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

Cloning and Functional Analysis of CncC and Keap1 Genes in Silkworm

CncC/keap1-ARE is an important signaling pathway for detoxification and antioxidation in Diptera and Coleoptera insects. However, such a signaling pathway has not been studied in Bombyx mori. In this study, BmCncC and Bmkeap1 genes were cloned, their amino acid sequences were analyzed, and each functional domain was mapped. Through phylogenetic analysis and sequence comparison among multiple species, we found that the Neh1 motif of CncC was highly conserved and the DLG motif was replaced by the DMG motif in Neh2. Conformational analysis showed that Neh1 of BmCncC forms a hairpin structure to bind DNA. The DGR region of Bmkeap1 contained abundant β sheets, which was involved in the recognition of Neh2. The transcription and expression analyses showed that both BmCncC and Bmkeap1 were highly expressed in the first instar larvae, and these two genes were expressed at a high level in the reproductive gland, fat body, and head. The transcriptional and expression levels of Akt and BmCncC in the fat body were significantly upregulated, and the expression of Bmkeap1 was downregulated after the phoxim treatment in silkworm. The transcriptional levels of CncC-regulated detoxification enzymes GST, cyp4M5, cyp6AE2, and cyp9G3 were increased by 4.026-, 5.246-, 3.821-, and 9.787-fold, respectively, while the activities of GST and CYP450 were increased by 1.521- and 1.231-fold, respectively, after phoxim treatment. These results indicated that the BmCncC/Bmkeap1 signaling pathway was activated by phoxim, leading to the expression of downstream detoxifying enzymes and detoxification of phoxim in silkworm.

Larval Exposure to Chlorpyrifos Affects Nutritional Physiology and Induces Genotoxicity in Silkworm Philosamia ricini (Lepidoptera: Saturniidae)

Chlorpyrifos is a most widely used organophosphate insecticide because of its cost effectiveness and degradable nature. However, this pesticide enters and contaminates the environment either by direct application, spray drifts or crop run off and shows adverse effect on the non-targeted organisms. Philosamia ricini (eri silkworm), one of the most exploited, domesticated and commercialized non mulberry silkworm is known for mass production of eri silk. The silkworm larvae get exposed to pesticide residues on the leaves of food plants. The present study investigates the effect of commercial formulation of chlorpyrifos (Pyrifos-20 EC) on eri silkworm. Initially the LC50 value of chlorpyrifos was determined at 24-96 h and further experiments were carried out with sub lethal concentrations of the chlorpyrifos after 24 h of exposure period. The potential toxicity of chlorpyrifos was evaluated as a fuction of metabolism and nutritional physiology in 3rd, 4th, and 5th instar larvae. Alteration in histoarchitecture of 5th instar eri silkworm gut exposed to sub lethal concentration of chlorpyrifos formulation was also studied. Chlorpyrifos induced genotoxicity in silkworm hemocytes was also investigated by single cell gel electrophoresis, micronuclei assay, and apoptosis assay. Herein, LC50 values of chlorpyrifos were calculated as 3.83, 3.35, 2.68, and 2.35 mg/L at 24, 48, 72, and 96h respectively. A significant decrease in trehalose activity along with digestive enzyme activity was observed in chlorpyrifos affected groups (P < 0.05). Further, genotoxicity study revealed higher tail percentage, tail length and tail moment of the damage DNA in chlorpyrifos exposed groups (P < 0.001). Moreover, at 2.0 mg/L concentration, ~10 fold increases in tail length was observed as compared to the control. Results showed activation of caspase activity following 24 h chlorpyrifos exposure (1.5 and 2.0 mg/L) in a dose-dependent manner. Moreover, in control group less number of apoptotic cells was detected, however in both chlorpyrifos exposed groups' numbers of apoptotic cells were statistically higher (P < 0.001). Taken together, this study provides evidence that chlorpyrifos pollution might have adverse effect on overall nutritional physiology and genotoxicity of eri silkworm that could lead to reduced survivability of this economically beneficial insect.

ace-3 plays an important role in phoxim resistance in Caenorhabditis elegans

Organophosphorus and carbamate are widely used in agricultural production. Caenorhabditis elegans is a model organism that is widely used in various toxicology studies. To understand the effects of two types of commonly used pesticides, phoxim (organophosphorus) and carbaryl (carbamate), we determined the activities of acetylcholinesterases (AChEs) and detected the expression of four ace genes by RT-qPCR in C. elegans following treatment with these pesticides. The results showed that phoxim and carbaryl could reduce acetylcholinesterase activities and up-regulate the ace-3 mRNA expression levels. We also detected the toxic effects of these pesticides on the ace-3 deletion mutant dc-2, and found that some characteristics, including LC50, development, movement, reproduction and lifespan, were reduced in the dc-2 mutant. However, the toxic effects of carbaryl were weaker than those of phoxim. Carbaryl treatment did not significantly affect the LC50, movement ability or lifespan. Interestingly, body and brood size increased with carbaryl treatment at low concentrations. These data showed that both phoxim and carbaryl could inhibit AChE but that the ace-3 was necessary for phoxim detoxification. The LC50 of phoxim and carbaryl in wild type N2 and the ace-3 deletion mutant dc-2. **Higher significant differences (P < 0.01).