Caffeine induction of Cyp6a2 and Cyp6a8 genes of Drosophila melanogaster is modulated by cAMP and D-JUN protein levels

Unveiling the role of bZIP transcription factors CREB and CEBP in detoxification metabolism of Nilaparvata lugens (Stål)

The basic leucine zipper (bZIP) superfamily is a crucial group of xenobiotics in insects. However, little is known about the function of CAAT enhancer binding proteins (CEBP) and cAMP response element binding protein (CREB) in Nilaparvata lugens. In the present study, NlCEBP and NlCREB were cloned and identified. Quantitative polymerase real-time chain reaction (qRT-PCR) analysis showed the expression of NlCEBP and NlCREB was significantly induced after chemical insecticides exposure. Silencing of NlCEBP and NlCREB increased the susceptibility of N. lugens to insecticides, and the detoxification enzyme activities were also significantly decreased. In addition, comparative transcriptome analysis revealed that 174 genes were significantly co-down-regulated after interfering with the two transcription factors. GO analysis showed that co-down-regulated genes are mostly related to energy transport and metabolic functions indicating the potential regulatory role of NlCEBP and NlCREB in detoxification metabolism. Our research shed lights on the functional roles of transcription factors NlCEBP and NlCREB in the detoxification metabolism of N. lugens, providing a theoretical basis for pest management and comprehensive control of this pest and increasing our understanding of insect toxicology.

Research Progress on the Regulation of Autophagy and Apoptosis in Insects by Sterol Hormone 20-Hydroxyecdysone

20E (20-Hydroxyecdysone) is a central steroid hormone that orchestrates developmental changes and metamorphosis in arthropods. While its molecular mechanisms have been recognized for some time, detailed elucidation has primarily emerged in the past decade. PCD (Programmed cell death), including apoptosis, necrosis, efferocytosis, pyroptosis, ferroptosis, and autophagy, plays a crucial role in regulated cell elimination, which is vital for cells' development and tissue homeostasis. This review summarizes recent findings on 20E signaling regulated autophagy and apoptosis in insects, including Drosophila melanogaster, Bombyx mori, Helicoverpa armigera, and other species. Firstly, we comprehensively explore the biosynthesis of the sterol hormone 20E and its subsequent signal transduction in various species. Then, we focus on the involvement of 20E in regulating autophagy and apoptosis, elucidating its roles in both developmental contexts and bacterial infection scenarios. Furthermore, our discussion unfolds as a panoramic exposition, where we delve into the fundamental questions with our findings, anchoring them within the grander scheme of our study in insects. Deepening the understanding of 20E-autophagy/apoptosis axis not only underscores the intricate tapestry of endocrine networks, but also offers fresh perspectives on the adaptive mechanisms that have evolved in the face of environmental challenges.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

MAPK-Activated Transcription Factor PxJun Suppresses PxABCB1 Expression and Confers Resistance to Bacillus thuringiensis Cry1Ac Toxin in Plutella xylostella (L.)

Deciphering the molecular mechanisms underlying insect resistance to Cry toxins produced by Bacillus thuringiensis (Bt) is pivotal for the sustainable utilization of Bt biopesticides and transgenic Bt crops. Previously, we identified that mitogen-activated protein kinase (MAPK)-mediated reduced expression of the PxABCB1 gene is associated with Bt Cry1Ac resistance in the diamondback moth, Plutella xylostella (L.). However, the underlying transcriptional regulation mechanism remains enigmatic. Here, the PxABCB1 promoter in Cry1Ac-susceptible and Cry1Ac-resistant P. xylostella strains was cloned and analyzed and found to contain a putative Jun binding site (JBS). A dual-luciferase reporter assay and yeast one-hybrid assay demonstrated that the transcription factor PxJun repressed PxABCB1 expression by interacting with this JBS. The expression levels of PxJun were increased in the midguts of all resistant strains compared to the susceptible strain. Silencing of PxJun expression significantly elevated PxABCB1 expression and Cry1Ac susceptibility in the resistant NIL-R strain, and silencing of PxMAP4K4 expression decreased PxJun expression and also increased PxABCB1 expression. These results indicate that MAPK-activated PxJun suppresses PxABCB1 expression to confer Cry1Ac resistance in P. xylostella, deepening our understanding of the transcriptional regulation of midgut Cry receptor genes and the molecular basis of insect resistance to Bt Cry toxins. IMPORTANCE The transcriptional regulation mechanisms underlying reduced expression of Bt toxin receptor genes in Bt-resistant insects remain elusive. This study unveils that a transcription factor PxJun activated by the MAPK signaling pathway represses PxABCB1 expression and confers Cry1Ac resistance in P. xylostella. Our results provide new insights into the transcriptional regulation mechanisms of midgut Cry receptor genes and deepen our understanding of the molecular basis of insect resistance to Bt Cry toxins. To our knowledge, this study identified the first transcription factor that can be involved in the transcriptional regulation mechanisms of midgut Cry receptor genes in Bt-resistant insects.

Regulation of insect P450s in response to phytochemicals

Insect herbivores use phytochemicals as signals to induce expression of their phytochemical-detoxifying cytochrome P450 monooxygenases (P450s). The regulatory cascades that transduce phytochemical signals to enhanced expression of P450s are the focus of this review. At least seven signaling pathways, including RTK/MAPK, GPCR/CREB, GPCR/NFκB, ROS/CncC/Keap1, AhR/ARNT, cytosol NR, and nucleus-located NR, may be involved in phytochemical induction of P450s. Constitutive overexpression, overphosphorylation, and/or activation of one or more effectors in the corresponding pathway are common causes of P450 overexpression that lead to phytochemical or insecticide resistance. Future research should pay more attentions to the starting point of each pathway, the number of pathways and their cross talk for a given phytochemical, and the pathways for downregulation of P450s.

The role of G protein-coupled receptor-related genes in cytochrome P450-mediated resistance of the house fly, Musca domestica (Diptera: Muscidae), to imidacloprid

Ninety-four putative G protein-coupled receptors (GPCRs) were identified in the Musca domestica genome. They were annotated and compared with their homologues in Drosophila melanogaster. Phylogenetic analyses of the GPCRs from both species revealed that several family members shared a closer relationship based on the domain architecture. The expression profiles of these genes were examined by quantitative real-time PCR amongst three strains of the house fly, a near-isogenic line strain with imidacloprid resistance (N-IRS), the corresponding susceptible strain (CSS) and another strain derived from field populations with imidacloprid resistance (IRS). We found that five GPCR genes were upregulated in the N-IRS and eight GPCR genes were upregulated in the IRS strains compared to the CSS strain. The transgenic lines of D. melanogaster with the GPCR genes (LOC101899380 in the N-IRS strain and LOC101895664 in the IRS strain) exhibited significantly increased tolerance to imidacloprid, and higher expression of cytochrome P450 genes. Bioinformatic analysis of LOC101899380 was carried out based on its full-length nucleic acid sequence and putative amino acid sequence, and it was named Methuselah-like10 (Mthl10) owing to its homology with D. melanogaster Mthl10. A cell-base cell counting kit-8 toxicity assay demonstrated that the expression of the GPCR gene LOC101899380 in Spodoptera frugiperda (Sf9) cells using a baculovirus-mediated expression system can elevate the cell tolerance to imidacloprid, indirectly supporting the hypothesis that the GPCR gene LOC101899380 plays some role in imidacloprid resistance. These results should be useful for furthering understanding of the regulatory pathway by which house flies develop resistance.

CYP4BN6 and CYP6BQ11 mediate insecticide susceptibility and their expression is regulated by Latrophilin in Tribolium castaneum

BACKGROUND

Many insect cytochrome P450 proteins (CYPs) are involved in the metabolic detoxification of exogenous compounds such as plant toxins and insecticides. Tribolium castaneum, the red flour beetle, is a major agricultural pest that damages stored grains and cereal products. With the completion of the sequencing of its genome, two T. castaneum species-specific CYP genes, CYP4BN6, and CYP6BQ11, were identified. However, it is unknown whether the functions of most CYPs are shared by TcCYP4BN6 and TcCYP6BQ11, and the upstream regulatory mechanism of these two CYPs remains elusive.

RESULTS

QRT-PCR analysis indicated that TcCYP4BN6 and TcCYP6BQ11 were both most highly expressed at the late pupal stage and were mainly observed in the head and gut, respectively, of adults. Moreover, the transcripts of these two CYPs were significantly induced by dichlorvos and carbofuran, and RNA interference (RNAi) targeting of each of them enhanced the susceptibility of beetles to these two insecticides. Intriguingly, knockdown of the latrophilin (lph) gene, which has been reported to be related to the insecticide susceptibility, reduced the expression of TcCYP4BN6 and TcCYP6BQ11 after insecticide treatment, suggesting that these two CYP genes are regulated by lph to participate in insecticide susceptibility in T. castaneum.

CONCLUSION

These results shed new light on the function and mechanism of CYP genes associated with insecticide susceptibility and could facilitate research on appropriate and sustainable pest control management. © 2019 Society of Chemical Industry.

Latrophilin participates in insecticide susceptibility through positively regulating CSP10 and partially compensated by OBPC01 in Tribolium castaneum

Latrophilin (LPH) is an adhesion G protein-coupled receptor (aGPCR) that participates in multiple essential physiological processes. Our previous studies have shown that lph is not only indispensable for the development and reproduction of red flour beetles (Tribolium castaneum), but also for their resistance against dichlorvos or carbofuran insecticides. However, the regulatory mechanism of lph-mediated insecticide susceptibility remains unclear. Here, we revealed that knockdown of lph in beetles resulted in opposing changes in two chemoreception genes, chemosensory protein 10 (CSP10) and odorant-binding protein C01 (OBPC01), in which the expression of TcCSP10 was downregulated, whereas the expression of TcOBPC01 was upregulated. TcCSP10 and TcOBPC01 were expressed at the highest levels in early pupal and late larval stages, respectively. High levels of expression of both these genes were observed in the heads (without antennae) of adults. TcCSP10 and TcOBPC01 were significantly induced by dichlorvos or carbofuran between 12 and 72 h (hrs) after exposure, suggesting that they are likely associated with increasing the binding affinity of insecticides, leading to a decrease in sensitivity to the insecticides. Moreover, once these two genes were knocked down, the susceptibility of the beetles to dichlorvos or carbofuran was enhanced. Additionally, RNA interference (RNAi) targeting of lph followed by exposure to dichlorvos or carbofuran also caused the opposing expression levels of TcCSP10 and TcOBPC01 compared to the expression levels of wild-type larvae treated with insecticides alone. All these results indicate that lph is involved in insecticide susceptibility through positively regulating TcCSP10; and the susceptibility could also further partially compensated for through the negative regulation of TcOBPC01 when lph was knockdown in the red flour beetle. Our studies shed new light on the molecular regulatory mechanisms of lph related to insecticide susceptibility.

Transcription factors CncC/Maf and AhR/ARNT coordinately regulate the expression of multiple GSTs conferring resistance to chlorpyrifos and cypermethrin in Spodoptera exigua

BACKGROUND

Glutathione S-transferases (GSTs) are a superfamily of multifunctional dimeric proteins existing in both prokaryotic and eukaryotic organisms. They are involved in the detoxification of both endogenous and exogenous electrophiles, including insecticides. However, the molecular mechanisms underlying the regulation of GST genes in insects are poorly understood.

RESULTS

We first identified at least three GST genes involved in resistance to the insecticides chlorpyrifos and cypermethrin. Analysis of upstream sequences revealed that three GSTs (SeGSTo2, SeGSTe6 and SeGSTd3) harbor the same cap 'n' collar C/muscle aponeurosis fibromatosis (CncC/Maf) binding site, and SeGSTo2 and SeGSTe6 contain the aryl hydrocarbon receptor/aryl hydrocarbon receptor nuclear translocator (AhR/ARNT) binding site. Luciferase reporter assay showed co-transfection of reporter plasmid containing the SeGSTe6 promoter with CncC and/or Maf expressing constructs significantly boosted transcription. Similarly, AhR and/or ARNT expressing constructs also significantly increased the promoter activities. The co-transfection of mutated reporter plasmid with CncC/Maf or AhR/ARNT did not increase transcription activity anymore. Constitutive over-expression of CncC, Maf and AhR was also found in the HZ16 strain, which might be the molecular mechanism for up-regulated expression of multiple detoxification genes conferring resistance to insecticides.

CONCLUSION

These results suggest that CncC/Maf and AhR/ARNT coordinately regulate the expression of multiple GST genes involved in insecticide resistance in Spodoptera exigua. © 2019 Society of Chemical Industry.

Transcription factor FTZ-F1 and cis-acting elements mediate expression of CYP6BG1 conferring resistance to chlorantraniliprole in Plutella xylostella

BACKGROUND

Cytochrome P450-mediated detoxification plays an important role in the development of insecticide resistance. Previous studies have demonstrated that overexpression of CYP6BG1 was responsible for permethrin resistance in Plutella xylostella, and our experiments also showed that upregulation of this gene is associated with chlorantraniliprole resistance in P. xylostella. However, the transcriptional regulation involved in the expression of CYP6BG1 remains unknown. To further investigate the regulation of CYP6BG1 expression, the promoters of this gene were cloned and analyzed from one susceptible and four different resistant populations of P. xylostella.

RESULTS

First, the promoter region of P. xylostella CYP6BG1 was compared in five populations, and three types of 5'-flanking region were found. Second, the region between -562 and +49 of CYP6BG1 in a field population (TH) of P. xylostella showed the highest promoter activity and could be induced by chlorantraniliprole. Third, the transcriptional factor FTZ-F1, which is an orphan nuclear receptor and binds to the fushi tarazu (ftz) gene, was predicted by the online software Alggen and Jaspar. It was proved to regulate the expression of CYP6BG1 by RNAi. The expression levels of FTZ-F1 and CYP6BG1 could be induced by chlorantraniliprole and were significantly higher in the resistant populations.

CONCLUSIONS

These data give a better understanding of the transcriptional regulation of an important insecticide detoxification enzyme gene, and therefore will help in understanding the molecular mechanisms of insecticide resistance in P. xylostella. © 2018 Society of Chemical Industry.

Identification of the 2-tridecanone cis-acting element in the promoter of cytochrome P450 CYP6B7 in Helicoverpa armigera

The expression level of cytochrome P450 genes in insects can be induced by plant allelochemicals, which is important for insects to adapt to host plants. Cytochrome P450 CYP6B7 has been reported to be involved in pyrethroid insecticide resistance in Helicoverpa armigera, and its transcription level was induced by some inducers. Currently, the regulatory mechanism of the induced expression of CYP6B7 remains unknown, although it is very important for understanding the detoxification mechanism to allelochemicals in host plants. The objective of the present study was to investigate the cis-acting element in the promoter of CYP6B7 mediating the inducible up-regulation of CYP6B7 in H. armigera by 2-tridecanone. The promoter region of CYP6B7 was cloned by genome walking technique and analyzed by transient transfection assay. Progressive 5' deletion of the promoter region of CYP6B7 revealed that the relative luciferase activity of construct -320/+232 could be significantly induced by 2-tridecanone. Further stepwise deletion between -320 and -238 bp found that construct -292/+232 could also be significantly induced by 2-tridecanone, but the adjacent construct -256/+232 could not, suggesting the essential role of the sequence between -292 and -257 bp for 2-tridecanone induction. Nucleotide mutations between -292 and -281 bp had no influence on the induction effect by 2-tridecanone, but nucleotide mutations between -280 and -257 bp significantly decreased the induction effect. These results demonstrated that the cis-acting element for 2-tridecanone induction was between -280 and -257 bp in the promoter of CYP6B7.

Multiple cis-acting elements involved in up-regulation of a cytochrome P450 gene conferring resistance to deltamethrin in smal brown planthopper, Laodelphax striatellus (Fallén)

As well as arising from single point mutations in binding sites or detoxifying enzymes, it is likely that insecticide resistance mechanisms are frequently controlled by multiple genetic factors, resulting in resistance being inherited as a quantitative trait. However, empirical evidence for this is still rare. Here we analyse the causes of up-regulation of CYP6FU1, a monoxygenase implicated in resistance to deltamethrin in the rice pest Laodelphax striatellus. The 5'-flanking region of this gene was cloned and sequenced from individuals of a susceptible and a resistant strain. A luminescent reporter assay was used to evaluate different 5'-flanking regions and their fragments for promoter activity. Mutations enhancing promoter activity in various fragments were characterized, singly and in combination, by site mutation recovery. Nucleotide diversity in flanking sequences was greatly reduced in deltamethrin-resistant insects compared to susceptible ones. Phylogenetic sequence analysis found that CYP6FU1 had five different types of 5'-flanking region. All five types were present in a susceptible strain but only a single type showing the highest promoter activity was present in a resistant strain. Four cis-acting elements were identified whose influence on up-regulation was much more pronounced in combination than when present singly. Of these, two were new transcription factor (TF) binding sites produced by mutations, another one was also a new TF binding site alternated from an existing one, and the fourth was a unique transcription start site. These results demonstrate that multiple cis-acting elements are involved in up-regulating CYP6FU1 to generate a resistance phenotype.

Aldose Reductase Acts as a Selective Derepressor of PPARγ and the Retinoic Acid Receptor

Histone deacetylase 3 (HDAC3), a chromatin-modifying enzyme, requires association with the deacetylase-containing domain (DAD) of the nuclear receptor corepressors NCOR1 and SMRT for its stability and activity. Here, we show that aldose reductase (AR), the rate-limiting enzyme of the polyol pathway, competes with HDAC3 to bind the NCOR1/SMRT DAD. Increased AR expression leads to HDAC3 degradation followed by increased PPARγ signaling, resulting in lipid accumulation in the heart. AR also downregulates expression of nuclear corepressor complex cofactors including Gps2 and Tblr1, thus affecting activity of the nuclear corepressor complex itself. Though AR reduces HDAC3-corepressor complex formation, it specifically derepresses the retinoic acid receptor (RAR), but not other nuclear receptors such as the thyroid receptor (TR) and liver X receptor (LXR). In summary, this work defines a distinct role for AR in lipid and retinoid metabolism through HDAC3 regulation and consequent derepression of PPARγ and RAR.

Caffeine and cardiovascular diseases: critical review of current research

Caffeine is a most widely consumed physiological stimulant worldwide, which is consumed via natural sources, such as coffee and tea, and now marketed sources such as energy drinks and other dietary supplements. This wide use has led to concerns regarding the safety of caffeine and its proposed beneficial role in alertness, performance and energy expenditure and side effects in the cardiovascular system. The question remains "Which dose is safe?", as the population does not appear to adhere to the strict guidelines listed on caffeine consumption. Studies in humans and animal models yield controversial results, which can be explained by population, type and dose of caffeine and low statistical power. This review will focus on comprehensive and critical review of the current literature and provide an avenue for further study.

A G-protein-coupled receptor regulation pathway in cytochrome P450-mediated permethrin-resistance in mosquitoes, Culex quinquefasciatus

Rhodopsin-like G protein-coupled receptors (GPCRs) are known to be involved in the GPCR signal transduction system and regulate many essential physiological processes in organisms. This study, for the first time, revealed that knockdown of the rhodopsin-like GPCR gene in resistant mosquitoes resulted in a reduction of mosquitoes’ resistance to permethrin, simultaneously reducing the expression of two cAMP-dependent protein kinase A genes (PKAs) and four resistance related cytochrome P450 genes. The function of rhodopsin-like GPCR was further confirmed using transgenic lines of Drosophila melanogaster, in which the tolerance to permethrin and the expression of Drosophila resistance P450 genes were both increased. The roles of GPCR signaling pathway second messenger cyclic adenosine monophosphate (cAMP) and downstream effectors PKAs in resistance were investigated using cAMP production inhibitor Bupivacaine HCl and the RNAi technique. Inhibition of cAMP production led to significant decreases in both the expression of four resistance P450 genes and two PKA genes and mosquito resistance to permethrin. Knockdown of the PKA genes had shown the similar effects on permethrin resistance and P450 gene expression. Taken together, our studies revealed, for the first time, the role of the GPCR/cAMP/PKA-mediated regulatory pathway governing P450 gene expression and P450-mediated resistance in Culex mosquitoes.

Expression analysis of two P450 monooxygenase genes of the tobacco cutworm moth (Spodoptera litura) at different developmental stages and in response to plant allelochemicals

Cytochrome P450 monooxygenases (P450s) of insects are known to be involved in the metabolism or detoxification of plant allelochemicals and insecticides. Spodoptera litura (Lepidoptera, Noctuidae) is a polyphagous moth responsible for severe yield losses in many crops. In this study, two full-length P450 genes, CYP6B48 and CYP6B58, were cloned from S. litura. The cDNA sequences encode proteins with 503 and 504 amino acids, respectively. Phylogenetic analysis revealed that CYP6B48 and CYP6B58 belong to the CYP6B subfamily of P450s. Quantitative real-time PCR analyses showed that CYP6B48 and CYP6B58 were expressed only at larval stage, but not at pupal and adult stages. The highest levels of transcripts were found in the midguts and fat bodies of the larvae. No expression was detected in the ovary or hemolymph. Feeding with diets containing cinnamic acid, quercetin, or coumarin did not affect expression of CYP6B48. In contrast, diet supplemented with xanthotoxin dramatically increased the levels of CYP6B48 transcript in the midgut and fat bodies. Larvae fed with flavone had high levels of transcript of CYP6B48 in the midgut, whereas only slightly elevated levels were found in the fat bodies. Effects of the tested allelochemicals on CYP6B58 expression were minor. Hence, our findings show that S. litura responds to specific allelochemicals such as xanthotoxin with the accumulation of CYP6B48 transcripts, suggesting that specific signals in the food control the insect's ability to convert toxic allelochemicals to less harmful forms at the transcriptional level.

Role of G-protein-coupled receptor-related genes in insecticide resistance of the mosquito, Culex quinquefasciatus

G-protein-coupled receptors regulate signal transduction pathways and play diverse and pivotal roles in the physiology of insects, however, the precise function of GPCRs in insecticide resistance remains unclear. Using quantitative RT-PCR and functional genomic methods, we, for the first time, explored the function of GPCRs and GPCR-related genes in insecticide resistance of mosquitoes, Culex quinquefasciatus. A comparison of the expression of 115 GPCR-related genes at a whole genome level between resistant and susceptible Culex mosquitoes identified one and three GPCR-related genes that were up-regulated in highly resistant Culex mosquito strains, HAmCq^G8 and MAmCq^G6, respectively. To characterize the function of these up-regulated GPCR-related genes in resistance, the up-regulated GPCR-related genes were knockdown in HAmCq^G8 and MAmCq^G6 using RNAi technique. Knockdown of these four GPCR-related genes not only decreased resistance of the mosquitoes to permethrin but also repressed the expression of four insecticide resistance-related P450 genes, suggesting the role of GPCR-related genes in resistance is involved in the regulation of resistance P450 gene expression. This results help in understanding of molecular regulation of resistance development in Cx. quinquefasciatus.

Genome-wide analysis of genes associated with moderate and high DDT resistance in Drosophila melanogaster

BACKGROUND

Moderate to high DDT resistance in generally associated with overexpression of multiple genes and therefore has been considered to be polygenic. However, very little information is available about the molecular mechanisms that insect populations employ when evolving increased levels of resistance. The presence of common regulatory motifs among resistance-associated genes may help to explain how and why certain suites of genes are preferentially represented in genomic-scale analyses.

RESULTS

A set of commonly differentially expressed genes associated with DDT resistance in the fruit fly was identified on the basis of genome-wide microarray analysis followed by qRT-PCR verification. More genes were observed to be overtranscribed in the highly resistant strain (91-R) than in the moderately resistant strain (Wisconsin) and susceptible strain (Canton-S). Furthermore, possible transcription factor binding sites that occurred in coexpressed resistance-associated genes were discovered by computational motif discovery methods.

CONCLUSION

A glucocorticoid receptor (GR)-like putative transcription factor binding motif (TFBM) was observed to be associated with genes commonly differentially transcribed in both the 91-R and Wisconsin lines of DDT-resistant Drosophila.

A portable system for monitoring the behavioral activity of Drosophila

We describe a low-cost system for monitoring the behavioral activity of the fruit fly, Drosophila melanogaster. The system is readily adaptable to one or more cameras for simultaneous recordings of behavior from different angles and can be used for monitoring multiple individuals in a population at the same time. Signal processing allows discriminating between active and inactive periods during locomotion or flying, and quantification of subtler movements related to changes in position of the wings or legs. The recordings can be taken continuously over long periods of time and can thus provide information about the dynamics of a population. The system was used to monitor responses to caffeine, changes in temperature and g-force, and activity in a variable size population.

Caffeine induction of sulfotransferases in rat liver and intestine

Sulfotransferases (SULTs) are important phase II drug-metabolizing enzymes. Regulation of SULTs by hormones and other endogenous molecules is relatively well understood, while xenobiotic induction of SULTs is not well studied. Caffeine is one of the most widely consumed psychoactive substances. However, SULT regulation by caffeine has not been reported. In this report, male and female rats were treated with different oral doses of caffeine (2, 10, 50 mg kg⁻¹ per day) for 7 days. Western blot and real-time RT-PCR were used to investigate the changes in SULT protein and mRNA expression following the caffeine treatment. Caffeine induced both rat aryl sulfotransferase (rSULT1A1, AST-IV) and rat hydroxysteroid sulfotransferase (rSULT2A1, STa) in the liver and intestine of female rats in a dose-dependent manner. Caffeine induction of rSULT1A1 and rSULT2A1 in the female rat intestine was much stronger than that in the liver. Although caffeine induced rSULT1A1 significantly in the male rat liver, it did not significantly induce rSULT2A1. In male rat intestine, caffeine significantly induced rSULT2A1. The different SULTs induction patterns in male and female rats suggest that the regulation of rat SULTs by caffeine may be affected by different hormone secretion patterns and levels. Our results suggest that consumption of caffeine can induce drug metabolizing SULTs in drug detoxification tissues.

Functional characterization of cis-acting elements mediating flavone-inducible expression of CYP321A1

How plant allelochemicals elicit herbivore counterdefense genes remains largely unknown. To define the cis-acting elements for flavone inducibility of the allelochemical-metabolizing CYP321A1 from Helicoverpa zea, functions of varying length of CYP321A1 promoter are examined in H. zea fatbody cells. Progressive 3' deletions reveal presence of positive elements in the 5' untranslated region (UTR). Progressive 5' deletions map out regions of one essential element, four enhancers, and two silencers. Further progressive 5'deletions localize the essential element to a 36-bp region from -109 to -74. This essential element, designated as xenobiotic response element to flavone (XRE-Fla), contains a 5' AT-only TAAT inverted repeat, a GCT mirror repeat and a 3' antioxidant response element-like element. Internal deletions and substitution mutations show that the TAAT repeat is only necessary for the maximal flavone inducibility, whereas the other two components are necessary for the basal and flavone-induced expression of CYP321A1. Electrophoresis mobility shift assays demonstrate that XRE-Fla specifically binds to H. zea fatbody cell nuclear extracts and flavone treatment increases the nuclear concentrations of the yet-to-be characterized transcription factors binding to XRE-Fla. Taken together, CYP321A1 expression is regulated primarily by XRE-Fla and secondarily by other cis elements scattered in its promoter and 5' UTR.

Functional analysis of the cis-acting elements responsible for the induction of the Cyp6a8 and Cyp6g1 genes of Drosophila melanogaster by DDT, phenobarbital and caffeine

Many Drosophila cytochrome P450 or Cyp genes are induced by caffeine and phenobarbital (PB). To understand the induction mechanism, we created Drosophila S2 cell lines stably transformed with different luciferase reporter plasmids carrying upstream DNAs of Cyp6a8 allele of the resistant 91-R strain, and the 1.1-kb upstream DNAs of Cyp6g1 of the 91-R and the susceptible 91-C strains. Following 24 h treatment with dichlorodiphenyltrichloroethane (DDT), caffeine or PB, luciferase activity of all cell lines was determined. Results showed that the 0.1-kb DNA of Cyp6a8 and the upstream DNAs of Cyp6g1 from both strains are not induced by these chemicals in S2 cells. However, the 0.2-, 0.5- and 0.8-kb DNAs of Cyp6a8 showed 13-24-, 4-5- and 2.2-2.7-fold induction with caffeine, PB and DDT, respectively. These DNAs also showed a 2-3-fold synergistic effect of caffeine and PB but not of caffeine and DDT. The results suggest that the cis-regulatory elements for all three chemicals are located within the -11/-199 DNA of Cyp6a8. Furthermore, caffeine and PB inductions appear to be mediated via different cis-elements, whereas caffeine and DDT induction may involve common regulatory elements. These stably transformed cell lines should help understand the mechanism of resistance-associated Cyp gene overexpression in Drosophila.

The effects of caffeine on sleep in Drosophila require PKA activity, but not the adenosine receptor

Caffeine is one of the most widely consumed stimulants in the world and has been proposed to promote wakefulness by antagonizing function of the adenosine A2A receptor. Here, we show that chronic administration of caffeine reduces and fragments sleep in Drosophila and also lengthens circadian period. To identify the mechanisms underlying these effects of caffeine, we first generated mutants of the only known adenosine receptor in flies (dAdoR), which by sequence is most similar to the mammalian A2A receptor. Mutants lacking dAdoR have normal amounts of baseline sleep, as well as normal homeostatic responses to sleep deprivation. Surprisingly, these mutants respond normally to caffeine. On the other hand, the effects of caffeine on sleep and circadian rhythms are mimicked by a potent phosphodiesterase inhibitor, IBMX (3-isobutyl-1-methylxanthine). Using in vivo fluorescence resonance energy transfer imaging, we find that caffeine induces widespread increase in cAMP levels throughout the brain. Finally, the effects of caffeine on sleep are blocked in flies that have reduced neuronal PKA activity. We suggest that chronic administration of caffeine promotes wakefulness in Drosophila, at least in part, by inhibiting cAMP phosphodiesterase activity.

Juvenile hormone regulation of Drosophila Epac--a guanine nucleotide exchange factor

Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to characterize the effects of juvenile hormone (JH) on Epac (Exchange Protein directly Activated by Cyclic AMP; NM_001103732), a guanine nucleotide exchange factor for Rap1 in Drosophila S2 cells. JH treatment led to a rapid, dose-dependent increase in Epac relative expression ratio (RER) when compared to treatment with methyl linoleate (MLA) that lacks biological activity. The minimal level of hormone needed to elicit a response was 100 ng/ml. Time-course studies indicated a significant rise in the RER 1h after treatment. S2 cells were challenged with 20-hydroxyecdysone and a series of compounds similar in structure to JH to determine the specificity of the response. Methoprene and JH III displayed the greatest increases in RER. Late third instar (96 h) Drosophila were exposed to diet containing methoprene (500 ng/g diet); significantly higher RERs for Epac were observed 12h after exposure. JH had no effect on Epac RERs in the human cell line HEK-293.