Superoxide dismutase down-regulation and the oxidative stress is required to initiate pupation in Bombyx mori

In silico identification and expression analysis of superoxide dismutases in Tenebrio molitor

BACKGROUND

Insects encounter various environmental stresses, in response to which they generate reactive oxygen species (ROS). Superoxide dismutase (SOD) is an antioxidant metalloenzyme that scavenges superoxide radicals to prevent oxidative damage.

OBJECTIVE

To investigate expressions of SODs under oxidative stress in Tenebrio molitor.

METHODS

Here, we investigated the transcriptional expression of SODs by pesticide and heavy metals in Tenebrio moltior. First, we searched an RNA-Seq database for T. molitor SOD (TmSOD) genes and identified two SOD isoforms (TmSOD1-iso1 and iso2). We examined their activities under developmental stage, tissue-specific, and various types (pesticide and heavy metal) of oxidative stress by using qPCR.

RESULTS

Our results revealed two novel forms of TmSODs. These TmSODs had a copper/zinc superoxide dismutase domain, active site, Cu2+ binding site, Zn2+ binding site, E-class dimer interface, and P-class dimer interface. TmSODs (TmSOD1-iso1 and iso2) were expressed in diverse developmental phases and tissues. Pesticides and heavy metals caused an upregulation of these TmSODs.

CONCLUSION

Our findings suggest that the two TmSODs have different functions in T. molitor, providing insights into the detoxification ability of T. molitor.

Notch Signaling in Insect Development: A Simple Pathway with Diverse Functions

Notch signaling is an evolutionarily conserved pathway which functions between adjacent cells to establish their distinct identities. Despite operating in a simple mechanism, Notch signaling plays remarkably diverse roles in development to regulate cell fate determination, organ growth and tissue patterning. While initially discovered and characterized in the model insect Drosophila melanogaster, recent studies across various insect species have revealed the broad involvement of Notch signaling in shaping insect tissues. This review focuses on providing a comprehensive picture regarding the roles of the Notch pathway in insect development. The roles of Notch in the formation and patterning of the insect embryo, wing, leg, ovary and several specific structures, as well as in physiological responses, are summarized. These results are discussed within the developmental context, aiming to deepen our understanding of the diversified functions of the Notch signaling pathway in different insect species.

Low dose γ-radiation induced effects on wax moth (Galleria mellonella) larvae

Larvae of the greater wax moth Galleria mellonella are common pests of beehives and commercial apiaries, and in more applied settings, these insects act as alternative in vivo bioassays to rodents for studying microbial virulence, antibiotic development, and toxicology. In the current study, our aim was to assess the putative adverse effects of background gamma radiation levels on G. mellonella. To achieve this, we exposed larvae to low (0.014 mGy/h), medium (0.056 mGy/h), and high (1.33 mGy/h) doses of caesium-137 and measured larval pupation events, weight, faecal discharge, susceptibility to bacterial and fungal challenges, immune cell counts, activity, and viability (i.e., haemocyte encapsulation) and melanisation levels. The effects of low and medium levels of radiation were distinguishable from the highest dose rates used - the latter insects weighed the least and pupated earlier. In general, radiation exposure modulated cellular and humoral immunity over time, with larvae showing heightened encapsulation/melanisation levels at the higher dose rates but were more susceptible to bacterial (Photorhabdus luminescens) infection. There were few signs of radiation impacts after 7 days exposure, whereas marked changes were recorded between 14 and 28 days. Our data suggest that G. mellonella demonstrates plasticity at the whole organism and cellular levels when irradiated and offers insight into how such animals may cope in radiologically contaminated environments (e.g. Chornobyl Exclusion Zone).

Characterization of a glutamate-cysteine ligase in Bombyx mori

Glutamate-cysteine ligase (GCL) is a crucial enzyme involved in the synthesis of glutathione (GSH). Despite various studies on glutathione transferase, and its essential role in detoxification and resistance to oxidative stress, GSH synthesis has not been described in Bombyx mori (silkworms) to date. Silkworms form part of the lepidopterans that are considered as a model of agricultural pests. This study aimed to understand the GSH synthesis by GCL in silkworms, which may help in developing insecticides to tackle agricultural pests. Based on the amino acid sequence and phylogenetic tree, the B. mori GCL belongs to group 2, and is designated bmGCL. Recombinant bmGCL was overexpressed and purified to ensure homogeneity. Biochemical studies revealed that bmGCL uses ATP and Mg²⁺ to ligate glutamate and cysteine. High expression levels of bmgcl mRNA and GSH were observed in the silkworm fat body after exposure to insecticides and UV-B irradiation. Moreover, we found an increase in bmgcl mRNA and GSH content during pupation in the silkworm fat body. In this study, we characterized the B. mori GCL and analyzed its biochemical properties. These observations indicate that bmGCL might play an important role in the resistance to oxidative stress in the silkworms.

Depletion of Tip60/Kat5 affects the hepatic antioxidant system in mice

Tat-interactive protein 60 kDa (TIP60, also known as lysine acetyltransferase 5 [KAT5]) is a member of the MYST protein family with histone acetyltransferase activity. Recent studies have reported that TIP60 has multiple functions in many signal transduction mechanisms, especially p53-mediated apoptosis. Although the activation of apoptosis signaling pathways requires the presence of cellular reactive oxygen species (ROS) at a certain level, an imbalance between the production and consumption of ROS in cells results in oxidative stress (OS). In this study, we investigated for the first time how the absence of the Tip60 gene in the liver affects gene expression, enzyme activity, and protein expression of the hepatic antioxidant members localized in the cytoplasm, including superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), and glutathione S-transferase (GST). First, we successfully generated liver-specific Tip60 knockout mice (mutants) using Cre/LoxP recombination. The reduced glutathione level and nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) expression, a marker of OS, increased significantly in the Tip60 mutant liver. Gene expression, activity, and protein expression of the enzymatic antioxidant system, including SOD, CAT, GR, GPx, and GST were investigated in mutants and control groups. Despite a significant correlation between the gene, enzyme activity, and protein content for CAT and GR, this was not true for SOD and GPx. The overall results suggest that TIP60 acts on the hepatic antioxidant system both at the gene and protein levels, but the actual effect of the deletion of Tip60 is observed at the protein level, especially for SOD and GPx.

Systematic Functional Annotation Workflow for Insects

Next-generation sequencing has revolutionized entomological study, rendering it possible to analyze the genomes and transcriptomes of non-model insects. However, use of this technology is often limited to obtaining the nucleotide sequences of target or related genes, with many of the acquired sequences remaining unused because other available sequences are not sufficiently annotated. To address this issue, we have developed a functional annotation workflow for transcriptome-sequenced insects to determine transcript descriptions, which represents a significant improvement over the previous method (functional annotation pipeline for insects). The developed workflow attempts to annotate not only the protein sequences obtained from transcriptome analysis but also the ncRNA sequences obtained simultaneously. In addition, the workflow integrates the expression-level information obtained from transcriptome sequencing for application as functional annotation information. Using the workflow, functional annotation was performed on the sequences obtained from transcriptome sequencing of the stick insect (Entoria okinawaensis) and silkworm (Bombyx mori), yielding richer functional annotation information than that obtained in our previous study. The improved workflow allows the more comprehensive exploitation of transcriptome data and is applicable to other insects because the workflow has been openly developed on GitHub.

Occurrence, Density, and Transcriptomic Response of the Leafhopper Erythroneura sudra (Hemiptera: Cicadellidae) When Confronted With Different Fruit Tree Species

The leafhopper, Erythroneura sudra (Distant) is becoming a dominant insect pest, and usually can cause significant damage to fruit production in northern China. We studied the occurrence and density of E. sudra on three fruit tree species and its transcriptomic responses when it was fed on leaves of these tree species. A higher density and survival rate of E. sudra were recorded when it fed on leaves of peach (Amygdalus persica L.) (Rosales: Rosaceae) and cherry (Cerasus pseudocerasus Lindl) (Rosales: Rosaceae) than on apple (Malus domestica Mill) (Rosales: Rosaceae). Also, feeding on M. domestica induced the largest variation in transcriptomic profiles in E. sudra. In total, 166 genes were differentially expressed (89 upregulated and 77 downregulated) in E. sudra when it fed on M. domestica, compared to when it fed on the other two tree species. The upregulated genes were mainly related to 'response to oxidative stress', 'stress-resistance', and 'xenobiotic metabolic process'. The downregulated genes were mainly related to 'structural constituent of cuticle', 'biosynthetic process', and 'development regulation'. These results suggested that M. domestica significantly changed the expression of many genes and consequently caused lower occurrence and density of E. sudra. Such information could enhance our understanding of the leafhopper-host plant relationship. Additionally, it can contribute to the improvement of current control strategies for this pest.

Superoxide dismutase 6 is required during metamorphosis for the development of properly movable legs in Tribolium castaneum

The body form of holometabolous insects dramatically transforms from larval to adult stages during metamorphosis that occurs in the pupal stage. The larval disorganization and then new adult tissues are built up at this time. In motoneuron, larval neuronal cells degenerate, and new adult neurons are remodeled. Finally, adult neurons reconnect to new adult muscles. However, the factors that control metamorphosis have not yet been fully elucidated. Here, we show that an antioxidant enzyme, Tribolium castaneum superoxide dismutase 6 (TcSOD6), is secreted into the haemolymph and is required for proper movable legs during metamorphosis. TcSOD6 has a unique domain architecture and is mainly expressed in the pupal stage. The depletion of TcSOD6 expression in the pupa inhibits normal axon development and results in adults that display dysfunctional leg motions, suggesting that SOD6 expression is required for the development of properly movable legs. Therefore, we speculate that TcSOD6 might participate in some of the processes for larval neurons to be remodelled to new adult functions in the legs during metamorphosis, providing new insight into the evolution of SOD functions.

Identification and Functional Characterization of Toxoneuron nigriceps Ovarian Proteins Involved in the Early Suppression of Host Immune Response

The endophagous parasitoid Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) of the larval stages of the tobacco budworm Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae) injects the egg, the venom, the calyx fluid, which includes a Polydnavirus (T. nigriceps BracoVirus: TnBV) and the Ovarian Proteins (OPs) into the host body during oviposition. The host metabolism and immune system are disrupted prematurely shortly after parasitization by the combined action of the TnBV, venom, and OPs. OPs are involved in the early suppression of host immune response, before TnBV infects and expresses its genes in the host tissues. In this work, we evaluated the effect of HPLC fractions deriving from in toto OPs. Two fractions caused a reduction in hemocyte viability and were subsequently tested to detect changes in hemocyte morphology and functionality. The two fractions provoked severe oxidative stress and actin cytoskeleton disruption, which might explain the high rate of hemocyte mortality, loss of hemocyte functioning, and hence the host’s reduced hemocyte encapsulation ability. Moreover, through a transcriptome and proteomic approach we identify the proteins of the two fractions: eight proteins were identified that might be involved in the observed host hemocyte changes. Our findings will contribute to a better understanding of the secreted ovarian components and their role in parasitoid wasp strategy for evading host immune responses.

cDNA Cloning and Partial Characterization of the DJ-1 Gene from Tribolium castaneum

The DJ-1 gene is highly conserved across a wide variety of organisms and it plays a role in anti-oxidative stress mechanisms in cells. The red flour beetle, Tribolium castaneum, is widely used as a model insect species because it is easy to evaluate gene function in this species using RNA interference (RNAi). The T. castaneum DJ-1 (TcDJ-1) sequence is annotated in the T. castaneum genome database; however, the function and characteristics of the TcDJ-1 gene have not been elucidated. Here, we investigated the cDNA sequence of TcDJ-1 and partially characterized its function. First, we examined the TcDJ-1 amino acid sequence and found that it was highly conserved with sequences from other species. TcDJ-1 mRNA expression was higher in the early pupal and adult developmental stages. We evaluated oxidant tolerance in TcDJ-1 knockdown adults using paraquat and found that adults with TcDJ-1 knockdown exhibited increased sensitivity to paraquat. Our findings show that TcDJ-1 has an antioxidant function, as observed for DJ-1 from other insects. Therefore, these results suggest that TcDJ-1 protects against oxidative stress during metamorphosis.

3-Bromopyruvate-induced glycolysis inhibition impacts larval growth and development and carbohydrate homeostasis in fall webworm, Hyphantria cunea Drury

As a typical glycolytic inhibitor, 3-bromopyruvate (3-BrPA) has been extensively studied in cancer therapy in recent decades. However, few studies focused on 3-BrPA in regulating the growth and development of insects, and the relationship and regulatory mechanism between glycolysis and chitin biosynthesis remain largely unknown. The Hyphantria cunea, named fall webworm, is a notorious defoliator, which caused a huge economic loss to agriculture and forestry. Here, we investigated the effects of 3-BrPA on the growth and development, glycolysis, carbohydrate homeostasis, as well as chitin synthesis in H. cunea larvae. To elucidate the action mechanism of 3-BrPA on H. cunea will provide a new insight for the control of this pest. The results showed that 3-BrPA dramatically restrained the growth and development of H. cunea larvae and resulted in larval lethality. Meanwhile, we confirmed that 3-BrPA caused a significant decrease in carbohydrate, adenosine triphosphate (ATP), pyruvic acid (PA), and triglyceride (TG) levels by inhibiting glycolysis in H. cunea larvae. Further studies indicated that 3-BrPA significantly affected the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), glucose 6-phosphate dehydrogenase (G6PDH) and trehalase, as well as expressions of the genes related to glycolysis, resulting in carbohydrate homeostasis disorder. Moreover, it was found that 3-BrPA enhanced 20-hydroxyecdysone (20E) signaling by upregulating HcCYP306A1 and HcCYP314A1, two critical genes in 20E synthesis pathway, and accelerated chitin synthesis by upregulating transcriptional levels of genes in the chitin synthesis pathway in H. cunea larvae. Taken together, our findings provide a novel insight into the mechanism of glycolytic inhibitor in regulating the growth and development of insects, and lay a foundation for the potential application of glycolytic inhibitors in pest control as well.

Characterization of Heat Shock Protein 60 as an Interacting Partner of Superoxide Dismutase 2 in the Silkworm, Bombyx mori, and Its Response to the Molting Hormone, 20-Hydroxyecdysone

Oxidative stress promotes pupation in some holometabolous insects. The levels of superoxide, a reactive oxygen species (ROS), are increased and superoxide dismutase 1 (BmSod1) and superoxide dismutase 2 (BmSod2) are decreased during metamorphic events in silkworm (Bombyx mori). These observations strongly suggest that pupation is initiated by oxidative stress via the down-regulation of BmSod1 and BmSod2. However, the molecular mechanisms underlying ROS production during metamorphic events in silkworm remain unknown. To investigate these molecular mechanisms, the peripheral proteins of BmSod1 and BmSod2 were identified and characterized using dry and wet approaches in this study. Based on the results, silkworm heat shock protein 60 (BmHsp60) was identified as an interacting partner of BmSod2, which belongs to the Fe/MnSOD family. Furthermore, the present study results showed that BmHsp60 mRNA expression levels were increased in response to oxidative stress caused by ultraviolet radiation and that BmHsp60 protein levels (but not mRNA levels) were decreased during metamorphic events, which are regulated by the molting hormone 20-hydroxyecdysone. These findings improve our understanding of the mechanisms by which holometabolous insects control ROS during metamorphosis.