A review on the DNA methyltransferase family of insects: Aspect and prospects

KDM1A, a potent and selective target, for the treatment of DNMT3A-deficient non-small cell lung cancer

BACKGROUND

DNMT3A is a crucial epigenetic regulation enzyme. However, due to its heterogeneous nature and frequent mutation in various cancers, the role of DNMT3A remains controversial. Here, we determine the role of DNMT3A in non-small cell lung cancer (NSCLC) to identify potential treatment strategies.

METHODS

To investigate the role of loss-of-function mutations of DNMT3A in NSCLC, CRISPR/Cas9 was used to induce DNMT3A-inactivating mutations. Epigenetic inhibitor library was screened to find the synthetic lethal partner of DNMT3A. Both pharmacological inhibitors and gene manipulation were used to evaluate the synthetic lethal efficacy of DNMT3A/KDM1A in vitro and in vivo. Lastly, MS-PCR, ChIP-qPCR, dual luciferase reporter gene assay and clinical sample analysis were applied to elucidate the regulation mechanism of synthetic lethal interaction.

RESULTS

We identified DNMT3A is a tumour suppressor gene in NSCLC and KDM1A as a synthetic lethal partner of DNMT3A deletion. Both chemical KDM1A inhibitors and gene manipulation can selectively reduce the viability of DNMT3A-KO cells through inducing cell apoptosis in vitro and in vivo. We clarified that the synthetic lethality is not only limited to the death mode, but also involved into tumour metastasis. Mechanistically, DNMT3A deficiency induces KDM1A upregulation through reducing the methylation status of the KDM1A promoter and analysis of clinical samples indicated that DNMT3A expression was negatively correlated with KDM1A level.

CONCLUSION

Our results provide new insight into the role of DNMT3A in NSCLC and elucidate the mechanism of synthetic lethal interaction between KDM1A and DNMT3A, which might represent a promising approach for treating patients with DNMT3A-deficient tumours.

A role of epigenetic mechanisms in regulating female reproductive responses to temperature in a pest beetle

Many species are threatened by climate change and must rapidly respond to survive in changing environments. Epigenetic modifications, such as DNA methylation, can facilitate plastic responses by regulating gene expression in response to environmental cues. Understanding epigenetic responses is therefore essential for predicting species' ability to rapidly adapt in the context of global environmental change. Here, we investigated the functional significance of different methylation-associated cellular processes on temperature-dependent life history in seed beetles, Callosobruchus maculatus Fabricius 1775 (Coleoptera: Bruchidae). We assessed changes under thermal stress in (1) DNA methyltransferase (Dnmt1 and Dnmt2) expression levels, (2) genome-wide methylation and (3) reproductive performance, with (2) and (3) following treatment with 3-aminobenzamide (3AB) and zebularine (Zeb) over two generations. These drugs are well-documented to alter DNA methylation across the tree of life. We found that Dnmt1 and Dnmt2 were expressed throughout the body in males and females, but were highly expressed in females compared with males and exhibited temperature dependence. However, whole-genome methylation did not significantly vary with temperature, and only marginally or inconclusively with drug treatment. Both 3AB and Zeb led to profound temperature-dependent shifts in female reproductive life history trade-off allocation, often increasing fitness compared with control beetles. Mismatch between magnitude of treatment effects on DNA methylation versus life history effects suggest potential of 3AB and Zeb to alter reproductive trade-offs via changes in DNA repair and recycling processes, rather than or in addition to (subtle) changes in DNA methylation. Together, our results suggest that epigenetic mechanisms relating to Dnmt expression, DNA repair and recycling pathways, and possibly DNA methylation, are strongly implicated in modulating insect life history trade-offs in response to temperature change.

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.

DNA methylase 1 influences temperature responses and development in the invasive pest Tuta absoluta

DNA methylase 1 (Dnmt1) is an important regulatory factor associated with biochemical signals required for insect development. It responds to changes in the environment and triggers phenotypic plasticity. Meanwhile, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae)-a destructive invasive pest-can rapidly invade and adapt to different habitats; however, the role of Dnmt1 in this organism has not been elucidated. Accordingly, this study investigates the mechanism(s) underlying the rapid adaptation of Tuta absoluta to temperature stress. Potential regulatory genes were screened via RNAi (RNA interference), and the DNA methylase in Tuta absoluta was cloned by RACE (Rapid amplification of cDNA ends). TaDnmt1 was identified as a potential regulatory gene via bioinformatics; its expression was evaluated in response to temperature stress and during different development stages using real-time polymerase chain reaction. Results revealed that TaDnmt1 participates in hot/cold tolerance, temperature preference and larval development. The full-length cDNA sequence of TaDnmt1 is 3765 bp and encodes a 1254 kDa protein with typical Dnmt1 node-conserved structural features and six conserved DNA-binding active motifs. Moreover, TaDnmt1 expression is significantly altered by temperature stress treatments and within different development stages. Hence, TaDnmt1 likely contributes to temperature responses and organismal development. Furthermore, after treating with double-stranded RNA and exposing Tuta absoluta to 35°C heat shock or -12°C cold shock for 1 h, the survival rate significantly decreases; the preferred temperature is 2°C lower than that of the control group. In addition, the epidermal segments become enlarged and irregularly folded while the surface dries up. This results in a significant increase in larval mortality (57%) and a decrease in pupation (49.3%) and eclosion (50.9%) rates. Hence, TaDnmt1 contributes to temperature stress responses and temperature perception, as well as organismal growth and development, via DNA methylation regulation. These findings suggest that the rapid geographic expansion of T absoluta has been closely associated with TaDnmt1-mediated temperature tolerance. This study advances the research on 'thermos Dnmt' and provides a potential target for RNAi-driven regulation of Tuta absoluta.

Untangling the gordian knot: The intertwining interactions between developmental hormone signaling and epigenetic mechanisms in insects

Hormones control developmental and physiological processes, often by regulating the expression of multiple genes simultaneously or sequentially. Crosstalk between hormones and epigenetics is pivotal to dynamically coordinate this process. Hormonal signals can guide the addition and removal of epigenetic marks, steering gene expression. Conversely, DNA methylation, histone modifications and non-coding RNAs can modulate regional chromatin structure and accessibility and regulate the expression of numerous (hormone-related) genes. Here, we provide a review of the interplay between the classical insect hormones, ecdysteroids and juvenile hormones, and epigenetics. We summarize the mode-of-action and roles of these hormones in post-embryonic development, and provide a general overview of epigenetic mechanisms. We then highlight recent advances on the interactions between these hormonal pathways and epigenetics, and their involvement in development. Furthermore, we give an overview of several 'omics techniques employed in the field. Finally, we discuss which questions remain unanswered and possible avenues for future research.

Downregulation of Ambra1 by altered DNA methylation exacerbates dopaminergic neuron damage in a fenpropathrin-induced Parkinson-like mouse model

Fenpropathrin (Fen), a volatile pyrethroid insecticide, is used widely for agricultural applications and has been reported to increase the risk of Parkinson's disease (PD). However, the molecular basis, underlying mechanisms, and pathophysiology of Fen-exposed Parkinsonism remain unknown. Recent studies have revealed epigenetic mechanisms underlying PD-related pathway regulation, including DNA methylation. Epigenetic mechanisms are potential targets for therapeutic intervention in neurodegenerative diseases. After whole-genome bisulfite sequencing (WGBS) of midbrain tissues from a Fen-exposed PD-like mouse model, we performed an association analysis of DNA methylation and gene expression. Then we successfully screened for the DNA methylation differential gene Ambra1, which is closely related to PD. The hypermethylation-low expression Ambra1 gene aggravated DA neuron damage in vitro and in vivo through the Ambra1/Parkin/LC3B-mediated mitophagy pathway. We administered 5-aza-2'-deoxycytidine (5-Aza-dC) to upregulate Ambra1 expression, thereby reducing Ambra1-mediated mitophagy and protecting DA neurons against Fen-induced damage. In conclusion, these findings elucidate the potential function of Ambra1 under the regulation of DNA methylation, suggesting that the inhibition of DNA methylation may alleviate Fen-exposed neuron damage.

Peroxiredoxin-2 gene in Antheraea pernyi modulates immune functions and protect DNA damage

Peroxiredoxins have been shown to protect insects from oxidative damage and to play a role in the immune system. In the present study, we cloned and characterized the Antheraea pernyi peroxiredoxin 2 (ApPrx-2) gene, then assessed its functional roles. The ApPrx-2 gene has a 687 bp open reading frame that encodes a protein with 288 amino acid residues. Quantitative real-time PCR analysis revealed that the mRNA levels of ApPrx-2 were highest in the hemocytes. Immune challenge assay revealed that ApPrx-2 transcription could be induced after microbial challenge. A DNA cleavage assay employing recombinant ApPrx-2 protein and a metal-catalyzed oxidation system showed that rApPrx-2 protein could protect supercoiled DNA against oxidative stress. The protein antioxidant activity of rApPrx-2 was examined, and it was found that rApPrx-2 exhibited a high level of antioxidant activity by removing H2O2. In addition, ApPrx-2 knockdown larvae had higher H2O2 levels and a lower survival rate when compared to controls. Interestingly, the antibacterial activity was significantly higher in ApPrx-2 depleted larvae compared with control. Overall, our findings indicate that ApPrx-2 may be involved in a range of physiological functions of A. pernyi, as it protects supercoiled DNA from oxidative stress and regulates antibacterial activity.

DNA methylation differences between stick insect ecotypes

Epigenetic mechanisms, such as DNA methylation, can influence gene regulation and affect phenotypic variation, raising the possibility that they contribute to ecological adaptation. Beginning to address this issue requires high-resolution sequencing studies of natural populations to pinpoint epigenetic regions of potential ecological and evolutionary significance. However, such studies are still relatively uncommon, especially in insects, and are mainly restricted to a few model organisms. Here, we characterize patterns of DNA methylation for natural populations of Timema cristinae adapted to two host plant species (i.e. ecotypes). By integrating results from sequencing of whole transcriptomes, genomes and methylomes, we investigate whether environmental, host and genetic differences of these stick insects are associated with methylation levels of cytosine nucleotides in the CpG context. We report an overall genome-wide methylation level for T. cristinae of ~14%, with methylation being enriched in gene bodies and impoverished in repetitive elements. Genome-wide DNA methylation variation was strongly positively correlated with genetic distance (relatedness), but also exhibited significant host-plant effects. Using methylome-environment association analysis, we pinpointed specific genomic regions that are differentially methylated between ecotypes, with these regions being enriched for genes with functions in membrane processes. The observed association between methylation variation and genetic relatedness, and with the ecologically important variable of host plant, suggests a potential role for epigenetic modification in T. cristinae adaptation. To substantiate such adaptive significance, future studies could test whether methylation can be transmitted across generations and the extent to which it responds to experimental manipulation in field and laboratory studies.

Pest status, molecular evolution, and epigenetic factors derived from the genome assembly of Frankliniella fusca, a thysanopteran phytovirus vector

BACKGROUND

The tobacco thrips (Frankliniella fusca Hinds; family Thripidae; order Thysanoptera) is an important pest that can transmit viruses such as the tomato spotted wilt orthotospovirus to numerous economically important agricultural row crops and vegetables. The structural and functional genomics within the order Thysanoptera has only begun to be explored. Within the > 7000 known thysanopteran species, the melon thrips (Thrips palmi Karny) and the western flower thrips (Frankliniella occidentalis Pergrande) are the only two thysanopteran species with assembled genomes.

RESULTS

A genome of F. fusca was assembled by long-read sequencing of DNA from an inbred line. The final assembly size was 370 Mb with a single copy ortholog completeness of ~ 99% with respect to Insecta. The annotated genome of F. fusca was compared with the genome of its congener, F. occidentalis. Results revealed many instances of lineage-specific differences in gene content. Analyses of sequence divergence between the two Frankliniella species' genomes revealed substitution patterns consistent with positive selection in ~ 5% of the protein-coding genes with 1:1 orthologs. Further, gene content related to its pest status, such as xenobiotic detoxification and response to an ambisense-tripartite RNA virus (orthotospovirus) infection was compared with F. occidentalis. Several F. fusca genes related to virus infection possessed signatures of positive selection. Estimation of CpG depletion, a mutational consequence of DNA methylation, revealed that F. fusca genes that were downregulated and alternatively spliced in response to virus infection were preferentially targeted by DNA methylation. As in many other insects, DNA methylation was enriched in exons in Frankliniella, but gene copies with homology to DNA methyltransferase 3 were numerous and fragmented. This phenomenon seems to be relatively unique to thrips among other insect groups.

CONCLUSIONS

The F. fusca genome assembly provides an important resource for comparative genomic analyses of thysanopterans. This genomic foundation allows for insights into molecular evolution, gene regulation, and loci important to agricultural pest status.

Insight into crustacean cathepsins: Structure-evolutionary relationships and functional roles in physiological processes

Cathepsins belong to a group of proteins that are present in both prokaryotic and eukaryotic organisms and have an extremely high degree of evolutionary conservation. These proteins are functionally active in extracellular environments as soluble enzymatic proteins or attached to plasma membrane receptors. In addition, they occur in cellular secretory vesicles, mitochondria, the cytosol, and within the nuclei of eukaryotic cells. Cathepsins are classified into various groups based on their sequence variations, leading to their structural and functional diversification. The molecular understanding of the physiology of crustaceans has shown that proteases, including cathepsins, are expressed ubiquitously. They also contain one of the central regulatory systems for crustacean reproduction, growth, and immune responses. This review focuses on various aspects of the crustaceans cathepsins and emphasizes their biological roles in different physiological processes such as reproduction, growth, development, and immune responses. We also describe the bioactivity of crustaceans cathepsins. Because of the vital biological roles that cathepsins play as cellular proteases in physiological processes, they have been proposed as potential novel targets for the development of management strategies for the aquaculture industries.

Peroxiredoxin 1 of Procambarus clarkii govern immune responses during pathogen infection

Members of the peroxiredoxin family are involved in a wide variety of physiological processes, including the ability to combat the effects of oxidative stress and immune responses, among others. Here, we cloned the cDNA of Procambarus clarkii Peroxiredoxin 1 (designated as PcPrx-1) and investigated its biological role in immune system functions in relation to microbial pathogens. The PcPrx-1 cDNA had 744 base pairs in an open reading frame that encoded 247 amino acid residues and contained a PRX_Typ2cys domain. The analysis of tissue specific expression patterns revealed that PcPrx-1 expression was ubiquitous in all tissues. In addition, the mRNA transcript of PcPrx-1 was found to be highest in the hepatopancreas. There was a significant upregulation of PcPrx-1 gene transcripts after exposure to LPS, PGN, and Poly I:C, but the transcription patterns were different after pathogen challenge. Double-stranded RNA was used to knockdown PcPrx-1, which resulted in a striking change in the expression of all the tested P. clarkii immune-associated genes, including lectin, Toll, cactus, chitinase, phospholipase, and sptzale. On the whole, these results suggest that PcPrx-1 is important to confer innate immunity against pathogens by governing the expression of critical transcripts that encode immune-associated genes.

The Potential Biological Roles of Circular RNAs in the Immune Systems of Insects to Pathogen Invasion

Circular RNAs (circRNAs) are a newly discovered class of endogenously expressed non-coding RNAs (ncRNAs). They are highly stable, covalently closed molecules that frequently exhibit tissue-specific expression in eukaryotes. A small number of circRNAs are abundant and have been remarkably conserved throughout evolution. Numerous circRNAs are known to play important biological roles by acting as microRNAs (miRNAs) or protein inhibitors ('sponges'), by regulating the function of proteins, or by being translated themselves. CircRNAs have distinct cellular functions due to structural and production differences from mRNAs. Recent advances highlight the importance of characterizing circRNAs and their targets in a variety of insect species in order to fully understand how they contribute to the immune responses of these insects. Here, we focus on the recent advances in our understanding of the biogenesis of circRNAs, regulation of their abundance, and biological roles, such as serving as templates for translation and in the regulation of signaling pathways. We also discuss the emerging roles of circRNAs in regulating immune responses to various microbial pathogens. Furthermore, we describe the functions of circRNAs encoded by microbial pathogens that play in their hosts.

Epigenetic regulations as drivers of insecticide resistance and resilience to climate change in arthropod pests

Arthropod pests are remarkably capable of rapidly adapting to novel forms of environmental stress, including insecticides and climate change. The dynamic interplay between epigenetics and genetics explains the largely unexplored reality underlying rapid climatic adaptation and the development of insecticide resistance in insects. Epigenetic regulation modulates gene expression by methylating DNA and acetylating histones that play an essential role in governing insecticide resistance and adaptation to climate change. This review summarises and discusses the significance of recent advances in epigenetic regulation that facilitate phenotypic plasticity in insects and their symbiotic microbes to cope with selection pressure implied by extensive insecticide applications and climate change. We also discuss how epigenetic changes are passed on to multiple generations through sexual recombination, which remains enigmatic. Finally, we explain how these epigenetic signatures can be utilized to manage insecticide resistance and pest resilience to climate change in Anthropocene.

MicroRNAs reshape the immunity of insects in response to bacterial infection

The interaction between bacteria and insects can significantly impact a wide range of different areas because bacteria and insects are widely distributed around the globe. The bacterial-insect interactions have the potential to directly affect human health since insects are vectors for disease transmission, and their interactions can also have economic consequences. In addition, they have been linked to high mortality rates in economically important insects, resulting in substantial economic losses. MicroRNAs (miRNAs) are types of non-coding RNAs involved in regulating gene expression post-transcriptionally. The length of miRNAs ranges from 19 to 22 nucleotides. MiRNAs, in addition to their ability to exhibit dynamic expression patterns, have a diverse range of targets. This enables them to govern various physiological activities in insects, like innate immune responses. Increasing evidence suggests that miRNAs have a crucial biological role in bacterial infection by influencing immune responses and other mechanisms for resistance. This review focuses on some of the most recent and exciting discoveries made in recent years, including the correlation between the dysregulation of miRNA expression in the context of bacterial infection and the progression of the infection. Furthermore, it describes how they profoundly impact the immune responses of the host by targeting the Toll, IMD, and JNK signaling pathways. It also emphasizes the biological function of miRNAs in regulating immune responses in insects. Finally, it also discusses current knowledge gaps about the function of miRNAs in insect immunity, in addition to areas that require more research in the future.

Age- and Lifespan-Dependent Differences in GO Caused DNA Damage in Acheta domesticus

The rising applicability of graphene oxide (GO) should be preceded by detailed tests confirming its safety and lack of toxicity. Sensitivity to GO of immature, or with different survival strategy, individuals has not been studied so far. Therefore, in the present research, we focused on the GO genotoxic effects, examining selected parameters of DNA damage (total DNA damage, double-strand breaks-DSB, 8-hydroxy-2'-deoxyguanosine-8-OHdG, abasic site-AP sites), DNA damage response parameters, and global methylation in the model organism Acheta domesticus. Special attention was paid to various life stages and lifespans, using wild (H), and selected for longevity (D) strains. DNA damage was significantly affected by stage and/or strain and GO exposure. Larvae and young imago were generally more sensitive than adults, revealing more severe DNA damage. Especially in the earlier life stages, the D strain reacted more intensely/inversely than the H strain. In contrast, DNA damage response parameters were not significantly related to stage and/or strain and GO exposure. Stage-dependent DNA damage, especially DSB and 8-OHdG, with the simultaneous lack or subtle activation of DNA damage response parameters, may result from the general life strategy of insects. Predominantly fast-living and fast-breeding organisms can minimize energy-demanding repair mechanisms.

Dynamic changes in genomic 5-hydroxymethyluracil and N6-methyladenine levels in the Drosophila melanogaster life cycle and in response to different temperature conditions

In this study, the level of DNA modifications was investigated in three developmental stages of Drosophila melanogaster (larvae, pupae, imago) and in an in vitro model (Schneider 2 cells). Analysis was carried out using two-dimensional ultra-performance liquid chromatography with tandem mass spectrometry. Our method made it possible, for the first time, to analyze a broad spectrum of DNA modifications in the three stages of Drosophila. Each stage was characterized by a specific modification pattern, and the levels of these compounds fluctuated throughout the D. melanogaster life cycle. The level of DNA modification was also compared between insects bred at 25 °C (optimal temperature) and at 18 °C, and the groups differed significantly. The profound changes in N6-methyladenine and 5-hydroxymethyluracil levels during the Drosophila life cycle and as a result of breeding temperature changes indicate that these DNA modifications can play important regulatory roles in response to environmental changes and/or biological conditions. Moreover, the supplementation of Schneider 2 cells with 1 mM L-ascorbic acid caused a time-dependent increase in the level of 5-(hydroxymethyl)-2'-deoxyuridine. These data suggest that a certain pool of this compound may arise from the enzymatic activity of the dTET protein.

Antheraea pernyi Suppressor of Cytokine Signaling 2 Negatively Modulates the JAK/STAT Pathway to Attenuate Microbial Infection

The Janus kinase (JAK) signal transducer and activator of transcription (STAT) pathway has been shown to govern various physiological processes, including immune responses, hematopoiesis, cell growth, and differentiation. Recent studies show that suppressors of cytokine signaling (SOCS) proteins attenuate JAK-STAT signaling in mammals; however, their functions are less clear in lepidopteran insects. Here, we report a full-length sequence of SOCS-2 from the Chinese oak silkworm Antheraea pernyi (designated as ApSOCS-2) and study its biological role in immune responses via the JAK-STAT pathway. ApSOCS-2 expression was high in the fat bodies and hemocytes of A. pernyi fifth instar larvae. After pathogen infection with nucleopolyhedrovirus, Beauveria bassiana, Escherichia coli, and Microccus luteus, ApSOCS-2 mRNA was strongly increased compared to the control group. To elucidate the possible involvement in innate immunity, we measured antimicrobial peptide genes expression profiles in the fat body of A. pernyi. In contrast, recombinant ApSOCS-2 protein administration significantly reduced the AMPs transcription, while the depletion of ApSOCS-2 by RNAi increased their expression. Furthermore, we observed higher antibacterial activity and lower bacterial replication in dsApSOCS-2-treated larvae. The ApSOCS-2 transcription level was reduced in STAT depleted A. pernyi larvae challenged by M. luteus. The ApSOCS-2 RNAi data sets were also subjected to transcriptomic analysis, which suggests that ApSOCS-2 is a key regulator of immune function. Taken together, our data suggest that ApSOCS-2 is required for the negative regulation of AMPs transcripts via the JAK-STAT pathway in the insect.

An insight into therapeutic efficacy of heterocycles as histone modifying enzyme inhibitors that targets cancer epigenetic pathways

Histone modifying enzymes are the key regulators involved in the post-translational modification of histone and non-histone. These enzymes are responsible for the epigenetic control of cellular functions. However, deregulation of the activity of these enzymes results in uncontrolled disorders such as cancer and inflammatory and neurological diseases. The study includes histone acetyltransferases, deacetylases, methyl transferases, demethylases, DNA methyl transferases, and their potent inhibitors which are in a clinical trial and used as medicinal drugs. The present review covers the heterocycles as target-specific inhibitors of histone-modifying enzyme, more specifically histone acetyltransferases. This review also confers more recent reports on heterocycles as potential HAT inhibitors covered from 2016-2022 and future perspectives of these heterocycles in epigenetic therapy.

Integrins in the Immunity of Insects: A Review

Integrins are a large group of cell-surface proteins that are classified as transmembrane proteins. Integrins are classified into different types based on sequence variations, leading to structural and functional diversity. They are broadly distributed in animals and have a wide range of biological functions such as cell-to-cell communication, intracellular cytoskeleton organization, cellular signaling, immune responses, etc. Integrins are among the most abundant cell surface proteins in insects, exhibiting their indispensability in insect physiology. Because of their critical biological involvement in physiological processes, they appear to be a novel target for designing effective pest control strategies. In the current literature review, we first discuss the discovery and expression responses of integrins against various types of pathogens. Secondly, we examine the specific biological roles of integrins in controlling microbial pathogens, such as phagocytosis, encapsulation, nodulation, immune signaling, and so on. Finally, we describe the possible uses of integrins to control agricultural insect pests.

The Emerging Role of STING in Insect Innate Immune Responses and Pathogen Evasion Strategies

Emerging evidence reveals that the stimulator of the interferon genes (STING) signaling pathway in insects and other animal cells helps them to sense and effectively respond to infection caused by numerous types of microbial pathogens. Recent studies have shown that genomic material from microbial pathogens induces the STING signaling pathway for the production of immune factors to attenuate infection. In contrast, microbial pathogens are equipped with various factors that assist them in evading the STING signaling cascade. Here we discuss the STING signaling pathway different animal groups compared to human and then focus on its crucial biological roles and application in the microbial infection of insects. In addition, we examine the negative and positive modulators of the STING signaling cascade. Finally, we describe the microbial pathogen strategies to evade this signaling cascade for successful invasion.

Molecular Identification of Two DNA Methyltransferase Genes and Their Functional Characterization in the Anti-Bacterial Immunity of Antheraea pernyi

Under different physiological conditions, such as microbial infection, epigenetic mechanisms regulate genes at the transcription level in living organisms. DNA methylation is a type of epigenetic mechanism in which DNA methyltransferases modify the expression of target genes. Here, we identified a full-length sequence of DNMT-1 and DNMT-2 from the Chinese oak silkworm, A. pernyi, which was highly similar to the homologous sequences of Bombyx mori. ApDNMT-1 and ApDNMT-2 have unique domain architectures of insect DNMTs, highlighting their conserved functions in A. pernyi. ApDNMT-1 and ApDNMT-2 were found to be widely expressed in various tissues, with the highest levels of expression in hemocytes, the ovary, testis, and fat bodies. To understand the biological role of these genes in microbial resistance, we challenged the fifth instar larvae of A. pernyi by administrating Gram-positive and Gram-negative bacteria and fungi. The results revealed that transcript levels of ApDNMT-1 and ApDNMT-2 were increased compared to the control group. The inhibition of these genes by a DNMTs inhibitor [5-azacytidine (5-AZA)] significantly reduced bacterial replication and larvae mortality. In addition, 5-AZA treatment modified the expression patterns of antimicrobial peptides (AMPs) in the A. pernyi larvae. Our results suggest that ApDNMT-1 and ApDNMT-2 seem to have a crucial role in innate immunity, mediating antimicrobial peptide responses against bacterial infection in A. pernyi.

Transcriptome Sequencing Highlights the Regulatory Role of DNA Methylation in Immune-Related Genes’ Expression of Chinese Oak Silkworm, Antheraea pernyi

Simple Summary

Antheraea pernyi is an important lepidopteran that has been used as a model insect for various physiological systems. DNA methylation has recently been discovered to control a variety of physiological processes in animals throughout their lives. We investigated the effect of DNA methylation on the innate immune system of A. pernyi and found that DNA methylation inhibition modifies gene expression, especially in immune-related genes. Finally, our data suggest that DNA methylation may regulate gene expression in insects, and microbial infection likely induces DNA methylation of the host genome.

Abstract

Antheraea pernyi is an important lepidopteran used as a model insect species to investigate immune responses, development, and metabolism modulation. DNA methylation has recently been found to control various physiological processes throughout the life of animals; however, DNA methylation and its effect on the physiology of insects have been poorly investigated so far. In the present study, to better understand DNA methylation and its biological role in the immune system, we analyzed transcriptome profiles of A. pernyi pupae following DNA methylation inhibitor injection and Gram-positive bacteria stimulation. We then compared the profiles with a control group. We identified a total of 55,131 unigenes from the RNA sequence data. A comparison of unigene expression profiles showed that a total of 680 were up-regulated and 631 unigenes were down-regulated in the DNA-methylation-inhibition-bacteria-infected group compared to the control group (only bacteria-injected pupae), respectively. Here, we focused on the immune-related differentially expressed genes (DEGs) and screened 10 genes that contribute to immune responses with an up-regulation trend, suggesting that microbial pathogens evade host immunity by increasing DNA methylation of the host genome. Furthermore, several other unigenes related to other pathways were also changed, as shown in the KEGG analysis. Taken together, our data revealed that DNA methylation seems to play a crucial biological role in the regulation of gene expression in insects, and that infection may enhance the host genome DNA methylation by a yet-unknown mechanism.

The emerging role of epigenetic mechanisms in insect defense against pathogens

Insects resist infection by natural selection that favors the survival and reproduction of the fittest phenotypes. Although the genetic mechanisms mediating the evolution of insect resistance have been investigated, little is known about the contribution of epigenetic mechanisms. Gene expression in response to a pathogen selection pressure is regulated by different mechanisms affecting chromatin plasticity. Whether transgenerational inheritance of genome-wide epigenetic marks contributes to the heritable manifestation of insect resistance is presently debated. Here, we review the latest works on the contributions of chromatin remodeling to insect immunity and adaptation to pathogens. We highlight DNA methylation, histone acetylation, and microRNAs in mediating the transgenerational inherited transcriptional reprogramming of defense-related gene expression and the evolution of insect resistance.

Hypermethylation of the Promoter of miR-338-5p Mediates Aberrant Expression of ETS-1 and Is Correlated With Disease Severity Of Astrocytoma Patients

The pro-oncogene ETS-1 (E26 transformation-specific sequence 1) is a key regulator of the proliferation and invasion of cancer cells. The present work examined the correlation of the aberrant expression of ETS-1 with histological or clinical classification of astrocytoma: grade I (pilocytic astrocytoma), grade II (diffuse astrocytoma), grade III (anaplastic astrocytoma), and grade IV (glioblastoma multiforme). MicroRNA, miR-338-5p, was predicted by an online tool (miRDB) to potentially target the 3’ untranslated region of ETS-1; this was confirmed by multi-assays, including western blot experiments or the point mutation of the targeting sites of miR-338-5p in ETS-1’s 3’untralation region (3’UTR). The expression of miR-338-5p was negatively associated with that of ETS-1 in astrocytoma, and deficiency of miR-338-5p would mediate aberrant expression of ETS-1 in astrocytoma. Mechanistically, hypermethylation of miR-338-5p by DNA methyltransferase 1 (DNMT1) resulted in repression of miR-338-5p expression and the aberrant expression of ETS-1. Knockdown or deactivation of DNMT1 decreased the methylation rate of the miR-338-5p promoter, increased the expression of miR-338-5p, and repressed the expression of ETS-1 in astrocytoma cell lines U251 and U87. These results indicate that hypermethylation of the miR-338-5p promoter by DNMT1 mediates the aberrant expression of ETS-1 related to disease severity of patients with astrocytoma.