading frame encoding 576 amino acid residues with predicted molecular mass of 64.24 kDa. The deduced amino acid sequence showed high identity to JHE-Related of Trichoplusia ni (65% amino acid identity) and 49-46% amino acid identity to JHEs of other lepidopterans and contained all five functional motifs of insect JHEs. The gene has been termed as SnJHE-Related (SnJHER) to denote its similarity to other insect JHE genes and the occurrence of an unusual cysteine residue immediately adjacent to the catalytic serine, instead of the conventional alanine residue. Phylogenetic analyses localised SnJHER together with TnJHER in a branch of the lepidopteran's JHEs group, with other carboxylesterases (COEs) occuring in separated groups. The JH analog methoprene did not affect the expression of SnJHER in contrast to other insect JHEs. Additionally, ecdysteroid analogs induced SnJHER gene expression. The SnJHER mRNA levels were higher in long-day non-diapausing larvae than in short-day diapausing ones. In the fifth instar of non-diapausing and ninth instar of diapausing larvae, the SnJHER mRNAs reached higher expression levels on the days close to each larval molt. In the last (sixth) non-diapausing larval instar, SnJHER mRNA levels peaked in the intermolt period but were lower than during the fifth instar.

The juvenile hormone (JH) epoxide hydrolase gene in the honey bee (Apis mellifera) genome encodes a protein which has negligible participation in JH degradation

Epoxide hydrolases are multifunctional enzymes that are best known in insects for their role in juvenile hormone (JH) degradation. Enzymes involved in JH catabolism can play major roles during metamorphosis and reproduction, such as the JH epoxide hydrolase (JHEH), which degrades JH through hydration of the epoxide moiety to form JH diol, and JH esterase (JHE), which hydrolyzes the methyl ester to produce JH acid. In the honey bee, JH has been co-opted for additional functions, mainly in caste differentiation and in age-related behavioral development of workers, where the activity of both enzymes could be important for JH titer regulation. Similarity searches for jheh candidate genes in the honey bee genome revealed a single Amjheh gene. Sequence analysis, quantification of Amjheh transcript levels and Western blot assays using an AmJHEH-specific antibody generated during this study revealed that the AmJHEH found in the fat body shares features with the microsomal JHEHs from several insect species. Using a partition assay we demonstrated that AmJHEH has a negligible role in JH degradation, which, in the honey bee, is thus performed primarily by JHE. High AmJHEH levels in larvae and adults were related to the ingestion of high loads of lipids, suggesting that AmJHEH has a role in dietary lipid catabolism.

Juvenile hormone esterase: biochemistry and structure

Normal insect development requires a precisely timed, precipitous drop in hemolymph juvenile hormone (JH) titer. This drop occurs through a coordinated halt in JH biosynthesis and increase in JH metabolism. In many species, JH esterase (JHE) is critical for metabolism of the resonance-stabilized methyl ester of JH. JHE metabolizes JH with a high kcat/KM ratio that results primarily from an exceptionally low KM. Here we review the biochemistry and structure of authentic and recombinant JHEs from six insect orders, and present updated diagnostic criteria that help to distinguish JHEs from other carboxylesterases. The use of a JHE-encoding gene to improve the insecticidal efficacy of biopesticides is also discussed.

Molecular characterization of a gene encoding juvenile hormone esterase in the red flour beetle, Tribolium castaneum

Juvenile hormone esterases (JHEs) are required for the degradation of juvenile hormones (JHs) in insects. Here, we report the cloning and analysis of the jhe gene in the red flour beetle, Tribolium castaneum, a model insect of Coleoptera. The Tcjhe gene was strongly expressed at the final instar larva, as would be expected if it functioned to decrease the JH titer at this stage. A recombinant TcJHE protein efficiently degraded JH III, suggesting that the enzyme functions in vivo as a JH-specific degradation enzyme. This is the first report describing the developmental expression profile of the jhe gene whose enzymatic activity was shown in Coleoptera, and the new data reported here will aid elucidation of the mechanism of JH titer regulation in insects.

Genomic analysis of carboxyl/cholinesterase genes in the silkworm Bombyx mori

Background

Carboxyl/cholinesterases (CCEs) have pivotal roles in dietary detoxification, pheromone or hormone degradation and neurodevelopment. The recent completion of genome projects in various insect species has led to the identification of multiple CCEs with unknown functions. Here, we analyzed the phylogeny, expression and genomic distribution of 69 putative CCEs in the silkworm, Bombyx mori (Lepidoptera: Bombycidae).

Results

A phylogenetic tree of CCEs in B. mori and other lepidopteran species was constructed. The expression pattern of each B. mori CCE was also investigated by a search of an expressed sequence tag (EST) database, and the relationship between phylogeny and expression was analyzed. A large number of B. mori CCEs were identified from a midgut EST library. CCEs expressed in the midgut formed a cluster in the phylogenetic tree that included not only B. mori genes but also those of other lepidopteran species. The silkworm, and possibly also other lepidopteran species, has a large number of CCEs, and this might be a consequence of the large cluster of midgut CCEs. Investigation of intron-exon organization in B. mori CCEs revealed that their positions and splicing site phases were strongly conserved. Several B. mori CCEs, including juvenile hormone esterase, not only showed clustering in the phylogenetic tree but were also closely located on silkworm chromosomes. We investigated the phylogeny and microsynteny of neuroligins in detail, among many CCEs. Interestingly, we found the evolution of this gene appeared not to be conserved between B. mori and other insect orders.

Conclusions

We analyzed 69 putative CCEs from B. mori. Comparison of these CCEs with other lepidopteran CCEs indicated that they had conserved expression and function in this insect order. The analyses showed that CCEs were unevenly distributed across the genome of B. mori and suggested that neuroligins may have a distinct evolutionary history from other insect order. It is possible that such an uneven genomic distribution and a unique neuroligin evolution are shared with other lepidopteran insects. Our genomic analysis has provided novel information on the CCEs of the silkworm, which will be of value to understanding the biology, physiology and evolution of insect CCEs.

Annotation and expression of carboxylesterases in the silkworm, Bombyx mori

BACKGROUND

Carboxylesterase is a multifunctional superfamily and ubiquitous in all living organisms, including animals, plants, insects, and microbes. It plays important roles in xenobiotic detoxification, and pheromone degradation, neurogenesis and regulating development. Previous studies mainly used Dipteran Drosophila and mosquitoes as model organisms to investigate the roles of the insect COEs in insecticide resistance. However, genome-wide characterization of COEs in phytophagous insects and comparative analysis remain to be performed.

RESULTS

Based on the newly assembled genome sequence, 76 putative COEs were identified in Bombyx mori. Relative to other Dipteran and Hymenopteran insects, alpha-esterases were significantly expanded in the silkworm. Genomics analysis suggested that BmCOEs showed chromosome preferable distribution and 55% of which were tandem arranged. Sixty-one BmCOEs were transcribed based on cDNA/ESTs and microarray data. Generally, most of the COEs showed tissue specific expressions and expression level between male and female did not display obvious differences. Three main patterns could be classified, i.e. midgut-, head and integument-, and silk gland-specific expressions. Midgut is the first barrier of xenobiotics peroral toxicity, in which COEs may be involved in eliminating secondary metabolites of mulberry leaves and contaminants of insecticides in diet. For head and integument-class, most of the members were homologous to odorant-degrading enzyme (ODE) and antennal esterase. RT-PCR verified that the ODE-like esterases were also highly expressed in larvae antenna and maxilla, and thus they may play important roles in degradation of plant volatiles or other xenobiotics.

CONCLUSION

B. mori has the largest number of insect COE genes characterized to date. Comparative genomic analysis suggested that the gene expansion mainly occurred in silkworm alpha-esterases. Expression evidence indicated that the expanded genes were specifically expressed in midgut, integument and head, implying that these genes may have important roles in detoxifying secondary metabolites of mulberry leaves, contaminants in diet, and odorants. Our results provide some new insights into functions and evolutionary characteristics of COEs in phytophagous insects.

Changes in gene expression in the permissive larval host lightbrown apple moth (Epiphyas postvittana, Tortricidae) in response to EppoNPV (Baculoviridae) infection

Host cell and virus gene expression were measured five days after per os inoculation of 3rd instar lightbrown apple moth (LBAM) larvae with the Epiphyas postvittana nucleopolyhedrovirus (EppoNPV). Microarray analysis identified 84 insect genes that were up-regulated and 18 genes that were down-regulated in virus-infected larvae compared with uninfected larvae. From the 134 viral open reading frames represented on the microarray, 81 genes showed strong expression. Of the 38 functionally identifiable regulated insect genes, 23 coded for proteins that have roles in one of five processes; regulation of transcription and translation, induction of apoptosis, and maintenance of both juvenility and actin cytoskeletal integrity. Of the 34 functionally identifiable viral genes that were most strongly expressed, 12 had functions associated with these five processes, as did a further seven viral genes which were expressed at slightly lower levels. A survey of the LBAM-expressed sequence tag library identified further genes involved in these processes. In total, 135 insect genes and 38 viral genes were analysed by quantitative polymerase chain reaction. Twenty-one insect genes were strongly up-regulated and 31 genes strongly down-regulated. All 38 viral genes examined were highly expressed. These data suggest that induction of apoptosis and regulation of juvenility are the major 'battlegrounds' between virus and insect, with the majority of changes observed representing viral control of insect gene expression. Transcription and translational effects seem to be exerted largely through modulation of mRNA and protein degradation. Examples of attempts by the insect to repel the infection via changes in gene expression within these same processes were, however, also noted. The data also showed the extent to which viral transcription dominated in the infected insects at five days post inoculation.

Molecular cloning and characterization of a juvenile hormone esterase gene from brown planthopper, Nilaparvata lugens

Juvenile hormone (JH) plays key roles in the regulation of growth, development, diapause and reproduction in insects, and juvenile hormone esterase (JHE) plays an important role in regulating JH titers. We obtained a full-length cDNA encoding JHE in Nilaparvata lugens (NlJHE), the first JHE gene cloned from the hemipteran insects. The deduced protein sequence of Nljhe contains the five conserved motifs identified in JHEs of other insect species, including a consensus GQSAG motif that is required for the enzymatic activity of JHE proteins. Nljhe showed high amino acid similarities with Athalia rosae JHE (40%) and Apis mellifera JHE (39%). Recombinant NlJHE protein expressed in the baculovirus expression system hydrolyzed [3H] JH III at high activity and yielded the specificity constants (kcat/KM=4.28x10(6) M(-1) s(-1)) close to those of the validated JHEs from other insect species, indicating that Nljhe cDNA encodes a functional JH esterase. The Nljhe transcript was expressed mainly in the fat body and the expression level reached a peak at 48 h after ecdysis of the 5th instar nymphs. In the 5th instar, macropterous insects showed significantly higher Nljhe mRNA levels and JHE activities, but much lower JH III levels, than those detected in the brachypterous insects soon after ecdysis and at 48 h after ecdysis. These data suggest that NlJHE might play important roles in regulation of JH levels and wing form differentiation.

Tissue and stage-specific juvenile hormone esterase (JHE) and epoxide hydrolase (JHEH) enzyme activities and Jhe transcript abundance in lines of the cricket Gryllus assimilis artificially selected for plasma JHE activity: implications for JHE microevolution

Fat body and midgut juvenile hormone esterase (JHE) and juvenile hormone epoxide hydrolase (JHEH) specific activities, and plasma JHE activity, were measured throughout the last stadium in two pairs (blocks) of lines of the cricket Gryllus assimilis, each pair of which had been artificially selected for high- or low-plasma JHE activity. Highly significant differences were observed between high- and low-activity lines of each block on most days for fat body JHE, and on one day for midgut JHE activity. In each block, line differences in developmental profiles for fat body JHE activity paralleled line differences in plasma JHE activity during the early-mid stadium, but not during the latter part of the stadium. The developmental profile of midgut JHE activity differed from that of plasma and fat body JHE activity, exhibiting peaks during the early and latter parts of the stadium. Midgut and fat body JHEH activities exhibited a mid-stadium peak in all lines, but activities were very similar in all lines. Fat body JHE appears to be a more significant contributor to plasma JHE than is midgut JHE. During the middle of the last stadium (day 4), Jhe transcript abundance was significantly higher in fat body or midgut of high- vs. low-JHE-activity lines. Jhe transcript abundance was positively correlated with JHE enzyme activity in either fat body or midgut, and with plasma JHE activity. Natural populations of G. assimilis harbor genetic variation for Jhe gene expression which appears to contribute to genetic variation in JHE specific activity in fat body and midgut. These genes appear to have been the targets of artificial selection that resulted in lines that differ dramatically in high- or low-plasma JHE activity. These genes appear to have little, if any, pleiotropic effects on JHEH specific activity.

The role of 20-hydroxyecdysone and juvenile hormone in pupal commitment of the epidermis of the silkworm, Bombyx mori

During the pupal metamorphosis in insects, cellular commitment for pupal differentiation must precede before its differentiation. The pupal commitment of Bombyx mori epidermis occurred from day 3 to day 6 last (5th) instar larvae in response to the gradual increase in ecdysteroid titer in the presence of a small amount of juvenile hormone (JH). Yet the concealed preparatory process of the commitment had begun in the newly synthesized 5th instar larval epidermis (approximately 6 h before the ecdysis) as a competence phase, in which pupal commitment in vitro was induced by 20-hydroxyecdysone (20E) but inhibited by JH. This competence phase continued until day 2 5th instar, and the decrease and increase in cellular sensitivity to JH and 20E, respectively, occurred gradually during this period. In early day 3, autonomous pupal commitment began in vitro and 20E stimulated the commitment, but JH could only partially prevent the commitment in both cases. This apparent reversible to irreversible transition ended in early day 6 by the completion of pupal commitment, when the cells completely lost their sensitivity to JH and no longer expressed the larval cuticle protein gene 30. The expression of the transcription factor, broad, closely followed the commitment, so that we could use this gene expression as a molecular marker for pupal commitment. These results indicate that exposure to 20E and loss of the sensitivity of the epidermal cells to JH are required for the completion of pupal commitment, and suggest that the unusually long process over 3 days could be due to the presence of the detectable JH during the commitment.

Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata

We have isolated the cDNAs of all enzymes involved in the mevalonate pathway portion of the juvenile hormone (JH) biosynthetic pathway in Bombyx mori, i.e., those responsible for the formation of farnesyl diphosphate from acetyl-CoA. There is a single gene encoding each enzyme of this pathway, with the exception of farnesyl diphosphate synthase (FPPS), for which we identified three homologs. All but two of these enzymes are expressed almost exclusively in the corpora allata (CA), as indicated by quantitative RT-PCR analyses. Phosphomevalonate kinase (MevPK) was expressed in many tissues, including the CA. In day 2 4th instars, FPPS1 expression was detected primarily in the Malpighian tubules, but expression of the structurally related FPPS2 and FPPS3 occurred mainly in the CA. Since FPPS3 transcripts were 55 times less abundant than those of FPPS2, the latter is expected to play a major role in JH biosynthesis at this stage. Studies on the developmental expression of these enzymes in the CA showed that the levels of all transcripts were high during the 4th instar larvae, a stage at which in vitro JH biosynthesis was high. However, the transcripts of all the mevalonate enzymes declined to low levels and JH acid O-methyltransferase (JHAMT) transcript disappeared by day 3 when CA ceased JH production after the final larval molt. The CA did not synthesize JH during the pupal stage, coincident with the limited expression of mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate kinase and isopentenyl diphosphate isomerase, and the inactivation of the JHAMT gene. Only female CA produced JH in the adult stage, a feature associated with the re-expression of JHAMT in female but little in male adult CA. Altogether, our results point to a relationship between JH biosynthesis and expression of most JH biosynthetic enzymes in the CA.

Identification and characterization of juvenile hormone esterase gene from the yellow fever mosquito, Aedes aegypti

Juvenile hormone esterase (JHE) plays an important role in regulating juvenile hormone titers. Recent sequencing and annotation of the Aedes aegypti genome identified ten putative jhe gene sequences. Analysis of these ten putative jhe gene sequences showed that only three of them, EAT43357, EAT43353 and EAT43354 contained GQSAG motif and showed high sequence similarity with the sequences of jhe genes identified from other insect species. To determine which putative jhe gene(s) code for functional JHE, the mRNA profiles of EAT43357, EAT43353 and EAT43354 were measured during the final instar larval and pupal stages by using quantitative real-time reverse transcriptase polymerase chain reaction (PCR). The mRNA for EAT43357 was detected during the late final instar larval stage. In contrast, EAT43354 mRNA was detected only during the pupal stage and EAT43353 mRNA was detected only during the larval stage. The mRNA of EAT43357 was detected in both fat body and midgut tissues. JHE enzyme levels gradually increased during the final instar larval stage reaching a peak at 42 h after ecdysis into the final instar larval stage. The mRNA expression profiles of EAT43357 correlate with the developmental expression profiles of JHE enzyme activity suggesting that this gene may encode for a functional JHE. The EAT43357 and EAT43354 cDNA were expressed in a baculovirus system. Proteins isolated from Sf9 cells infected with recombinant baculovirus expressing EAT43357 but not EAT43354 gene exhibited JHE activity confirming that EAT43357 gene codes for a functional JHE enzyme.

Tissue-specific regulation of juvenile hormone esterase gene expression by 20-hydroxyecdysone and juvenile hormone in Bombyx mori

Juvenile hormone esterase (JHE) is the primary juvenile hormone (JH) metabolic enzyme in insects and plays important roles in the regulation of molt and metamorphosis. We investigated its mRNA expression profiles and hormonal control in Bombyx mori larvae. JHE mRNA was expressed at the end of the 4th and 5th (last) larval instars in the midgut and in all the three (anterior, middle, posterior) parts of the silk gland. In the fat body, JHE expression peaked twice in the 5th instar, at wandering and before pupation, while it gradually decreased through the 4th instar. When 20-hydroxyecdysone (20E) was injected into mid-5th instar larvae, JHE mRNA expression was induced in the anterior silk gland but suppressed in the fat body. Topical application of a juvenile hormone analog fenoxycarb to early-5th instar larvae induced JHE expression in both tissues. In the anterior silk gland, JHE expression was accelerated and strengthened by 20E plus fenoxycarb treatments compared with 20E or fenoxycarb single treatment, indicating positive interaction of 20E and JH. JHE mRNA is thus expressed in tissue-specific manners under the control of ecdysteroids and JH.

Sterol demethylation inhibitor fungicides as disruptors of insect development and inducers of glutathione S-transferase activities in Mamestra brassicae

To study physiological and biochemical effects of demethylation inhibitor (DMI) fungicides on non-target insects, larvae of the cabbage moth, Mamestra brassicae L., were exposed orally to propiconazole, (R,S)-1-[2-(2,4-diclophenyl)-4-propyl-1,3-dioolan-2-ylmetyl]-1H-1,2,4-triazole (100, 200 and 600 mg L(-1)) and fenpropimorph, (+/-)-cis-4-[3-(4-tert-butylphenyl)-2-methylpropyl] 2,6-dimethylmorpholinc (10, 100, 200 and 600 mg L(-1)) in a semi-synthetic diet. Ten mg L(-1) of fenpropimorph reduced larval weight and induced in vitro glutathione S-transferase activity. Reduced larval and pupal growth rate, reduced survival, prolonged developmental time, and altered patterns of larval survival and adult emergence were found for one or both fungicides in at least one of the concentrations tested. The results suggest, that although the use of agricultural fungicides is generally regarded as of minor ecotoxicological consequence for insects, feeding on DMI-treated crops may influence insect fitness, and may also leave them susceptible to pesticide treatments or to residues of pesticides and other pollutants in their food. Standard methods to detect such effects should be developed for use in the environmental risk assessment of these products.

Enhanced production of secretory beta1,3-N-acetylglucosaminyltransferase 2 fusion protein into hemolymph of Bombyx mori larvae using recombinant BmNPV bacmid integrated signal sequence

The enhanced secretion of beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) fusion protein into the hemolymph of Bombyx mori larvae was studied using a recombinant B. mori nucleopolyhedrovirus (BmNPV) bacmid integrating seven signal sequences. When the BmNPV bacmid encoding the signal sequences from the silkworm B. mori bombyxin (bx) and B. mori prophenoloxidase-activating enzyme (ppae) was injected into silkworm larvae, 56.1 and 51.5mU/ml beta3GnT, respectively, were secreted into the hemolymph of silkworm larvae. For bx, 97.3% of the total beta3GnT activity was secreted into hemolymph, and only 1.1% remained in the intestines of silkworm larvae. For ppae, 90.8% of the total beta3GnT activity was secreted to the hemolymph, but 7.8% remained in the intestines of silkworm larvae. Using the BmNPV bacmid encoding bx, the amount of secreted beta3GnT was 91mug per larva, which was 2.5% of the total amount of protein in the hemolymph.

Cloning and expression analysis of takeout/JHBP family genes of silkworm, Bombyx mori

A Bombyx EST cDNA database was searched using the Drosophila takeout gene and nine cDNAs were obtained. The homology search suggested that these genes are widespread in insects and organize a large gene family, and that they have hydrophobic ligands. A phylogenetic tree indicated that the genes are first divided into two large groups, juvenile hormone binding protein and other protein genes, and the latter group diversified within a short time at an early stage. The expression study of five Bombyx genes indicated that they are expressed in various tissues and are regulated by development and feeding conditions. The Bombyx genes might have roles related to the regulation of metabolism, growth or development related to nutritional conditions.

Juvenile hormone diol kinase, a calcium-binding protein with kinase activity, from the silkworm, Bombyx mori

Juvenile hormone (JH) diol kinase (JHDK) is an important enzyme involved in the JH degradation pathway. Bombyx mori (Bommo)-JHDK cDNA (637bp) contains an open reading frame encoding a 183-amino acid protein, which reveals a high degree of identity to the two previously reported JHDKs. JHDK is similar to GTP-binding proteins with three conserved sequence elements involved in purine nucleotide binding, contains eight alpha-helices and three EF-hand motifs, and resembles the three-dimensional model of 2SCP and some other calcium-binding proteins. The Bommo-JHDK gene has only a single copy in the silkworm haploid genome, contains only one exon, and its 5'-upstream sequence does not have a JH response element. Although Bommo-JHDK is highly expressed in the gut of the silkworm, its mRNA expression remains at a constant level during larval development suggesting this enzyme is constitutive and not regulated by JH, at least at the transcriptional level. Recombinant Bommo-JHDK catalyzed the conversion of 10S-JH diol into JH diol phosphate, confirming its enzymatic function. Recombinant enzyme formed a dimer and had biochemical characteristics similar to other JHDKs. Bommo-JHDK, a calcium-binding protein with kinase activity, provides unique insights on how JH levels are regulated in the silkworm.

Precocious metamorphosis in transgenic silkworms overexpressing juvenile hormone esterase

Insect growth and development are intricately regulated by the titers of juvenile hormones (JHs) and ecdysteroids (and/or their metabolites) in the insect hemolymph. Hydrolysis of the methyl ester of JH by a JH-specific esterase (JHE) is a key pathway for the degradation of JH. Here, we generate transgenic silkworm strains that overexpress JHE by using the binary GAL4/UAS system. Overexpression of JHE from the embryonic stage resulted in larval-pupal metamorphosis after the third stadium, two stadia earlier than that observed in wild-type insects. This precocious metamorphosis suggests that JHs are not critical for normal development of embryo or larva before the second molt in Lepidoptera (moths and butterflies). Our transgenic approach allowed us to dissect the function of key physiological events that occur from embryogenesis. Until now, these types of studies were possible only in later larval stadia by using physical techniques such as allatectomy or the application of JH analogues. We believe that our system will allow further pioneering studies in insect physiology.

Developmental and hormonal regulation of juvenile hormone esterase gene in Drosophila melanogaster

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to study developmental expression and hormonal regulation of the juvenile hormone esterase gene (DmJhe) in the fruit fly, Drosophila melanogaster. The levels of DmJhe mRNA were low during the embryonic stage. A peak of Dmjhe mRNA was detected in the first, second and third instar larvae. The Dmjhe mRNA levels also increased soon after pupal ecdysis. The Dmjhe mRNA was detected in both male and female adult flies. The peaks of Dmjhe mRNA observed in the larvae coincided with the peaks of juvenile hormone (JH). In contrast, the mRNA for ecdysone-induced transcription factor, Drosophila hormone receptor 3 (DHR3) showed peaks of expression that coincided with the ecdysteroid peaks in embryo, larva and pupa. JH III induced Dmjhe mRNA but not DHR3 mRNA in explanted tissues cultured in Grace's medium. 20-hydroxyecdysone induced DHR3 mRNA and suppressed JH III induction of DmJhe mRNA. These studies show that the expression of jhe in D. melanogaster is regulated by both JH and 20E.

Molecular and biochemical characterization of juvenile hormone epoxide hydrolase from the silkworm, Bombyx mori

One major route of insect juvenile hormone (JH) degradation is epoxide hydration by JH epoxide hydrolase (JHEH). A full-length cDNA (1536 bp) encoding a microsomal JHEH was isolated from the silkworm, Bombyx mori. Bommo-JHEH cDNA contains an open reading frame encoding a 461-amino acid protein (52 kDa), which reveals a high degree of similarity to the previously reported insect JHEHs. The residues Tyr298, Tyr373, and the HGWP motif corresponding to the oxyanion hole of JHEHs and the residues Asp227, His430, and Glu403 in the catalytic triad are well conserved in Bommo-JHEH. Bommo-JHEH was highly expressed in the fat body, where its mRNA expression pattern was in contrast to the pattern of hemolymph levels of JH during the larval development, suggesting that Bommo-JHEH plays an important role in JH degradation. Recombinant Bommo-JHEH (52 kDa) expressed in Sf9 insect cells was membrane-bound and had a high level of enzyme activity (300-fold over the control activity). This Bommo-JHEH study provides a better understanding of how JH levels are regulated in the domesticated silkworm.

Comparison of gene representation in midguts from two phytophagous insects, Bombyx mori and Ips pini, using expressed sequence tags

Midgut proteins may provide new molecular targets for insect control. This could be particularly important for some pests, such as pine bark beetles, which are difficult to control by conventional methods. Expressed sequence tags (ESTs) provide information about the activity of a particular tissue, and, in the case of pest insects, may quickly identify potential targets. We present here an EST project representing 574 tentative unique genes (TUGs) expressed in the midgut of the male pine engraver beetle, Ips pini. This tissue uses the mevalonate pathway to produce the monoterpenoid pheromone component, ipsdienol, de novo in response to juvenile hormone (JH) III. Comparison of our ESTs with those previously isolated from larval silkmoth (Bombyx mori) midguts revealed interesting similarities and differences in gene representation that correlate with the conserved and divergent functions of these two tissues. For example, seven mevalonate pathway genes were represented in the I. pini ESTs, while none were found from B. mori. This type of comparison may assist the identification of species-specific targets for future pest control strategies.