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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 H2O2 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 [ABSTRACT FROM AUTHOR]

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, Ca2+/Mg2+-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. [ABSTRACT FROM AUTHOR]

Silk gland is a silkworm organ where silk proteins are synthesized and secreted. Dietary supplement of TiO 2 nanoparticles (NPs) promotes silk protein synthesis in silkworms. In this study, digital gene expression (DGE) tag was used to analyze the gene expression profile of the posterior silk gland of silkworms that were fed with TiO 2 NPs. In total, 5,702,823 and 6,150,719 clean tags, 55,096 and 74,715 distinct tags were detected in TiO 2 NPs treated and control groups, respectively. Compared with the control, TiO 2 NPs treated silkworms showed 306 differentially expressed genes, including 137 upregulated genes and 169 downregulated genes. Of these differentially expressed genes, 106 genes were related to silk protein synthesis, among which 97 genes were upregulated and 9 genes were downregulated. Pathway mapping using the Kyoto Encyclopedia of Genes and Genomes (KEGG) showed that 20 pathways were significantly enriched in TiO 2 NPs treated silkworms, and the metabolic pathway-related genes were the most significantly enriched. The DGE results were verified by qRT-PCR analysis of eight differentially expressed genes. The DGE and qRT-PCR results were consistent for all three upregulated genes and three of the five downregulated genes, but the expression trends of the remaining two genes were different between qRT-PCR and DGE analysis. This study enhances our understanding of the mechanism of TiO 2 NPs promoted silk protein synthesis. [ABSTRACT FROM AUTHOR]

Folate metabolism pathway is mainly associated with syntheses of nucleic acids and proteins as well as DNA methylation and repair. Cytoplasmic C 1 tetrahydrofolate (C 1 -THF) synthase is a central enzyme in folate metabolism and plays an important role in C 1 -THF conversion. The full-length sequence of silkworm (Bombyx mori) cytoplasmic C 1 -THF synthase (BmC 1 -THF synthase) gene including an open reading frame (ORF) of 932 amino acid residues was cloned. Phylogenetic analysis indicated that BmC 1 -THF synthase shares 84% and 81% identity with C 1 -THF synthase of Papilio Xuthus and Danaus plexippus, respectively. Conserved sequence analysis showed that the 330 to 710 amino acid residues of BmC 1 -THF synthase were highly conserved among various organisms. Recombinant BmC 1 -THF synthase protein with a molecular weight of about 105.5 kDa was expressed in E. coli cells and identified using SDS-PAGE and western blot analysis. The expression of BmC 1 -THF synthase gene in eight silkworm tissues revealed that BmC 1 -THF synthase gene is widely expressed in various tissues of silkworm and highly expressed in the fat body. The expression characteristics of BmC 1 -THF synthase gene in response to oxidative stress were conducted under phoxim and high temperature (30 °C) exposure. The results showed that the transcriptional level of BmC 1 -THF synthase gene was upregulated by 3.435-fold and 6.845-fold after phoxim and high temperature (30 °C) exposure, respectively, indicating that BmC 1 -THF synthase gene may play a significant role in response of silkworm to oxidative stresses., (Copyright © 2018 Elsevier B.V. All rights reserved.)