Innate immune responses in the Chinese oak silkworm, Antheraea pernyi

Molecular characterization, immune functions and DNA protective effects of peroxiredoxin-1 gene in Antheraea pernyi

Peroxiredoxins are antioxidant proteins that detoxify peroxynitrite, hydrogen peroxide, and organic hydroperoxides, impacting various physiological processes such as immune responses, apoptosis, cellular homeostasis, and so on. In the present study, we identified and characterized peroxiredoxin 1 from Antheraea pernyi (thereafter designated as ApPrx-1) that encodes a predicted 195 amino acid residue protein with a 21.8 kDa molecular weight. Quantitative real-time PCR analysis revealed that the mRNA level of ApPrx-1 was highest in the hemocyte, fat body, and midgut. Immune-challenged larval fat bodies and hemocytes showed increased ApPrx-1 transcript. Moreover, ApPrx-1 expression was induced in hemocytes and the whole body of A. pernyi following exogenous H2O2 administration. A DNA cleavage assay performed using recombinant ApPrx-1 protein showed that rApPrx-1 protein manifests the ability to protect supercoiled DNA damage from oxidative stress. To test the rApPrx-1 protein antioxidant activity, the ability of the rApPrx-1 protein to remove H2O2 was assessed in vitro using rApPrx-1 protein and DTT, while BSA + DDT served as a control group. The results revealed that ApPrx-1 can efficiently remove H2O2 in vitro. In the loss of function analysis, we found that ApPrx-1 significantly increased the levels of H2O2 in ApPrx-1-depleted larvae compared to the control group. We also found a significantly lower survival rate in the larvae in which ApPrx-1 was knocked down. Interestingly, the antibacterial activity was significantly higher in the ApPrx-1 depleted larvae, compared to the control. Collectively, evidence strongly suggests that ApPrx-1 may regulate physiological activities and provides a reference for further studies to validate the utility of the key genes involved in reliving oxidative stress conditions and regulating the immune responses of insects.

Enhanced resistance to Bacillus thuringiensis Cry1Ac toxin mediated by the activation of prophenoloxidase in a cosmopolitan pest

Plutella xylostella has evolved resistance to Bacillus thuringiensis Cry1Ac toxin over a long evolutionary period. Enhanced immune response is an important factor in insect resistance to a variety of insecticides, and whether phenoloxidase (PO), an immune protein, is involved in resistance to Cry1Ac toxin in P. xylostella remains unclear. Here, spatial and temporal expression patterns showed that prophenoloxidase (PxPPO1 and PxPPO2) in the Cry1S1000-resistant strain was more highly expressed in eggs, 4th instar, head, and hemolymph than those in G88-susceptible strain. The results of PO activity analysis showed that after treatment with Cry1Ac toxin PO activity was about 3 times higher than that before treatment. Furthermore, knockout of PxPPO1 and PxPPO2 significantly increased the susceptibility to Cry1Ac toxin. These findings were further supported by the knockdown of Clip-SPH2, a negative regulator of PO, which resulted in increased PxPPO1 and PxPPO2 expression and Cry1Ac susceptibility in the Cry1S1000-resistant strain. Finally, the synergistic effect of quercetin showed that larval survival decreased from 100 % to <20 % compared to the control group. This study will provide a theoretical basis for the analysis of immune-related genes (PO) genes involved in the resistance mechanism and pest control of P. xylostella.

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.

Larval crowding effects during early development in the Chinese oak silkmoth Antheraea pernyi (Lepidoptera: Saturniidae)

Chinese sericulture relies in part on the rearing of the Chinese oak silkmoth Antheraea pernyi, an insect with key cultural and ecological roles. While feeding primarily on oak, Antheraea species are known to accept alternative hosts such as birch Betula sp with little to no apparent negative fitness consequences. This opens up the range of hostplants that could be used for large-scale rearing of A. pernyi for silk production and food, or used by this species in possible invasions. To date, however, the natural history and ecology of A. pernyi remain subject of investigation. For instance, we still do not know how individuals respond to crowding developmental environments, which is an important factor to consider for the ecology of the species as well as for commercial rearing. Here, I describe the implications of larval crowding to the survival and growth of A. pernyi larvae during early development. I show that higher crowding is associated with stronger negative effects on growth and survival, corroborating findings from other holometabolous insects. I then discuss the implications of this findings for our understanding of optimum larval crowding. Overall, the findings reveal important ecological information for an insect species key for provisioning and cultural ecosystem services.

Silencing β-1,3-glucan binding protein enhances the susceptibility of Plutella xylostella to entomopathogenic fungus Isaria cicadae

BACKGROUND

The diamondback moth, Plutella xylostella is a notorious pest of brassicaceae crops globally and has developed serious resistance to insecticide. Insects primarily rely on their innate immunity to defense against various pathogens. In this study, we investigated the immunological functions of a β-1,3-glucan binding protein from P. xylostella (PxβGBP) and evaluated its potential for biocontrolling P. xylostella.

RESULTS

The open reading frame of PxβGBP is 1422 bp encoding 473 amino acids residues. PxβGBP contained a CBM39 domain, a PAC domain and a GH16 domain and shared evolutionary conservation with other lepidoptera βGRPs. PxβGBP was strongly expressed in the third instar larvae and fat body. PxβGBP transcript levels increased significantly after the challenge with microbes, including Isaria cicadae, Escherichia coli and Staphylococcus aureus. PxβGBP was identified in P. xylostella larvae challenged by I cicadae, but not in the naïve insects. Recombinant PxβGBP can directly bind fungal and bacterial cells, and also agglutinate the cells of I cicadae, S. aureus and E coli in a zinc-dependent manner. Knockdown of PxβGBP via RNA interference significantly down-regulated the expression of antimicrobial peptide gene gloverin, and enhanced the susceptibility of P. xylostella to I. cicadae infection, leading to high mortality.

CONCLUSION

These results indicated that PxβGBP plays an important role in the immune response of P. xylostella against I. cicadae infection, and could serve as a potential novel target for pest control. © 2022 Society of Chemical Industry.

Relish regulates innate immunity via mediating ATG5 activity in Antheraea pernyi

In innate immunity, autophagy is an important molecular mechanism that plays a critical role in the animal defense system. Given the importance of anti-microbial autophagy in the innate immune processes, the relationship between anti-microbial autophagy and LPS-induced innate immunity in A. pernyi was investigated. Quantitative RT-PCR analysis revealed that autophagy-related genes (ATG6, ATG5, and ATG12) were induced following LPS injection. LPS treatment in the Relish knockdown larvae reduced the expression of autophagy-related genes, especially ATG5. Furthermore, ATG5 depletion decreased the innate immune effect, while its over-expression with ATG12 was induced after the LPS challenge. The dual-luciferase assay revealed that Relish could regulate ATG5 expression by binding directly to the promoter of the ATG5 gene. Overall, our findings show that Relish regulates the ATG5 transcription to eliminate Gram-negative bacteria by anti-microbial autophagy, implying a strong connection between autophagy and innate immunity in immunologic homeostasis.

A Gut-Specific LITAF-Like Gene in Antheraea pernyi (Lepidoptera: Saturniidae) Involved in the Immune Response to Three Pathogens

Antheraea pernyi (Guérin-Méneville 1855) is an important resource for silk, food, and biohealth products; however, exogenous pathogens largely affect the commercial application potential of this species. Since the gut is a key organ for the digestion and absorption of nutrients as well as for immune defense, we used comparative transcriptome analysis to screen for a gut-specific molecular tool for further functional research in A. pernyi. In total, 3,331 differentially expressed genes (DEGs) were identified in the gut compared with all other pooled tissues of A. pernyi, including 1,463 upregulated genes in the gut. Among these, we further focused on a lipopolysaccharide-induced tumor necrosis factor-α factor (LITAF) gene because of its high gut-specific expression and the presence of a highly conserved SIMPLE-like domain, which is related to the immune response to pathogenic infections in many species. The cDNA sequence of ApLITAF was 447-bp long and contained a 243-bp open reading frame encoding an 80-amino acid protein. Immune challenge assays indicated that ApLITAF expression was significantly upregulated in the gut of A. pernyi naturally infected with nucleopolyhedrovirus (NPV) or fed leaves infected with the gram-negative bacterium Escherichia coli (Migula 1895) and the gram-positive bacterium Bacillus subtilis (Ehrenberg 1835). Cell transfection showed that ApLITAF localized to the lysosome. Collectively, these results suggested that ApLITAF played a role in the immune response of A. pernyi and could facilitate the future research and breeding application in this species.

Integrative multiomics analysis of Premolis semirufa caterpillar venom in the search for molecules leading to a joint disease

The joint disease called pararamosis is an occupational disease caused by accidental contact with bristles of the caterpillar Premolis semirufa. The chronic inflammatory process narrows the joint space and causes alterations in bone structure and cartilage degeneration, leading to joint stiffness. Aiming to determine the bristle components that could be responsible for this peculiar envenomation, in this work we have examined the toxin composition of the caterpillar bristles extract and compared it with the differentially expressed genes (DEGs) in synovial biopsies of patients affected with rheumatoid arthritis (RA) and osteoarthritis (OA). Among the proteins identified, 129 presented an average of 63% homology with human proteins and shared important conserved domains. Among the human homologous proteins, we identified seven DEGs upregulated in synovial biopsies from RA or OA patients using meta-analysis. This approach allowed us to suggest possible toxins from the pararama bristles that could be responsible for starting the joint disease observed in pararamosis. Moreover, the study of pararamosis, in turn, may lead to the discovery of specific pharmacological targets related to the early stages of articular diseases.

Transcriptome sequencing reveals Cnaphalocrocis medinalis against baculovirus infection by oxidative stress

Cnaphalocrocis medinalis granulovirus (CnmeGV) is a potential microbial agent against the rice leaffolder. Innate immunity is essential for insects to survive pathogenic infection. Therefore, to clarify the immune response of Cnaphalocrocis medinalis to the viral colonization, the gene expression profile of C. medinalis infected with CnmeGV was constructed by RNA-seq. A total of 8,503 differentially expressed genes (DEGs) were found including 5,304 up-regulated and 3,199 down-regulated unigenes. Gene enrichment analysis indicated that these DEGs were mainly linked to protein synthesis and metabolic process as well as ribosome and virus-infection pathways. Specifically, a significantly up-regulated PiggyBac-like transposon gene was identified suggested that the enhancement of transposon activity is related to host immunity. Further, the DEGs encoding oxidative stress related genes were identified and validated by RT-qPCR. Overall, 9 antioxidant enzyme genes and 4 antioxidant protein genes were up-regulated, and the extensive glutathione S-transferase genes were down-regulated. Our results provide a basis for understanding the molecular mechanisms of baculovirus action and oxidative stress response in C. medinalis and other insects.

Clathrin-dependent endocytosis predominantly mediates protein absorption by fat body from the hemolymph in Bombyx mori

During insect larval-pupal metamorphosis, proteins in the hemolymph are absorbed by the fat body for the maintenance of intracellular homeostasis; however, the type of proteins and how these proteins are internalized into the fat body are unclear. In Bombyx mori, the developmental profiles of total proteins in the hemolymph and fat body showed that hemolymph-decreased protein bands (55-100 kDa) were in accordance with those protein bands that increased in the fat body. Inhibition of clathrin-dependent endocytosis predominantly blocked the transportation of 55-100 kDa proteins from the hemolymph into the fat body, which was further verified by RNA interference treatment of Bmclathrin. Six hexamerins were shown to comprise ∼90% of the total identified proteins in both the hemolymph and fat body by mass spectrum (MS) analysis. In addition, hemolymph-specific proteins were mainly involved in material transportation, while fat body-specific proteins particularly participated in metabolism. In this paper, four hexamerins were found for the first time, and potential proteins absorbed by the fat body from the hemolymph through clathrin-dependent endocytosis were identified. This study sheds light on the protein absorption mechanism during insect metamorphosis.

Transcriptome Analysis Reveals Potential Antioxidant Defense Mechanisms in Antheraea pernyi in Response to Zinc Stress

The growth and development of the Chinese oak silkworm, Antheraea pernyi, are strongly influenced by environmental conditions, including heavy metal pollution. An excess of heavy metals causes cellular damage through the production of free radical reactive oxygen species. In this study, transcriptome analysis was performed to investigate global gene expression when A. pernyi was exposed to zinc infection. With RNA sequencing (RNA-Seq), a total of 25 795 510 and 38 158 855 clean reads were obtained from zinc-treated and control fat body libraries, respectively. We identified 2399 differential expression genes (DEGs) (1845 upregulated and 544 downregulated genes) in the zinc-treated library. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these DEGs were related to the peroxisome pathway that was associated with antioxidant defense. Our results suggest that fat bodies of A. pernyi constitute a strong antioxidant defense against heavy metal contamination.