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      Two Roles for the Tenebrio molitor Relish in the Regulation of Antimicrobial Peptides and Autophagy-Related Genes in Response to Listeria monocytogenes


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          Relish is a key NF-κB transcription factor of the immune-deficiency (Imd) pathway that combats infection by regulating antimicrobial peptides (AMPs). Understanding of the fundamental role of Tenebrio molitor Relish ( TmRelish) in controlling of Listeria monocytogenes virulence through the regulation of both AMPs and autophagy-related (ATG) genes is unclear. Here, we show that TmRelish transcripts were highly abundant in the larval fat body and hemocytes compared to the gut upon L. monocytogenes infection. Furthermore, significant mortality was observed in TmRelish-silenced larvae after intracellular insult. To investigate the cause of this lethality, we measured the induction of AMPs and ATG genes in the TmRelish dsRNA-treated T. molitor larvae. The expression of TmTenecin- 1, TmTenecin- 4, TmColeptericin- 1, TmAttacin- 2, and TmCecropin- 2 were suppressed in the fat body and hemocytes of ds TmRelish-injected larvae during L. monocytogenes infection. In addition, TmRelish knockdown led to a noticeable downregulation of TmATG1 (a serine-threonine protein kinase) in the fat body and hemocytes of young larvae 6 h post-infection (pi). The notable increase of autophagy genes in the early stage of infection (6 h pi), suggesting autophagy response is crucial for Listeria clearance. Taken together, these results suggest that TmRelish plays pivotal roles in not only regulation of AMP genes but also induction of autophagy genes in response to L. monocytogenes challenge in fat body and hemocytes of T. molitor larvae. Furthermore, negative regulation of several AMPs by TmRelish in the fat body, hemocytes, and gut leaves open the possibility of a crosstalk between Toll and Imd pathway.

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          Role and regulation of starvation-induced autophagy in the Drosophila fat body.

          In response to starvation, eukaryotic cells recover nutrients through autophagy, a lysosomal-mediated process of cytoplasmic degradation. Autophagy is known to be inhibited by TOR signaling, but the mechanisms of autophagy regulation and its role in TOR-mediated cell growth are unclear. Here, we show that signaling through TOR and its upstream regulators PI3K and Rheb is necessary and sufficient to suppress starvation-induced autophagy in the Drosophila fat body. In contrast, TOR's downstream effector S6K promotes rather than suppresses autophagy, suggesting S6K downregulation may limit autophagy during extended starvation. Despite the catabolic potential of autophagy, disruption of conserved components of the autophagic machinery, including ATG1 and ATG5, does not restore growth to TOR mutant cells. Instead, inhibition of autophagy enhances TOR mutant phenotypes, including reduced cell size, growth rate, and survival. Thus, in cells lacking TOR, autophagy plays a protective role that is dominant over its potential role as a growth suppressor.
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            The Drosophila systemic immune response: sensing and signalling during bacterial and fungal infections.

            A hallmark of the potent, multifaceted antimicrobial defence of Drosophila melanogaster is the challenge-induced synthesis of several families of antimicrobial peptides by cells in the fat body. The basic mechanisms of recognition of various types of microbial infections by the adult fly are now understood, often in great detail. We have further gained valuable insight into the infection-induced gene reprogramming by nuclear factor-kappaB (NF-kappaB) family members under the dependence of complex intracellular signalling cascades. The striking parallels between the adult fly response and mammalian innate immune defences described below point to a common ancestry and validate the relevance of the fly defence as a paradigm for innate immunity.
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              Tissue-specific inducible expression of antimicrobial peptide genes in Drosophila surface epithelia.

              The production of antimicrobial peptides is an important aspect of host defense in multicellular organisms. In Drosophila, seven antimicrobial peptides with different spectra of activities are synthesized by the fat body during the immune response and secreted into the hemolymph. Using GFP reporter transgenes, we show here that all seven Drosophila antimicrobial peptides can be induced in surface epithelia in a tissue-specific manner. The imd gene plays a critical role in the activation of this local response to infection. In particular, drosomycin expression, which is regulated by the Toll pathway during the systemic response, is regulated by imd in the respiratory tract, thus demonstrating the existence of distinct regulatory mechanisms for local and systemic induction of antimicrobial peptide genes in Drosophila.

                Author and article information

                16 March 2020
                March 2020
                : 11
                : 3
                : 188
                Department of Applied Biology, Institute of Environmentally-Friendly Agriculture (IEFA), College of Agriculture and Life Sciences, Chonnam National University, Gwangju 61186, Korea; mariakeshavarz1990@ 123456gmail.com (M.K.); bunchk.2000@ 123456gmail.com (T.T.E.)
                Author notes
                [* ]Correspondence: yhun1228@ 123456jnu.ac.kr (Y.H.J.); hanys@ 123456jnu.ac.kr (Y.S.H.); Tel.: +82-62-530-0316 (Y.H.J.); +82-62-530-2072 (Y.S.H.); Fax: +82-62-530-2069 (Y.H.J.&Y.S.H.)
                Author information
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                : 17 February 2020
                : 12 March 2020

                tenebrio molitor,relish,nf-κb,antimicrobial peptides,autophagy,listeria monocytogenes


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