Changes in the activity and the expression of detoxification enzymes in silkworms (Bombyx mori) after phoxim feeding

Transcriptome Analysis Reveals Antioxidant Defense Mechanisms in the Silkworm Bombyx mori after Exposure to Lead

Lead (Pb) is a major source of heavy metal contamination, and poses a threat to biodiversity and human health. Elevated levels of Pb can hinder insect growth and development, leading to apoptosis via mechanisms like oxidative damage. The midgut of silkworms is the main organ exposed to heavy metals. As an economically important lepidopteran model insect in China, heavy metal-induced stress on silkworms causes considerable losses in sericulture, thereby causing substantial economic damage. This study aimed to investigate Pb-induced detoxification-related genes in the midgut of silkworms using high-throughput sequencing methods to achieve a deeper comprehension of the genes' reactions to lead exposure. This study identified 11,567 unigenes and 14,978 transcripts. A total of 1265 differentially expressed genes (DEGs) were screened, comprising 907 upregulated and 358 downregulated genes. Subsequently, Gene Ontology (GO) classification analysis revealed that the 1265 DEGs were distributed across biological processes, cellular components, and molecular functions. This suggests that the silkworm midgut may affect various organelle functions and biological processes, providing crucial clues for further exploration of DEG function. Additionally, the expression levels of 12 selected detoxification-related DEGs were validated using qRT-PCR, which confirmed the reliability of the RNA-seq results. This study not only provides new insights into the detoxification defense mechanisms of silkworms after Pb exposure, but also establishes a valuable foundation for further investigation into the molecular detoxification mechanisms in silkworms.

Different binding properties of odorant-binding protein 8 to insecticides in Orius sauteri

Chemical sensing systems are vital in the growth and development of insects. Orius sauteri (Poppius) (Hemiptera: Anthocoridae) is an important natural enemy of many pests. The molecular mechanism of odorant binding proteins (OBPs) binding with common insecticides is still unknow in O. sauteri. In this study, we expressed in vitro OsauOBP8 and conducted fluorescence competition binding assay to investigate the function of OsauOBP8 to insecticides. The results showed that OsauOBP8 could bind with four common insecticides (phoxim, fenitrothion, chlorpyrifos, deltamethrin). Subsequently, we used molecular docking to predict and obtained candidate six amino acid residues (K4, K6, K13, R31, K49, K55) and then mutated. The result showed that three key residues (K4, K6, R31) play important role in OsauOBP8 bound to insecticides. Our study identified the key binding sites of OsauOBP8 to insecticides and help to better understand the molecular mechanism of OBPs to insecticides in O. sauteri.

Molecular characterization of MyD88 as a potential biomarker for pesticide-induced stress in Bombyx mori

The widespread use of pesticides hampers the immune system of non-target organisms, however, there is a lack of common biomarkers to detect such effects. Myeloid differentiation primary response factor 88 (MyD88) is a crucial junction protein in the Toll-like receptor signaling pathway, which plays an important role in the inflammatory response. In this study, we investigated MyD88 as a potential biomarker for pesticide-induced stress. Phylogenetic analysis revealed that MyD88 was a conserved protein in the evolution of vertebrates and invertebrates. MyD88s usually have death domain (DD) and Toll/interleukin-1 receptor (TIR) domain. Bombyx mori (B. mori) is an important economic insect that is sensitive to toxic substances. We found microbial pesticides enhanced the expression level of MyD88 in B. mori. Transcriptome analysis demonstrated that MyD88 expression level was increased in the fatbody after dinotefuran exposure, a third-generation neonicotinoid pesticide. Moreover, the expression of MyD88 was upregulated in fatbody and midgut by imidacloprid, a first-generation neonicotinoid pesticide. Additionally, insect growth regulator (IGR) pesticides, such as methoprene and fenoxycarb, could induce MyD88 expression in the fatbody of B. mori. These results indicated that MyD88 is a potential biomarker for pesticide-induced stress in B. mori. This study provides novel insights into screening common biomarkers for multiple pesticide stresses and important implications for the development of more sustainable pest management strategies.

Low concentration of indoxacarb interferes with the growth and development of silkworm by damaging the structure of midgut cells

As an important economic insect, Bombyx mori plays an essential role in the development of the agricultural economy. Indoxacarb, a novel sodium channel blocker insecticide, has been widely used for the control of various pests in agriculture and forestry, and its environmental pollution caused by flight control operations has seriously affected the safe production of sericulture in recent years. However, the lethal toxicity and adverse effects of indoxacarb on silkworm remain largely unknown. In this study, the toxicity of indoxacarb on the 5th instar larvae of silkworm was determined, with an LC50 (72 h) of 2.07 mg/L. Short-term exposure (24 h) to a low concentration of indoxacarb (1/2 LC50) showed significantly reduced body weight and survival rate of silkworm larvae. In addition, indoxacarb also led to decreased cocoon weight and cocoon shell weight, but had no significant effects on pupation, adult eclosion, and oviposition. Histopathological and ultrastructural analysis indicated that indoxacarb could severely damage the structure of the midgut epithelial cells, and lead to physiological impairment of the midgut. A total of 3883 differentially expressed genes (DEGs) were identified by midgut transcriptome sequencing and functionally annotated using GO and KEGG. Furthermore, the transcription level and enzyme activity of the detoxification related genes were determined, and our results suggested that esterases (ESTs) might play a major role in metabolism of indoxacarb in the midgut of B. mori. Future studies to examine the detoxification or biotransformation function of candidate genes will greatly enhance our understanding of indoxacarb metabolism in B. mori. The results of this study provide a theoretical basis for elucidating the mechanism of toxic effects of indoxacarb on silkworm by interfering with the normal physiological functions of the midgut.

Effects of different insecticides on transcripts of key genes in CncC pathway and detoxification genes in Helicoverpa armigera

The CncC pathway regulates the expression of multiple detoxification genes and contributes to the detoxification and antioxidation in insects. Many studies have focused on the impacts of plant allelochemicals on the CncC pathway, whereas studies on the effects of pesticides on key genes involved in this pathway are very limited. In this study, the effects of different types of commonly used insecticides on the transcripts of CncC, Keap1, and Maf and multiple detoxification genes of Helicoverpa armigera were evaluated using real-time quantitative polymerase chain reaction. The results showed that 8 insecticides (bifenthrin, λ-cyhalothrin, chlorantraniliprole, cyantraniliprole, spinosad, indoxacarb, chlorfenapyr, tolfenpyrad, and thiacloprid) significantly induced the expression of CncC and 4 insecticides (cypermethrin, acetamiprid, thiacloprid, and indoxacarb) suppressed the expression of Keap1 both at 24 h and 48 h; meanwhile, the expression levels of Maf were induced by 5 insecticides (fenvalerate, chlorantraniliprole, cyantraniliprole, lufenuron, and tolfenpyrad) at 24 h or 48 h. Multiple detoxification genes, especially cytochrome P450s genes, showed different up-regulation after bifenthrin, λ-cyhalothrin, chlorantraniliprole, cyantraniliprole, indoxacarb, and spinosad treatment for 48 h. Our results suggest that the CncC pathway and detoxification genes can be activated by different insecticides in H. armigera. These results establish a foundation for further studies on the relationship between the CncC pathway and the detoxification genes in H. armigera.

The inhibition of ecdysone signal pathway was the key of pyriproxyfen poisoning for silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone-like pesticide. Once intake occurs, it leads to a series of poisoning characters consequences in silkworm, Bombyx mori (ID: 7091, Lepidoptera), such as non- cocooning, non-pupation, production of low-active eggs, and extended stages. However, the poisoning mechanism is still unclear. Here, silkworms were fed mulberry leaves soaked with different pyriproxyfen concentrations, and the heads were dissected for transcriptome analysis, while the hemolymph was used for determinations of ecdysone and juvenile hormone titers. As a result, after conjoint analysis of 3 feeding groups and a control group, 555 differentially expressed genes (DEGs) were obtained, which were mainly involved in hormone metabolism, glycometabolism and protein metabolism. Meanwhile, 119 genes were significantly correlated with the pyriproxyfen concentrations, and they were mainly involved in drug metabolism and glycometabolism. The ecdysone titers in several feeding groups were significantly lower than those of the control group, while juvenile hormone was not detected in all groups, including the control and feeding groups. Correspondingly, due to activation of the juvenile hormone signaling pathway by pyriproxyfen, key genes in the ecdysone synthesis pathway were downregulated, and a large number of downstream genes were up- or downregulated. In addition, nearly all genes in the detoxification pathway were upregulated. These results suggested that, affected by the juvenile hormone signaling pathway, ecdysone titers decreased and further affected a series of downstream processes, and this was the key reason for pyriproxyfen poisoning in silkworm, B. mori, which could lay a foundation for the study of pyriproxyfen resistance in silkworm.

Toxicological effects of trace amounts of pyriproxyfen on the midgut of non-target insect silkworm

Pyriproxyfen is an insect growth regulator that is widely used in public health and pest control in agriculture. Our previous studies have shown that trace amounts of pyriproxyfen in the environment can cause serious toxic effects in the non-target insect silkworm, including failing to pupate, metamorphose and spin cocoons. However, it is unknown why pyriproxyfen not only has no lethal effects on fifth instar larvae but also tend to increase their body weight. The midgut is the main digestive organs of the silkworm, our results showed that the residual of pyriproxyfen in the silkworm at 24 h after 1 × 10^-4 mg/L pyriproxyfen treatment caused severe damage to the midgut microvilli, goblet cells, and nuclei of the silkworm, but body weight and digestibility of the larval were both increased. In addition, pyriproxyfen significantly (p < 0.05) increased the activities of digestive enzymes (α-amylase, trehalase, trypsin and lipase) in the midgut of silkworm. However, it caused down-regulation of ecdysone synthesis-related genes at the end of the fifth instar silkworm, decreased ecdysone titer, and prolonged larval instar. At the same time, pyriproxyfen also activated transcription of detoxification enzymes-related genes such as the cytochrome P450 enzyme genes Cyp9a22 and Cyp15C1, the carboxylesterase genes CarE-8 and CarE-11, and the glutathione S-transferase gene GSTo2. This study elucidated a novel toxicological effect of pyriproxyfen to insects, which not only expands the understanding of the effects of juvenile hormone pesticides on lepidopteran insects but also provides a reference for exploring the ecological security of non-target organisms.

Unraveling the innate immune responses of Bombyx mori hemolymph, fat body, and midgut to Bombyx mori nucleopolyhedrovirus oral infection by metabolomic analysis

Bombyx mori nucleopolyhedrovirus (BmNPV) infection causes a series of physiological and pathological changes in Bombyx mori (B. mori). Here, a metabolomic study of the innate immunity organs including hemolymph, fat body, and midgut of the silkworm strain Dazao following BmNPV challenge was conducted to reveal the metabolic variations in B. mori. Compared to the control, 4964 and 4942 features with 4077 and 4327 high-quality features were generated under positive and negative modes, respectively, from BmNPV-infected larvae. The principal component analysis and supervised learning method using partial least squares discrimination analysis demonstrated good analytical stability and experimental reproducibility of the metabolic profiles. Based on database annotations, a total of 296, 108, and 215 differential expressed metabolites (DEMs) were identified from BmNPV-infected group of hemolymph, fat body, and midgut, respectively, which were all mainly grouped into carboxylic acids and derivatives, fatty acyls, and glycerophospholipids. Kyoto Encyclopedia of Genes and Genomes Database enrichment analysis of the DEMs showed that amino acid metabolism was increased at 24 h after BmNPV infection. BmNPV induction was adopted to significantly alter a series of immune-related pathways including phospholipase D signaling pathway, FoxO signaling pathway, metabolism of xenobiotics by cytochrome P450, melanogenesis, membrane transport, carbohydrate metabolism, and lipid metabolism. The different levels of expression of several DEMs including l-glutamate, naphthalene, 3-succinoylpyridine 1-acyl-sn-glycerol 3-phosphate, and l-tyrosine which were involved in those pathways exhibited the immune responses of B. mori to BmNPV infection. Our findings are valuable for a better understanding of the antiviral mechanism of B. mori underlying the interaction between the silkworm and BmNPV.

Protective effects of pretreatment with Fe2+, Cu2+, and Rb+ on phoxim poisoning in silkworm, Bombyx mori

BACKGROUND

Phoxim is a widely used organophosphorus pesticide in agriculture. People are paying more and more attention to its toxicity. At present, there is no appropriate way to solve the phoxim poisoning of silkworm, which severely affected the development of sericulture. Fe²⁺, Cu²⁺, Rb⁺ exerted their biological effects through various forms in vivo.

METHODS

To evaluate the effect of Fe²⁺/Cu²⁺/Rb⁺ on phoxim poisoning in silkworm, Bombyx mori were treated with fresh mulberry leaves soaked in 2.5 mg/L phoxim for 2 min with 50 mg/L FeCl₂, 150 mg/L CuCl₂, or 0.5 mg/L RbCl from 5 days of the fifth-instar silkworm.

RESULTS

Fe²⁺, Cu²⁺, and Rb⁺ pretreatments significantly inhibited the phoxim-induced reduction of survival rate and alleviated the phoxim-induced poisoning symptoms. The protective effects of Fe²⁺, Cu²⁺, and Rb⁺ on phoxim poisoning might be due to their enhancement of superoxide dismutase (SOD), catalase (CAT), and carboxylesterase (CarE) in the hemolymph and fat body of silkworm. This enhancement might reduce reactive oxygen species (ROS) accumulation and oxidative stress (OS) caused by phoxim poisoning. Thereby it reduced the damage to silkworm tissues and cells.

CONCLUSIONS

These results showed that Fe²⁺, Cu²⁺, and Rb⁺ treatments protected the silkworm from phoxim poisoning by directly enhancing the activity of SOD, CAT, and CarE enzymes and reducing oxidative stress, but not dependent on the high expression of CYP genes. The use of Fe²⁺, Cu²⁺, and Rb⁺ to enhance the activity of SOD, CAT, and CarE enzymes may be an underlying effective way to solve phoxim poisoning in the silkworm industry.

Construction and analysis of the protein-protein interaction network for the detoxification enzymes of the silkworm, Bombyx mori

Detoxification enzymes are necessary for insects to metabolize toxic substances and maintain physiological activities. Cytochromes P450 (CYPs), glutathione S-transferases (GSTs), and carboxylesterase (CarEs) are the main detoxification enzymes in insects. In addition, UDP-glucosyltransferase and ATP-binding cassette transporter also participate in the process of material metabolism. This study collected proteins related to detoxification in the silkworm, Bombyx mori (Lepidoptera: Bombycidae). And we performed Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis on these proteins to understand their biological function. We constructed the protein-protein interaction network for the silkworm's detoxification enzymes and analyzed the network's topological properties. We found that BGIBMGA014046-TA, BGIBMGA003221-TA, BGIBMGA011092-TA, BGIBMGA000074-TA, and LOC732976 are the essential proteins in the network. These proteins are primarily involved in the process of ribosome biogenesis and may be related to protein synthesis. We integrated GO, KEGG, and network analysis and found that ribosome-associated protein and GSTs played a vital role in the detoxification process.

A role of peptidoglycan recognition protein in mediating insecticide detoxification in Glyphodes pyloalis

Glyphodes pyloalis Walker has become one of the most significant mulberry pests, and it has caused serious economic losses in major mulberry growing regions in China. Peptidoglycan recognition proteins (PGRPs) are responsible for initiating and regulating immune signalling pathways in insects. However, their roles responding to chemical pesticides is still less known. This study aimed to investigate the possible detoxication function of GpPGRP-S2 and GpPGRP-S3 in G. pyloalis in response to chlorfenapyr and phoxim. The chlorfenapyr and phoxim treatment significantly induced the expression level of GpPGRP-S3 at 48 h. In addition, the expression levels of GpPGRP-S2 and GpPGRP-S3 in the chlorfenapyr/phoxim treatment group were significantly higher in midgut than those in the control group at 48 h. The results of the survival experiment showed that silencing either GpPGRP-S2 or GpPGRP-S3 would not influence the survival rate of G. pyloalis which treated with phoxim, however, silencing GpPGRP-S2 or GpPGRP-S3 would cause G. pyloalis to be more easily killed by chlorfenapyr. The expression of carboxylesterase GpCXE1 was significantly induced by chlorfenapyr/phoxim treatment, while it was suppressed once silenced GpPGRP-S2 followed with chlorfenapyr treatment or silenced GpPGRP-S3 followed with phoxim treatment. These results might suggest that under the chlorfenapyr/phoxim treatment condition, the connection between GpPGRPs and detoxification genes in insect was induced to maintain physiological homeostasis; and these results may further enrich the mechanisms of insects challenged by insecticides.

The Expression of UGT46A1 Gene and Its Effect on Silkworm Feeding

The silkworm, Bombyx mori, uses a complex olfactory system to determine whether the food is edible. As an odor degrading enzyme, UDP-glycosyltransferase (UGT) participates in the degradation of odor molecules in the olfactory system of the silkworm. By sequencing the whole genome of the silkworm NB and using comparative genomics methods, we found that UGT46A1 is unique in species that eat mulberry leaves. Bioinformatics shows that its function may be related to the feeding habits of the silkworm. In this study, it was found through quantitative real-time polymerase chain reaction (qRT-PCR) that UGT46A1 was highly expressed in the heads of silkworms, which was consistent with the conjecture that UGT46A1 was involved in silkworm olfactory recognition. RNA interference (RNAi) was used to knock down the expression of UGT46A1. By observing the silkworm’s tendency toward mulberry leaves and food selectivity, it was found that the silkworms that successfully knocked down the UGT46A1 gene altered their feeding habits and that their ability to find food was weakened, but they could eat more leaves of plants other than mulberry leaves. This evidence indicates that UGT46A1 may affect the silkworm’s feeding by influencing the olfactory system of the silkworm.

Transcriptional response of detoxifying enzyme genes in Bombyx mori under chlorfenapyr exposure

The silkworm, Bombyx mori (B. mori) is an important economic insect which ingests mulberry leaves and products the silk in industry. Chlorfenapyr is a new halogenated pyrrole insecticide which has been promoted for the control of mulberry insect pests in China. However, the detoxification mechanism of the silkworm to chlorfenapyr has not been investigated yet. In the present study, we first estimated the LC₃₀ dose of chlorfenapyr for 3rd instar B. mori larvae, and then, in order to characterise the chlorfenapyr detoxification mechanism, the transcriptomes of chlorfenapyr-treated and untreated 3rd instar B. mori larvae were compared using RNA-sequencing. In total, 146, 533, 126 and 148, 957, 676 clean reads were obtained from insecticide-treated and control silkworm larvae, respectively, and these reads generated 10, 954 genes. The transcriptional profile of silkworm larvae was significantly influenced by chlorfenapyr treatment. A total of 1196 differentially expressed genes (DEGs) were identified in insecticide-treated and control B. mori larvae, in which 644 genes were upregulated and 552 genes were downregulated. Results showed that multiple DEGs were enriched in detoxication-related gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Eleven detoxifying enzyme genes which differentially expressed were screened, and their expression patterns were validated by qRT-PCR. Furthermore, we successfully knocked down all differentially upregulated detoxifying enzyme genes, and a bioassay showed that the mortality of chlorfenapyr-treated silkworm larvae was significantly higher after silencing these genes than in groups injected with dsGFP. The present study reveals the molecular basis of silkworm detoxification to chlorfenapyr exposure, and provides new insights into the management of insecticide damage in the silkworm.

A deep insight into the transcriptome of midgut and fat body reveals the toxic mechanism of fluoride exposure in silkworm

Fluoride generally exists in the natural environment, and has been reported to induce serious environmental hazard to animals, plants, and even humans via ecological cycle. Silkworm, Bombyx mori, which showed significant growth and reproductivity reduction when exposed to fluoride, has become a model to evaluate the toxicity of fluoride. However, the detailed mechanism underlying fluoride toxicity and corresponding transport proteins remain unclear. In this study, we performed RNA-seq of the larval midgut and fat body with fluoride exposure and normal treatment. Differential analysis showed that there were 4405 differentially expressed genes in fat body and 4430 DEGs in midgut with fluoride stress. By Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses, we identified several key pathways involved in the fluoride exposure and poisoning. We focused on the oxidative phosphorylation and MAPK signal pathway. QRT-PCR confirmed that oxidative phosphorylation process was remarkably inhibited by fluoride exposure and resulted in the blocking of ATP synthesis. The MAPK signal pathway was stimulated via phosphorylation signal transduction. Moreover, by protein structure analysis combined with the DEGs, we screen 36 potential membrane proteins which might take part in transporting fluoride. Taken together, the results of our study expanded the underlying mechanisms of fluoride poisoning on silkworm larval growth and development, and implied potential fluoride transport proteins in silkworm.

Transcriptome analysis of Penaeus vannamei hepatopancreas reveals differences in toxicity mechanisms between phoxim and prometryne

Due to overuse and terrestrial input, there are large quantities of phoxim and prometryne residues in some aquatic environments. In the present study, the effects of these compounds on Penaeus vannamei hepatopancreas were analysed at the transcriptome level to investigate toxicity in this nontarget aquaculture organism. Twelve normalised cDNA libraries were constructed using RNA from phoxim and prometryne treatment groups, and an untreated control group. A total of 667,750,902 clean reads were obtained. Analysis of differentially expressed genes (DEGs) identified 449 in control vs phoxim groups, 185 in control vs prometryne groups, and 183 in prometryne vs phoxim groups. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, arachidonic acid metabolism, pancreatic secretion, linoleic acid metabolism, and beta-alanine metabolism pathways were significantly enriched in control vs phoxim groups. In control vs prometryne groups, lysosome, pentose and glucuronate interconversion, antigen processing and presentation, and glycosaminoglycan degradation pathways were significantly enriched. In prometryne vs phoxim groups, protein digestion and absorption, extracellular matrix (ECM)-receptor interaction, PI3K-Akt signalling, cell adhesion molecule (CAM), AGE-RAGE signalling related to diabetic complications, focal adhesion, and renin secretion pathways were significantly enriched. In further detailed analysis, glutathione S-transferase (GST), glutathione peroxidase and basic phospholipase A2 were downregulated in the phoxim treatment group, indicating that phoxim damaged hepatopancreas. Upregulation of phospholipase A2 (secretory phospholipase A2-like) indicates possible inflammatory pathological injury to hepatopancreas caused by phoxim. Meanwhile, downregulation of CD63 indicates that prometryne affect the immune system.

Effect of pyriproxyfen exposure on cocooning and gene expression in the silk gland of Bombyx mori （Linnaeus, 1758）

Bombyx mori（Linnaeus, 1758） is an important economical insect, and the sericulture is a flourishing industry in many developing countries. Pyriproxyfen, a juvenile hormone pesticide, is often applied to cultivations widely in the world, and its exposure often resulted in silk yield reduction and non-cocooning. However, the effect of pyriproxyfen exposure on cocooning and gene expression level in the silk gland of B. mori has not been studied yet, and this study focused on the above issues. The result indicated that pyriproxyfen exposure can lead to silk gland injury, reduction of silk yield and cocooning rate. Furthermore, the expression levels of silk protein synthesis related genes were down regulated significantly. The same change trends were shown between PI3K/Akt and CncC/Keap1 pathway, which is the expressions of key genes can be elevated by pyriproxyfen exposure. In addition, the activity of detoxification enzymes (P450, GST and CarE) and the expression levels of detoxification genes were elevated after pyriproxyfen exposure, suggesting that detoxification enzymes may play an important role in detoxification of pyriproxyfen in silk gland. These results provided possible clues to the silk gland injury and gene transcriptional level changes in silkworm after pyriproxyfen exposure.

Physiological adaptations to sugar-mimic alkaloids: Insights from Bombyx mori for long-term adaption and short-term response

Insects evolved adaptive plasticity to minimize the effects of the chemical defenses of their host plants. Nevertheless, the expressional response and adaptation of phytophagous specialists for long-term adaption and short-term response to host phytochemicals remains largely unexplored. The mulberry (Morus alba)-silkworm (Bombyx mori) interaction is an old and well-known model of plant-insect interaction. In this study, we examined the long-term adaption and short-term response of the mulberry-specialist silkworm to two sugar-mimic alkaloids in mulberry: the commonly encountered 1-deoxynojirimycin (1-DNJ) and occasionally encountered 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1), respectively. Global transcriptional patterns revealed that the physiological responses induced by the selective expression of genes involved in manifold cellular processes, including detoxification networks, canonical digestion processes, target enzymes, and other fundamental physiological processes, were crucial for regulating metabolic homeostasis. Comparative network analysis of the effects of exposure to D-AB1 and 1-DNJ supported the contention that B. mori produced similar and specific trajectories of changed gene expression in response to different sugar-mimic alkaloids. D-AB1 elicited a substantial proportion of downregulated genes relating to carbohydrate metabolism, catabolic process, lipid metabolism, and glycan biosynthesis and metabolism. This study dramatically expands our knowledge of the physiological adaptations to dietary sugar-mimic alkaloid intake and uncovered both metabolic evolutionarily responses and unique adaptive mechanisms previously unknown in insects.

Effects of pyriproxyfen exposure on immune signaling pathway and transcription of detoxification enzyme genes in fat body of silkworm, Bombyx mori

Sericulture is a very important and flourishing industry in developing countries. Bombyx mori is a kind of important and well-studied economic insects in the whole world. In China, applying of pyriproxyfen pesticide often resulted in non-cocooning and silk yield reduction. However, the effects of pyriproxyfen exposure on immune signaling pathway in fat body of silkworm has not been reported yet now. In the present study, we found that the growth and development of silkworm were significantly affected by pyriproxyfen exposure and the fat body tissues were injured after treatment. It was also showed that the expressions of key genes of PI3K/Akt and CncC/Keap1 pathway can be elevated at 24-96 h after pyriproxyfen exposure. Furtherly, the relative expression levels of detoxification enzyme genes and the activities of detoxification enzymes were both increased by pyriproxyfen exposure. These results provided comprehensive view of fat body injury and gene expression changes in silkworm after pyriproxyfen exposure.

Responses of detoxification enzymes in the midgut of Bombyx mori after exposure to low-dose of acetamiprid

Bombyx mori is an important economic insect. However, the environmental pollution caused by the widespread use of neonicotinoid insecticides has significantly affected the safe production of sericulture. In this paper, we determined the LC₅₀ of acetamiprid, a kind of neonicotinoid insecticides, to 5th instar silkworm larvae, examined its residues in hemolymph and midgut of silkworm after continuous exposure to low-dose of acetamiprid, and investigated the transcription level of detoxifying-related genes and the activity of detoxifying enzymes. The results showed that acetamiprid was highly toxic (24-h LC₅₀, 1.50 mg/L) to silkworm larvae. After continuous exposure to low-dose of acetamiprid (0.15 mg/L), the acetamiprid residue concentrations in hemolymph and midgut were 0.90 and 0.58 μg/mg, respectively, at 48 h, but all decreased at 96 h. At 24 h of acetamiprid exposure, the transcription levels of CYP4M5 and CYP6AB4 and the P450 enzyme activity were significantly enhanced. However, the transcription levels of CarE and CarE-11 and the activity of CarE enzymes were both inhibited by acetamiprid exposure. After 24 h-72 h of acetamiprid exposure, the transcription levels of GSTe3 and GSTd1 were significantly up-regulated, and the GST enzyme activity was also significantly elevated from 48 h to 96 h. Furthermore, the expression levels of FoxO, CncC and Keap1, the key upstream genes of detoxification enzymes, showed a similar trend as the GST genes. These results indicated that acetamiprid was reduced in midgut and the expression of GSTs was upregulated may via FoxO/CncC/Keap1 signaling pathway, which plays a key role in detoxification responses.

Effects of phoxim pesticide on the immune system of silkworm midgut

Silkworm (Bombyx mori) is an important economic insect. Bombyx mori, which is exposed to sublethal doses of pesticides, has a low or no mortality rate, while it is susceptible to infections triggered by foreign pathogens. The immune regulatory mechanism of silkworms caused by trace pesticides still remains unclear. The midgut is the major organ of silkworm for digestion and nutrient absorption, and it plays a critical defensive role against pathogens. In the present study, the silkworm was susceptible to Enterobacter cloacae sp. (E. cloacae) after exposure to sublethal dose of phoxim. The body weight and survival rate of the phoxim-E. cloacae co-treatment group were significantly decreased after 120 h of treatment compared with the phoxim treatment group. The immune responses and expressions of immune-related genes were dysregulated in the midgut of silkworm following exposure to phoxim. Digital gene expression (DGE) analysis revealed that 44 immune response-related and immune defense-related genes were differentially expressed. qRT-PCR results indicated that the transcriptional levels of antimicrobial peptide genes Bmdefensin1, BmcecA, Bmglv1, Bmglv2, Bmmoricin and BmmoricinB3 were down-regulated by 0.77-, 0.37-, 0.05-, 0.19-, 0.34- and 0.54-fold, respectively. The transcriptional levels of Toll signaling pathway genes Bmcactus, Bmspatzle and Bmrel were down-regulated by 0.4-, 0.37- and 0.96-fold, respectively. Peritrophic membrane (PM) protein-related genes BmCBP-02, BmPM-41, BmPM-43 and BmCDA7 were down-regulated by 0.18-, 0.02-, 0.66- and 0.16-fold, respectively. The expressions of Toll signaling pathway genes were down-regulated at 48 h and 72 h. Immune deficiency (IMD) and Janus kinase and signal transducer and activator of transcription (JAK/STAT) signaling pathway genes were dysregulated after phoxim exposure. These results indicated that phoxim might cause damage to the PM and reduce the immune response of the silkworm, leading to susceptibility of silkworm to disease and damage from foreign pathogens.

Evaluation of the Strain Bacillus amyloliquefaciens YP6 in Phoxim Degradation via Transcriptomic Data and Product Analysis

Phoxim, a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries. The persistence of phoxim has caused serious environmental pollution problems. In this study, Bacillus amyloliquefaciens YP6 (YP6), which is capable of promoting plant growth and degrading broad-spectrum OPs, was used to study phoxim degradation. Different culture media were applied to evaluate the growth and phoxim degradation of YP6. YP6 can grow rapidly and degrade phoxim efficiently in Luria-Bertani broth (LB broth) medium. Furthermore, it can also utilize phoxim as the sole phosphorus source in a mineral salt medium. Response surface methodology was performed to optimize the degradation conditions of phoxim by YP6 in LB broth medium. The optimum biodegradation conditions were 40 °C, pH 7.20, and an inoculum size of 4.17% (v/v). The phoxim metabolites, O,O-diethylthiophosphoric ester, phoxom, and α-cyanobenzylideneaminooxy phosphonic acid, were confirmed by liquid chromatography-mass spectrometry. Meanwhile, transcriptome analysis and qRT-PCR were performed to give insight into the phoxim-stress response at the transcriptome level. The hydrolase-, oxidase-, and NADPH-cytochrome P450 reductase-encoding genes were significantly upregulated for phoxim hydrolysis, sulfoxidation, and o-dealkylation. Furthermore, the phoxim biodegradation pathways by YP6 were proposed, for the first time, based on transcriptomic data and product analysis.

Effects of chlorantraniliprole exposure on detoxification enzyme activities and detoxification-related gene expression in the fat body of the silkworm, Bombyx mori

Chlorantraniliprole (CAP) can induce excessive calcium release from muscle of insects, causing muscle paralysis until death, and its residues in farmland can cause poisoning in Bombyx mori (B. mori), resulting in the failure of cocooning. No reports have investigated the effects of CAP exposure on detoxification enzyme activities and detoxification-related gene expression in B. mori. In the present study, we treated mulberry leaves with CAP by the leaf-dipping method, and then B. mori larvae were continuously fed with the polluted mulberry leaves. Moreover, the detoxification enzyme activities and the expressions of detoxification-related genes in the fat body of B. mori were examined. The results showed that at 24 h after CAP exposure, the activities of P450 and GST enzymes were all significantly increased, with P450 enzymes responding fastest. CarE enzyme activity was up-regulated in 24 h, and then it was decreased compared with the control group. Furthermore, the expressions of the key genes in the PI3K/Akt/CncC signaling pathway (PI3K, PDK, Akt, CncC and Keap1) at the mRNA were significantly increased. Western blotting analysis revealed that Akt was inhibited at the protein level, resulting in decreased expression of Keap1 and increased expression of CncC. These results indicated that the PI3K/Akt/CncC signaling pathway in the fat body of B. mori responded to CAP exposure and regulated the expressions of downstream detoxification enzymes, thus enhancing the detoxifying capability of B. mori.

The silk gland damage and the transcriptional response to detoxifying enzymes-related genes of Bombyx mori under phoxim exposure

Silk gland is a major organ of Bombyx mori for the synthesis and secretion of silk protein. Phoxim exposure can be toxic to B. mori and causes a decrease of fibroin synthesis, finally affecting the silk production in industry. To study the mechanism of metabolism and detoxification of silk gland under phoxim exposure, we measured the residual quantity of phoxim in silk gland and hemolymph after phoxim exposure, and the detoxifying enzymes-related genes and enzyme activity were also investigated. Results indicated that the residual amount of phoxim existed up to 24 h in silk gland compared with that in hemolymph, suggesting that phoxim can accumulate in the silk glands within a certain time course. The transcriptional levels of PI3K/Akt genes, including Akt, Tor1, p70s6k and 4e-bp, were up-regulated by 6.919, 1.358, 10.766 and 7.708-fold, respectively. The expression of two downstream genes (CncC and Keap1) was up-regulated by 1.939 and 3.373-fold, respectively. In addition, the transcriptional levels of detoxification-related genes including CYP6AB, CYP306A, CarE2, GST1 and GSTd1 were up-regulated by 1.731, 1.221, 1.366, 1.376 and 6.591-fold, respectively. The enzymatic activity of CYP450, CarE and GST were increased over time. These results provided possible insights into the injury of silk gland and the transcriptional response to detoxifying enzymes-related genes in silkworm after phoxim exposure.

The immune strategies of mosquito Aedes aegypti against microbial infection

Yellow fever mosquito Aedes aegypti transmits many devastating arthropod-borne viruses (arboviruses), such as dengue virus, yellow fever virus, Chikungunya virus, and Zika virus, which cause great concern to human health. Mosquito control is an effective method to block the spread of infectious diseases. Ae. aegypti uses its innate immune system to fight against arboviruses, parasites, and fungi. In this review, we briefly summarize the recent findings in the immune response of Ae. aegypti against arboviral and entomopathogenic infections. This review enriches our understanding of the mosquito immune system and provides evidence to support the development of novel mosquito control strategies.

Changes in glucose metabolism and mRNA expression of IRS-2 in rats exposed to phoxim and the protective effects of vitamin E

Research has shown that organophosphorus pesticides impair glucose homeostasis and cause insulin resistance and type 2 diabetes. The current study investigates the influence of phoxim on insulin signaling pathways and the protective effects of vitamin E. Phoxim (180 mg kg-1) and VE (200 mg kg-1) were administered orally to Sprague-Dawley rats over a period of 28 consecutive days. After exposure to phoxim, the animals showed glucose intolerance and hyperinsulinemia during glucose tolerance tests, and insulin tolerance tests demonstrated an impaired glucose-lowering effect of insulin. Phoxim increases the fasting glucose, insulin and cholesterol levels, as well as the liver hexokinase activity (HK) significantly while decreasing the high density lipoprotein (HDL) cholesterol, and glycogen content in the liver and skeletal muscles observably. Furthermore, we observed an increase of insulin resistance biomarkers and a decrease of insulin sensitivity indices. The insulin receptor substrate (IRS)-2 mRNA expressions of liver and skeletal muscles were down-regulated by phoxim, while the expression of IRS-1 showed no difference. There were no differences in triglycerides, LDL-cholesterol, and fasting glucose treated with phoxim. On the basis of biochemical and molecular findings, phoxim has been determined to impair glucose homeostasis through insulin resistance and insulin signaling pathway disruptions resulting in a reduced function of insulin in hepatocytes and muscles. VE supplementation reduced the fasting glucose, increased the glycogen content and HDL-cholesterol, but did not reduce the insulin resistance indices, when phoxim-treated rats were compared to VE supplemented rats. Overall, this study shows that vitamin E modifies the phoxim toxicity in rats only to a moderate degree.

Activation of Aedes aegypti prophenoloxidase-3 and its role in the immune response against entomopathogenic fungi

Serine protease cascade-mediated melanization is an important innate immune response in insects and crustaceans, which involves the proteolytic activation of prophenoloxidase (PPO). In this study, we investigated the role of Aedes aegypti PPO3 in antifungal immune defence. We expressed and purified recombinant PPO3 (rPPO3) in Escherichia coli and demonstrated that rPPO3 was activated by ethanol and, to a lesser extent, by cetylpyridinium chloride. In the presence of Cu²⁺ , rPPO3 exhibited enzyme activity. Immunoblot results revealed that the rPPO3 was cleaved by the haemolymph from immune-challenged mosquitoes or purified Ostrinia furnacalis serine protease 105 in vitro. The cleaved rPPO3 converted dopamine to toxic intermediates that killed fungal conidia of Beauveria bassiana in vitro. In mosquitoes challenged with Be. bassiana, cleavage of rPPO3 produced a 50 kDa phenoloxidase (PO) fragment. Further analysis revealed that the survival rate of mosquitoes with fungal infection increased significantly following injection of rPPO3 into the haemocoel. Taken together, our results suggest that proteolytic cleavage of the mosquito PPO3 plays an important role in the antifungal immune response. This has led to a better understanding of the mechanism of PPO activation in the mosquito and the role of melanization in the antifungal immune response.

Two genomes of highly polyphagous lepidopteran pests (Spodoptera frugiperda, Noctuidae) with different host-plant ranges

Emergence of polyphagous herbivorous insects entails significant adaptation to recognize, detoxify and digest a variety of host-plants. Despite of its biological and practical importance - since insects eat 20% of crops - no exhaustive analysis of gene repertoires required for adaptations in generalist insect herbivores has previously been performed. The noctuid moth Spodoptera frugiperda ranks as one of the world’s worst agricultural pests. This insect is polyphagous while the majority of other lepidopteran herbivores are specialist. It consists of two morphologically indistinguishable strains (“C” and “R”) that have different host plant ranges. To describe the evolutionary mechanisms that both enable the emergence of polyphagous herbivory and lead to the shift in the host preference, we analyzed whole genome sequences from laboratory and natural populations of both strains. We observed huge expansions of genes associated with chemosensation and detoxification compared with specialist Lepidoptera. These expansions are largely due to tandem duplication, a possible adaptation mechanism enabling polyphagy. Individuals from natural C and R populations show significant genomic differentiation. We found signatures of positive selection in genes involved in chemoreception, detoxification and digestion, and copy number variation in the two latter gene families, suggesting an adaptive role for structural variation.

Antioxidant enzymes and their role in phoxim and carbaryl stress in Caenorhabditis elegans

Pesticide exposure can induce oxidative stress and cause changes to antioxidant enzymes in living organisms. In the present study, the effects of phoxim (an organophosphorus insecticide) and carbaryl (a carbamate insecticide) on antioxidant enzyme activity and gene expression were investigated in the model organism Caenorhabditis elegans. The results show that phoxim exposure can induce superoxide dismutase (SOD) and catalase (CAT) activities and decrease glutathione peroxidase (GPx) activity at lower concentrations. The expression levels of sod-3, sod-5, ctl-1, gpx-6, and gpx-8 were up-regulated after treatment with phoxim. The mRNA expression levels of sod-5, ctl-1 and gpx-6 were increased approximately 70-, 170- and 130-fold, respectively, in the 0.25mM treatment group compared to the control group. Carbaryl exposure decreased SOD activity and induced CAT and GPx activities. The addition of carbaryl up-regulated the expression of sod-5, ctl-1, ctl-3 and gpx-8. Specifically, ctl-1 expression increased approximately 10-fold, and gpx-8 expression increased <30-fold in the 0.5mM treatment group relative to the control group. The transcript level of sod-5 increased >20-fold, and ctl-3 increased approximately 10-fold in the 1mM treatment group. The functions of the antioxidant enzymes during oxidative stress caused by the two insecticides were investigated using deletion mutants. The LC₅₀ values phoxim for the of sod-3 (tm760), sod-5 (tm1146), ctl-1 (ok1242), ctl-3 (ok2042) and gpx-8 (tm2108) mutant strains were lower than those observed for the N2 strain. The LC₅₀ values of carbaryl for the ctl-1 (ok1242), ctl-3 (ok2042) and gpx-6 (tm2535) deletion mutant strains decreased in comparison to the N2 strain. The results suggest that these two insecticides caused oxidative stress and changed altered the antioxidant enzyme activities and their gene expressions in C. elegans. The sod-3, sod-5, ctl-1, ctl-3, gpx-6, and gpx-8 encoding enzymes may play roles in defending cells from oxidative stress caused by these two insecticides.

Sublethal dose of phoxim and Bombyx mori nucleopolyhedrovirus interact to elevate silkworm mortality

BACKGROUND

Silkworm (Bombyx mori) is an economically important insect. It is relatively less resistant to certain chemicals and environment exposures such as pesticides and pathogens. After pesticide exposures, the silkworms are more susceptible to microbial infections. The mechanism underlying the susceptibility might be related to immune response and oxidative stress.

RESULTS

A sublethal dose of phoxim combined with Bombyx mori nucleopolyhedrovirus (BmNPV) elevated the silkworm mortality at 96 h. We found a higher content of H₂ O₂ and increased levels of genes related to oxidative stress and immune response after treatment with a sublethal dose of phoxim for 24 h or 48 h. However, such response decreased with longer pesticide treatment. Mortality increased by 44% when B. mori was exposed to combined treatment with BmNPV and phoxim rather than BmNPV alone. The level of examined immune-related and oxidative-stress-related genes significantly decreased in the combined treatment group compared with the BmNPV group. Our results indicated that, with long-term exposure to pesticides such as OPs, even at sublethal dose, the oxidative stress response and immune responses in silkworm were inhibited, which may lead to further immune impairment and accumulation of oxidative stress, resulting in susceptibility to the virus and harm to the silkworm.

CONCLUSION

Our study provided insights for understanding the susceptibility to pathogen after pesticide exposures, which may promote the development of better pesticide controls to avoid significant economic losses. © 2016 Society of Chemical Industry.

Effect of oxidative phosphorylation signaling pathway on silkworm midgut following exposure to phoxim

Organophosphate pesticides are applied widely in the world for agricultural purposes, and their exposures often resulted in non-cocooning of Bombyx mori in China. Silkworm midgut is the major organ for digestion and nutrient absorption, importantly it is also a barrier against foreign substances and chemical pesticides. The purpose of this study was to determine the mechanism of oxidative injury in silkworm midgut with phoxim induction. The results showed that the transcription level of oxidative phosphorylation signaling pathway genes of midgut under phoxim stress. Digital gene expression (DGE) analysis revealed that 24 electron transport chain (ETC)-related genes were upregulated. Quantitative real time polymerase chain reaction results indicated that the ETC the genes encoding NADH-CoQ1, Succinic-Q, cyt c reductase-S, cyt c oxidase-S, cytochrome c oxidase polypeptide IV, ATP synthase, and vacuolar H+ ATP synthase were all significantly up-regulated by 1.50-, 1.31-, 1.42-, 1.44-, 1.70-, 2.03- and 1.43-fold, respectively. Phoxim induction enhanced the activity of ETC complex in mitochondria, and induced the accumulation of ROS in midgut. These results indicated that trace phoxim enhanced respiration in midgut, and the imbalance between the activity changes of ETC may led to reactive oxygen species accumulation. The ETC of mitochondria may be potential biomarkers of midgut toxicity in B. mori caused by phoxim exposure. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 167-175, 2017.

EXPRESSION AND EFFECTS OF MUTANT Bombyx mori ACETYLCHOLINESTRASE1 IN BmN CELLS

The main mechanism of toxicity of organophosphate (OP) and carbamate (CB) insecticides is their irreversible binding and inhibition of acetylcholinestrase (AChE), encoded by ace1 (acetylcholinestrase gene 1), leading to eventual death of insects. Mutations in AChE may significantly reduce insects susceptibility to these pesticides. Bombyx mori is an important beneficial insect, and no OP- or CB-resistant strains have been generated. In this study, wild-type ace1 (wace1) and mutant ace1 (mace1) were introduced into BmN cells, confirmed by screening and identification. The expression of wace1 and mace1 in the cells was confirmed by Western blot and their expression levels were about 21-fold higher than the endogenous ace1 level. The activities of AChE in wace1 and mace1 transgenic cells were 10.6 and 20.2% higher compared to control cells, respectively. mace1 transgenic cells had higher remaining activity than wace1 transgenic cells under the treatment of physostigmine (a reversible cholinesterase inhibitor) and phoxim (an OP acaricide). The results showed that ace1 transgene can significantly improve ace1 expression, and ace1 mutation at a specific site can reduce the sensitivity to AChE inhibitors. Our study provides a new direction for the exploration of the relationship between AChE mutations and drug resistance.

Induction of Cytochrome P450 Activity by the Interaction of Chlorantraniliprole and Sinigrin in the Spodoptera exigua (Lepidoptera: Noctuidae)

The joint toxicity of chlorantraniliprole, a novel insecticide that acts on ryanodine receptors, and sinigrin, a natural plant defense compound from brassicaceous vegetables, to the larvae of Spodoptera exigua (Hübner) was determined in this paper. Additionally, the joint effects of the two compounds on cytochrome P450 enzyme activity and on the expression levels of mRNA of three P450 genes (including CYP9A9, CYP6B, and CYP4G37) and an NADPH cytochrome P450 reductase gene (HQ852049) were investigated. The toxicity of the mixture of chlorantraniliprole and sinigrin to fourth-instar S. exigua larvae was 1.60-fold higher than the toxicity of the chlorantraniliprole-only treatment after 24 h. Induced by chlorantraniliprole and sinigrin, the specific activity of the P450 O-deethylase was affected in a time-, dose-, and organ-specific manner in fifth-instar S. exigua larvae. The effects were more pronounced in the midgut than in the fat body. The specific activity of the P450 O-deethylase in almost all treatments increased at 12, 24, and 36 h posttreatment compared with that in the control. Based on real-time PCR analyses, the expression levels of the P450 genes CYP9A9, CYP6B, and CYP4G37 and the NADPH cytochrome P450 reductase gene HQ852049 in fifth-instar S. exigua larvae were induced by chlorantraniliprole and sinigrin, and the trends were similar to the specific activity of the P450 O-deethylase. Therefore, the CYP9A9, CYP6B, and HQ852049 in the tested genes were the most inducible genes that were expressed when the S. exigua larvae were exposed to chlorantraniliprole and sinigrin.

Deltamethrin-Mediated Toxicity and Cytomorphological Changes in the Midgut and Nervous System of the Mayfly Callibaetis radiatus

Immature instars of mayflies are important constituents of the food web in aquatic ecosystems (especially in Neotropical regions) and they are among the most susceptible arthropods to pyrethroid insecticides. These insecticides have been recognized as important stressors of freshwater ecosystems, but their cellular effects in aquatic insects have been neglected. Here, we assessed the susceptibility to deltamethrin (a typical type II pyrethroid) as well as the deltamethrin-mediated cytomorphological changes in the central nervous system and midgut of the mayfly Callibaetis radiatus. While the deltamethrin LC50 for 24 h of exposure was of 0.60 (0.46-0.78) μg of a.i/L, the survival of C. radiatus was significantly reduced in deltamethrin concentrations ≥ 0.25 μg a.i/L at 96 h of exposure. Sub-lethal deltamethrin exposure severely affected the cytomorphology of C. radiatus midgut (e.g., muscle layer retraction, cytoplasm vacuolation, nucleus and striated border disorganization) and also induced slight cytomorphological changes in the brain (e.g., presence of pyknotic nuclei) and in the thoracic ganglia (e.g., vacuolation of neurons and presence of pyknotic nuclei) of these insects. However, DNA damage was absent in all of these organs, suggesting that the sublethal cellular stress induced by deltamethrin might disrupt physiological processes (e.g., metabolism or electrical signal transmission) rather than cause cell death (e.g., apoptosis) in C. radiatus. Thus, our findings indicated that deltamethrin actions at cellular levels represent a clear indication of sublethal effects on the C. radiatus survival abilities.

Effects of phoxim on nutrient metabolism and insulin signaling pathway in silkworm midgut

Silkworm (Bombyx mori) is an important economic insect. Each year, poisoning caused by phoxim pesticide leads to huge economic losses in sericulture in China. Silkworm midgut is the major organ for food digestion and nutrient absorption. In this study, we found that the activity and expression of nutrition metabolism-related enzymes were dysregulated in midgut by phoxim exposure. DGE analysis revealed that 40 nutrition metabolism-related genes were differentially expressed. qRT-PCR results indicated that the expression levels of insulin/insulin growth factor signaling (IIS) pathway genes Akt, PI3K, PI3K60, PI3K110, IRS and PDK were reduced, whereas PTEN's expression was significantly increased in the midgut at 24 h after phoxim treatment. However, the transcription levels of Akt, PI3K60, PI3K110, IRS, InR and PDK were elevated and reached the peaks at 48 h, which were 1.48-, 1.35-, 1.21-, 2.24-, 2.89-, and 1.44-fold of those of the control, respectively. At 72 h, the transcription of these genes was reduced. Akt phosphorylation level was increasing along with the growth of silkworms in the control group. However, phoxim treatment led to increased Akt phosphorylation that surged at 24 h but gradually decreased at 48 h and 72 h. The results indicated that phoxim dysregulated the expression of IIS pathway genes and induced abnormal nutrient metabolism in silkworm midgut, which may be the reason of the slow growth of silkworms.

Molecular mechanisms of silk gland damage caused by phoxim exposure and protection of phoxim-induced damage by cerium chloride in Bombyx mori

It is known that exposure to organophosphorus pesticides (OP) including phoxim can produce oxidative stress, neurotoxicity, and greatly attenuate cocooning rate in the silkworm, Bombyx mori. Cerium treatment has been demonstrated to relieve phoxim-induced toxicity in B. mori; however, very little is known about the molecular mechanisms of silk gland injury due to OP exposure and protection of gland damage due to cerium pretreatment. The aim of this study was to evaluate silk gland damage and its molecular mechanisms in phoxim-induced silkworm toxicity and the protective mechanisms of cerium following exposure to phoxim. The results showed that phoxim exposure resulted in severe gland damage, reductions in protein synthesis and the cocooning rate of silkworms. Cerium (Ce) attenuated gland damage caused by phoxim, promoted protein synthesis, increased the antioxidant capacity of the gland and increased the cocooning rate of B. mori. Furthermore, digital gene expression data suggested that phoxim exposure led to significant up-regulation of 714 genes and down-regulation of 120 genes. Of these genes, 122 were related to protein metabolism, specifically, the down-regulated Ser2, Ser3, Fib-L, P25, and CYP450. Ce pretreatment resulted in up-regulation of 162 genes, and down-regulation of 141 genes, importantly, Ser2, Ser3, Fib-L, P25, and CYP333B8 were up-regulated. Treatment with CeCl3 + phoxim resulted in higher levels of Fib-L, P25, Ser2, Ser3, CAT, TPx, and CYP333B8 expression in the silk gland of silkworms. These findings indicated that Ce increased cocooning rate via the promotion of silk protein synthesis-related gene expression in the gland under phoxim-induced toxicity. These findings may expand the application of rare earths in sericulture.

Molecular Signatures of Reduced Nerve Toxicity by CeCl3 in Phoxim-exposed Silkworm Brains

CeCl3 can reduce the damage caused by OP pesticides, in this study we used the brain of silkworms to investigate the mechanism of CeCl3 effects on pesticide resistance. The results showed that phoxim treatments led to brain damages, swelling and death of neurons, chromatin condensation, and mitochondrial damage. Normal nerve conduction was severely affected by phoxim treatments, as revealed by: increases in the contents of neurotransmitters Glu, NO, and ACh by 63.65%, 61.14%, and 98.54%, respectively; decreases in the contents of 5-HT and DA by 53.19% and 43.71%, respectively; reductions in the activities of Na(+)/K(+)-ATPase, Ca(2+)/Mg(2+)-ATPase, and AChE by 85.27%, 85.63%, and 85.63%, respectively; and increase in the activity of TNOS by 22.33%. CeCl3 pretreatment can significantly reduce such damages. Results of DGE and qRT-PCR indicated that CeCl3 treatments significantly upregulated the expression levels of CYP4G23, cyt-b5, GSTs-σ1, ace1, esterase-FE4, and β-esterase 2. Overall, phoxim treatments cause nerve tissue lesions, neuron death, and nerve conduction hindrance, but CeCl3 pretreatments can promote the expression of phoxim resistance-related genes in silkworm brains to reduce phoxim-induced damages. Our study provides a potential new method to improve the resistance of silkworms against OP pesticides.

Expression profile analysis of silkworm P450 family genes after phoxim induction

Silkworm (Bombyx mori) is an important economic insect and a model species for Lepidopteran. Each year, O,O-diethyl O-(alpha-cyanobenzylideneamino) phosphorothioate (phoxim) pesticide poisoning in China results in huge economic losses in sericulture. Silkworm fat body is the main organ for nutrient storage, energy supply, intermediary metabolism, and detoxification. Microarray analysis of silkworm Cytochrome P450 detoxification enzyme genes revealed that all tested P450 4 (CYP4) family genes are expressed in the fat body. Quantitative Real-time PCR (QRT-PCR) was used to detect the expression of CYP4 family genes in silkworm fat body 0, 24, 48, and 72 h after phoxim exposure. The expression levels of silkworm molting hormone synthesis-related genes started to change 24 h after phoxim exposure, with those of CYP302A1, CYP306A1, and CYP314A1 being elevated by 1.38-, 1.33-, and 2.10-fold, respectively. The CYP18A1 gene that participates in steroid hormone inactivation and the CYP15C1 gene that participates in the epoxidation during the synthesis of juvenile hormone (JH) from methyl farnesoate (MF) were increased by 3.85- and 7.82-fold, respectively. Phylogenetic analysis indicated that these endogenous hormone metabolism-related genes belong to CYP mito clan and clan 2, and that phoxim exposure may affect silkworm development and metamorphosis. The CYP4, CYP6, and CYP9 families all showed some degrees of increases in gene expression; among them, CYP49A1, CYP4L6, CYP6AB4, CYP9G3, CYP9A19, and CYP9A22's transcription levels were significantly upregulated to 12.77-, 2.64-, 2.42-, 4.06-, 3.32-, and 2.98-fold, respectively, of the control levels. In the fat body, CYP49A1, CYP6AB4, CYP9A19, and CYP9A22 were constantly expressed at high levels after 24, 48, and 72 h of phoxim treatments; according to phylogenetic analysis, these genes belong to detoxification-related clan 3 and clan 4 CYP families. These genes may participate in the metabolism of phoxim in silkworm fat body. The results obtained in this study provide a basis for future in-depth investigations of insect P450 family genes in metabolic detoxification.

Nanoparticulate anatase TiO2 (TiO2 NPs) upregulates the expression of silkworm (Bombyx mori) neuropeptide receptor and promotes silkworm feeding, growth, and silking

Bombyx mori orphan G protein-coupled receptor, BNGR-A4, is the specific receptor of B. mori neuropeptide F (BmNPFR, neuropeptide F designated NPF). BmNPFR binds specifically and efficiently to B. mori neuropeptides BmNPF1a and BmNPF1b, which activates the ERK1/2 signaling pathway to regulate B. mori food intake and growth. Titanium dioxide nanoparticles (TiO2 NPs) can promote B. mori growth. However, whether the mechanisms of TiO2 NPs' effects are correlated with BmNPFR remains unknown. In this study, the effects of TiO2 NPs (5mg/L) feeding and BmNPFR-dsRNA injection on B. mori food intake and growth were investigated; after TiO2 NPs treatments, B. mori food intake, body weight, and cocoon shell weight were 5.82%, 4.64%, and 9.30% higher, respectively, than those of controls. The food intake, body weight, and cocoon shell weight of the BmNPFR-dsRNA injection group were reduced by 8.05%, 6.28%, and 6.98%, respectively, compared to the control. After TiO2 NPs treatment for 72h, the transcriptional levels of BmNPFR, BmNPF1a, and BmNPF1b in the midgut were 1.58, 1.43, and 1.34-folds, respectively, of those of the control, but 1.99, 2.26, and 2.19-folds, respectively, of the BmNPFR-dsRNA injection group; the phosphorylation level of MAPK was 24.03% higher than the control, while the phosphorylation level of BmNPFR-dsRNA injection group was 71.00% of control. The results indicated that TiO2 NPs affect B. mori feeding and growth through increasing the expression of BmNPFR. This study helps clarify the roles of BmNPF/BmNPFR system in TiO2 NPs' effects on B. mori feeding, growth, and development.

Mechanisms of larval midgut damage following exposure to phoxim and repair of phoxim-induced damage by cerium in Bombyx mori

Bombyx mori is an important economic animal for silk production. However, it is liable to be infected by organophosphorus pesticide that can contaminate its food and growing environment. It has been known that organophosphorus pesticide including phoxim exposure may damage the digestive systems, produce oxidative stress and neurotoxicity in silkworm B. mori, whereas cerium treatment has been demonstrated to relieve phoxim-induced toxicity in B. mori. However, very little is known about the molecular mechanisms of midgut injury due to phoxim exposure and B. mori protection after cerium pretreatment. The aim of this study was to evaluate the midgut damage and its molecular mechanisms, and the protective role of cerium in B. mori following exposure to phoxim. The results showed that phoxim exposure led to severe midgut damages and oxidative stress; whereas cerium relieved midgut damage and oxidative stress caused by phoxim in B. mori. Furthermore, digital gene expression suggested that phoxim exposure led to significant up-regulation of 94 genes and down-regulation of 52 genes. Of these genes, 52 genes were related with digestion and absorption, specifically, the significant alterations of esterase, lysozyme, amylase 48, and lipase expressions. Cerium pretreatment resulted in up-regulation of 116 genes, and down-regulation of 29 genes, importantly, esterase 48, lipase, lysozyme, and α-amylase were up-regulated. Treatment with Phoxim + CeCl3 resulted in 66 genes up-regulation and 39 genes down-regulation; specifically, levels of esterase 48, lipase, lysozyme, and α-amylase expression in the midgut of silkworms were significantly increased. Therefore, esterase 48, lipase, lysozyme, and α-amylase may be potential biomarkers of midgut toxicity caused by phoxim exposure. These findings may expand the application of rare earths in sericulture.

Mechanism of enhanced Bombyx mori nucleopolyhedrovirus-resistance by titanium dioxide nanoparticles in silkworm

The infection of Bombyx mori nucleopolyhedrovirus (BmNPV) in silkworms is often lethal. It is difficult to prevent, and its lethality is correlated with both viral particle characteristics and silkworm strains. Low doses of titanium dioxide nanoparticles (TiO2 NPs) can promote silkworm growth and improve its resistance to organophosphate pesticides. In this study, TiO2 NPs' effect on BmNPV resistance was investigated by analyzing the characteristics of BmNPV proliferation and transcriptional differences in silkworm midgut and the transcriptional changes of immunity related genes after feeding with TiO2 NPs. We found that low doses of TiO2 NPs improved the resistance of silkworm against BmNPV by 14.88-fold, with the mortalities of the experimental group and control group being 0.56% and 8.33% at 144 h, respectively. The proliferation of BmNPV in the midgut was significantly increased 72 h after infection in both experimental and control groups; the control group reached the peak at 120 h, while the experimental group took 24 more hours to reach the maximal value that was 12.63 times lower than the control, indicating that TiO2 NPs can inhibit BmNPV proliferation in the midgut. Consistently, the expression of the BmNPV-resistant gene Bmlipase-1 had the same increase pattern as the proliferation changes. Immune signaling pathway analysis revealed that TiO2 NPs inhibited the proliferation of silkworm BmNPV to reduce the activation levels of janus kinase/signal transducer and activator of transcription (JAK/STAT) and phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway, while promoting the expression of Bmakt to improve the immunity. Overall, our results demonstrate that TiO2 NPs increase silkworm resistance against BmNPV by inhibiting virus proliferation and improving immunity in silkworms.

Differentially expressed genes in the fat body of Bombyx mori in response to phoxim insecticide

The silkworm, Bombyx mori, is an economically important insect. However, poisoning of silkworms by organophosphate pesticides causes tremendous loss to the sericulture. The fat body is the major tissue involved in detoxification and produces antimicrobial peptides and regulates hormones. In this study, a microarray system comprising 22,987 oligonucluotide 70-mer probes was employed to examine differentially expressed genes in the fat body of B. mori exposed to phoxim insecticide. The results showed that a total of 774 genes were differentially expressed upon phoxim exposure, including 500 up-regulated genes and 274 down-regulated genes. The expression levels of eight detoxification-related genes were up-regulated upon phoxim exposure, including six cytochrome P450s and two glutathione-S-transferases. It was firstly found that eight antimicrobial peptide genes were down-regulated, which might provide important references for studying the larvae of B. mori become more susceptible to microbial infections after phoxim treatment. In addition, we firstly detected the expression level of metamorphosis-related genes after phoxim exposure, which may lead to impacted reproduction. Our results may facilitate the overall understanding of the molecular mechanism of multiple pathways following exposure to phoxim insecticide in the fat body of B. mori.

Molecular mechanisms of reduced nerve toxicity by titanium dioxide nanoparticles in the phoxim-exposed brain of Bombyx mori

Bombyx mori (B. mori), silkworm, is one of the most important economic insects in the world, while phoxim, an organophosphorus (OP) pesticide, impact its economic benefits seriously. Phoxim exposure can damage the brain, fatbody, midgut and haemolymph of B. mori. However the metabolism of proteins and carbohydrates in phoxim-exposed B. mori can be improved by Titanium dioxide nanoparticles (TiO2 NPs). In this study, we explored whether TiO2 NPs treatment can reduce the phoxim-induced brain damage of the 5th larval instar of B. mori. We observed that TiO2 NPs pretreatments significantly reduced the mortality of phoxim-exposed larva and relieved severe brain damage and oxidative stress under phoxim exposure in the brain. The treatments also relieved the phoxim-induced increases in the contents of acetylcholine (Ach), glutamate (Glu) and nitric oxide (NO) and the phoxim-induced decreases in the contents of norepinephrine (NE), Dopamine (DA), and 5-hydroxytryptamine (5-HT), and reduced the inhibition of acetylcholinesterase (AChE), Na+/K+-ATPase, Ca2+-ATPase, and Ca2+/Mg2+-ATPase activities and the activation of total nitric oxide synthase (TNOS) in the brain. Furthermore, digital gene expression profile (DGE) analysis and real time quantitative PCR (qRT-PCR) assay revealed that TiO2 NPs pretreatment inhibited the up-regulated expression of ace1, cytochrome c, caspase-9, caspase-3, Bm109 and down-regulated expression of BmIap caused by phoxim; these genes are involved in nerve conduction, oxidative stress and apoptosis. TiO2 NPs pretreatment also inhibited the down-regulated expression of H+ transporting ATP synthase and vacuolar ATP synthase under phoxim exposure, which are involved in ion transport and energy metabolism. These results indicate that TiO2 NPs pretreatment reduced the phoxim-induced nerve toxicity in the brain of B. mori.

Molecular mechanisms of phoxim-induced silk gland damage and TiO2 nanoparticle-attenuated damage in Bombyx mori

Phoxim is a useful organophosphate (OP) pesticide used in agriculture in China, however, exposure to this pesticide can result in a significant reduction in cocooning in Bombyx mori (B. mori). Titanium dioxide nanoparticles (TiO2 NPs) have been shown to decrease phoxim-induced toxicity in B. mori; however, very little is known about the molecular mechanisms of silk gland damage due to OP exposure and repair of gland damage by TiO2 NP pretreatment. In the present study, exposure to phoxim resulted in a significant reduction in cocooning rate in addition to silk gland damage, whereas TiO2 NP attenuated phoxim-induced gland damage, increased the antioxidant capacity of the gland, and increased cocooning rate in B. mori. Furthermore, digital gene expression data suggested that phoxim exposure led to significant alterations in the expression of 833 genes. In particular, phoxim exposure caused significant down-regulation of Fib-L, Ser2, Ser3, and P25 genes involved in silk protein synthesis, and up-regulation of SFGH, UCH3, and Salhh genes involved in silk protein hydrolysis. A combination of both phoxim and TiO2 NP treatment resulted in marked changes in the expression of 754 genes, while treatment with TiO2 NPs led to significant alterations in the expression of 308 genes. Importantly, pretreatment with TiO2 NPs increased Fib-L, Ser2, Ser3, and P25 expression, and decreased SFGH, UCH3, and Salhh expression in silk protein in the silk gland under phoxim stress. Therefore, Fib-L, Ser2, Ser3, P25, SFGH, UCH3, and Salhh may be potential biomarkers of silk gland toxicity in B. mori caused by phoxim exposure.

The adverse effects of phoxim exposure in the midgut of silkworm, Bombyx mori

The silkworm is an important economic insect. Poisoning of silkworms by organophosphate pesticides causes tremendous loss to the sericulture. In this study, Solexa sequencing technology was performed to profile the gene expression changes in the midgut of silkworms in response to 24h of phoxim exposure and the impact on detoxification, apoptosis and immune defense were addressed. The results showed that 254 genes displayed at least 2.0-fold changes in expression levels, with 148 genes up-regulated and 106 genes down-regulated. Cytochrome P450 played an important role in detoxification. Histopathology examination and transmission electron microscope revealed swollen mitochondria and disappearance of the cristae of mitochondria, which are the important features in insect apoptotic cells. Cytochrome C release from mitochondria into the cytoplasm was confirmed. In addition, the Toll and immune deficiency (IMD) signal pathways were all inhibited using qRT-PCR. Our results could help better understand the impact of phoxim exposure on silkworm.

Titanium dioxide nanoparticles relieve silk gland damage and increase cocooning of Bombyx mori under phoxim-induced toxicity

Organophosphate pesticides are applied widely in the world for agricultural purposes, and their exposures often resulted in non-cocooning of Bombyx mori in China. TiO2 nanoparticles have been demonstrated to increase pesticide resistance of Bombyx mori. While the toxicity of phoxim is well-documented, very limited information exists on the mechanisms of TiO2 nanoparticles improving the cocooning function of Bombyx mori following exposure to phoxim. The present study was, therefore, undertaken to determine whether TiO2 nanoparticles attenuate silk gland injury and elevate cocooning of B. mori following exposure to phoxim. The findings suggested that phoxim exposure resulted in severe damages of the silk gland structure and significantly decreased the cocooning in the silk gland of Bombyx mori. Furthermore, phoxim exposure significantly resulted in reductions of total protein concentrations and suppressed expressions of silk protein synthesis-related genes, including Fib-L, Fib-H, P25, Ser-2, and Ser-3, in the silk gland. TiO2 nanoparticle pretreatment, however, could significantly relieve silk gland injury of Bombyx mori. Importantly, TiO2 nanoparticles could remarkably elevate cocooning and total protein contents and promote expressions of Fib-L, Fib-H, P25, Ser-2, and Ser-3 in the silk gland following exposure to phoxim.

Characterization and functional analysis of four glutathione S-transferases from the migratory locust, Locusta migratoria

Glutathione S-transferases (GSTs) play an important role in detoxification of xenobiotics in both prokaryotic and eukaryotic cells. In this study, four GSTs (LmGSTd1, LmGSTs5, LmGSTt1, and LmGSTu1) representing different classes were identified from the migratory locust, Locusta migratoria. These four proteins were heterologously expressed in Escherichia coli as soluble fusion proteins, purified by Ni(2+)-nitrilotriacetic acid agarose column and biochemically characterized. LmGSTd1, LmGSTs5, and LmGSTu1 showed high activities with 1-chloro-2, 4-dinitrobenzene (CDNB), detectable activity with p-nitro-benzyl chloride (p-NBC) and 1, 2-dichloro-4-nitrobenzene (DCNB), whereas LmGSTt1 showed high activity with p-NBC and detectable activity with CDNB. The optimal pH of the locust GSTs ranged between 7.0 to 9.0. Ethacrynic acid and reactive blue effectively inhibited all four GSTs. LmGSTs5 was most sensitive to heavy metals (Cu(2+) and Cd(2+)). The maximum expression of the four GSTs was observed in Malpighian tubules and fat bodies as evaluated by western blot. The nymph mortalities after carbaryl treatment increased by 28 and 12% after LmGSTs5 and LmGSTu1 were silenced, respectively. The nymph mortalities after malathion and chlorpyrifos treatments increased by 26 and 18% after LmGSTs5 and LmGSTu1 were silenced, respectively. These results suggest that sigma GSTs in L. migratoria play a significant role in carbaryl detoxification, whereas some of other GSTs may also involve in the detoxification of carbaryl and chlorpyrifos.