The Malpighian tubule: rapid insights from post-genomic biology

The Role of TcCYP6K1 and TcCYP9F2 Influences Trehalose Metabolism under High-CO2 Stress in Tribolium castaneum (Coleoptera)

Cytochrome P450 monooxygenases (CYP), crucial detoxification enzymes in insects, are involved in the metabolism of endogenous substances as well as the activation and degradation of exogenous compounds. In this study, T. castaneum was utilized to investigate the roles of TcCYP6K1 and TcCYP9F2 genes influencing in the trehalose metabolism pathway under high-CO2 stress. By predicting the functional sequences of TcCYP6K1 and TcCYP9F2 genes and analyzing their spatiotemporal expression patterns, it was discovered that both genes belong to the CYP3 group and exhibit high expression levels during the larval stage, decreasing during the pupal stage, while showing high expression in the fatty body, intestine, and malpighian tubules. Furthermore, following the knockdown of TcCYP6K1 and TcCYP9F2 genes in combination with treating larvae with 75% CO2, it was observed that larval mortality increased, and glycogen content significantly decreased, while trehalose content increased significantly. Additionally, membrane-bound trehalase enzyme activity declined, TPS gene expression was significantly upregulated, GS gene expression was significantly downregulated, and ATP content showed a marked decrease. In conclusion, CYP genes are critical responsive genes of T. castaneum to high CO2 levels, potentially impacting the insect's resistance to carbon dioxide through their involvement in the synthesis or breakdown of the carbohydrate metabolism pathway. These findings could serve as a theoretical basis for the utilization of novel pesticides in low-oxygen grain storage techniques and offer new insights for environmentally friendly pest control strategies in grain storage.

Duplications and Losses of the Detoxification Enzyme Glycosyltransferase 1 Are Related to Insect Adaptations to Plant Feeding

Insects have developed sophisticated detoxification systems to protect them from plant secondary metabolites while feeding on plants to obtain necessary nutrients. As an important enzyme in the system, glycosyltransferase 1 (GT1) conjugates toxic compounds to mitigate their harm to insects. However, the evolutionary link between GT1s and insect plant feeding remains elusive. In this study, we explored the evolution of GT1s across different insect orders and feeding niches using publicly available insect genomes. GT1 is widely present in insect species; however, its gene number differs among insect orders. Notably, plant-sap-feeding species have the highest GT1 gene numbers, whereas blood-feeding species display the lowest. GT1s appear to be associated with insect adaptations to different plant substrates in different orders, while the shift to non-plant feeding is related to several losses of GT1s. Most large gene numbers are likely the consequence of tandem duplications showing variations in collinearity among insect orders. These results reveal the potential relationships between the evolution of GT1s and insect adaptation to plant feeding, facilitating our understanding of the molecular mechanisms underlying insect-plant interactions.

CRISPR/Cas9-Based Functional Characterization of SfUGT50A15 Reveals Its Roles in the Resistance of Spodoptera frugiperda to Chlorantraniliprole, Emamectin Benzoate, and Benzoxazinoids

UDP-glycosyltransferases (UGTs) are a diverse superfamily of enzymes. Insects utilize uridine diphosphate-glucose (UDP-glucose) as a glycosyl donor for glycosylation in vivo, involved in the glycosylation of lipophilic endosymbionts and xenobiotics, including phytotoxins. UGTs act as second-stage detoxification metabolizing enzymes, which are essential for the detoxification metabolism of insecticides and benzoxazine compounds. However, the UGT genes responsible for specific glycosylation functions in S. frugiperda are unclear at present. In this study, we utilized CRISPR/Cas9 to produce a SfUGT50A15-KO strain to explore its possible function in governing sensitivity to chemical insecticides or benzoxazinoids. The bioassay results suggested that the SfUGT50A15-KO strain was significantly more sensitive to chlorantraniliprole, emamectin benzoate, and benzoxazinoids than the wild-type strains. This finding suggests that the overexpression of the SfUGT50A15 gene may be linked to S. frugiperda resistance to pesticides (chlorantraniliprole and emamectin benzoate) as well as benzoxazinoids (BXDs).

Functional Characterization of CYP6QE1 and CYP6FV21 in Resistance to λ-Cyhalothrin and Imidacloprid in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) belong to a family of metabolic enzymes that are involved in the detoxification of insecticides. In this study, our bioassay results showed that a field-collected population of Bradysia odoriphaga displayed a moderate resistance to λ-cyhalothrin and imidacloprid. Compared to susceptible population, CYP6QE1 and CYP6FV21 were significantly overexpressed in the field population. The expression of CYP6QE1 and CYP6FV21 was more abundant in the third and fourth larval stages, and CYP6QE1 and CYP6FV21 were most highly expressed in the midgut and Malpighian tubules. Exposure to λ-cyhalothrin and imidacloprid significantly increased the expression levels of CYP6QE1 and CYP6FV21. Furthermore, the silencing of CYP6QE1 and CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to λ-cyhalothrin and imidacloprid. The overexpression of CYP6QE1 and CYP6FV21 significantly enhanced the tolerance of transgenic Drosophila melanogaster lines to λ-cyhalothrin and imidacloprid. In addition, molecular docking revealed that these two P450 proteins have strong binding affinity toward λ-cyhalothrin and imidacloprid insecticides. Taken together, these results indicate that the overexpression of CYP6QE1 and CYP6FV21 is responsible for resistance to λ-cyhalothrin and imidacloprid in B. odoriphaga.

Developmental and Nutritional Dynamics of Malpighian Tubule Autofluorescence in the Asian Tiger Mosquito Aedes albopictus

Malpighian tubules (MTs) are arthropod excretory organs crucial for the osmoregulation, detoxification and excretion of xenobiotics and metabolic wastes, which include tryptophan degradation products along the kynurenine (KYN) pathway. Specifically, the toxic intermediate 3-hydroxy kynurenine (3-HK) is metabolized through transamination to xanthurenic acid or in the synthesis of ommochrome pigments. Early investigations in Drosophila larval fat bodies revealed an intracellular autofluorescence (AF) that depended on tryptophan administration. Subsequent observations documented AF changes in the MTs of Drosophila eye-color mutants genetically affecting the conversion of tryptophan to KYN or 3-HK and the intracellular availability of zinc ions. In the present study, the AF properties of the MTs in the Asian tiger mosquito, Aedes albopictus, were characterized in different stages of the insect's life cycle, tryptophan-administered larvae and blood-fed adult females. Confocal imaging and microspectroscopy showed AF changes in the distribution of intracellular, brilliant granules and in the emission spectral shape and amplitude between the proximal and distal segments of MTs across the different samples. The findings suggest AF can serve as a promising marker for investigating the functional status of MTs in response to metabolic alterations, contributing to the use of MTs as a potential research model in biomedicine.

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.

The chemosensory protein 1 contributes to indoxacarb resistance in Plutella xylostella (L.)

BACKGROUND

Insecticide resistance continuously poses a threat to agricultural production. Chemosensory protein-mediated resistance is a new mechanism of insecticide resistance discovered in recent years. In-depth research on resistance mediated by chemosensory proteins (CSPs) provides new insight into aid insecticide resistance management.

RESULTS

Chemosensory protein 1 in Plutella xylostella (PxCSP1) was overexpressed in the two indoxacarb-resistant field populations and PxCSP1 has a high affinity with indoxacarb. PxCSP1 was upregulated when exposed to indoxacarb and the knockdown of this gene elevated sensitivity to indoxacarb, which demonstrate that PxCSP1 is involved in the indoxacarb resistance. Considering that CSPs may confer resistance in insects via binding or sequestering, we explored the binding mechanism of indoxacarb in PxCSP1-mediated resistance. Using molecular dynamics simulations and site-directed mutation, we found that indoxacarb forms a solid complex with PxCSP1 mainly through van der Waals interactions and electrostatic interactions. Between these, the electrostatic interaction provided by the Lys100 side chain in PxCSP1, and especially the hydrogen bonding between the NZ atom and the O of the carbamoyl carbonyl group of indoxacarb, are the key factors for the high affinity of PxCSP1 to indoxacarb.

CONCLUSIONS

The overexpression of PxCPS1 and its high affinity to indoxacarb is partially responsible for indoxacarb resistance in P. xylostella. Modification of indoxacarb's carbamoyl group has the potential to alleviate indoxacarb resistance in P. xylostella. These findings will contribute to solving chemosensory protein-mediated indoxacarb resistance and provide a better understanding of the insecticide resistance mechanism. © 2023 Society of Chemical Industry.

Adaptive Changes in Detoxification Metabolism and Transmembrane Transport of Bombyx mori Malpighian Tubules to Artificial Diet

The high adaptability of insects to food sources has contributed to their ranking among the most abundant and diverse species on Earth. However, the molecular mechanisms underlying the rapid adaptation of insects to different foods remain unclear. We explored the changes in gene expression and metabolic composition of the Malpighian tubules as an important metabolic excretion and detoxification organ in silkworms (Bombyx mori) fed mulberry leaf and artificial diets. A total of 2436 differentially expressed genes (DEGs) and 245 differential metabolites were identified between groups, with the majority of DEGs associated with metabolic detoxification, transmembrane transport, and mitochondrial function. Detoxification enzymes, such as cytochrome P450 (CYP), glutathione-S-transferase (GST), and UDP-glycosyltransferase, and ABC and SLC transporters of endogenous and exogenous solutes were more abundant in the artificial diet group. Enzyme activity assays confirmed increased CYP and GST activity in the Malpighian tubules of the artificial diet-fed group. Metabolome analysis showed increased contents of secondary metabolites, terpenoids, flavonoids, alkaloids, organic acids, lipids, and food additives in the artificial diet group. Our findings highlight the important role of the Malpighian tubules in adaptation to different foods and provide guidance for further optimization of artificial diets to improve silkworm breeding.

Malpighian tubules of Rhodnius prolixus: More than post-prandial diuresis

Rhodnius prolixus, a major vector of Chagas disease, may be considered the model upon which the foundations of insect physiology and biochemistry were built. It is an obligate blood feeder in which the blood meal triggers growth, development and reproduction. The blood meal also triggers a post-prandial diuresis to maintain osmotic homeostasis. In R. prolixus, as with other insects, the Malpighian tubules play a critical role in this diuresis, and much has been learned about diuresis in R. prolixus, and in other model insects. But the post-genomic era has brought new insights, identifying functions quite apart from diuresis for Malpighian tubules. Indeed, microarrays, transcriptomes, and proteomics have revealed the major roles that Malpighian tubules play in immunity, detoxification, pesticide resistance, and in tolerance to overall stress. This is particularly relevant to R. prolixus since gorging on blood creates several challenges in addition to osmotic balance. Xenobiotics may be present in the blood or toxins may be produced by metabolism of blood; and these must be neutralized and excreted. These processes have not been well described at the molecular level for Malpighian tubules of R. prolixus. This paper will review the involvement of Malpighian tubules in immunity and detoxification, identifying new aspects for Malpighian tubule physiology of R. prolixus by virtue of a transcriptome analysis. The transcriptome analysis indicates the potential of Malpighian tubules of R. prolixus to mount a robust innate immune response, and to contribute to antioxidant production and heme detoxification.

Identification and Functional Characterization of the Transcription Factors AhR/ARNT in Dendroctonus armandi

The aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) belong to the bHLH-PAS (basic Helix-Loop-Helix-Period/ARNT/Single-minded) family of transcription factors, which participate in the sensing and transmitting stimuli of exogenous and endogenous chemical substances, and subsequently activates genes transcription involved in various detoxification and physiological functions. However, they have not been identified in Dendroctonus armandi, and their roles in the detoxification metabolism are unclear. In the present study, AhR and ARNT of D. armandi were characterized. Spatiotemporal expression profiling indicated that DaAhR and DaARNT were highly expressed in the adult and larval stages of D. armandi and mainly expressed in the midgut and Malpighian tubules of adults. Additionally, the expression of DaAhR and DaARNT significantly increased after exposure to (-)-𝛽-pinene, (+)-3-carene, and (±)-limonene. Silencing DaAhR and DaARNT increased the susceptibility of D. armandi to (-)-𝛽-pinene, (+)-3-carene, and (±)-limonene, and the activities of detoxification enzyme were also remarkably reduced. Moreover, DaCYP6DF1 and DaGSTs2 were significantly down-regulated after injections of dsAhR and dsARNT in the male and female adults, with the expression of DaCYP6DF1 decreasing by higher than 70%. The present study revealed that the transcription factors AhR and ARNT of D. armandi were induced by terpenoids and participated in the regulation of DaCYP6DF1 expression, which was associated with D. armandi's susceptibility to (-)-𝛽-pinene and (±)-limonene. These results may provide a theoretical basis for the integrated control of D. armandi and improve our comprehension of insect toxicology.

Disruption of CYP6DF1 and CYP6DJ2 increases the susceptibility of Dendroctonus armandi to (+)-α-pinene

Bark beetles rely on detoxifying enzymes to resist the defensive oleoresin terpenes of the host tree. Insect cytochrome P450 (CYPs) plays a key role in the detoxification of plant allelochemicals and pesticides. CYP6 family is unique to Insecta, and its biochemical function is basically related to catabolize heterologous substances. In this study, two Dendroctonus armandi CYP6 genes, CYP6DF1 and CYP6DJ2, were characterized. Spatiotemporal expression profiling revealed that CYP6DF1 and CYP6DJ2 expressions were higher in larvae and adult stages of D. armandi than in egg and pupae stages, and that two genes predominantly expressed in brain, midgut, fat body, or Malpighian tubules. Moreover, CYP6DF1 and CYP6DJ2 expressions were significantly induced after exposure to (+)-α-pinene. Importantly, silencing CYP6DF1 and CYP6DJ2 significantly inhibited the CYP activity and increased the mortality in the adults fumigated with (+)-α-pinene. Additionally, piperonyl butoxide exposure to adults also increase the sensitivity after treatment with (+)-α-pinene, which led to a significant reduction of the CYP activity, resulting a significant increase in adult mortality. These results suggest that the CYP6 family plays a key role in determining the susceptibility of D. armandi to (+)-α-pinene, which may have implications for the development of novel therapeutics to control this important pest.

Multiple Functions of Malpighian Tubules in Insects: A Review

The Malpighian Tubules (MTs) are the main excretory organs in most insects. They play a key role in the production of primary urine and osmoregulation, selectively reabsorbing water, ions, and solutes. Besides these functions conserved in most insects, MTs can serve some specialized tasks at different stages of some species' development. The specialized functions include the synthesis of mucopolysaccharides and proteins for the building of foam nests, mucofibrils for the construction of dwelling tubes, adhesive secretions to help the locomotion, and brochosomes for protection as well as the usage of inorganic salts to harden the puparia, eggs chorion, and pupal cells' closing lids. MTs are also the organs responsible for the astonishing bioluminescence of some Diptera glowworms and can go through some drastic histological changes to produce a silk-like fiber utilized to spin cocoons. The specialized functions are associated with modifications of cells within the entire tubules, in specific segments, or, more rarely, modified secretory cells scattered along the MTs. In this review, we attempted to summarize the observations and experiments made over more than a century concerning the non-excretive functions of insects' MTs, underlying the need for new investigations supported by the current, advanced technologies available to validate outdated theories and clarify some dubious aspects.

Knockdown of CYP6CR2 and CYP6DE5 reduces tolerance to host plant allelochemicals in the Chinese white pine beetle Dendroctonus armandi

Bark beetles rely on detoxifying enzymes to resist the defensive terpenoids of the host tree. Insect cytochrome P450 (CYPs) plays a key role in the detoxification of pesticides and plant allelochemicals. CYP6 family is unique to Insecta, and its biochemical function is basically related to the metabolism of exogenous substances. In this study, we sequenced and characterized the full-length cDNAs of two CYP6 genes from Chinese white pine beetle, Dendroctonus armandi. Spatiotemporal expression profiling revealed that the expression of CYP6CR2 and CYP6DE5 was higher in larval and adult stages of D. armandi than that in other developmental stages, and that two genes predominantly expressed in brain, midgut, fat body, Malpighian tubules or hemolymph. The expression of CYP6CR2 and CYP6DE5 was significantly induced after feeding on the phloem of Pinus armandii and exposure to six stimuli [(±)- α -pinene, (-)-α-pinene, (-)-β-pinene, (+)-3-carene, (±)-limonene and turpentine]. Importantly, silencing CYP6CR2 and CYP6DE5 separately could increase the sensitivity, led to a significant reduction of the activity of P450, resulting a significant increase in adult mortality after treatment with terpenoids. The comprehensive results of this study showed that in the process of host selection and colonization, the functions of CYPs were mainly to hydrolyze the chemical defense of the host and degrade odor molecules. These findings may help to develop new treatments to control this important pest.

A Functional Analysis of the Purine Salvage Pathway in Acetobacter fabarum

Acetobacter species are a major component of the gut microbiome of the fruit fly Drosophila melanogaster, a widely used model organism. While a range of studies have illuminated impacts of Acetobacter on their hosts, less is known about how association with the host impacts bacteria. A previous study identified that a purine salvage locus was commonly found in Acetobacter associated with Drosophila. In this study, we sought to verify the functions of predicted purine salvage genes in Acetobacter fabarum DsW_054 and to test the hypothesis that these bacteria can utilize host metabolites as a sole source of nitrogen. Targeted gene deletion and complementation experiments confirmed that genes encoding xanthine dehydrogenase (xdhB), urate hydroxylase (urhA), and allantoinase (puuE) were required for growth on their respective substrates as the sole source of nitrogen. Utilization of urate by Acetobacter is significant because this substrate is the major nitrogenous waste product of Drosophila, and its accumulation in the excretory system is detrimental to both flies and humans. The potential significance of our findings for host purine homeostasis and health are discussed, as are the implications for interactions among microbiota members, which differ in their capacity to utilize host metabolites for nitrogen. IMPORTANCEAcetobacter are commonly found in the gut microbiota of fruit flies, including Drosophila melanogaster. We evaluated the function of purine salvage genes in Acetobacter fabarum to test the hypothesis that this bacterium can utilize host metabolites as a source of nitrogen. Our results identify functions for three genes required for growth on urate, a major host waste product. The utilization of this and other Drosophila metabolites by gut bacteria may play a role in their survival in the host environment. Future research into how microbial metabolism impacts host purine homeostasis may lead to therapies because urate accumulation in the excretory system is detrimental to flies and humans.

Functional characterization of a diuretic hormone receptor associated with desiccation, starvation and temperature tolerance in gypsy moth, Lymantria dispar

Variety of diuretic hormone neuropeptides is known to regulate water and ion balance in invertebrates. By activating their specific neuropeptide, diuretic hormone receptor (DHR) transmits extracellular signals into the cell, and then produces functional cell activity, which plays an important role in regulating physiology and behavior. However, little is known about the function of DHR gene in Lymantria dispar. DHR gene was firstly identified in L. dispar and its physiological functions were investigated using RNA interference (RNAi) technology. The results showed that except for the 6^th instar larvae, the expression levels of DHR gene in the larval stages are higher than that in the egg, pupal and adult stages. The DHR gene is highly expressed in hindgut and midgut tissues. The L. dispar larvae significantly increased their water content and high temperature tolerance after the DHR was silenced, while decreasing excretion and feeding behavior. The physiological function of DHR is associated with desiccation, high temperature and starvation resistance. DHR could contribute to future development of novel insecticide to manage this global forest pest population.

Molecular Detection of Malpighamoeba mellificae in Honey Bees

Malpighamoeba mellificae is a protozoan that infects the Malpighian tubules of honey bees. The amoebae, ingested as cysts, develop into trophozoites that feed upon tubule epithelia. The resulting damage of the Malpighian tubules can induce an imbalance of waste excretion and hemolymph exchange. This causes the so-called amoebiasis disease in adult bees, which may co-occur with Nosema infections. Most reports of this amoeba are from the 1960s and earlier, and knowledge of the disease and its spreading is very poor. The lack of any genetic marker for the species hampers its sensitive identification using molecular tools and gaining knowledge on its epidemiology. Here, we present a diagnostic RT-qPCR assay, consisting of two primers and one probe that were developed based on 18S rRNA sequences of the amoeba, generated with metagenomic sequencing of Malpighian tubules with and without M. mellificae cysts. The assay was initially tested and adjusted with samples microscopically tested for the presence of M. mellificae cysts. Later, it was validated and material with unknown infection status was tested. The sensitive diagnostic Malpighamoeba disease 18S assay is now ready to be applied for honey bee health monitoring purposes and to investigate the prevalence of M. mellificae in more detail.

Gene expression profiles in Malpighian tubules of the vector leafhopper Psammotettix striatus (L.) revealed regional functional diversity and heterogeneity

Background

Many leafhoppers are known as pests and disease vectors of economically important plants. Previous studies of the physiological functions of vector leafhoppers have mainly focused on the salivary glands and the alimentary tract that are deemed to be associated with digestion, host defense and phytoplasma and/or virus transmission. By contrast, the significance of Malpighian tubules (MTs) is less studied. To clarify the physiological function of MTs of the vector leafhopper Psammotettix striatus that transmits phytoplasma triggering the wheat blue dwarf disease, we performed a transcriptome study on P. striatus MTs and compared gene expression profiles among different anatomical regions in the tubules (i.e., MT1+2, the anterior segment together with the sub-anterior segment; MT3, the inflated segment; and MT4, the distal segment).

Results

Transcriptome of P. striatus MTs generate a total of 42,815 high-quality unigenes, among which highly expressed unigenes are mainly involved in organic solute transport, detoxification and immunity in addition to osmoregulation. Region-specific comparative analyses reveal that all these MT regions have functions in osmoregulation, organic solute transport and detoxification, but each region targets different substrates. Differential expression and regional enrichment of immunity-related effector activities and molecules involved in phagocytosis and the biosynthesis of antimicrobial peptides among different regions indicate that MT1+2 and MT4 have the ability to eliminate the invading pathogens. However, in MT3 which secrets brochosomes to the integument and eggs as physical barriers, disulfide-isomerase, acidic ribosomal protein P and many other unigenes were highly expressed, which can be attractive candidate genes for future studies of the biosynthesis and the origin of brochosomes.

Conclusions

Psammotettix striatus MTs perform multiple physiological functions as versatile organs than just excretory organs with osmoregulatory function. Heterogeneity of physiological functions among different MT regions is related to organic solute transport, detoxification, immunity and brochosome biosynthesis in addition to osmoregulation, and each region targets different substrates. These functions may be helpful for P. striatus to resist pathogens from habitats and to utilize a wider range of host plants, which may assist the transmission and spread of phytoplasmas. The results provide potential molecular targets for the exploit of chemical and/or gene-silencing insecticides.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08300-6.

Functional Identification and Characterization of Leucokinin and Its Receptor in the Fall Webworm, Hyphantria cunea

Neuropeptides function as central neuromodulators and circulating hormones that modulate insect behavior and physiology. Leucokinin (LK) is an intercellular signaling molecule that mediates many physiological and behavioral processes. However, the functions of LK associated with environmental stress and feeding behavior in the fall webworm, Hyphantria cunea, is little known. Our primary objective is to understand the function of LK and LK receptor (LKR) neuroendocrine system in H. cunea. In the present study, the results showed that LK/LKR are expressed at different developmental stages and in various tissues of H. cunea. A candidate receptor-ligand pairing for LK was identified in the larval transcriptome of H. cunea. In a heterologous expression system, the calcium assay was used to demonstrate that LKR is activated by HcLKs in a dose-dependent manner, with 50% effective concentration (EC50) values of 8.44-90.44nM. Knockdown of HcLK and HcLKR by microinjecting target-specific dsRNA leads to several effects in H. cunea, including feeding promotion, increase in resistance to desiccation and starvation stress, and regulation of water homeostasis. The transcript levels of HILP2 (except in the LK knockdown group), HILP5, and HILP8 increased, whereas those of HILP3, HILP4, and HILP6 decreased; HILP1, HILP2 (in the LK knockdown group), and HILP7 gene expression was not influenced after LK and LKR knockdown. Variations in mRNA expression levels in insulin-like peptide genes in the knockdown larvae suggest an essential role of these genes in survival in H. cunea. To our knowledge, the present study is the first comprehensive study of LK and LKR - from gene to behavior - in H. cunea.

Expression pattern of CAPA/pyrokinin neuropeptide genes in Remipedia and silverfish: Rapid differentiation after gene duplication in early Hexapoda, followed by strong conservation of newly established features in insects

Only few genes are known from insects that encode multiple neuropeptides, i.e., peptides that activate different receptors. Among those are the capa and pk genes, which differentiated within Hexapoda following gene duplication. In our study, we focus on the early stages of differentiation of these genes. Specifically: (1) What was the expression pattern of the ancestral capa/pk gene, i.e., prior to gene duplication? (2) What is the expression pattern of capa and pk in silverfish, whose ancestors diverged from Pterygota more than 400 mya? Our results suggest the location and projection of CAPA immunoreactive Va cells in abdominal ganglia (trunk ganglia in Remipedia) are a plesiomorphic trait that was already present in the ancestor of Remipedia and Hexapoda. General features of serial homology such as location of cells bodies, contralateral projection of primary neurites, and presumed peripheral peptide release from segmentally arranged neurohemal release sites could be observed in Remipedia and silverfish, but also in all Pterygota studied so far. Differences are mainly in the specific location of these peripheral release sites. This hypothetical basic pattern of capa/pk neurons underwent modifications in the anterior ganglia of the ventral nerve cord already in Remipedia. In silverfish, as in all Pterygota studied so far, pk expression in the CNS is apparently restricted to the gnathal ganglia, whereas capa expression is typical of abdominal Va cells. Thus, differentiation in the expression pattern of capa and pk genes occurred early in the evolution of Hexapoda; likely soon after the appearance of two separate genes.

Fluid Secretion by Malpighian Tubules of Rhodnius prolixus: Neuroendocrine Control With New Insights From a Transcriptome Analysis

Rhodnius prolixus (the kissing bug and a major vector of Chagas disease) is an obligate blood feeder that in the case of the fifth instar consumes up to 10 times its unfed body weight in a single 20-minute feed. A post-prandial diuresis is initiated, within minutes of the start of gorging, in order to lower the mass and concentrate the nutrients of the meal. Thus, R. prolixus rapidly excretes a fluid that is high in NaCl content and hypo-osmotic to the hemolymph, thereby eliminating 50% of the volume of the blood meal within 3 hours of gorging. In R. prolixus, as with other insects, the Malpighian tubules play a critical role in diuresis. Malpighian tubules are not innervated, and their fine control comes under the influence of the neuroendocrine system that releases amines and neuropeptides as diuretic or antidiuretic hormones. These hormones act upon the Malpighian tubules via a variety of G protein-coupled receptors linked to second messenger systems that influence ion transporters and aquaporins; thereby regulating fluid secretion. Much has been discovered about the control of diuresis in R. prolixus, and other model insects, using classical endocrinological studies. The post-genomic era, however, has brought new insights, identifying novel diuretic and antidiuretic hormone-signaling pathways whilst also validating many of the classical discoveries. This paper will focus on recent discoveries into the neuroendocrine control of the rapid post-prandial diuresis in R. prolixus, in order to emphasize new insights from a transcriptome analysis of Malpighian tubules taken from unfed and fed bugs.

The Fall Armyworm Spodoptera frugiperda Utilizes Specific UDP-Glycosyltransferases to Inactivate Maize Defensive Benzoxazinoids

The relationship between plants and insects is continuously evolving, and many insects rely on biochemical strategies to mitigate the effects of toxic chemicals in their food plants, allowing them to feed on well-defended plants. Spodoptera frugiperda, the fall armyworm (FAW), accepts a number of plants as hosts, and has particular success on plants of the Poaceae family such as maize, despite their benzoxazinoid (BXD) defenses. BXDs stored as inert glucosides are converted into toxic aglucones by plant glucosidases upon herbivory. DIMBOA, the main BXD aglucone released by maize leaves, can be stereoselectively re-glucosylated by UDP-glycosyltransferases (UGTs) in the insect gut, rendering it non-toxic. Here, we identify UGTs involved in BXD detoxification by FAW larvae and examine how RNAi-mediated manipulation of the larval glucosylation capacity toward the major maize BXD, DIMBOA, affects larval growth. Our findings highlight the involvement of members of two major UGT families, UGT33 and UGT40, in the glycosylation of BXDs. Most of the BXD excretion in the frass occurs in the form of glucosylated products. Furthermore, the DIMBOA-associated activity was enriched in the gut tissue, with a single conserved UGT33 enzyme (SfUGT33F28) being dedicated to DIMBOA re-glucosylation in the FAW gut. The knock-down of its encoding gene reduces larval performance in a strain-specific manner. This study thus reveals that a single UGT enzyme is responsible for detoxification of the major maize-defensive BXD in this pest insect.

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.

Identification and Functional Analysis of a Delta Class Glutathione S-Transferase Gene Associated with Insecticide Detoxification in Bradysia odoriphaga

A delta class glutathione S-transferase gene (BoGSTd2) is identified from Bradysia odoriphaga for the first time. Developmental expression analysis showed that expression of BoGSTd2 is significantly higher in the fourth instar larval stage and the adult stage. Tissue-specific expression analysis found that BoGSTd2 was expressed predominantly in the midgut and Malpighian tubules in the fourth instar larvae and the abdomen of adults. Expression of BoGSTd2 was significantly upregulated following exposure to chlorpyrifos and clothianidin. In vitro inhibition and metabolic assays indicated that recombinant BoGSTd2 could not directly metabolize chlorpyrifos and clothianidin. Nevertheless, disk diffusion assays indicated that BoGSTd2 plays an important role in protection against oxidative stress. RNAi assays showed that BoGSTd2 participates in the elimination of reactive oxygen species induced by chlorpyrifos and clothianidin. These results strongly suggest that BoGSTd2 plays an important role in chlorpyrifos and clothianidin detoxification in B. odoriphaga by protecting tissues from oxidative stress induced by these insecticides.

Simple techniques to study multifaceted diabesity in the fly model

Diabetes and obesity are the two notorious metabolic disorders in today's world. Both diabetes and obesity are interlinked with each other and often referred to as 'Diabesity'. It is a complex and multi-organ failure disorder. Thus, many researches and tremendous efforts have been made toward prevention, treatment as well as early detection of diabesity. However, and still, there is a large gap in understanding the etiology as well as treatment of diabesity. Various animal models are also used to decipher the mechanism underlying diabesity. Among all the model organism, recently Drosophila melanogaster is gaining its importance to study diabetes, obesity, and other metabolic disorder. Various experimental methods like histological, biochemical, developmental, and behavioral assays are described in this study to detect diabetes as well as obesity in the fly model.

Helicokinin alters ion transport in the secondary cell-containing region of the Malpighian tubule of the larval cabbage looper Trichoplusia ni

Excretion in insects is accomplished by the combined actions of the Malpighian tubules (MTs) and hindgut, which together form the functional kidney. MTs of many insect groups consist of principal cells (PC) and secondary cells (SC). In most insect groups SCs are reported to secrete ions from haemolymph into the tubule lumen. Paradoxically, SCs in the MTs of the lepidopteran cabbage looper T. ni are used to reabsorb Na⁺ and K⁺ back into haemolymph. The current study was designed to investigate the effects and mode of action of the lepidopteran kinin, Helicokinin (HK), on ion transport in the SC-containing region of MT of T. ni. We identified a HK receptor (HK-R) homologue in T. ni and detected its expression in the SC-containing region of the MTs. The mRNA abundance of hk-r altered in response to changes in dietary K⁺ and Na⁺ content. HK-R immunolocalized to both PCs and SCs. Ramsay assays of preparations of the isolated distal ileac plexus (DIP) indicated that [HK] = 10^-8 M: (i) decreased fluid secretion rate in unstimulated and serotonin-stimulated preparations, and (ii) increased [Na⁺]/[K⁺] ratio in the secreted fluid. Scanning ion-selective electrode technique measurements revealed that HK reduced: (i) K⁺ secretion by the PCs, and (ii) Na⁺ reabsorption by the SCs in intact tubules. In vitro incubation of the DIP with HK resulted in reduced mRNA abundance of hk-r as well as Na⁺/K⁺-ATPase subunit α (NKAα), Na⁺/K⁺/Cl^- co-transporter (nkcc), Na⁺/H⁺ exchangers (nhe) 7 and 8, and aquaporin (aqp) 1. Taken together, results of the current study suggest that HK is capable of altering fluid secretion rate and [Na⁺]/[K⁺] ratio of the fluid, and that HK targets both PCs and SCs in the DIP of T. ni.

Differential Expression of Cytochrome P450 CYP6 Genes in the Brown Marmorated Stink Bug, Halyomorpha halys (Hemiptera: Pentatomidae)

Cytochrome (CYP) P450s are a superfamily of enzymes that detoxify xenobiotics and regulate numerous physiological processes in insects. The genomes of phytophagous insects usually contain large numbers of P450s, especially within the CYP3 clan. Within this clan, CYP6 subfamily members help detoxify plant host secondary metabolites. In this study, we analyzed three CYP6 genes in the highly polyphagous invasive pest, Halyomorpha halys (Stål), commonly known as brown marmorated stink bug. We characterized and validated the expression of HhCYP6BQ27, HhCYP6BK13, and HhCYP6BK24 among sexes, tissues (gut, fat body, and Malpighian tubules) and hosts (apple, corn, soybean). Sequence characterization by amino acid alignments confirmed the presence of conserved motifs typical of the P450 superfamily. No significant differences existed in gene expression among sexes or when fed different hosts, suggesting that these transcripts might have broad substrate specificities. However, significant differences in gene expression were observed among the tissues studied and were gene-dependent. Collectively, the results show that H. halys differentially expressed CYP6 genes among tissues, which may be related to important and specific physiological functions. This study has increased our understanding of H. halys biology that can be useful for functional studies and can potentially be exploited in developing sustainable pest management strategies.

The expression of Spodoptera exigua P450 and UGT genes: tissue specificity and response to insecticides

Cytochrome P450 and UDP-glucosyltransferase (UGT) as phase I and phase II metabolism enzymes, respectively, play vital roles in the breakdown of endobiotics and xenobiotics. Insects can increase the expression of detoxification enzymes to cope with the stress from xenobiotics including insecticides. However, the molecular mechanisms for insecticide detoxification in Spodoptera exigua remain elusive, and the genes conferring insecticide metabolisms in this species are less well reported. In this study, 68 P450 and 32 UGT genes were identified. Phylogenetic analysis showed gene expansions in CYP3 and CYP4 clans of P450 genes and UGT33 family of this pest. P450 and UGT genes exhibited specific tissue expression patterns. Insecticide treatments in fat body cells of S. exigua revealed that the expression levels of P450 and UGT genes were significantly influenced by challenges of abamectin, lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb. Multiple genes for detoxification were affected in expression levels after insecticide exposures. The results demonstrated that lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb induced similar responses in the expression of P450 and UGT genes in fat body cells; eight P450 genes and four UGT genes were co-up-regulated significantly, and no or only a few CYP/UGT genes were down-regulated significantly by these four insecticides. However, abamectin triggered a distinct response for P450 and UGT gene expression; more P450 and UGT genes were down-regulated by abamectin than by the other four compounds. In conclusion, P450 and UGT genes from S. exigua were identified, and different responses to abamectin suggest a different mechanism for insecticide detoxification.

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

Epithelial Function in the Drosophila Malpighian Tubule: An In Vivo Renal Model

The insect renal (Malpighian) tubule has long been a model system for the study of fluid secretion and its neurohormonal control, as well as studies on ion transport mechanisms. To extend these studies beyond the boundaries of classical physiology, a molecular genetic approach together with the 'omics technologies is required. To achieve this in any vertebrate transporting epithelium remains a daunting task, as the genetic tools available are still relatively unsophisticated. Drosophila melanogaster, however, is an outstanding model organism for molecular genetics. Here we describe a technique for fluid secretion assays in the D. melanogaster equivalent of the kidney nephron. The development of this first physiological assay for a Drosophila epithelium, allowing combined approaches of integrative physiology and functional genomics, has now provided biologists with an entirely new model system, the Drosophila Malpighian tubule, which is utilized in multiple fields as diverse as kidney disease research and development of new modes of pest insect control.

Septate junction in the distal ileac plexus of larval lepidopteran Trichoplusia ni: alterations in paracellular permeability during ion transport reversal

The Malpighian tubules (MTs) and hindgut together act as the functional kidney in insects. MTs of caterpillars are notably complex and consist of several regions that display prominent differences in ion transport. The distal ileac plexus (DIP) is a region of Malpighian tubule that is of particular interest because it switches from ion secretion to ion reabsorption in larvae fed on ion-rich diets. The pathways of solute transport in the DIP are not well understood, but one potential route is the paracellular pathway between epithelial cells. This pathway is regulated by the septate junctions (SJs) in invertebrates, and in this study, we found regional and cellular heterogeneity in expression of several integral SJ proteins. DIP of larvae fed ion-rich diets demonstrated a reduction in paracellular permeability, coupled with alterations in both SJ morphology and the abundance of its molecular components. Similarly, treatment in vitro with helicokinin (HK), an antidiuretic hormone identified by previous studies, altered mRNA abundance of many SJ proteins and reduced paracellular permeability. HK was also shown to target a secondary cell-specific SJ protein Tsp2A. Taken together, our data suggest that dietary ion loading, known to cause ion transport reversal in the DIP of larval T. ni, leads to alterations in the paracellular permeability, SJ morphology and its molecular component abundance. The results suggest that HK is an important endocrine factor that co-regulates ion transport, water transport and paracellular permeability in MTs of larval lepidopterans. We propose that co-regulation of all three components of the MT function in larval lepidopterans allows for safe toggling between ion secretion and reabsorption in the DIP in response to variations in dietary ion availability.

Malpighian tubules of caterpillars: blending RNAseq and physiology to reveal regional functional diversity and novel epithelial ion transport control mechanisms

Malpighian tubules (MTs) and hindgut constitute the functional kidney of insects. MTs are outpouches of the gut and in most insects demonstrate proximodistal heterogeneity in function. In most insects, such heterogeneity is confined to ion/fluid secretion in the distal portion and ion/fluid reabsorption in the proximal portion. In contrast, MTs of larval Lepidoptera (caterpillars of butterflies and moths), are comprised of five regions that differ in their association with the gut, their structure, and ion/fluid transport function. Recent studies have shown that several regions can rapidly and reversibly switch between ion secretion and reabsorption. The current study employed RNAseq, pharmacology and electrophysiology to characterize four distinct regions of the MT in larval Trichoplusia ni. Luminal microelectrode measurements indicate changes in [K+], [Na+] and pH as fluid passes through different regions of the tubule. In addition, the regions examined differ in gene ontology enrichment, and demonstrate robust gradients in expression of ion transporters and endocrine ligand receptors. Lastly, the study provides evidence for direct involvement of voltage-gated and ligand-gated ion channels in epithelial ion transport of insect MTs.

Comparative transcriptomic analysis of larval and adult Malpighian tubules from the cotton bollworm Helicoverpa armigera

Malpighian tubules (MTs) are usually considered the key excretory and osmoregulatory organs of insects. However, increasing evidence has suggested that MTs perform many more functions than just osmoregulation. Until now, the molecular and physiological functions of MTs in the cotton bollworm (Helicoverpa armigera), a very important agricultural pest, are largely unknown. In this study, the transcriptomes of H. armigera MTs from larvae, male adults and female adults were sequenced using RNA-Seq technology, and comparative analyses of transcriptomes between two life stages (larval and adult) and between adult sexes were conducted. We generated a total of 84 643 high-quality unigenes, and identified a large number of abundant transcripts putatively encoding proteins involved in diuresis, detoxification, immunity, carbohydrate transport and metabolism, development and reproduction. We found that the expression pattern of unigenes was relatively similar between female and male adult MTs, but different between larval and adult MTs. Our data suggest that insect MTs may take multiple physiological functions as versatile organs. The extensive alterations in gene expression in MTs occurred from larvae to adults reflect an ecological adaptation to different feeding habits. Sexual dimorphism in the cotton bollworm is somewhat indicated by the transcriptional difference of genes related to carbohydrate metabolism, detoxification, immunity and reproduction in the MTs of male and female adults.

Comparison of the Malpighian tubules and fat body transcriptional profiles of Zophobas morio larvae (Coleoptera: Tenebrionidae)

The Malpighian tubules in insects play an essential role in osmoregulation, through the transport of ions during excretion, whereas the fat body is usually associated with the intermediary metabolism. The tubules also are involved in excretion of organic solutes and xenobiotics. However, with the exception of a preliminary transcriptional survey of the Zophobas morio (Tenebrionidae) larval tubules, there are no detailed transcriptional analysis of this organ in Coleoptera. A luciferase-like enzyme that displays weak luminescence activity in the presence of firefly D-luciferin and ATP was cloned from the tubules of Z. morio larvae. In order to better understand the molecular physiology of Malpighian tubules and fat body in Coleoptera larvae, and to investigate the occurrence and functions of AMP-CoA ligases in these tissues, we performed a comparative transcriptional analysis of these tissues using Z. morio giant-mealworms. As expected, the tubules displayed organic and inorganic transporters, xenobiotic metabolism enzymes, V-ATPases, channels, and pumps. The fat body showed proteins that are synthesized in this tissue and secreted to the hemolymph, as well as enzymes involved in lipid and carbohydrate metabolism. These tissues are also involved in common pathways, such as nitrogen metabolism to degradation/excretion, eye pigments biosynthesis, immunity, and detoxification. The presence of coumarate-CoA ligase-like enzymes in these tissues suggest their involvement in the degradation of coumaric acid derivatives obtained from the diet, or alternatively, in the biosynthesis of compounds structurally related to coumaric acids such as eye pigments. Our results confirm to the physiological versatility of tubules and fat body in larval Coleoptera.

Identification and expression profiles of twenty-six glutathione S-transferase genes from rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae)

The rice weevil, Sitophilus oryzae, is one of the most destructive pests in stored cereals products. In this study, 26 cDNAs encoding glutathione S-transferases (GSTs) were sequenced and characterized in S. oryzae. Phylogenetic analysis displayed the categorization of 26 GSTs into six different cytosolic classes, including two in the delta, twelve in epsilon, three in omega, six in sigma, two in theta, and one in zeta class. RT-qPCR assay illustrated that the relative expression of ten GST genes was significantly higher in adult stages than in larval and pupal developmental stages. Tissue-specific expression analysis revealed that the SoGSTe5, SoGSTe7, SoGSTe12, and SoGSTz1 were up-regulated in the midgut, SoGSTe2, SoGSTe6, and SoGSTs2 were up-regulated in the fat body, and three GSTs (SoGSTd1, SoGSTd2 and SoGSTe4) were up-regulated in Malpighian tubules. RT-qPCR indicated that five GST genes were over expressed after exposure to phosphine at various times and concentrations. The increase in GST gene expressions after phosphine exposure in S. oryzae may lead to an improved tolerance for fumigations and xenobiotics.

Gene Regulatory Variation in Drosophila melanogaster Renal Tissue

Genetic variation influencing levels of gene expression is abundant in natural populations, and may exert its effects through complex mechanisms that depend on an organism's genetic background and the tissue in which expression is measured. We investigated natural variation in gene expression in the Malpighian tubules of three inbred Drosophila melanogaster strains and their F₁ hybrids. One of the strains was from a population in the species' ancestral range (Zambia), while the other two were from a more recently derived population (Sweden). Although closely related, the two Swedish strains differed greatly in terms of their expression inheritance when hybridized with the Zambian strain, with one Swedish strain showing a large excess of genes with recessive expression inheritance, as well as a large number of genes with overdominant inheritance. Although most expression variation could be attributed to trans-regulation, there were ∼200 genes that showed allele-specific expression differences in each of the between-population hybrids, indicating that cis-regulation contributes as well. The cis-regulated genes were enriched with cytochrome P450 genes, and the upstream regions of six of these genes were incorporated into transgenic reporter gene constructs to test their effects on expression. Differential expression was observed for five of the six reporter genes in the Malpighian tubule, suggesting that a large proportion of cis-regulatory variation lies directly upstream of the affected gene. In most cases, the differential expression was specific to the Malpighian tubule or greater in this tissue than in the rest of the body, highlighting the importance of single-tissue studies of gene expression variation.

Modeling Renal Disease "On the Fly"

Detoxification is a fundamental function for all living organisms that need to excrete catabolites and toxins to maintain homeostasis. Kidneys are major organs of detoxification that maintain water and electrolyte balance to preserve physiological functions of vertebrates. In insects, the renal function is carried out by Malpighian tubules and nephrocytes. Due to differences in their circulation, the renal systems of mammalians and insects differ in their functional modalities, yet carry out similar biochemical and physiological functions and share extensive genetic and molecular similarities. Evolutionary conservation can be leveraged to model specific aspects of the complex mammalian kidney function in the genetic powerhouse Drosophila melanogaster to study how genes interact in diseased states. Here, we compare the human and Drosophila renal systems and present selected fly disease models.

Tissue Localization and Variation of Major Symbionts in Haemaphysalis longicornis, Rhipicephalus haemaphysaloides, and Dermacentor silvarum in China

Ticks are important disease vectors, as they transmit a variety of human and animal pathogens worldwide. Symbionts that coevolved with ticks confer crucial benefits to their host in nutrition metabolism, fecundity, and vector competence. Although over 100 tick species have been identified in China, general information on tick symbiosis is limited. Here, we visualized the tissue distribution of Coxiella sp. and Rickettsia sp. in lab-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides by fluorescent in situ hybridization. We found that Coxiella sp. colonized exclusively the Malpighian tubules and ovaries of H. longicornis, while Rickettsia sp. additionally colonized the midgut of R. haemaphysaloides We also investigated the population structure of microbiota in Dermacentor silvarum ticks collected from Inner Mongolia, China, and found that Coxiella, Rickettsia, and Pseudomonas are the three dominant genera. No significant difference in microbiota composition was found between male and female D. silvarum ticks. We again analyzed the tissue localization of Coxiella sp. and Rickettsia sp. and found that they displayed tissue tropisms similar to those in R. haemaphysaloides, except that Rickettsia sp. colonized the nuclei of spermatids instead of ovaries in D. silvarum Altogether, our results suggest that Coxiella sp. and Rickettsia sp. are the main symbionts in the three ticks and reside primarily in midgut, Malpighian tubules, and reproductive tissues, but their tissue distribution varies in association with species and sexes.IMPORTANCE Tick-borne diseases constitute a major public health burden, as they are increasing in frequency and severity worldwide. The presence of symbionts helps ticks to metabolize nutrients, promotes fecundity, and influences pathogen infections. Increasing numbers of tick-borne pathogens have been identified in China; however, knowledge of native ticks, especially tick symbiosis, is limited. In this study, we analyze the distribution of Coxiella sp. and Rickettsia sp. in tissues of laboratory-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides and field-collected Dermacentor silvarum We found that the localization patterns of Coxiella sp. in three Chinese tick species were similar to those of other tick species. We also found a previously undefined intracellular localization of Rickettsia sp. in tick midgut and spermatids. In addition, we demonstrate that tissue tropisms of symbionts vary between species and sexes. Our findings provide new insights into the tissue localization of symbionts in native Chinese ticks and pave the way for further understanding of their functional capabilities and symbiotic interactions with ticks.

Multiple Glutathione S-Transferase Genes in Heortia vitessoides (Lepidoptera: Crambidae): Identification and Expression Patterns

To elucidate the role of glutathione S-transferases (GSTs) in Heortia vitessoides Moore (Lepidoptera: Crambidae), one of the most destructive defoliating pests in Aquilaria sinensis (Lour.) Gilg (Thymelaeaceae) forests, 16 GST cDNAs were identified in the transcriptome of adult H. vitessoides. All cDNAs included a complete open reading frame and were designated HvGSTd1-HvGSTu2. A phylogenetic analysis showed that the 16 HvGSTs were classified into seven different cytosolic classes; three in delta, two in epsilon, three in omega, three in sigma, one in theta, two in zeta, and two in unclassified. The expression patterns of these HvGSTs in various larval and adult tissues, following exposure to half the lethal concentrations (LC50s) of chlorantraniliprole and beta-cypermethrin, were determined using real-time quantitative polymerase chain reaction (RT-qPCR). The expression levels of the 16 HvGSTs were found to differ among various larval and adult tissues. Furthermore, the RT-qPCR confirmed that the transcription levels of nine (HvGSTd1, HvGSTd3, HvGSTe2, HvGSTe3, HvGSTo3, HvGSTs1, HvGSTs3, HvGSTu1, and HvGSTu2) and six (HvGSTd1, HvGSTd3, HvGSTe2, HvGSTo2, HvGSTs1, and HvGSTu1) HvGST genes were significantly higher in the fourth-instar larvae following exposure to the insecticides chlorantraniliprole and beta-cypermethrin, respectively. These genes are potential candidates involved in the detoxification of these two insecticides. Further studies utilizing the RNA interference approach are required to enhance our understanding of the functions of these genes in this forest pest.

Brochosomins and other novel proteins from brochosomes of leafhoppers (Insecta, Hemiptera, Cicadellidae)

Brochosomes (BS) are secretory granules resembling buckyballs, produced intracellularly in specialized glandular segments of the Malpighian tubules and forming superhydrophobic coatings on the integuments of leafhoppers (Hemiptera, Cicadellidae). Their composition is poorly known. Using a combination of SDS-PAGE, LC-MS/MS, next-generation sequencing (RNAseq) and bioinformatics we demonstrate that the major structural component of BS of the leafhopper Graphocephala fennahi Young is a novel family of 21-40-kDa secretory proteins, referred to herein as brochosomins (BSM), apparently cross-linked by disulfide bonds. At least 28 paralogous BSM were identified in a transcriptome assembly of this species, most of which were detected in BS. Multiple additional BS-associated proteins (BSAP), possibly loosely attached to the outer and inner surfaces of BS, were also identified; some of these were glycine-, tyrosine- and proline-rich. BSM and BSAP together accounted for half of the 100 most expressed transcripts in the Malpighian tubules of G. fennahi. Except for several minor BSAP possibly related to cyclases, BSM and BSAP had no homologs among known proteins, thus representing taxonomically restricted gene families (orphans). Searching in 50 whole-body transcriptome assemblies of Hemiptera found homologs of BSM in representatives of all five families of the superfamily Membracoidea (Cicadellidae, Myerslopiidae, Aetalionidae, Membracidae, and Melizoderidae), but not in other lineages. Among the identified proteins only BSM were shared in common between all 17 surveyed leafhoppers known to produce BS. Combined CHN elemental and aminoacid analyses estimated the total protein content of BS from the integument of G. fennahi to be 60-70%.

Expansion of cytochrome P450 and cathepsin genes in the generalist herbivore brown marmorated stink bug

BACKGROUND

The brown marmorated stink bug (Halyomorpha halys) is an invasive pest in North America which causes severe economic losses on tree fruits, ornamentals, vegetables, and field crops. The H. halys is an extreme generalist and this feeding behaviour may have been a major contributor behind its establishment and successful adaptation in invasive habitats of North America. To develop an understanding into the mechanism of H. halys' generalist herbivory, here we specifically focused on genes putatively facilitating its adaptation on diverse host plants.

RESULTS

We generated over 142 million reads via sequencing eight RNA-Seq libraries, each representing an individual H. halys adult. The de novo assembly contained 79,855 high quality transcripts, totalling 39,600,178 bases. Following a comprehensive transcriptome analysis, H. halys had an expanded suite of cytochrome P450 and cathepsin-L genes compared to other insects. Detailed characterization of P450 genes from the CYP6 family, known for herbivore adaptation on host plants, strongly hinted towards H. halys-specific expansions involving gene duplications. In subsequent RT-PCR experiments, both P450 and cathepsin genes exhibited tissue-specific or distinct expression patterns which supported their principal roles of detoxification and/or digestion in a particular tissue.

CONCLUSIONS

Our analysis into P450 and cathepsin genes in H. halys offers new insights into potential mechanisms for understanding generalist herbivory and adaptation success in invasive habitats. Additionally, the large-scale transcriptomic resource developed here provides highly useful data for gene discovery; functional, population and comparative genomics as well as efforts to assemble and annotate the H. halys genome.

Metabolomics: State-of-the-Art Technologies and Applications on Drosophila melanogaster

Metabolomics is one of the latest "omics" technology concerned with the high-throughput identification and quantification of metabolites, the final products of cellular processes. The revealed data provide an instantaneous snapshot of an organism's metabolic pathways, which can be used to explain its phenotype or physiology. On the other hand, Drosophila has shown its power in studying metabolism and related diseases. At this stage, we have the state-of-the-art knowledge in place: a potential candidate to study cellular metabolism (Drosophila melanogaster) and a powerful methodology for metabolic network decipherer (metabolomics). Yet missing is advanced metabolomics technologies like isotope-assisted metabolomics optimized for Drosophila. In this chapter, we will discuss on the current status and future perspectives in technologies and applications of Drosophila metabolomics.

Identification and characterisation of seventeen glutathione S-transferase genes from the cabbage white butterfly Pieris rapae

Insect glutathione S-transferases (GSTs) play essential roles in the detoxification of insecticides and other xenobiotic compounds. The cabbage white butterfly, Pieris rapae, is an economically important agricultural pest. In this study, 17 cDNA sequences encoding putative GSTs were identified in P. rapae. All cDNAs include a complete open reading frame and were designated PrGSTd1-PrGSTz2. Based on phylogenetic analysis, PrGSTs were divided into six classes (delta, epsilon, omega, sigma, theta and zeta). The exon-intron organizations of these PrGSTs were also analysed. Recombinant proteins of eight PrGSTs (PrGSTD1, PrGSTD2, PrGSTE1, PrGSTE2, PrGSTO1, PrGSTS1, PrGSTT1 and PrGSTZ1) were heterologously expressed in Escherichia coli, and all of these proteins displayed glutathione-conjugating activity towards 1-chloro-2,4-dinitrobenzene (CDNB). Expression patterns in various larval tissues, at different life stages, and following exposure to sublethal doses of abamectin, chlorantraniliprole or lambda-cyhalothrin were determined by reverse transcription-quantitative PCR. The results showed that PrGSTe3, PrGSTs1, PrGSTs2, and PrGSTs4 were mainly transcribed in the fat body, while PrGSTe2 was expressed predominantly in the Malpighian tubules. Four genes (PrGSTe2, PrGSTo4, PrGSTs4 and PrGSTt1) were mainly expressed in fourth-instar larvae, while others were ubiquitously expressed in egg, larval, pupa and/or adult stages. Abamectin treatment significantly upregulated ten genes (PrGSTd1, PrGSTd3, PrGSTe1, PrGSTe2, PrGSTo1, PrGSTo3, PrGSTs1, PrGSTs3, PrGSTs4 and PrGSTt1). Chlorantraniliprole and lambda-cyhalothrin treatment significantly upregulated nine genes (PrGSTd1, PrGSTd2, PrGSTe1, PrGSTe2, PrGSTe3, PrGSTs1, PrGSTs3, PrGSTs4 and PrGSTz1) and ten genes (PrGSTd1, PrGSTd3, PrGSTe1, PrGSTe2, PrGSTo1, PrGSTo2, PrGSTs1, PrGSTs2, PrGSTs3 and PrGSTz2), respectively. These GSTs are potentially involved in the detoxification of insecticides.

Genome-wide identification, phylogenetic analysis, and expression profiles of ATP-binding cassette transporter genes in the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

The ATP-binding cassette (ABC) is the largest transporter gene family and the genes play key roles in xenobiotic resistance, metabolism, and development of all phyla. However, the specific functions of ABC gene families in insects is unclear. We report a genome-wide identification, phylogenetic, and transcriptional analysis of the ABC genes in the oriental fruit fly, Bactrocera dorsalis (Hendel). We identified a total of 47 ABC genes (BdABCs) from the transcriptomic and genomic databases of B. dorsalis and classified these genes into eight subfamilies (A-H), including 7 ABCAs, 7 ABCBs, 9 ABCCs, 2 ABCDs, 1 ABCE, 3 ABCFs, 15 ABCGs, and 3 ABCHs. Comparative phylogenetic analysis of the ABCs suggests an orthologous relationship between B. dorsalis and other insect species in which these genes have been related to pesticide resistance and essential biological processes. Comparison of transcriptome and relative expression patterns of BdABCs indicated diverse multifunctions within different B. dorsalis tissues. The expression of 4, 10, and 14 BdABCs from 18 BdABCs was significantly upregulated after exposure to LD₅₀s of malathion, avermectin, and beta-cypermethrin, respectively. The maximum expression level of most BdABCs (including BdABCFs, BdABCGs, and BdABCHs) occurred at 48h post exposures, whereas BdABCEs peaked at 24h after treatment. Furthermore, RNA interference-mediated suppression of BdABCB7 resulted in increased toxicity of malathion against B. dorsalis. These data suggest that ABC transporter genes might play key roles in xenobiotic metabolism and biosynthesis in B. dorsalis.

Tissue-resident stem cell activity: a view from the adult Drosophila gastrointestinal tract

The gastrointestinal tract serves as a fast-renewing model for unraveling the multifaceted molecular mechanisms underlying remarkably rapid cell renewal, which is exclusively fueled by a small number of long-lived stem cells and their progeny. Stem cell activity is the best-characterized aspect of mucosal homeostasis in mitotically active tissues, and the dysregulation of regenerative capacity is a hallmark of epithelial immune defects. This dysregulation is frequently associated with pathologies ranging from chronic enteritis to malignancies in humans. Application of the adult Drosophila gastrointestinal tract model in current and future studies to analyze the immuno-physiological aspects of epithelial defense strategies, including stem cell behavior and re-epithelialization, will be necessary to improve our general understanding of stem cell participation in epithelial turnover. In this review, which describes exciting observations obtained from the adult Drosophila gastrointestinal tract, we summarize a remarkable series of recent findings in the literature to decipher the molecular mechanisms through which stem cells respond to nonsterile environments.

The chicken or the egg? Adaptation to desiccation and salinity tolerance in a lineage of water beetles

Transitions from fresh to saline habitats are restricted to a handful of insect lineages, as the colonization of saline waters requires specialized mechanisms to deal with osmotic stress. Previous studies have suggested that tolerance to salinity and desiccation could be mechanistically and evolutionarily linked, but the temporal sequence of these adaptations is not well established for individual lineages. We combined molecular, physiological and ecological data to explore the evolution of desiccation resistance, hyporegulation ability (i.e., the ability to osmoregulate in hyperosmotic media) and habitat transitions in the water beetle genus Enochrus subgenus Lumetus (Hydrophilidae). We tested whether enhanced desiccation resistance evolved before increases in hyporegulation ability or vice versa, or whether the two mechanisms evolved in parallel. The most recent ancestor of Lumetus was inferred to have high desiccation resistance and moderate hyporegulation ability. There were repeated shifts between habitats with differing levels of salinity in the radiation of the group, those to the most saline habitats generally occurring more rapidly than those to less saline ones. Significant and accelerated changes in hyporegulation ability evolved in parallel with smaller and more progressive increases in desiccation resistance across the phylogeny, associated with the colonization of meso- and hypersaline waters during global aridification events. All species with high hyporegulation ability were also desiccation-resistant, but not vice versa. Overall, results are consistent with the hypothesis that desiccation resistance mechanisms evolved first and provided the physiological basis for the development of hyporegulation ability, allowing these insects to colonize and diversify across meso- and hypersaline habitats.

Naturally Segregating Variation at Ugt86Dd Contributes to Nicotine Resistance in Drosophila melanogaster

Identifying the sequence polymorphisms underlying complex trait variation is a key goal of genetics research, since knowing the precise causative molecular events allows insight into the pathways governing trait variation. Genetic analysis of complex traits in model systems regularly starts by constructing QTL maps, but generally fails to identify causative sequence polymorphisms. Previously we mapped a series of QTL contributing to resistance to nicotine in a Drosophila melanogaster multiparental mapping resource and here use a battery of functional tests to resolve QTL to the molecular level. One large-effect QTL resided over a cluster of UDP-glucuronosyltransferases, and quantitative complementation tests using deficiencies eliminating subsets of these detoxification genes revealed allelic variation impacting resistance. RNAseq showed that Ugt86Dd had significantly higher expression in genotypes that are more resistant to nicotine, and anterior midgut-specific RNA interference (RNAi) of this gene reduced resistance. We discovered a segregating 22-bp frameshift deletion in Ugt86Dd, and accounting for the InDel during mapping largely eliminates the QTL, implying the event explains the bulk of the effect of the mapped locus. CRISPR/Cas9 editing of a relatively resistant genotype to generate lesions in Ugt86Dd that recapitulate the naturally occurring putative loss-of-function allele, leads to a large reduction in resistance. Despite this major effect of the deletion, the allele appears to be very rare in wild-caught populations and likely explains only a small fraction of the natural variation for the trait. Nonetheless, this putatively causative coding InDel can be a launchpad for future mechanistic exploration of xenobiotic detoxification.

Colony Collapse Disorder (CCD) and bee age impact honey bee pathophysiology

Honey bee (Apis mellifera) colonies continue to experience high annual losses that remain poorly explained. Numerous interacting factors have been linked to colony declines. Understanding the pathways linking pathophysiology with symptoms is an important step in understanding the mechanisms of disease. In this study we examined the specific pathologies associated with honey bees collected from colonies suffering from Colony Collapse Disorder (CCD) and compared these with bees collected from apparently healthy colonies. We identified a set of pathological physical characteristics that occurred at different rates in CCD diagnosed colonies prior to their collapse: rectum distension, Malpighian tubule iridescence, fecal matter consistency, rectal enteroliths (hard concretions), and venom sac color. The multiple differences in rectum symptomology in bees from CCD apiaries and colonies suggest effected bees had trouble regulating water. To ensure that pathologies we found associated with CCD were indeed pathologies and not due to normal changes in physical appearances that occur as an adult bee ages (CCD colonies are assumed to be composed mostly of young bees), we documented the changes in bees of different ages taken from healthy colonies. We found that young bees had much greater incidences of white nodules than older cohorts. Prevalent in newly-emerged bees, these white nodules or cellular encapsulations indicate an active immune response. Comparing the two sets of characteristics, we determined a subset of pathologies that reliably predict CCD status rather than bee age (fecal matter consistency, rectal distension size, rectal enteroliths and Malpighian tubule iridescence) and that may serve as biomarkers for colony health. In addition, these pathologies suggest that CCD bees are experiencing disrupted excretory physiology. Our identification of these symptoms is an important first step in understanding the physiological pathways that underlie CCD and factors impacting bee health.

Loci Contributing to Boric Acid Toxicity in Two Reference Populations of Drosophila melanogaster

Populations maintain considerable segregating variation in the response to toxic, xenobiotic compounds. To identify variants associated with resistance to boric acid, a commonly-used household insecticide with a poorly understood mechanism of action, we assayed thousands of individuals from hundreds of strains. Using the Drosophila Synthetic Population Resource (DSPR), a multi-parental population (MPP) of inbred genotypes, we mapped six QTL to short genomic regions containing few protein-coding genes (3–188), allowing us to identify plausible candidate genes underlying resistance to boric acid toxicity. One interval contains multiple genes from the cytochrome P450 family, and we show that ubiquitous RNAi of one of these genes, Cyp9b2, markedly reduces resistance to the toxin. Resistance to boric acid is positively correlated with caffeine resistance. The two phenotypes additionally share a pair of QTL, potentially suggesting a degree of pleiotropy in the genetic control of resistance to these two distinct xenobiotics. Finally, we screened the Drosophila Genetic Reference Panel (DGRP) in an attempt to identify sequence variants within mapped QTL that are associated with boric acid resistance. The approach was largely unsuccessful, with only one QTL showing any associations at QTL-specific 20% False Discovery Rate (FDR) thresholds. Nonetheless, these associations point to a potential candidate gene that can be targeted in future validation efforts. Although the mapping data resulting from the two reference populations do not clearly overlap, our work provides a starting point for further genetic dissection of the processes underlying boric acid toxicity in insects.

De novo transcriptome analysis of the excretory tubules of Carausius morosus (Phasmatodea) and possible functions of the midgut 'appendices'

The Malpighian tubules are the insect excretory organs, responsible for ion and water homeostasis and elimination of nitrogenous wastes. Post-genomic assays suggest they also metabolize and detoxify xenobiotic compounds and have antimicrobial properties. The Phasmatodea have an additional, unique set of excretory organs referred to predominantly as midgut appendices. Their function and how it compares to phasmid and other insect Malpighian tubules is unknown. Hypotheses include carbonic anhydrase activity, calcium and metal cation sequestration, and xenobiotic transport. This work presents the first comparative transcriptomic analysis of the Phasmatodean excretory organs, using the model insect Carausius morosus. I produced de novo transcriptomes of the midgut appendices, midgut wall, and Malpighian tubules, and looked for differentially expressed genes associated with putative organ functions. The appendices differentially and highly express lipid transport and metabolism proteins, and the biomineralization gene otopetrin. The Malpighian tubules differentially and highly express acid phosphatases and multiple transporter types, while appendices express fat-soluble vitamin and peptide transporters. Many defense proteins such as multidrug resistance proteins, ABC transporters, cytochrome P450's, and glutathione-S-transferases were differentially expressed in specific excretory organs. I hypothesize that the appendices and Malpighian tubules both have defensive / xenobiotic metabolism functions, but each likely target different substrates. Phasmid Malpighian tubules excrete as in other insects, while the appendices may predominantly regulate amino acids, fats, and fat-soluble compounds. Lipid metabolism in insects is poorly understood, and the Phasmatodea may thus serve as a model for studying this further.