Temporal dynamics of the ABC transporter response to insecticide treatment: insights from the malaria vector Anopheles stephensi

Overexpression of ABCB transporter genes confer multiple insecticide tolerances in Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Bactrocera dorsalis is a notable invasive pest that has developed resistance to several commonly used insecticides in the field, such as avermectin, beta-cypermethrin and malathion. Investigating the mechanisms of insecticide resistance in this pest is of paramount importance for ensuring its effective control. The ATP-binding cassette transporter subfamily B (ABCB) genes, responsible for encoding transmembrane efflux transporters, represent a potential source of insecticide detoxification activity or transportation that remains largely unexplored in B. dorsalis. In this study, seven BdABCB genes were identified and comprehensive analyzed based on the latest genome and transcriptome dataset. Subsequently, we characterized the expression profiles of these genes across different development stages and tissues, as well as under different insecticide exposures. The results showed that the BdABCB genes were expressed at all stages in B. dorsalis, with BdABCB2 and BdABCB7 being highly expressed in the pupal stage, while BdABCB5 and BdABCB6 were highly expressed in the larval stage. Besides, the BdABCBs were highly expressed in the detoxification metabolic tissues. Among them, BdABCB5 and BdABCB6 were significantly overexpressed in the midgut and Malpighian tubules, respectively. Furthermore, with the exception of BdABCB6, the expression levels of the other six BdABCBs were significantly up-regulated following induction with avermectin, beta-cypermethrin and malathion. Six BdABCBs (BdABCB1-5 and BdABCB7) were knocked down by RNA interference, and the interference efficiencies were 46.58%, 39.50%, 45.60%, 33.74%, 66.37% and 63.83%, respectively. After injecting dsBdABCBs, the mortality of flies increased by 25.23% to 39.67% compared to the control upon exposure to the three insecticides. These results suggested that BdABCBs play crucial roles in the detoxification or tolerance of B. dorsalis to multiple insecticides.

Pb exposure causes non-linear accumulation of Pb in D. melanogaster controlled by metallothionein B and exerts ecological effects

Pb pollution can harm human health and the ecosystem. Therefore, it is worthwhile to study the metabolic processes of heavy metals in individual bodies and their influence on ecological systems. In this work, we analyzed the genetic responses and physiological changes of D. melanogaster which took diets exposed to different doses of Pb using transcriptomic analysis, ICP-MS, and various other physiological methods. We found that the Pb accumulated in D. melanogaster in a nonlinear pattern with the increase of Pb content in food. Metallothioneins (Mtns), especially the MtnB directly affects the accumulation and excretion of metal Pb in D. melanogaster, and causes the nonlinear accumulation. Metal regulatory transcription factor-1 (MTF-1) is involved in the regulation of Pb-induced high expressions of Mtns. Furthermore, an interaction between the metal metabolism pathway and xenobiotic response pathway leads to the cross-tolerances of Pb-exposed D. melanogaster to insecticides and other toxins. The oxidative stress induced by Pb toxicity may be the bridge between them. Our findings provide a physiological and molecular genetic basis for further study of the accumulation and metabolism of Pb in D. melanogaster.

ABCH2 transporter mediates deltamethrin uptake and toxicity in the malaria vector Anopheles coluzzii

Contact insecticides are primarily used for the control of Anopheles malaria vectors. These chemicals penetrate mosquito legs and other appendages; the first barriers to reaching their neuronal targets. An ATP-Binding Cassette transporter from the H family (ABCH2) is highly expressed in Anopheles coluzzii legs, and further induced upon insecticide exposure. RNAi-mediated silencing of the ABCH2 caused a significant increase in deltamethrin mortality compared to control mosquitoes, coincident with a corresponding increase in 14C-deltamethrin penetration. RT-qPCR analysis and immunolocalization revealed ABCH2 to be mainly localized in the legs and head appendages, and more specifically, the apical part of the epidermis, underneath the cuticle. To unravel the molecular mechanism underlying the role of ABCH2 in modulating pyrethroid toxicity, two hypotheses were investigated: An indirect role, based on the orthology with other insect ABCH transporters involved with lipid transport and deposition of CHC lipids in Anopheles legs which may increase cuticle thickness, slowing down the penetration rate of deltamethrin; or the direct pumping of deltamethrin out of the organism. Evaluation of the leg cuticular hydrocarbon (CHC) content showed no affect by ABCH2 silencing, indicating this protein is not associated with the transport of leg CHCs. Homology-based modeling suggested that the ABCH2 half-transporter adopts a physiological homodimeric state, in line with its ability to hydrolyze ATP in vitro when expressed on its own in insect cells. Docking analysis revealed a deltamethrin pocket in the homodimeric transporter. Furthermore, deltamethrin-induced ATP hydrolysis in ABCH2-expressing cell membranes, further supports that deltamethrin is indeed an ABCH2 substrate. Overall, our findings pinpoint ABCH2 participating in deltamethrin toxicity regulation.

Time- and dose-dependent detoxification and reproductive endocrine disruption induced by tetrabromobisphenol A (TBBPA) in mussel Mytilus galloprovincialis

As a typical brominated flame retardant (BFR), tetrabromobisphenol A (TBBPA) has been frequently detected in both biotic and abiotic matrices in marine environment. Our previous study found that genes related to metabolism phase I/II/III as well as steroid metabolism in Mytilus galloprovincialis were significantly altered by TBBPA treatment. However, the time- and dose-dependent response profiles of these genes to TBBPA exposure were rarely reported. In this study, the time- and dose-dependent effects of TBBPA on detoxification and reproductive endocrine disruption in M. galloprovincialis were explored by evaluating the responses of related gene expressions, enzymatic activities and gametogenesis to different concentrations of TBBPA (0.6, 3, 15, 75 and 375 μg/L) for different durations (14, 21 and 28 days). The results showed that the TBBPA accumulation increased linearly with the increases of exposure time and dose. Cytochrome P450 family 3 (CYP3A1-like) cooperated with CYP4Y1 for phase I biotransformation of TBBPA in mussels. The dose-response curves of phase II/III genes (glutathione-S-transferase (GST), P-glycoprotein (ABCB), and multidrug resistance protein (ABCC)) showed similar response profiles to TBBPA exposure. The common induction of phase I/II/III (CYPs, GST, ABCB and ABCC) suggested TBBPA detoxification regulation in mussels probably occurred in a step-wise manner. Concurrently, direct sulfation mediated by sulfotransferases (SULTs) on TBBPA was also the vital metabolic mechanism for TBBPA detoxification, which was supported by the coincidence between up-regulation of SULT1B1 and TBBPA accumulation. The significant promotion of steroid sulfatase (STS) might result from TBBPA-sulfate catalyzed by SULT1B1 due to its chemical similarity to estrone-sulfate. Furthermore, the promotion of gametogenesis was consistent with the induction of STS, suggesting that STS might interrupt steroids hydrolysis process and was responsible for reproductive endocrine disruption in M. galloprovincialis. This study provides a better understanding of the detoxification and endocrine-disrupting mechanisms of TBBPA.

miRNA novel_268 targeting NlABCG3 is involved in nitenpyram and clothianidin resistance in Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive pests that seriously threatens the high-quality and safe production of rice. However, due to the unscientific use of chemical insecticides, N. lugens has developed varying levels of resistance to insecticides, including nitenpyram and clothianidin. The ATP-binding cassette (ABC) transporter plays a nonnegligible role in phase III of the detoxification process, which may play an important role in insecticide resistance. In the present study, NlABCG3 was significantly overexpressed in both the NR and CR populations compared with susceptible populations. Silencing NlABCG3 significantly increased the susceptibility of BPH to nitenpyram and clothianidin. In addition, RNAi-mediated knockdown of three key genes in the miRNA biogenesis pathway altered the level of NlABCG3. Subsequently, the luciferase reporter assays demonstrated that novel_268 binds to the NlABCG3 coding region and downregulates its expression. Furthermore, injection of miRNA inhibitors or mimics of novel_268 significantly altered the susceptibility of N. lugens to nitenpyram and clothianidin. These results suggest that miRNA novel_268 targeting NlABCG3 is involved in nitenpyram and clothianidin resistance in N. lugens. These findings may help to enhance our knowledge of the transcriptional regulation of the ABC transporter that mediate insecticide resistance in N. lugens.

Xenobiotic responses in insects

Insects have evolved a powerful detoxification system to protect themselves against environmental and anthropogenic xenobiotics including pesticides and nanoparticles. The resulting tolerance to insecticides is an immense problem in agriculture. In this study, we summarize advances in our understanding of insect xenobiotic responses: the detoxification strategies and the regulation mechanisms against xenobiotics including nanoparticles, the problem of response specificity and the potential usefulness of this study field for an elaborate pest management. In particular, we highlight that versatility of the detoxification system relies on the relatively unspecific recognition of a broad range of potential toxic substances that trigger either of various canonical xenobiotic responses signaling pathways, including CncC/Keap1, HR96, AHR/ARNT, GPCR, and MAPK/CREB. However, it has emerged that the actual response to an inducer may nevertheless be specific. There are two nonexclusive possibilities that may explain response specificity: (1) differential cross-talk between the known pathways and (2) additional, yet unidentified regulators and pathways of detoxification. Hence, a deeper and broader understanding of the regulation mechanisms of xenobiotic response in insects in the future might facilitate the development and application of highly efficient and environmentally friendly pest control methods, allowing us to face the challenge of the world population growth.

Transcriptomic analysis of resistance and short-term induction response to pyrethroids, in Anopheles coluzzii legs

BACKGROUND

Insecticide-treated bed nets and indoor residual spraying comprise the major control measures against Anopheles gambiae sl, the dominant vector in sub-Saharan Africa. The primary site of contact with insecticide is through the mosquitoes' legs, which represents the first barrier insecticides have to bypass to reach their neuronal targets. Proteomic changes and leg cuticle modifications have been associated with insecticide resistance that may reduce the rate of penetration of insecticides. Here, we performed a multiple transcriptomic analyses focusing on An. coluzzii legs.

RESULTS

Firstly, leg-specific enrichment analysis identified 359 genes including the pyrethroid-binder SAP2 and 2 other chemosensory proteins, along with 4 ABCG transporters previously shown to be leg enriched. Enrichment of gene families included those involved in detecting chemical stimuli, including gustatory and ionotropic receptors and genes implicated in hydrocarbon-synthesis. Subsequently, we compared transcript expression in the legs of a highly resistant strain (VK7-HR) to both a strain with very similar genetic background which has reverted to susceptibility after several generations without insecticide pressure (VK7-LR) and a lab susceptible population (NG). Two hundred thirty-two differentially expressed genes (73 up-regulated and 159 down-regulated) were identified in the resistant strain when compared to the two susceptible counterparts, indicating an over-expression of phase I detoxification enzymes and cuticular proteins, with decrease in hormone-related metabolic processes in legs from the insecticide resistant population. Finally, we analysed the short-term effect of pyrethroid exposure on An. coluzzii legs, comparing legs of 1 h-deltamethrin-exposed An. coluzzii (VK7-IN) to those of unexposed mosquitoes (VK7-HR) and identified 348 up-regulated genes including those encoding for GPCRs, ABC transporters, odorant-binding proteins and members of the divergent salivary gland protein family.

CONCLUSIONS

The data on An. coluzzii leg-specific transcriptome provides valuable insights into the first line of defense in pyrethroid resistant and short-term deltamethrin-exposed mosquitoes. Our results suggest that xenobiotic detoxification is likely occurring in legs, while the enrichment of sensory proteins, ABCG transporters and cuticular genes is also evident. Constitutive resistance is primarily associated with elevated levels of detoxification and cuticular genes, while short-term insecticide-induced tolerance is linked with overexpression of transporters, GPCRs and GPCR-related genes, sensory/binding and salivary gland proteins.

Transcriptome Analysis of Aedes albopictus (Diptera: Culicidae) Larvae Exposed With a Sublethal Dose of Haedoxan A

Aedes albopictus is the vector of arbovirus diseases including yellow fever, dengue, Zika virus, and chikungunya fever, and it poses an enormous threat to human health worldwide. Previous studies have revealed that haedoxan A (HA), which is an insecticidal sesquilignan from Phryma leptostachya L., is a highly effective natural insecticide for managing mosquitoes and houseflies; however, the mechanisms underlying the response of Ae. albopictus after treatment with sublethal concentrations of HA is not clear. Here, high-throughput sequencing was used to analyze the gene expression changes in Ae. albopictus larvae after treatment with the LC30 of HA. In total, 416 differentially expressed genes (DEGs) were identified, including 328 upregulated genes and 88 downregulated genes. Identification and verification of related DEGs were performed by RT-qPCR. The results showed that two P450 unigenes (CYP4C21 and CYP304A1), one carboxylesterase, and one ABC transporter (ABCG1) were induced by HA, which indicated that these detoxifying enzyme genes might play a major role in the metabolic and detoxification processes of HA. Additionally, acetylcholine receptor subunit ɑ2 (AChRα2), AChRα5, AChRα9, and the glutamate receptor ionotropic kainate 2 (GRIK2) were found to be upregulated in HA-treated larvae, suggesting that HA affected the conduction of action potentials and synaptic transmission by disrupting the function of neural receptors. These results provide a foundation for further elucidating the target of HA and the mechanism of detoxification metabolism in Ae. albopictus.

Functional analysis of ABCG and ABCH transporters from the red flour beetle, Tribolium castaneum

BACKGROUND

ATP-binding cassette transporter (ABC transporter) subfamilies ABCA-C and ABCG-H have been implicated in insecticide detoxification, mostly based on findings of elevated gene expression in response to insecticide treatment. We previously characterized TcABCA-C genes from the model beetle and pest Tribolium castaneum and demonstrated that TcABCA and TcABCC genes are involved in the elimination of diflubenzuron, because RNA interference (RNAi)-mediated gene silencing increased susceptibility. In this study, we focused on the potential functions of TcABCG and TcABCH genes in insecticide detoxification.

RESULTS

When we silenced the expression of TcABCG-H genes using RNAi, we noticed a previously unreported developmental RNAi phenotype for TcABCG-4F, which is characterized by 50% mortality and ecdysial arrest during adult moult. When we knocked down the Drosophila brown orthologue TcABCG-XC, we did not obtain apparent eye colour phenotypes but did observe a loss of riboflavin uptake by Malpighian tubules. Next, we determined the expression profiles of all TcABCG-H genes in different tissues and developmental stages and analysed transcript levels in response to treatment with four chemically unrelated insecticides. We found that some genes were specifically upregulated after insecticide treatment. However, when we determined insecticide-induced mortalities in larvae that were treated by double-stranded RNA injection to silence those TcABCG-H genes that were upregulated, we did not observe a significant increase in susceptibility to insecticides.

CONCLUSION

Our findings suggest that the observed insecticide-dependent induction of TcABCG-H gene expression reflects an unspecific stress response, and hence underlines the significance of functional studies on insecticide detoxification. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

From Global to Local-New Insights into Features of Pyrethroid Detoxification in Vector Mosquitoes

The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. As a result, the prevalence of pyrethroid-resistant genetic markers in natural mosquito populations has increased at an alarming rate. This review details recent advances in the understanding of specific mechanisms associated with pyrethroid resistance, with emphasis on features of insecticide detoxification and the interdependence of multiple cellular pathways. Together, these advances add important context to the understanding of the processes that are selected in resistant mosquitoes. Specifically, before pyrethroids bind to their targets on motoneurons, they must first permeate the outer cuticle and diffuse to inner tissues. Resistant mosquitoes have evolved detoxification mechanisms that rely on cytochrome P450s (CYP), esterases, carboxyesterases, and other oxidation/reduction (redox) components to effectively detoxify pyrethroids to nontoxic breakdown products that are then excreted. Enhanced resistance mechanisms have evolved to include alteration of gene copy number, transcriptional and post-transcriptional regulation of gene expression, as well as changes to cellular signaling mechanisms. Here, we outline the variety of ways in which detoxification has been selected in various mosquito populations, as well as key gene categories involved. Pathways associated with potential new genes of interest are proposed. Consideration of multiple cellular pathways could provide opportunities for development of new insecticides.

Transcriptional Response of ATP-Binding Cassette (ABC) Transporters to Insecticide in the Brown Planthopper, Nilaparvata lugens (Stål)

The ATP-binding cassette (ABC) transporter superfamily is one of the largest groups of proteins and plays a non-negligible role in phase III of the detoxification process, which is highly involved in the response of insects to environmental stress (plant secondary metabolites and insecticides). In the present study, in Nilaparvata lugens, we identified 32 ABC transporters, which are grouped into eight subfamilies (ABCA–H) based on phylogenetic analysis. The temporal and spatial expression profiles suggested that the nymphal stages (1st–5th) and adult males showed similarity, which was different from eggs and adult females, and NlABCA1, NlABCA2, NlABCB6, NlABCD2, NlABCG4, NlABCG12, NlABCG15, and NlABCH1 were highly expressed in the midgut and Malpighian tubules. In addition, ABCG12, which belongs to the ABC transporter G subfamily, was significantly upregulated after exposure to sulfoxaflor, nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. Moreover, verapamil significantly increased the sensitivity of N. lugens to nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. These results provide a basis for further research on ABC transporters involved in detoxification in N. lugens, and for a more comprehensive understanding of the response of N. lugens to environmental stress.

Comparative transcriptome profiling reveals candidate genes related to insecticide resistance of Glyphodes pyloalis

Glyphodes pyloalis Walker (Lepidoptera: Pyralididae) is a common pest in sericulture and has developed resistance to different insecticides. However, the mechanisms involved in insecticide resistance of G. pyloalis are poorly understood. Here, we present the first whole-transcriptome analysis of differential expression genes in insecticide-resistant and susceptible G. pyloalis. Clustering and enrichment analysis of DEGs revealed several biological pathways and enriched Gene Ontology terms were related to detoxification or insecticide resistance. Genes involved in insecticide metabolic processes, including cytochrome P450, glutathione S-transferases and carboxylesterase, were identified in the larval midgut of G. pyloalis. Among them, CYP324A19, CYP304F17, CYP6AW1, CYP6AB10, GSTs5, and AChE-like were significantly increased after propoxur treatment, while CYP324A19, CCE001c, and AChE-like were significantly induced by phoxim, suggesting that these genes were involved in insecticide metabolism. Furthermore, the sequence variation analysis identified 21 single nucleotide polymorphisms within CYP9A20, CYP6AB47, and CYP6AW1. Our findings reveal many candidate genes related to insecticide resistance of G. pyloalis. These results provide novel insights into insecticide resistance and facilitate the development of insecticides with greater specificity to G. pyloalis.

Age- and sex-related ABC transporter expression in pyrethroid-susceptible and -resistant Aedes aegypti

Resistance mechanisms to synthetic insecticides often include point mutations and increased expression of genes encoding detoxification enzymes. Since pyrethroids are the main adulticides used against Aedes aegypti, which vectors pathogens such as Zika virus, understanding resistance to this insecticide class is of significant relevance. We focused on adenosine triphosphate (ATP)-binding cassette (ABC) transporters in the pyrethroid-resistant Puerto Rico (PR) strain of Ae. aegypti. We investigated the expression patterns of six ABC transporters previously characterized as differentially expressed in insecticide-challenged mosquitoes, or increased mRNA expression in pyrethroid-resistant Ae. aegypti, by comparing PR to the Rockefeller (Rock) susceptible strain. No constitutive differential expression between strains was detected, but expression differences for these genes was influenced by sex and age, suggesting that their role is independent from resistance in PR. Instead, ABC transporters may be induced after insecticide exposure. Challenging mosquitoes with deltamethrin, with or without ABC transporter modulators, showed that Rock and PR responded differently, but a contribution of ABC transporters to deltamethrin toxicity is suspected. Moreover, the effect of dexamethasone, which enhanced the inhibition of nerve firing by deltamethrin, was observed using a Drosophila central nervous system preparation, showing synergy of these two compounds through the potential inhibition of ABC transporters.

Gene silencing through RNAi and antisense Vivo-Morpholino increases the efficacy of pyrethroids on larvae of Anopheles stephensi

Background

Insecticides are still at the core of insect pest and vector control programmes. Several lines of evidence indicate that ABC transporters are involved in detoxification processes against insecticides, including permethrin and other pyrethroids. In particular, the ABCG4 gene, a member of the G subfamily, has consistently been shown to be up-regulated in response to insecticide treatments in the mosquito malaria vector Anopheles stephensi (both adults and larvae).

Methods

To verify the actual involvement of this transmembrane protein in the detoxification process of permethrin, bioassays on larvae of An. stephensi, combining the insecticide with a siRNA, specifically designed for the inhibition of ABCG4 gene expression were performed. Administration to larvae of the same siRNA, labeled with a fluorescent molecule, was effected to investigate the systemic distribution of the inhibitory RNA into the larval bodies. Based on siRNA results, similar experiments using antisense Vivo-Morpholinos (Vivo-MOs) were effected. These molecules, compared to siRNA, are expected to guarantee a higher stability in environmental conditions and in the insect gut, and present thus a higher potential for future in-field applications.

Results

Bioassays using two different concentrations of siRNA, associated with permethrin, led to an increase of larval mortality, compared with results with permethrin alone. These outcomes confirm that ABCG4 transporter plays a role in the detoxification process against the selected insecticide. Moreover, after fluorescent labelling, it was shown the systemic dissemination of siRNA in different body districts of An. stephensi larvae, which suggest a potential systemic effect of the molecule. At the same time, results of Vivo-MO experiments were congruent with those obtained using siRNA, thus confirming the potential of ABCG4 inhibition as a strategy to increase permethrin susceptibility in mosquitoes. For the first time, Vivo-MOs were administered in water to larvae, with evidence for a biological effect.

Conclusions

Targeting ABCG4 gene for silencing through both techniques resulted in an increased pyrethroid efficacy. These results open the way toward the possibility to exploit ABCG4 inhibition in the context of integrated programmes for the control An. stephensi mosquitoes and malaria transmission.

ATP-Binding Cassette (ABC) Transporter Genes Involved in Pyrethroid Resistance in the Malaria Vector Anopheles sinensis: Genome-Wide Identification, Characteristics, Phylogenetics, and Expression Profile

background: The ATP-binding cassette (ABC) transporters family is one of the largest families of membrane proteins existing in all living organisms. Pyrethroid resistance has become the largest unique obstacle for mosquito control worldwide. ABC transporters are thought to be associated with pyrethroid resistance in some agricultural pests, but little information is known for mosquitoes. Herein, we investigated the diversity, location, characteristics, phylogenetics, and evolution of ABC transporter family of genes in the Anopheles sinensis genome, and identified the ABC transporter genes associated with pyrethroid resistance through expression profiles using RNA-seq and qPCR. Results: 61 ABC transporter genes are identified and divided into eight subfamilies (ABCA-H), located on 22 different scaffolds. Phylogenetic and evolution analyses with ABC transporters of A. gambiae, Drosophila melanogaster, and Homo sapiens suggest that the ABCD, ABCG, and ABCH subfamilies are monophyly, and that the ABCC and ABCG subfamilies have experienced a gene duplication event. Both RNA-seq and qPCR analyses show that the AsABCG28 gene is uniquely significantly upregulated gene in all three field pyrethroid-resistant populations (Anhui, Chongqing, and Yunnan provinces) in comparison with a laboratory-susceptible strain from Jiangsu province. The AsABCG28 is significantly upregulated at 12-h and 24-h after deltamethrin exposure in three-day-old female adults. Conclusion: This study provides the information frame for ABC transporter subfamily of genes, and lays an important basis for the better understanding and further research of ABC transporter function in insecticide toxification. The AsABCG28 gene is associated with pyrethroid detoxification, and it functions at later period in the detoxification process for xenobiotics transportation.

Insecticide Exposure Triggers a Modulated Expression of ABC Transporter Genes in Larvae of Anopheles gambiae s.s

Insecticides remain a main tool for the control of arthropod vectors. The urgency to prevent the insurgence of insecticide resistance and the perspective to find new target sites, for the development of novel molecules, are fuelling the study of the molecular mechanisms involved in insect defence against xenobiotic compounds. In this study, we have investigated if ATP-binding cassette (ABC) transporters, a major component of the defensome machinery, are involved in defence against the insecticide permethrin, in susceptible larvae of the malaria vector Anopheles gambiae sensu stricto. Bioassays were performed with permethrin alone, or in combination with an ABC transporter inhibitor. Then we have investigated the expression profiles of five ABC transporter genes at different time points following permethrin exposure, to assess their expression patterns across time. The inhibition of ABC transporters increased the larval mortality by about 15-fold. Likewise, three genes were up-regulated after exposure to permethrin, showing different patterns of expression across the 48 h. Our results provide the first evidences of ABC transporters involvement in defence against a toxic in larvae of An. gambiae s.s. and show that the gene expression response is modulated across time, being continuous, but stronger at the earliest and latest times after exposure.

Paternal leakage and mtDNA heteroplasmy in Rhipicephalus spp. ticks

Paternal leakage of mitochondrial DNA (mtDNA) and heteroplasmy have been recently described in several animal species. In arthropods, by searching in the Scopus database, we found only 23 documented cases of paternal leakage. Therefore, although arthropods represent a large fraction of animal biodiversity, this phenomenon has been investigated only in a paucity of species in this phylum, thus preventing a reliable estimate of its frequency. Here, we investigated the occurrence of paternal leakage and mtDNA heteroplasmy in ticks belonging to one of the most significant tick species complexes, the so-called Rhipicephalus sanguineussensu lato. By developing a multiplex allele-specific PCR assay targeting a fragment of the 12S rRNA ribosomal region of the mtDNA, we showed the occurrence of paternal leakage and mtDNA heteroplasmy in R. sanguineuss.l. ticks originated from experimental crosses, as well as in individuals collected from the field. Our results add a new evidence of paternal leakage in arthropods and document for the first time this phenomenon in ticks. Furthermore, they suggest the importance of using allele-specific assays when searching for paternal leakage and/or heteroplasmy, as standard sequencing methods may fail to detect the rare mtDNA molecules.

Changes in the expression of four ABC transporter genes in response to imidacloprid in Bemisia tabaci Q (Hemiptera: Aleyrodidae)

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), a globally invasive species complex that causes serious damage to field crops, has developed resistance to imidacloprid and many other pesticides. Insect detoxify to pesticides may partially depend on ABC transporters, which contribute to the detoxification of xenobiotics. To determine whether genes in the ABCG subfamily are involved in imidacloprid detoxification in B. tabaci Q, we cloned four ABCG subfamily genes based on the published MED/Q genome and on our previous study of the transcriptional response of ABC transporters in B. tabaci Q adults to imidacloprid. As indicated by the quantification of mRNA levels after a 6-h exposure, the expression level of ABCG3 was 3.3-fold higher in B. tabaci Q adults exposed to 100 μg/mL imidacloprid rather than to the buffer control. The expression level of ABCG3 was higher in females than in males but did not significantly differ among eggs or nymphal stages and did not significantly differ among head, thorax, and abdomen tissues of adults. Knockdown of ABCG3 via RNA interference significantly increased the mortality of imidacloprid-treated laboratory and field-collected adults of B. tabaci Q. These results indicate that the ABCG3 gene may be involved in imidacloprid detoxification by B. tabaci Q.

Adenosine Triphosphate-Binding Cassette Transporters Are Not Involved In the Detoxification of Azadirachta indica Extracts In Anopheles stephensi Larvae

Detoxifying pathways of mosquitoes against the neem (Azadirachta indica) extracts are still unclear. The aim of the present study was to investigate the role of adenosine triphosphate-binding cassette (ABC) transporters in this process in Anopheles stephensi, one of the main malaria vectors in southern Asia. Third-stage larvae of An. stephensi were fed with fish food alone or in combination with neem extract at 0.5%, 1%, 5%, and 10%. Six ABC-transporter genes from 3 different subfamilies (B, C, and G) were analyzed to assess their relative expression compared with controls. A bioassay was also performed to assess larval mortality rate at different concentrations and in combination with verapamil, an ABC-transporter inhibitor. No significant variation in the expression levels of any transporter belonging to the B, C, and G subfamilies was detected. Furthermore, the use of verapamil did not induce an increase in mortality at any of the tested neem extract concentrations, indicating that ABC transporters are not involved in the detoxification of neem extracts in An. stephensi larvae.

How do oral insecticidal compounds cross the insect midgut epithelium?

The use of oral insecticidal molecules (small molecules, peptides, dsRNA) via spray or plant mediated applications represents an efficient way to manage damaging insect species. With the exception of Bt toxins that target the midgut epithelium itself, most of these compounds have targets that lie within the hemocoel (body) of the insect. Because of this, one of the greatest factors in determining the effectiveness of an oral insecticidal compound is its ability to traverse the gut epithelium and enter the hemolymph. However, for many types of insecticidal compounds, neither the pathway taken across the gut nor the specific genes which influence uptake are fully characterized. Here, we review how different types of insecticidal compounds enter or cross the midgut epithelium through passive (diffusion) or active (transporter based, endocytosis) routes. A deeper understanding of how insecticidal molecules cross the gut will help to best utilize current insecticides and also provide for more rational design of future ones.

Exposure to amitraz, fipronil and permethrin affects cell viability and ABC transporter gene expression in an Ixodes ricinus cell line

BACKGROUND

Over-expression of ATP-binding cassette (ABC) transporter proteins has been implicated in resistance of ticks to acaricides. Tick cell lines are useful for investigating resistance mechanisms, as development of an in vitro model for the study of acaricide resistance would contribute to improving knowledge of the molecular basis behind drug processing and exclusion in ticks. In the present study, cultures of the Ixodes ricinus-derived cell line IRE/CTVM19 were treated with the acaricides amitraz, permethrin or fipronil to determine modulation of ABC transporter gene expression. Cells were treated with different drug concentrations (25, 50, 100, 150 μM) and incubated for ten days. Cell morphology, viability, metabolic activity and relative expression of ABC (B1, B6, B8 and B10) genes were determined at day 10 post-treatment.

RESULTS

Cell morphology determined by light microscopy was altered following treatment with all drugs, but only at high concentrations, while total cell numbers decreased with increasing drug dose. Cell viability determined by trypan blue exclusion was not significantly different from untreated controls (P > 0.1) following treatment with amitraz and permethrin, but high concentrations of fipronil caused decrease (up to 37%, P < 0.01) in viability. At all drug concentrations, fipronil and permethrin induced dose-dependent reduction in cell metabolic activity measured by MTT assay (P < 0.01). Quantitative RT-PCR showed that the drugs significantly affected expression of ABC genes. In particular, fipronil treatment downregulated ABCB1 (P < 0.001) and upregulated ABCB6, ABCB8 and ABCB10 (P < 0.01); amitraz treatment down regulated ABCB1 (significant difference between 25 and 150 μM, P < 0.001) and upregulated ABCB8 and ABCB10 at lower concentrations (25 and 50 μM, P < 0.05); and permethrin upregulated ABCB6, ABCB8 and ABCB10 only at 150 μM (P < 0.01).

CONCLUSIONS

The adverse effects on cell viability and metabolic activity, and changes in expression of different ABC transporter genes, detected in IRE/CTVM19 cells following treatment with amitraz, permethrin and fipronil, support the proposed application of tick cell lines as in vitro models for the study of resistance to these acaricides in ticks.

Cap n collar transcription factor regulates multiple genes coding for proteins involved in insecticide detoxification in the red flour beetle, Tribolium castaneum

In invertebrates, a heterodimer of xenobiotic transcription factors, cap n collar C isoform (CncC) and muscle aponeurosis fibromatosis (Maf) mediate cellular defense. In insects, these proteins regulate expression of genes involved in insecticide detoxification. In the current study, we performed sequencing of cDNA copied from RNA isolated from Tribolium castaneum pyrethroid resistant strain (QTC279) beetles injected with CncC or green fluorescence protein (GFP, control) dsRNA. Differential expression analysis of sequences identified 662 genes that showed a decrease and 91 genes that showed an increase in expression (p value ≤ 0.01 and log2 fold change of ≥ 1.5) in CncC knockdown insects when compared to their expression in control insects. We selected a subset of 27 downregulated genes and verified their differential expression using qRT-PCR. This subset of 27 genes included 21 genes with a predicted function in xenobiotic detoxification. RNAi and insecticide bioassays were employed to study the function of six of these genes coding for CYP4G7, CYP4G14, GST-1 and four ABC transporters, ABCA-UB, ABCA-A1 and ABCA-A1L and ABCA-9B involved in all three phases of insecticide detoxification. These data suggest that CncC regulates genes coding for proteins involved in detoxification of insecticides.

Gene expression modulation of ABC transporter genes in response to permethrin in adults of the mosquito malaria vector Anopheles stephensi

Living organisms have evolved an array of genes coding for detoxifying enzymes and efflux protein pumps, to cope with endogenous and xenobiotic toxic compounds. The study of the genes activated during toxic exposure is relevant to the area of arthropod vector control, since these genes are one of the targets upon which natural selection acts for the evolution of insecticide resistance. ATP-binding cassette (ABC) transporters participate to insecticide detoxification acting as efflux pumps, that reduce the intracellular concentration of toxic compounds, or of their metabolic derivatives. Here we analyzed the modulation of the expression of six genes coding for ABC transporters, after the exposure of adult females and males of the mosquito Anopheles stephensi, a major malaria vector in Asia, to permethrin. Male and female mosquitoes were exposed to insecticide for one hour, then the expression profiles of the ABC transporter genes AnstABCB2, AnstABCB3, AnstABCB4, AnstABCBmember6, AnstABCC11, and AnstABCG4 were analysed after one and 24h. Our results showed that three genes (AnstABCB2, AnstABCBmember6, AnstABCG4) were up-regulated in both sexes; two of these (AnstABCBmember6 and AnstABCG4) have previously been shown to be up-regulated also in larval stages of An. stephensi, supporting a role for these genes in permethrin defence in larvae as well as in adults. Finally, the same ABC transporter genes were activated both in females and males; however, the timing of gene induction was different, with a prompter induction in females than in males.

Genome-wide analysis of ATP-binding cassette (ABC) transporters in the sweetpotato whitefly, Bemisia tabaci

Background

ABC transporter superfamily is one of the largest and ubiquitous groups of proteins. Because of their role in detoxification, insect ABC transporters have gained more attention in recent years. In this study, we annotated ABC transporters from a newly sequenced sweetpotato whitefly genome. Bemisia tabaci Q biotype is an emerging global invasive species that has caused extensive damages to field crops as well as ornamental plants.

Results

A total of 55 ABC transporters containing all eight described subfamilies (A to H) were identified in the B. tabaci Q genome, including 8 ABCAs, 3 ABCBs, 6 ABCCs, 2 ABCDs, 1 ABCE, 3 ABCFs, 23 ABCGs and 9 ABCHs. In comparison to other species, subfamilies G and H in both phloem- and blood-sucking arthropods are expanded. The temporal expression profiles of these 55 ABC transporters throughout B. tabaci developmental stages and their responses to imidacloprid, a neonicotinoid insecticide, were investigated using RNA-seq analysis. Furthermore, the mRNA expression of 24 ABC transporters (44% of the total) representing all eight subfamilies was confirmed by the quantitative real-time PCR (RT-qPCR). Furthermore, mRNA expression levels estimated by RT-qPCR and RNA-seq analyses were significantly correlated (r = 0.684, p < 0.01).

Conclusions

It is the first genome-wide analysis of the entire repertoire of ABC transporters in B. tabaci. The identification of these ABC transporters, their temporal expression profiles during B. tabaci development, and their response to a neonicotinoid insecticide lay the foundation for functional genomic understanding of their contribution to the invasiveness of B. tabaci.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3706-6) contains supplementary material, which is available to authorized users.

Analysis of Differentially Expressed Genes Related to Resistance in Spinosad- and Neonicotinoid-Resistant Musca domestica L. (Diptera: Muscidae) Strains

Background

The housefly is a global pest that has developed resistance to most insecticides applied against it. Resistance of the spinosad-resistant strain 791spin and the neonicotinoid-resistant 766b strain is believed to be due to metabolism. We investigate differentially expressed genes in these two resistant strains related to metabolism in comparison with an insecticide-susceptible reference strain.

Results

Genes involved in metabolism of xenobiotics were primarily up-regulated in resistant flies with some differences between resistant strains. The cyp4g98 and cyp6g4 genes proved interesting in terms of neonicotinoid resistance, while cyp4d9 was overexpressed in 791spin compared to spinosad-susceptible strains. GSTs, ESTs and UGTs were mostly overexpressed, but not to the same degree as P450s. We present a comprehensive and comparative picture of gene expression in three housefly strains differing significantly in their response to insecticides. High differential expression of P450s and genes coding for cuticle protein indicates a combination of factors involved in metabolic neonicotinoid and spinosad resistance.

Conclusion

Resistance in these strains is apparently not linked to the alteration of a single gene but is composed of several changes including differential expression of genes encoding metabolic detoxification enzymes.

The choreography of the chemical defensome response to insecticide stress: insights into the Anopheles stephensi transcriptome using RNA-Seq

Animals respond to chemical stress with an array of gene families and pathways termed “chemical defensome”. In arthropods, despite many defensome genes have been detected, how their activation is arranged during toxic exposure remains poorly understood. Here, we sequenced the transcriptome of Anopheles stephensi larvae exposed for six, 24 and 48 hours to the LD₅₀ dose of the insecticide permethrin to monitor transcriptional changes of defensome genes across time. A total of 177 genes involved in insecticide defense were differentially expressed (DE) in at least one time-point, including genes encoding for Phase 0, I, II, III and antioxidant enzymes and for Heat Shock and Cuticular Proteins. Three major patterns emerged throughout time. First, most of DE genes were down-regulated at all time-points, suggesting a reallocation of energetic resources during insecticide stress. Second, single genes and clusters of genes turn off and on from six to 48 hours of treatment, showing a modulated response across time. Third, the number of up-regulated genes peaked at six hours and then decreased during exposure. Our results give a first picture of how defensome gene families respond against toxicants and provide a valuable resource for understanding how defensome genes work together during insecticide stress.

Identification of Four ATP-Binding Cassette Transporter Genes in Cnaphalocrocis medinalis and Their Expression in Response to Insecticide Treatment

The ATP-binding cassette (ABC) transporters belong to a superfamily of genes involved in the transport of specific molecules across lipid membranes, as well as insecticide resistance, present in all living organisms. In this study, we combined the Cnaphalocrocis medinals transcriptome database with a bioinformatics approach to identify four C. medinals ABCs (CmABCs), including CmABCG1, CmABCG4, CmABCC2 and CmABCC3. Tissue expression analysis showed that these genes had a tissue-specific expression pattern. CmABCG1 had significantly higher expression in the haemolymph and head compared to the other tissues. The expression of CmABCG4, CmABCC2 and CmABCC3 was highest in the midgut, followed by expression in the fat body. The developmental stage expression analysis showed that CmABCG1, CmABCG4, CmABCC2 and CmABCC3 were mainly expressed in adults. The transcription of CmABCG1, CmABCG4 and CmABCC2 was significantly induced by chlorpyrifos. Taken together, the results of our study provided useful information for understanding of the detoxification system of C. medinalis.

Increased Expression of P-Glycoprotein Is Associated With Chlorpyrifos Resistance in the German Cockroach (Blattodea: Blattellidae)

A principal method for control of the German cockroach, Blattella germanica (L.), is the broad-spectrum organophosphorus insecticide, chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate); however, extensive and repeated application has resulted in the development of resistance to chlorpyrifos in this insect. Evidence suggests that ATP-binding cassette protein transporters, including P-glycoprotein, are involved in insecticide resistance. However, little is known of the role of P-glycoprotein in insecticide resistance in the German cockroach. Here, we developed a chlorpyrifos-resistant strain of German cockroach and investigated the relationship between P-glycoprotein and chlorpyrifos resistance using toxicity assays; inhibition studies with two P-glycoprotein inhibitors, verapamil and quinine; P-glycoprotein-ATPase activity assays; and western blotting analysis. After 23 generations of selection from susceptible strain cockroaches, we obtained animals with high resistance to chlorpyrifos. When P-glycoprotein-ATPase activity was inhibited by verapamil and quinine, we observed enhanced susceptibility to chlorpyrifos in both control and chlorpyrifos-resistant cockroaches. No significant alterations of P-glycoprotein expression or ATPase activity were observed in cockroaches acutely exposed to LD50 doses of chlorpyrifos for 24 h, while P-glycoprotein expression and ATPase activity were clearly elevated in the chlorpyrifos-resistant cockroach strain. Thus, we conclude that P-glycoprotein is associated with chlorpyrifos resistance in the German cockroach and that elevated levels of P-glycoprotein expression and ATPase activity may be an important mechanism of chlorpyrifos resistance in the German cockroach.

How heterogeneous is the involvement of ABC transporters against insecticides?

Understanding the molecular mechanisms underlying cellular defense against xenobiotic compounds is a main research issue in medical and veterinary entomology, as insecticide/acaricide resistance is a major threat in the control of arthropods. ABC transporters are recognized as a component of the detoxifying mechanism in arthropods. We investigated the possible involvement of ABC transporters in defense to the organophosphate insecticide temephos in the malarial vector Anopheles stephensi. We performed bioassays on larvae of An. stephensi, using insecticide alone and in combination with ABC-transporter inhibitors, to assess synergism between these compounds. Next, we investigated the expression profiles of six ABC transporter genes in larvae exposed to temephos. Surprisingly, neither bioassays nor gene expression analyses provided any evidence for a major role of ABC transporters in defense against temephos in An. stephensi. We thus decided to review existing literature to generate a record of other studies that failed to reveal a role for ABC transporters against particular insecticides/acaricides. A review of the scientific literature led to the recovery of 569 papers about ABC transporters; among these, 50 involved arthropods, and 10 reported negative results. Our study on An. stephensi and accompanying literature review highlight the heterogeneity that exists in ABC transporter involvement in defense/resistance mechanisms in arthropods.

Splice form variant and amino acid changes in MDR49 confers DDT resistance in transgenic Drosophila

The ATP-binding cassette (ABC) transporters represent a superfamily of proteins that have important physiological roles in both prokaryotes and eukaryotes. In insects, ABC transporters have previously been implicated in insecticide resistance. The 91-R strain of Drosophila melanogaster has been intensely selected with DDT over six decades. A recent selective sweeps analysis of 91-R implicated the potential role of MDR49, an ABC transporter, in DDT resistance, however, to date the details of how MDR49 may play a role in resistance have not been elucidated. In this study, we investigated the impact of structural changes and an alternative splicing event in MDR49 on DDT-resistance in 91-R, as compared to the DDT susceptible strain 91-C. We observed three amino acid differences in MDR49 when 91-R was compared with 91-C, and only one isoform (MDR49B) was implicated in DDT resistance. A transgenic Drosophila strain containing the 91-R-MDR49B isoform had a significantly higher LD₅₀ value as compared to the 91-C-MDR49B isoform at the early time points (6 h to 12 h) during DDT exposure. Our data support the hypothesis that the MDR49B isoform, with three amino acid mutations, plays a role in the early aspects of DDT resistance in 91-R.

Transcriptome of larvae representing the Rhipicephalus sanguineus complex

Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) is possibly the most widespread tick species worldwide, responsible for transmitting several vector-borne pathogens of medical and veterinary importance. Here, we explore the transcriptome of R. sanguineus s.l. larvae (Putignano strain). We sequenced total RNA from R. sanguineus s.l. larvae. A total of 15,566,986 short paired-end reads were de novo-assembled into 33,396 transcripts and then annotated and analyzed. Particular attention was paid to transcripts putatively encoding ATP-binding proteins, due to their importance as mechanisms of detoxification and acaricide resistance. Additionally, microsatellite loci were investigated, as these are useful markers for population genetic studies. The present data and analyses provide a comprehensive transcriptomic resource for R. sanguineus. The results presented here will aid further genetic and genomic studies of this important tick species.