TmIKKε Is Required to Confer Protection Against Gram-Negative Bacteria, E. coli by the Regulation of Antimicrobial Peptide Production in the Tenebrio molitor Fat Body

The allatotropin/orexin system as an example of immunomodulatory properties of neuropeptides

The central nervous system (CNS) plays a critical role in signal integration in animals and allows the orchestration of life processes to maintain homeostasis. Current research clearly shows that inflammatory processes can also be modulated by the CNS via the neuroendocrine system. One of the neuropeptide families that participate in vertebrates in this process is orexins (OXs). Interestingly, our previous results suggested that a similar dependency may also exist between neuropeptides and immune system activity in insects. Due to the structural homology of orexin and allatotropin receptors and the functional similarity between these two neuropeptide families, the main aim of this research was to perform a complex analysis of the relationships between allatotropin (AT) and the insect immune response. Our results revealed functional similarities between vertebrate OXs and insect ATs. Similar effects were observed in the profile of the expression level of the gene encoding the AT precursor in the Tenebrio molitor nervous system and in the general action of Tenmo-AT on selected immune parameters of the tested beetles. Moreover, for the first time in insects, we confirmed the role of cytokines in the modulation of neuroendocrine system by determining the effect of Spätzle-like protein injection on the expression of genes encoding AT precursor and receptor. All these results are important for understanding the evolutionary basis of hormonal regulation of the immune response.

Transcriptome sequencing of the endangered land snail Karaftohelix adamsi from the Island Ulleung: De novo assembly, annotation, valuation of fitness genes and SSR markers

BACKGROUND

The Bradybaenidae snail Karaftohelix adamsi is endemic to Korea, with the species tracked from Island Ulleung in North Gyeongsang Province of South Korea. K. adamsi has been classified under the Endangered Wildlife Class II species of Korea and poses a severe risk of extinction following habitat disturbances. With no available information at the DNA (genome) or mRNA (transcriptome) level for the species, conservation by utilizing informed molecular resources seems difficult.

OBJECTIVE

In this study, we used the Illumina short-read sequencing and Trinity de novo assembly to draft the reference transcriptome of K. adamsi.

RESULTS

After assembly, 13,753 unigenes were obtained of which 10,511 were annotated to public databases (a maximum of 10,165 unigenes found homologs in PANM DB). A total of 6,351, 3,535, 358, and 3,407 unigenes were ascribed to the functional categories under KOG, GO, KEGG, and IPS, respectively. The transcripts such as the HSP 70, aquaporin, TLR, and MAPK, among others, were screened as putative functional resources for adaptation. DNA transposons were found to be thickly populated in comparison to retrotransposons in the assembled unigenes. Further, 2,164 SSRs were screened with the promiscuous presence of dinucleotide repeats such as AC/GT and AG/CT.

CONCLUSION

The transcriptome-guided discovery of molecular resources in K. adamsi will not only serve as a basis for functional genomics studies but also provide sustainable tools to be utilized for the protection of the species in the wild. Moreover, the development of polymorphic SSRs is valuable for the identification of species from newer habitats and cross-species genotyping.

Cereal weevils' antimicrobial peptides: at the crosstalk between development, endosymbiosis and immune response

Interactions between animals and microbes are ubiquitous in nature and strongly impact animal physiology. These interactions are shaped by the host immune system, which responds to infections and contributes to tailor the associations with beneficial microorganisms. In many insects, beneficial symbiotic associations not only include gut commensals, but also intracellular bacteria, or endosymbionts. Endosymbionts are housed within specialized host cells, the bacteriocytes, and are transmitted vertically across host generations. Host-endosymbiont co-evolution shapes the endosymbiont genome and host immune system, which not only fights against microbial intruders, but also ensures the preservation of endosymbionts and the control of their load and location. The cereal weevil Sitophilus spp. is a remarkable model in which to study the evolutionary adaptation of the immune system to endosymbiosis owing to its binary association with a unique, relatively recently acquired nutritional endosymbiont, Sodalis pierantonius. This Gram-negative bacterium has not experienced the genome size shrinkage observed in long-term endosymbioses and has retained immunogenicity. We focus here on the sixteen antimicrobial peptides (AMPs) identified in the Sitophilus oryzae genome and their expression patterns in different tissues, along host development or upon immune challenges, to address their potential functions in the defensive response and endosymbiosis homeostasis along the insect life cycle. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Effects of TmTak1 silencing on AMP production as an Imd pathway component in Tenebrio molitor

Mealworms beetles, Tenebrio molitor, are the limelight next-generation food for humans due to their high nutrient contents. Since Tenebrio molitor is used as feed for pets and livestock in addition to their ability to decompose polystyrene and plastic waste, it is recognized as an insect with an industrial core value. Therefore, it is important to study the immune mechanism related to the development and infection of mealworms for mass breeding purposes. The immune deficiency (Imd) signaling is one of the main pathways with pivotal roles in the production of antimicrobial peptides (AMPs). Transforming growth factor-β activated kinase (TAK1) is one of the Imd pathway components, forms a complex with TAK1 binding protein 2 (TAB2) to ultimately help activate the transcription factor Relish and eventually induce host to produce AMPs. Relatively, little has been revealed about TAK1 in insect models, especially in the T. molitor. Therefore, this study was conducted to elucidate the function of TmTak1 in T. molitor. Our results showed that the highest and lowest mRNA expression of TmTak1 were found in egg and young larvae respectively. The tissue-specific expression patterns were reported in the gut of T. molitor larvae and the fat bodies of adults. Systemic microbial challenge illustrated TmTak1 high expression following the fungal infection in all dissected tissues except for the whole body. However, silencing TmTak1 experiments showed that the survivability of T. molitor larvae affected significantly following Escherichia coli infection. Accordingly, AMP induction after TmTak1 knock down was mainly reported in the integument and the fat bodies.

Transcriptome analysis of the endangered dung beetle Copris tripartitus (Coleoptera: Scarabaeidae) and characterization of genes associated to immunity, growth, and reproduction

BACKGROUND

Dung beetles recycle organic matter through the decomposition of feces and support ecological balance. However, these insects are threatened by the indiscriminate use of agrochemicals and habitat destruction. Copris tripartitus Waterhouse (Coleoptera: Scarabaeidae), a dung beetle, is listed as a class-II Korean endangered species. Although the genetic diversity of C. tripartitus populations has been investigated through analysis of mitochondrial genes, genomic resources for this species remain limited. In this study, we analyzed the transcriptome of C. tripartitus to elucidate functions related to growth, immunity and reproduction for the purpose of informed conservation planning.

RESULTS

The transcriptome of C. tripartitus was generated using next-generation Illumina sequencing and assembled de novo using a Trinity-based platform. In total, 98.59% of the raw sequence reads were processed as clean reads. These reads were assembled into 151,177 contigs, 101,352 transcripts, and 25,106 unigenes. A total of 23,450 unigenes (93.40%) were annotated to at least one database. The largest proportion of unigenes (92.76%) were annotated to the locally curated PANM-DB. A maximum of 5,512 unigenes had homologous sequences in Tribolium castaneum. Gene Ontology (GO) analysis revealed a maximum of 5,174 unigenes in the Molecular function category. Further, in Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, a total of 462 enzymes were associated with established biological pathways. Based on sequence homology to known proteins in PANM-DB, representative immunity, growth, and reproduction-related genes were screened. Potential immunity-related genes were categorized into pattern recognition receptors (PRRs), the Toll-like receptor signaling pathway, the MyD88- dependent pathway, endogenous ligands, immune effectors, antimicrobial peptides, apoptosis, and adaptation-related transcripts. Among PRRs, we conducted detailed in silico characterization of TLR-2, CTL, and PGRP_SC2-like. Repetitive elements such as long terminal repeats, short interspersed nuclear elements, long interspersed nuclear elements and DNA elements were enriched in the unigene sequences. A total of 1,493 SSRs were identified among all unigenes of C. tripartitus.

CONCLUSIONS

This study provides a comprehensive resource for analysis of the genomic topography of the beetle C. tripartitus. The data presented here clarify the fitness phenotypes of this species in the wild and provide insight to support informed conservation planning.

Immunological Roles of TmToll-2 in Response to Escherichia coli Systemic Infection in Tenebrio molitor

The antimicrobial roles of Toll-like receptors have been mainly identified in mammalian models and Drosophila. However, its immunological function in other insects has yet to be fully clarified. Here, we determined the innate immune response involvement of TmToll-2 encountering Gram-negative, Gram-positive, and fungal infection. Our data revealed that TmToll-2 expression could be induced by Escherichia coli, Staphylococcus aureus, and Candida albicans infections in the fat bodies, gut, Malpighian tubules, and hemolymph of Tenebrio molitor young larvae. However, TmToll-2 silencing via RNAi technology revealed that sole E. coli systemic infection caused mortality in the double-strand RNA TmToll-2-injected group compared with that in the control group. Further investigation indicated that in the absence of TmToll-2, the final effector of Toll signaling pathway, antimicrobial peptide (AMP) genes and relevant transcription factors were significantly downregulated, mainly E. coli post-insult. We showed that the expression of all AMP genes was suppressed in the main immune organ of insects, namely, fat bodies, in silenced individuals, while the relevant expressions were not affected after fungal infection. Thus, our research revealed the immunological roles of TmToll-2 in different organs of T. molitor in response to pathogenic insults.

Emerging Evidence on Tenebrio molitor Immunity: A Focus on Gene Expression Involved in Microbial Infection for Host-Pathogen Interaction Studies

In recent years, the scientific community's interest in T. molitor as an insect model to investigate immunity and host-pathogen interactions has considerably increased. The reasons for this growing interest could be explained by the peculiar features of this beetle, which offers various advantages compared to other invertebrates models commonly used in laboratory studies. Thus, this review aimed at providing a broad view of the T. molitor immune system in light of the new scientific evidence on the developmental/tissue-specific gene expression studies related to microbial infection. In addition to the well-known cellular component and humoral response process, several studies investigating the factors associated with T. molitor immune response or deepening of those already known have been reported. However, various aspects remain still less understood, namely the possible crosstalk between the immune deficiency protein and Toll pathways and the role exerted by T. molitor apolipoprotein III in the expression of the antimicrobial peptides. Therefore, further research is required for T. molitor to be recommended as an alternative insect model for pathogen-host interaction and immunity studies.

Current Status of Immune Deficiency Pathway in Tenebrio molitor Innate Immunity

Yellow mealworm (Tenebrio molitor) is a highly beneficial beetle that serves as an excellent source of edible protein as well as a practical study model. Therefore, studying its immune system is important. Like in other insects, the innate immune response effected through antimicrobial peptides production provides the most critical defense armory in T. molitor. Immune deficiency (Imd) signaling is one of the major pathways involved in the humoral innate immune response in this beetle. However, the nature of the molecules involved in the signaling cascade of the Imd pathway, from recognition to the production of final effectors, and their mechanism of action are yet to be elucidated in T. molitor model. In this review, we present a general overview of the current literature available on the Imd signaling pathway and its identified interaction partners in T. molitor.