An epoxide hydrolase involved in the biosynthesis of an insect sex attractant and its use to localize the production site

Fatty Acid Origin of Insect Pheromones

Pheromones are utilized to a great extent in insects. Many of these pheromones are biosynthesized through a pathway involving fatty acids. This chapter will provide examples where the biosynthetic pathways of fatty acid-derived pheromones have been studied in detail. These include pheromones from Lepidoptera, Coleoptera, and Hymenoptera. Many species of Lepidoptera utilize fatty acids as precursors to pheromones with a functional group that include aldehydes, alcohols, and acetate esters. In addition, the biosynthesis of hydrocarbons will be briefly examined because many insects utilize hydrocarbons or modified hydrocarbons as pheromones.

Sublethal Effects of Four Insecticides Targeting Cholinergic Neurons on Partner and Host Finding in the Parasitic Wasp Nasonia vitripennis

Lethal and sublethal effects of pesticides on nontarget organisms are one of the causes of the current decline of many insect species. However, research in the past decades has focused primarily on pollinators, although other beneficial nontarget organisms such as parasitic wasps may also be affected. We studied the sublethal effects of the four insecticides acetamiprid, dimethoate, flupyradifurone, and sulfoxaflor on pheromone-mediated sexual communication and olfactory host finding of the parasitic wasp Nasonia vitripennis. All agents target cholinergic neurons, which are involved in the processing of chemical information by insects. We applied insecticide doses topically and tested the response of treated wasps to sex pheromones and host-associated chemical cues. In addition, we investigated the mating rate of insecticide-treated wasps. The pheromone response of females surviving insecticide treatment was disrupted by acetamiprid (≥0.63 ng), dimethoate (≥0.105 ng), and flupyradifurone (≥21 ng), whereas sulfoxaflor had no significant effects at the tested doses. Olfactory host finding was affected by all insecticides (acetamiprid ≥1.05 ng, dimethoate ≥0.105 ng, flupyradifurone ≥5.25 ng, sulfoxaflor ≥0.52 ng). Remarkably, females treated with ≥0.21 ng dimethoate even avoided host odor. The mating rate of treated N. vitripennis couples was decreased by acetamiprid (6.3 ng), flupyradifurone (≥2.63 ng), and sulfoxaflor (2.63 ng), whereas dimethoate showed only minor effects. Finally, we determined the amount of artificial nectar consumed by N. vitripennis females within 48 h. Considering this amount (∼2 µL) and the maximum concentrations of the insecticides reported in nectar, tested doses can be considered field-realistic. Our results suggest that exposure of parasitic wasps to field-realistic doses of insecticides targeting the cholinergic system reduces their effectiveness as natural enemies by impairing the olfactory sense. Environ Toxicol Chem 2023;42:2400-2411. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

Male sex pheromone in the parasitoid wasp Nasonia longicornis: Chemical and behavioral analyses

The use of sex pheromones for the attraction of potential mating partners is widespread in insects. Species-specificity of these chemical signals is essential, particularly in closely related species with overlapping habitats. In parasitoid wasps of the genus Nasonia, it is the males that produce sex pheromones in their rectal vesicles. The genus consists of four species: N. vitripennis (Nv), N. giraulti (Ng), N. oneida (No), and N. longicornis (Nl). The cosmopolitan species Nv is sympatric with Ng and No in eastern North America and with Nl in the west. Interspecific courtship is common in Nasonia although hybridization is prevented in most combinations by Wolbachia-mediated cytoplasmic incompatibility. The pheromone of Nv males differs from all Nasonia congeners by an additional component that is believed to ensure precopulatory isolation from the sympatric congeners. Detailed investigations on these interactions, however, exist only for the species combination Nv/Ng. Here, we report the results of chemical and behavioral investigations on the sex pheromone of Nl males. The pheromone consists of (4R,5S)-5-hydroxy-4-decanolide (RS) and 4-methylquinazoline (MQ) as a minor component which are produced only after eclosion. Pheromone titers peaked 2 days after eclosion and remained constant on day three. The pheromone is deposited by abdomen dipping which males increasingly exhibited after mating or brief contact with a female. The presence of hosts containing females about to emerge did not increase marking behavior. Site fidelity of males at their own pheromone markings is mediated by MQ. Both natural and synthetic pheromone attracted virgin but not mated females and both RS and MQ are required for female attraction. Females collected during emergence from the host responded likewise to the pheromone and 84% of them produced mixed-sex offspring showing that most of them emerge unmated. Nl females preferred pheromone extract from conspecific males to extract from Nv males, and the addition of the Nv-specific component (4R,5R)-5-hydroxy-4-decanolide (RR) to the Nl pheromone made them unresponsive. The present study demonstrates that Nl uses the male sex pheromone in a similar way as previously shown for Nv and Ng. Furthermore, it shows that Nl females use the Nv-specific pheromone component RR to avoid costly sexual interactions with Nv males in regions of sympatry.

Characterization of male-biased fatty acid desaturase in the jewel wasp Nasonia vitripennis and its role in pheromone production

Linoleic acid is the material for biosynthesis of sex attracting and blocking (postmating) pheromones in Nasonia vitripennis, it is synthesized from oleic acid by a male-biased fatty acid desaturase (SCD5a). In this study, we developed a specific antibody and further characterized the expression patterns of SCD5a in males at different mating stages by western blot. SCD5a was mainly expressed in male heads rather than in abdomens. Along with the aging process (from Day 1 to Day 3), SCD5a increased significantly. Compared with virgin males, mated males showed higher levels of SCD5a. Likewise, abdomen dipping frequency, during which males release attracting pheromone, increased with age and mating. Moreover, real-time quantitative PCR revealed that genes responsible for the first three steps of attracting pheromone biosynthesis were more highly expressed in head than in abdomen, but the final gene for transformation of attracting pheromone was more highly expressed in abdomen than in head. These results suggest that linoleic acid for biosynthesis of attracting pheromones may also originate from the head rather than only synthesized at the rectal vesicles.

Silencing Doublesex expression triggers three-level pheromonal feminization in Nasonia vitripennis males

Doublesex (Dsx) has a conserved function in controlling sexual morphological differences in insects, but our knowledge of its role in regulating sexual behaviour is primarily limited to Drosophila. Here, we show with the parasitoid wasp Nasonia vitripennis that males whose Dsx gene had been silenced (NvDsx-i) underwent a three-level pheromonal feminization: (i) NvDsx-i males were no longer able to attract females from a distance, owing to drastically reduced titres of the long-range sex pheromone; (ii) NvDsx-i males were courted by wild-type males as though they were females, which correlated with a lower abundance of alkenes in their cuticular hydrocarbon (CHC) profiles. Supplementation with realistic amounts of synthetic (Z)-9-hentriacontene (Z9C31), the most significantly reduced alkene in NvDsx-i males, to NvDsx-i males interrupted courtship by wild-type conspecific males. Supplementation of female CHC profiles with Z9C31 reduced courtship and mating attempts by wild-type males. These results prove that Z9C31 is crucial for sex discrimination in N. vitripennis; and (iii) Nvdsx-i males were hampered in eliciting female receptivity and thus experienced severely reduced mating success, suggesting that they are unable to produce the to-date unidentified oral aphrodisiac pheromone reported in N. vitripennis males. We conclude that Dsx is a multi-level key regulator of pheromone-mediated sexual communication in N. vitripennis.

Parasitic wasps do not lack lipogenesis

Fatty acids are crucial primary metabolites for virtually all creatures on earth. Most organisms thus do not rely exclusively on a nutritional supply containing fatty acids, but have the ability to synthesize fatty acids and triacylglycerides de novo from carbohydrates in a process called lipogenesis. The ubiquity of lipogenesis has been questioned by a series of studies reporting that many parasitic wasps (parasitoids) do not accumulate lipid mass despite having unlimited access to sugar. This has been interpreted as an evolutionary metabolic trait loss in parasitoids. Here, we demonstrate de novo biosynthesis of fatty acids from 13C-labelled α-d-glucose in 13 species of parasitoids from seven families. We furthermore show in the model organism Nasonia vitripennis that lipogenesis occurs even when lipid reserves are still intact, but relative 13C-incorporation rates increase in females with widely depleted fat reserves. We therefore conclude that the presumed 'lack of lipogenesis' in parasitoids needs to be re-evaluated.

Acetone application for administration of bioactive substances has no negative effects on longevity, fitness, and sexual communication in a parasitic wasp

Administration of defined amounts of bioactive substances is a perseverative problem in physiological studies on insects. Apart from feeding and injection, topical application of solutions of the chemicals is most commonly used for this purpose. The solvents used should be non-toxic and have least possible effects on the studied parameters. Acetone is widely used for administration of chemical substances to insects, but possible side-effects of acetone application on fitness and behavioral parameters have been rarely investigated. Here we study the effects of acetone application (207 nl) on fitness and sexual communication in the parasitic wasp Nasonia giraulti Darling. Application of acetone had neither negative effects on longevity nor on offspring number and offspring sex ratio of treated wasps. Treatment of females hampered courtship and mating of N. giraulti couples neither directly after application nor one day after. Male sex pheromone titers were not influenced by acetone treatment. Three application examples demonstrate that topical acetone application is capable of bringing active amounts of insect hormones, neuromodulators, and biosynthetic precursors even in tiny insects. We advocate the use of acetone as a convenient, conservative, and broadly applicable vehicle for studying the effects of bioactive substances in insects.

Mutation of an atypical oxirane oxyanion hole improves regioselectivity of the α/β-fold epoxide hydrolase Alp1U

Epoxide hydrolases (EHs) have been characterized and engineered as biocatalysts that convert epoxides to valuable chiral vicinal diol precursors of drugs and bioactive compounds. Nonetheless, the regioselectivity control of the epoxide ring opening by EHs remains challenging. Alp1U is an α/β-fold EH that exhibits poor regioselectivity in the epoxide hydrolysis of fluostatin C (compound 1) and produces a pair of stereoisomers. Herein, we established the absolute configuration of the two stereoisomeric products and determined the crystal structure of Alp1U. A Trp-186/Trp-187/Tyr-247 oxirane oxygen hole was identified in Alp1U that replaced the canonical Tyr/Tyr pair in α/β-EHs. Mutation of residues in the atypical oxirane oxygen hole of Alp1U improved the regioselectivity for epoxide hydrolysis on 1. The single site Y247F mutation led to highly regioselective (98%) attack at C-3 of 1, whereas the double mutation W187F/Y247F resulted in regioselective (94%) nucleophilic attack at C-2. Furthermore, single-crystal X-ray structures of the two regioselective Alp1U variants in complex with 1 were determined. These findings allowed insights into the reaction details of Alp1U and provided a new approach for engineering regioselective epoxide hydrolases.

De novo biosynthesis of fatty acids from α-D-glucose in parasitoid wasps of the Nasonia group

Fatty acids are indispensable primary metabolites for virtually any organism on earth and thus enzymatic machinery enabling de novo production of fatty acids from carbohydrates is highly conserved. A series of studies has questioned the ubiquity of lipogenesis in parasitoid wasps suggesting that the vast majority of species have lost the ability to synthesize fatty acids de novo. One such species is Nasonia vitripennis, which, like the congeneric species N. giraulti and N. longicornis, uses a fatty acid-derived male sex pheromone for sexual communication. Here we demonstrate by feeding fully ¹³C-labeled α-D-glucose and analyzing insect-derived fatty acid methyl esters and the male sex pheromone by coupled gas chromatography/mass spectrometry that both males and females of N. vitripennis as well as N. giraulti and N. longicornis are capable of synthesizing fatty acids de novo. We furthermore show by a proteomics approach that predicted fatty acid synthase, ATP-citrate synthase, and acetyl-CoA carboxylase, key enzymes of lipogenesis, are expressed in the male pheromone gland of N. vitripennis and N. giraulti. Labeling experiments with Urolepis rufipes, a closely related species producing a male sex pheromone independently of fatty acids via the mevalonate pathway, revealed that both sexes are likewise able to synthesize fatty acids de novo. We conclude that the parasitoid wasp species studied here, irrespective of the biosynthetic origin of their sex pheromones, are capable of responding flexibly to lipid shortage during their adult life by keeping enzymatic machinery for lipogenesis running.

Functional characterisation of two Δ12-desaturases demonstrates targeted production of linoleic acid as pheromone precursor in Nasonia

Insect pheromones are often derived from fatty acid metabolism. Fatty acid desaturases, enzymes introducing double bonds into fatty acids, are crucial for the biosynthesis of these chemical signals. Δ12-desaturases catalyse the biosynthesis of linoleic acid by introducing a second double bond into oleic acid, but have been identified in only a few animal species. Here, we report the functional characterisation of two Δ12-desaturases, Nvit_D12a and Nvit_D12b, from the parasitic wasp Nasonia vitripennis. We demonstrate that Nvit_D12a is expressed in the rectal vesicle of males where they produce a linoleic acid-derived sex pheromone to attract virgin females. ¹³C-labelling experiments with Urolepis rufipes, a closely related species belonging to the 'Nasonia group', revealed that females, but not males, are able to synthesise linoleic acid. U. rufipes males produce an isoprenoid sex pheromone in the same gland and do not depend on linoleic acid for pheromone production. This suggests that Δ12-desaturases are common in the 'Nasonia group', but acquired a specialised function in chemical communication of those species that use linoleic acid as a pheromone precursor. Phylogenetic analysis suggests that insect Δ12-desaturases have evolved repeatedly from Δ9-desaturases in different insect taxa. Hence, insects have developed a way to produce linoleic acid independent of the omega desaturase subfamily which harbours all of the eukaryotic Δ12-desaturases known so far.

The Post-mating Switch in the Pheromone Response of Nasonia Females Is Mediated by Dopamine and Can Be Reversed by Appetitive Learning

The olfactory sense is of crucial importance for animals, but their response to chemical stimuli is plastic and depends on their physiological state and prior experience. In many insect species, mating status influences the response to sex pheromones, but the underlying neuromodulatory mechanisms are poorly understood. After mating, females of the parasitic wasp Nasonia vitripennis are no longer attracted to the male sex pheromone. Here we show that this post-mating behavioral switch is mediated by dopamine (DA). Females fed a DA-receptor antagonist prior to mating maintained their attraction to the male pheromone after mating while virgin females injected with DA became unresponsive. However, the switch is reversible as mated females regained their pheromone preference after appetitive learning. Feeding mated N. vitripennis females with antagonists of either octopamine- (OA) or DA-receptors prevented relearning of the pheromone preference suggesting that both receptors are involved in appetitive learning. Moreover, DA injection into mated females was sufficient to mimic the oviposition reward during odor conditioning with the male pheromone. Our data indicate that DA plays a key role in the plastic pheromone response of N. vitripennis females and reveal some striking parallels between insects and mammals in the neuromodulatory mechanisms underlying olfactory plasticity.

Epimerisation of chiral hydroxylactones by short-chain dehydrogenases/reductases accounts for sex pheromone evolution in Nasonia

Males of all species of the parasitic wasp genus Nasonia use (4R,5S)-5-hydroxy-4-decanolide (RS) as component of their sex pheromone while only N. vitripennis (Nv), employs additionally (4R,5R)-5-hydroxy-4-decanolide (RR). Three genes coding for the NAD⁺-dependent short-chain dehydrogenases/reductases (SDRs) NV10127, NV10128, and NV10129 are linked to the ability of Nv to produce RR. Here we show by assaying recombinant enzymes that SDRs from both Nv and N. giraulti (Ng), the latter a species with only RS in the pheromone, epimerise RS into RR and vice versa with (4R)-5-oxo-4-decanolide as an intermediate. Nv-derived SDR orthologues generally had higher epimerisation rates, which were also influenced by NAD⁺ availability. Semiquantitative protein analyses of the pheromone glands by tandem mass spectrometry revealed that NV10127 as well as NV10128 and/or NV10129 were more abundant in Nv compared to Ng. We conclude that the interplay of differential expression patterns and SDR epimerisation rates on the ancestral pheromone component RS accounts for the evolution of a novel pheromone phenotype in Nv.

Species Specificity of the Putative Male Antennal Aphrodisiac Pheromone in Leptopilina heterotoma, Leptopilina boulardi, and Leptopilina victoriae

Male antennal aphrodisiac pheromones have been suggested to elicit female receptiveness in several parasitic Hymenoptera, including Leptopilina boulardi. None of the proposed pheromones, however, has been fully identified to date. It is also unknown whether these antennal pheromones are species specific, because the species specificity of mate recognition and courtship elicitation in Leptopilina prevented such experiments. In this study we present an experimental design that allows the investigation of the species specificity of the putative male aphrodisiac pheromone of L. heterotoma, L. boulardi, and L. victoriae. This is achieved by chemical manipulation of the odour profile of heterospecific females, so that males perceive them as conspecifics and show antennal courtship behaviour. Males courted the manipulated heterospecific females and antennal contact between the male and the female was observed. However, males elicited receptiveness only in conspecific females, never in the manipulated heterospecific females. Chemical analysis showed the presence of species specific unsaturated hydrocarbons on the antennae of males. Only trace amounts of these hydrocarbons are found on the antennae of females. Our results are an important step towards the understanding and identification of antennal pheromones of parasitic wasps.

The expanding genetic toolbox of the wasp Nasonia vitripennis and its relatives

The parasitoid wasp Nasonia represents a genus of four species that is emerging as a powerful genetic model system that has made and will continue to make important contributions to our understanding of evolutionary biology, development, ecology, and behavior. Particularly powerful are the haplodiploid genetics of the system, which allow some of the advantages of microbial genetics to be applied to a complex multicellular eukaryote. In addition, fertile, viable hybrids can be made among the four species in the genus. This makes Nasonia exceptionally well suited for evolutionary genetics approaches, especially when combined with its haploid genetics and tractability in the laboratory. These features are complemented by an expanding array of genomic, transcriptomic, and functional resources, the application of which has already made Nasonia an important model system in such emerging fields as evolutionary developmental biology and microbiomics. This article describes the genetic and genomic advantages of Nasonia wasps and the resources available for their genetic analysis.

The use of the lactone motif in chemical communication

A wide variety of organisms communicate via the chemical channel using small molecules. A structural feature quite often found is the lactone motif. In the present paper, the current knowledge on such lactones will be described, concentrating on the structure, chemistry, function, biosynthesis and synthesis of these compounds. Lactone semiochemicals from insects, vertebrates and bacteria, which this article will focus on, are particularly well investigated. In addition, some ideas on the advantageous use of lactones as volatile signals, which promoted their evolutionary development, will be discussed.

A combined approach to heat stress effect on male fertility in Nasonia vitripennis: from the physiological consequences on spermatogenesis to the reproductive adjustment of females mated with stressed males

In recent years, several studies have shown a decline in reproductive success in males in both humans and wildlife. Research on male fertility has largely focused on vertebrates, although invertebrates constitute the vast majority of terrestrial biodiversity. The reduction of their reproductive capacities due to environmental stresses can have strong negative ecological impacts, and also dramatic consequences on world food production if it affects the reproductive success of biological control agents, such as parasitic wasps used to control crop pests. Here Nasonia vitripennis, a parasitic wasp of various fly species, was studied to test the effects of 24h-heat stress applied during the first pupal stage on male fertility. Results showed that only primary spermatocytes were present at the first pupal stage in all cysts of the testes. Heat stress caused a delay in spermatogenesis during development and a significant decrease in sperm stock at emergence. Females mated with these heat-stressed males showed a reduce sperm count stored in their spermatheca. Females did not appear to distinguish heat-stressed from control males and did not remate more frequently to compensate for the lack of sperm transferred. As a result, females mated with heat-stressed males produced a suboptimal lifetime offspring sex ratio compared to those mated with control males. This could further impact the population dynamics of this species. N. vitripennis appears to be an interesting biological model to study the mechanisms of subfertility and its consequence on female reproductive strategies and provides new research perspectives in both invertebrates and vertebrates.

Oleic acid is a precursor of linoleic acid and the male sex pheromone in Nasonia vitripennis

Linoleic acid (C18:2(Δ9,12), LA) is crucial for many cell functions in organisms. It has long been a paradigm that animals are unable to synthesize LA from oleic acid (C18:1(Δ9), OA) because they were thought to miss Δ(12)-desaturases for inserting a double bound at the Δ(12)-position. Today it is clear that this is not true for all animals because some insects and other invertebrates have been demonstrated to synthesize LA. However, the ability to synthesize LA is known in only five insect orders and no examples have been reported so far in the Hymenoptera. LA plays a particular role in the parasitic wasp Nasonia vitripennis, because it is the precursor of the male sex pheromone consisting of (4R,5R)- and (4R,5S)-5-hydroxy-4-decanolides. Here we demonstrate by stable isotope labeling that N. vitripennis is able to incorporate externally applied fully (13)C-labeled OA into the male sex pheromone suggesting that they convert initially OA into LA. To verify this assumption, we produced fly hosts (Lucilia caesar) which were experimentally enriched in (13)C-labeled OA and reared male parasitoids on these hosts. Chemical analysis of transesterified lipid raw extracts from hosts and parasitoids revealed that N. vitripennis but not L. caesar contained (13)C-labeled LA methyl ester. Furthermore, male wasps from the manipulated hosts produced significant amounts of (13)C-labeled sex pheromone. These results suggest that N. vitripennis possesses a Δ(12)-desaturase. The additional fitness relevant function as pheromone precursor might have favored the evolution of LA biosynthesis in N. vitripennis to make the wasps independent of the formerly essential nutrient.

Functional activity of allatotropin and allatostatin in the pupal stage of a holometablous insect, Tribolium castaneum (Coleoptera, Tenebrionidae)

Allatotropin (AT) and allatostatin (AS) neuropeptides are known to regulate the biosynthesis of juvenile hormones (JH) in insects. Furthermore, they possess myoregulatory and other activities in a wide range of insect species. The genome of Tribolium castaneum encodes two AS and one AT precursors. Here we cloned the cDNAs of the precursors, followed their expression patterns during the pupal stage, and established their putative roles in adult development and oviposition of the females using RNA interference (RNAi). Cloning of the cDNA and gene structure analyses of the Tc-AT gene confirmed that the gene is expressed in three mRNA isoforms. Real-time PCR data demonstrate that the Tc-AT isoforms and the AS genes, Tc-AS C and Tc-AS B, are expressed in discerning developmental and tissue-specific patterns. Single injections of dsRNAi (targeted against the Tc-AT, Tc-AS C, and Tc-AS B, respectively), into young pupae resulted in abnormal adult phenotypes, whereby about half of the animals (P1 phenotype) looked relatively normal, but the females laid low numbers of eggs. The other halves (P2) exhibited strong developmental defects with abnormal duration of the pupal stage, abnormal head and body sizes, short elytra, and incomplete sclerotization. Moreover, these females deposited no eggs and died within one week after emergence. Individual silencing of the Tc-AT mRNA isoforms showed that Tc-AT3 had the most disruptive influence on adult development and fecundity of the females. Our findings clearly indicate a significant role of AT and AS neuropeptides in the pupa. The distinct mechanisms of action, however, remain to be determined.

Crystal structure of the invertebrate bifunctional purine biosynthesis enzyme PAICS at 2.8 Å resolution

Two important steps of the de novo purine biosynthesis pathway are catalyzed by the 5-aminoimidazole ribonucleotide carboxylase and the 4-(N-succinylcarboxamide)-5-aminoimidazole ribonucleotide synthetase enzymes. In most eukaryotic organisms, these two activities are present in the bifunctional enzyme complex known as PAICS. We have determined the 2.8-Å resolution crystal structure of the 350-kDa invertebrate PAICS from insect cells (Trichoplusia ni) using single-wavelength anomalous dispersion methods. Comparison of insect PAICS to human and prokaryotic homologs provides insights into substrate binding and reveals a highly conserved enzymatic framework across divergent species.

Cloning and characterization of a microsomal epoxide hydrolase from Heliothis virescens

Epoxide hydrolases (EHs) are α/β-hydrolase fold superfamily enzymes that convert epoxides to 1,2-trans diols. In insects EHs play critical roles in the metabolism of toxic compounds and allelochemicals found in the diet and for the regulation of endogenous juvenile hormones (JHs). In this study we obtained a full-length cDNA, hvmeh1, from the generalist feeder Heliothis virescens that encoded a highly active EH, Hv-mEH1. Of the 10 different EH substrates that were tested, Hv-mEH1 showed the highest specific activity (1180 nmol min(-1) mg(-1)) for a 1,2-disubstituted epoxide-containing fluorescent substrate. This specific activity was more than 25- and 3900-fold higher than that for the general EH substrates cis-stilbene oxide and trans-stilbene oxide, respectively. Although phylogenetic analysis placed Hv-mEH1 in a clade with some lepidopteran JH metabolizing EHs (JHEHs), JH III was a relatively poor substrate for Hv-mEH1. Hv-mEH1 showed a unique substrate selectivity profile for the substrates tested in comparison to those of MsJHEH, a well-characterized JHEH from Manduca sexta, and hmEH, a human microsomal EH. Hv-mEH1 also showed unique enzyme inhibition profiles to JH-like urea, JH-like secondary amide, JH-like primary amide, and non-JH-like primary amide compounds in comparison to MsJHEH and hmEH. Although Hv-mEH1 is capable of metabolizing JH III, our findings suggest that this enzymatic activity does not play a significant role in the metabolism of JH in the caterpillar. The ability of Hv-mEH1 to rapidly hydrolyze 1,2-disubstituted epoxides suggests that it may play roles in the metabolism of fatty acid epoxides such as those that are commonly found in the diet of Heliothis.

Behavioural and genetic analyses of Nasonia shed light on the evolution of sex pheromones

Sex pheromones play a pivotal role in the communication of many sexually reproducing organisms. Accordingly, speciation is often accompanied by pheromone diversification enabling proper mate finding and recognition. Current theory implies that chemical signals are under stabilizing selection by the receivers who thereby maintain the integrity of the signals. How the tremendous diversity of sex pheromones seen today evolved is poorly understood. Here we unravel the genetics of a newly evolved pheromone phenotype in wasps and present results from behavioural experiments indicating how the evolution of a new pheromone component occurred in an established sender-receiver system. We show that male Nasonia vitripennis evolved an additional pheromone compound differing only in its stereochemistry from a pre-existing one. Comparative behavioural studies show that conspecific females responded neutrally to the new pheromone phenotype when it evolved. Genetic mapping and gene knockdown show that a cluster of three closely linked genes accounts for the ability to produce this new pheromone phenotype. Our data suggest that new pheromone compounds can persist in a sender's population, without being selected against by the receiver and without the receiver having a pre-existing preference for the new pheromone phenotype, by initially remaining unperceived. Our results thus contribute valuable new insights into the evolutionary mechanisms underlying the diversification of sex pheromones. Furthermore, they indicate that the genetic basis of new pheromone compounds can be simple, allowing them to persist long enough in a population for receivers to evolve chemosensory adaptations for their exploitation.

Identification of sex pheromone components in Trissolcus brochymenae females

Long- and short-range sex pheromones appear to play a crucial role in the mate finding and courtship behaviour of most parasitic Hymenoptera. Yet these parasitoids have been rarely investigated and only a few pheromones have been identified. Recent studies have shown that sexual communication of Trissolcus brochymenae (Hymenoptera: Platygastridae), a quasi-gregarious egg parasitoid of the harlequin bug, Murgantia histrionica (Heteroptera: Pentatomidae), starts before contact between males and females when chemical compounds produced by virgin females trigger the courtship behaviour of males. In the present study, the pheromone components involved in the short-range recognition of T. brochymenae females by males were investigated using electrophysiological and behavioural methods. Female body extracts were analyzed through EAG and GC-EAD and the active compounds were identified through GC-MS. The behavioural responses of virgin males to the GC-EAD active compounds were subsequently evaluated in closed arena bioassays. Two active compounds in EAG and behavioural tests, tetradecyl acetate and (Z)-11-hexadecen-1-yl acetate, were identified as sex pheromone components. Both compounds triggered intense male antennation and mount when applied to solvent-washed female cadavers. Dose-response tests showed different curves for the two compounds. This is the first study on the identification of sexual pheromones in Platygastridae.

Precise RNAi-mediated silencing of metabolically active proteins in the defence secretions of juvenile leaf beetles

Allomones are widely used by insects to impede predation. Frequently these chemical stimuli are released from specialized glands. The larvae of Chrysomelina leaf beetles produce allomones in gland reservoirs into which the required precursors and also the enzymes are secreted from attached gland cells. Hence, the reservoirs can be considered as closed bio-reactors for producing defensive secretions. We used RNA interference (RNAi) to analyse in vivo functions of proteins in biosynthetic pathways occurring in insect secretions. After a salicyl alcohol oxidase was silenced in juveniles of the poplar leaf beetles, Chrysomela populi, the precursor salicyl alcohol increased to 98 per cent, while salicyl aldehyde was reduced to 2 per cent within 5 days. By analogy, we have silenced a novel protein annotated as a member of the juvenile hormone-binding protein superfamily in the juvenile defensive glands of the related mustard leaf beetle, Phaedon cochleariae. The protein is associated with the cyclization of 8-oxogeranial to iridoids (methylcyclopentanoid monoterpenes) in the larval exudates made clear by the accumulation of the acylic precursor 5 days after RNAi triggering. A similar cyclization reaction produces the secologanin part of indole alkaloids in plants.

Role of epoxide hydrolases in lipid metabolism

Epoxide hydrolases (EH), enzymes present in all living organisms, transform epoxide-containing lipids to 1,2-diols by the addition of a molecule of water. Many of these oxygenated lipid substrates have potent biological activities: host defense, control of development, regulation of blood pressure, inflammation, and pain. In general, the bioactivity of these natural epoxides is significantly reduced upon metabolism to diols. Thus, through the regulation of the titer of lipid epoxides, EHs have important and diverse biological roles with profound effects on the physiological state of the host organism. This review will discuss the biological activity of key lipid epoxides in mammals. In addition, the use of EH specific inhibitors will be highlighted as possible therapeutic disease interventions.

Expression and cellular localization of inducible nitric oxide synthase in lipopolysaccharide-treated rat kidneys

Although inducible nitric oxide synthase (iNOS) is known to play significant roles in the kidney, its renal localization has long been controversial. To resolve this issue, the authors identified iNOS-positive cell types in rat kidneys using double immunohistochemistry and confirmed iNOS positivity using enzyme histochemistry with NADPH-diaphorase (NADPH-d) and in situ RT-PCR. Adult male Sprague-Dawley rats were injected intraperitoneally with lipopolysaccharide (LPS) or saline as a control and sacrificed at various time intervals after injection. Quantitative real-time reverse transcriptase polymerase chain reaction showed that iNOS was not expressed in control kidneys but was induced in LPS-treated kidneys. iNOS immunostaining was strongest 6 to 18 hr after injection and decreased gradually to control levels by day 7. Double immunohistochemistry and NADPH-d revealed that iNOS expression was induced in the interstitial cells, glomerular parietal epithelial cells, the proximal part of the short-looped descending thin limb, the upper and middle papillary parts of the long-looped descending thin limb, some inner medullary collecting duct cells, and almost all calyceal and papillary epithelial cells. The present study determines the precise localization of iNOS in LPS-treated rat kidneys and provides an important morphological basis for examining the roles of iNOS in sepsis-induced acute kidney injury.

How parasitoid females produce sexy sons: a causal link between oviposition preference, dietary lipids and mate choice in Nasonia

Sexual selection theory predicts that phenotypic traits used to choose a mate should reflect honestly the quality of the sender and thus, are often costly. Physiological costs arise if a signal depends on limited nutritional resources. Hence, the nutritional condition of an organism should determine both its quality as a potential mate and its ability to advertise this quality to the choosing sex. In insects, the quality of the offspring's nutrition is often determined by the ovipositing female. A causal connection, however, between the oviposition decisions of the mother and the mating chances of her offspring has never been shown. Here, we demonstrate that females of the parasitic wasp Nasonia vitripennis prefer those hosts for oviposition that have been experimentally enriched in linoleic acid (LA). We show by (13)C-labelling that LA from the host diet is a precursor of the male sex pheromone. Consequently, males from LA-rich hosts produce and release higher amounts of the pheromone and attract more virgin females than males from LA-poor hosts. Finally, males from LA-rich hosts possess three times as many spermatozoa as those from LA-poor hosts. Hence, females making the right oviposition decisions may increase both the fertility and the sexual attractiveness of their sons.

Pheromone communication in Nasonia vitripennis: abdominal sex attractant mediates site fidelity of releasing males

Males of the parasitic wasp Nasonia vitripennis (Hymenoptera: Pteromalidae) use a substrate-borne sex pheromone to attract virgin females. The pheromone is synthesized in the rectal vesicle and deposited via the anus by dabbing movements of the abdominal tip. The chemicals attracting the females are composed of a mixture (4R,5R- and (4R,5 S)-5-hydroxy-4-decanolides (HDL) being synergized by the trace component 4-methylquinazoline (4-MeQ) which is not attractive for females when offered alone. Here we show that male pheromone deposits are not only attractive to virgin females but also for the releasing males themselves. In an olfactometer bioassay, males were strongly attracted by their own pheromone markings but were unable to discriminate between their own markings and those deposited by other males. Polar fractions of pheromone gland extracts containing the HDLs and 4-MeQ were also highly attractive for males. Bioassays using synthetic pheromones in natural doses revealed that combinations of HDL/4-MeQ and 4-MeQ alone attracted males whereas the HDLs alone were behaviorally inactive. Furthermore, males did not discriminate between HDL/4-MeQ and 4-MeQ alone. We conclude that the trace component 4-MeQ mediates site fidelity of N. vitripennis males at sites previously marked with the abdominal sex pheromone. The use of 4-MeQ to stay at and to return to scent-marked patches rather than marking new ones might be a strategy to economize semiochemical use in N. vitripennis males.

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.

Molecular characterization and enzymatic analysis of juvenile hormone epoxide hydrolase genes in the red flour beetle Tribolium castaneum

Juvenile hormone epoxide hydrolases (JHEHs) degrade juvenile hormones (JHs) and are important for JH titre regulation. Here, we report the cloning and analysis of five jheh-related (jheh-r1-r5) genes in the red flour beetle, Tribolium castaneum, a model species for the coleopteran insects. T. castaneum JHEH-r (TcJHEH-r) proteins show high homology to lepidopteran JHEHs and also to human microsomal epoxide hydrolase. In the phylogenetic tree, Tcjheh-rs were clustered, and interestingly, they were also clustered in the genome. Examination of enzymatic activities using recombinant TcJHEH-r proteins showed that TcJHEH-r3 had strong degradation activity for JH III, whereas TcJHEH-r4 had weak activity. The study has yielded significant information that will facilitate further analysis of JHEHs and epoxide hydrolases.

Characterization of the SgcF epoxide hydrolase supporting an (R)-vicinal diol intermediate for enediyne antitumor antibiotic C-1027 biosynthesis

C-1027 is a chromoprotein antitumor antibiotic consisting of an apoprotein and the C-1027 chromophore. The C-1027 chromophore possesses four distinct structural moieties-an enediyne core, a deoxy aminosugar, a benzoxazolinate, and an (S)-3-chloro-5-hydroxy-beta-tyrosine-the latter two of which are proposed to be appended to the enediyne core via a convergent biosynthetic strategy. Here we report the in vitro characterization of SgcF, an epoxide hydrolase from the C-1027 biosynthetic gene cluster that catalyzes regio- and stereospecific hydrolysis of styrene oxide, serving as an enediyne core epoxide intermediate mimic, to form a vicinal diol. Abolishment of C-1027 production in the DeltasgcF mutant strain Streptomyces globisporus SB1010 unambiguously establishes that sgcF plays an indispensable role in C-1027 biosynthesis. SgcF efficiently hydrolyzes (S)-styrene oxide, displaying an apparent K(m) of 0.6 +/- 0.1 mM and k(cat) of 48 +/- 1 min(-1), via attack at the alpha-position to exclusively generate the (R)-phenyl vicinal diol, consistent with the stereochemistry of the C-1027 chromophore. These findings support the role of SgcF in the proposed convergent pathway for C-1027 biosynthesis, unveiling an (R)-vicinal diol as a key intermediate. Interestingly, SgcF can also hydrolyze (R)-styrene oxide to afford preferentially the (R)-phenyl vicinal diol via attack at the beta-position, albeit with significantly reduced efficiency (apparent K(m) of 2.0 +/- 0.4 mM and k(cat) = 4.3 +/- 0.3 min(-1)). Although the latter activity unlikely contributes to C-1027 biosynthesis in vivo, such enantioconvergence arising from complementary regioselective hydrolysis of a racemic substrate could be exploited to engineer epoxide hydrolases with improved regio- and/or enantiospecificity.

Deciphering proteomic signatures of early diapause in Nasonia

Insect diapause is an alternative life-history strategy used to increase longevity and survival in harsh environmental conditions. Even though some aspects of diapause are well investigated, broader scale studies that elucidate the global metabolic adjustments required for this remarkable trait, are rare. In order to better understand the metabolic changes during early insect diapause, we used a shotgun proteomics approach on early diapausing and non-diapausing larvae of the recently sequenced hymenopteran model organism Nasonia vitripennis. Our results deliver insights into the molecular underpinnings of diapause in Nasonia and corroborate previously reported diapause-associated features for invertebrates, such as a diapause-dependent abundance change for heat shock and storage proteins. Furthermore, we observed a diapause-dependent switch in enzymes involved in glycerol synthesis and a vastly changed capacity for protein synthesis and degradation. The abundance of structural proteins and proteins involved in protein synthesis decreased with increasing diapause duration, while the abundance of proteins likely involved in diapause maintenance (e.g. ferritins) increased. Only few potentially diapause-specific proteins were identified suggesting that diapause in Nasonia relies to a large extent on a modulation of pre-existing pathways. Studying a diapause syndrome on a proteomic level rather than isolated pathways or physiological networks, has proven to be an efficient and successful avenue to understand molecular mechanisms involved in diapause.

Quantity matters: male sex pheromone signals mate quality in the parasitic wasp Nasonia vitripennis

Sexual selection theory asserts that females are well adapted to sense signals indicating the quality of potential mates. One crucial male quality parameter is functional fertility (i.e. the success of ejaculates in fertilizing eggs). The phenotype-linked fertility hypothesis (PLFH) predicts that functional fertility of males is reflected by phenotypic traits that influence female mate choice. Here, we show for Nasonia vitripennis, a parasitic wasp with haplodiploid sex determination and female-biased sex ratios, that females use olfactory cues to discriminate against sperm-limited males. We found sperm limitation in newly emerged and multiply mated males (seven or more previous matings) as indicated by a higher proportion of sons in the offspring fathered by these males. Sperm limitation correlated with clearly reduced pheromone titres. In behavioural bioassays, females oriented towards higher doses of the synthetic pheromone and were attracted more often to scent marks of males with a full sperm load than to those of sperm-limited males. Our data support the PLFH and suggest that N. vitripennis females are able to decrease the risk of getting constrained to produce suboptimal offspring sex ratios by orienting towards gradients of the male sex pheromone.

Mechanism and behavioral context of male sex pheromone release in Nasonia vitripennis

Males of the parasitic wasp Nasonia vitripennis (Hymenoptera: Pteromalidae) attract virgin females by releasing a sex pheromone composed of (4R,5R)- and (4R,5S)-5-hydroxy-4-decanolide (HDL). The pheromone is biosynthesized in the rectal vesicle of males. In the present study, we investigated the mechanism and behavioral context of pheromone release, and determined the range of activity and the longevity of the chemical signal. Our data show that the sex pheromone of N. vitripennis is substrate-borne and is deposited on surfaces by dabbing movements of the abdominal tip, a behavior previously described in N. vitripennis males as 'abdomen dipping'. Chemical markings deposited by a single male were highly attractive to virgin females. Chemical analyses revealed the presence of HDL in surface washings of marked areas, and HDL amounts correlated with male marking activity. Pheromone deposition occurred spontaneously without any additional cues being present, but marking intensity increased greatly after copulation or after a single contact with a virgin female. In contrast, marking intensity was not influenced by the presence of host puparia. Male pheromone deposits were perceived by females in a still-air olfactometer at distances of up to 4.5 cm and remained attractive for at least 2 h. The function of the substrate-borne sex pheromone is discussed with respect to the mating system of N. vitripennis.