Defense In Drosophila Research Articles

Endoplasmic reticulum-associated protein degradation contributes to Toll innate immune defense in Drosophila melanogaster.

In Drosophila, the endoplasmic reticulum-associated protein degradation (ERAD) is engaged in regulating pleiotropic biological processes, with regard to retinal degeneration, intestinal homeostasis, and organismal development. The extent to which it functions in controlling the fly innate immune defense, however, remains largely unknown. Here, we show that blockade of the ERAD in fat bodies antagonizes the Toll but not the IMD innate immune defense in Drosophila. Genetic approaches further suggest a functional role of Me31B in the ERAD-mediated fly innate immunity. Moreover, we provide evidence that silence of Xbp1 other than PERK or Atf6 partially rescues the immune defects by the dysregulated ERAD in fat bodies. Collectively, our study uncovers an essential function of the ERAD in mediating the Toll innate immune reaction in Drosophila.

The Posterior Signaling Center Is an Important Microenvironment for Homeostasis of the Drosophila Lymph Gland.

Hematopoiesis is a necessary process for development and immune defense in Drosophila from the embryonic period to adulthood. There are two main stages in this process: the first stage occurs in the head mesoderm during the embryonic stage, and the second occurs in a specialized hematopoietic organ along the dorsal vessel, the lymph gland, during the larval stage. The lymph gland consists of paired lobes, each of which has distinct regions: the cortical zone (CZ), which contains mature hemocytes; the medullary zone (MZ), which contains hematopoietic progenitors; and the posterior signaling center (PSC), which specifically expresses the early B-cell factor (EBF) transcription factor Collier (Col) and the HOX factor Antennapedia (Antp) to form a microenvironment similar to that of the mammalian bone marrow hematopoietic stem cell niche. The PSC plays a key role in regulating hematopoietic progenitor differentiation. Moreover, the PSC contributes to the cellular immune response to wasp parasitism triggered by elevated ROS levels. Two recent studies have revealed that hematopoietic progenitor maintenance is directly regulated by Col expressed in the MZ and is independent of the PSC, challenging the traditional model. In this review, we summarize the regulatory networks of PSC cell proliferation, the controversy regarding PSC-mediated regulation of hematopoietic progenitor differentiation, and the wasp egg infection response. In addition, we discuss why the PSC is an ideal model for investigating mammalian hematopoietic stem cell niches and leukemia.

Beyond immunity: The Imd pathway as a coordinator of host defense, organismal physiology and behavior

The humoral arm of host defense in Drosophila relies on two evolutionarily conserved NFκB signaling cascades, the Toll and the immune deficiency (Imd) pathways. The Imd signaling pathway senses and neutralizes Gram-negative bacteria. Its activity is tightly adjusted, allowing the host to simultaneously prevent infection by pathogenic bacteria and tolerate beneficial gut microbiota. Over-activation of Imd signaling is detrimental at least in part by causing gut dysbiosis that further exacerbates intestinal pathologies. Furthermore, it is increasingly recognized that the Imd pathway or its components also play non-immune roles. In this review, we summarize recent advances in Imd signal transduction, discuss the gut-microbiota interactions mediated by Imd signaling, and finally elaborate on its diverse physiological functions beyond immunity. Understanding the multifaceted physiological outputs of Imd activation will help integrate its immune role into the regulation of whole organismal physiology.

The Drosophila Thioester containing Protein-4 participates in the induction of the cellular immune response to the pathogen Photorhabdus

The function of thioester-containing proteins (TEPs) in the immune defense of the fruit fly Drosophila melanogaster is yet mostly unexplored. Recently, we showed the involvement of TEP4 in the activation of humoral and phenoloxidase immune responses of Drosophila against the pathogenic bacteria Photorhabdus luminescens and Photorhabdus asymbiotica. Here, we investigated the participation of Tep4 in the cellular defense of Drosophila against the two pathogens. We report significantly lower numbers of live and dead plasmatocytes in the tep4 mutants compared to control flies in response to Photorhabdus infection. We also find fewer crystal cells in the control flies than in tep4 mutants upon infection with Photorhabdus. Our results further suggest that Drosophila hemocytes constitute a major source for the transcript levels of Tep4 in flies infected by Photorhabdus. Finally, we show that Tep4 participates in the phagocytic function in Drosophila adult flies. Collectively our data support the protective role for TEP4 in the cellular immune response of Drosophila against the entomopathogen Photorhabdus.

The distinct function of Tep2 and Tep6 in the immune defense of Drosophila melanogaster against the pathogen Photorhabdus

ABSTRACT Previous and recent investigations on the innate immune response of Drosophila have identified certain mechanisms that promote pathogen elimination. However, the function of Thioester-containing proteins (TEPs) in the fly still remains elusive. Recently we have shown the contribution of TEP4 in the antibacterial immune defense of Drosophila against non-pathogenic E. coli, and the pathogens Photorhabdus luminescens and P. asymbiotica. Here we studied the function of Tep genes in both humoral and cellular immunity upon E. coli and Photorhabdus infection. We found that while Tep2 is induced after Photorhabdus and E. coli infection; Tep6 is induced by P. asymbiotica only. Moreover, functional ablation of hemocytes results in significantly low transcript levels of Tep2 and Tep6 in response to Photorhabdus. We show that Tep2 and Tep6 loss-of-function mutants have prolonged survival against P. asymbiotica, Tep6 mutants survive better the infection of P. luminescens, and both tep mutants are resistant to E. coli and Photorhabdus. We also find a distinct pattern of immune signaling pathway induction in E. coli or Photorhabdus infected Tep2 and Tep6 mutants. We further show that Tep2 and Tep6 participate in the activation of hemocytes in Drosophila responding to Photorhabdus. Finally, inactivation of Tep2 or Tep6 affects phagocytosis and melanization in flies infected with Photorhabdus. Our results indicate that distinct Tep genes might be involved in different yet crucial functions in the Drosophila antibacterial immune response.

Innate and intrinsic antiviral immunity in Drosophila.

The fruit fly Drosophila melanogaster has been a valuable model to investigate the genetic mechanisms of innate immunity. Initially focused on the resistance to bacteria and fungi, these studies have been extended to include antiviral immunity over the last decade. Like all living organisms, insects are continually exposed to viruses and have developed efficient defense mechanisms. We review here our current understanding on antiviral host defense in fruit flies. A major antiviral defense in Drosophila is RNA interference, in particular the small interfering (si) RNA pathway. In addition, complex inducible responses and restriction factors contribute to the control of infections. Some of the genes involved in these pathways have been conserved through evolution, highlighting loci that may account for susceptibility to viral infections in humans. Other genes are not conserved and represent species-specific innovations.

Charon Mediates Immune Deficiency-Driven PARP-1-Dependent Immune Responses in Drosophila.

Regulation of NF-κB nuclear translocation and stability is central to mounting an effective innate immune response. In this article, we describe a novel molecular mechanism controlling NF-κB-dependent innate immune response. We show that a previously unknown protein, termed as Charon, functions as a regulator of antibacterial and antifungal immune defense in Drosophila Charon is an ankyrin repeat-containing protein that mediates poly(ADP-ribose) polymerase-1 (PARP-1)-dependent transcriptional responses downstream of the innate immune pathway. Our results demonstrate that Charon interacts with the NF-κB ortholog Relish inside perinuclear particles and delivers active Relish to PARP-1-bearing promoters, thus triggering NF-κB/PARP-1-dependent transcription of antimicrobial peptides. Ablating the expression of Charon prevents Relish from targeting promoters of antimicrobial genes and effectively suppresses the innate immune transcriptional response. Taken together, these results implicate Charon as an essential mediator of PARP-1-dependent transcription in the innate immune pathway. Thus, to our knowledge, our results are the first to describe the molecular mechanism regulating translocation of the NF-κB subunit from cytoplasm to chromatin.

PiRNA pathway is not required for antiviral defense in Drosophila melanogaster

Since its discovery, RNA interference has been identified as involved in many different cellular processes, and as a natural antiviral response in plants, nematodes, and insects. In insects, the small interfering RNA (siRNA) pathway is the major antiviral response. In recent years, the Piwi-interacting RNA (piRNA) pathway also has been implicated in antiviral defense in mosquitoes infected with arboviruses. Using Drosophila melanogaster and an array of viruses that infect the fruit fly acutely or persistently or are vertically transmitted through the germ line, we investigated in detail the extent to which the piRNA pathway contributes to antiviral defense in adult flies. Following virus infection, the survival and viral titers of Piwi, Aubergine, Argonaute-3, and Zucchini mutant flies were similar to those of wild type flies. Using next-generation sequencing of small RNAs from wild type and siRNA mutant flies, we showed that no viral-derived piRNAs were produced in fruit flies during different types of viral infection. Our study provides the first evidence, to our knowledge, that the piRNA pathway does not play a major role in antiviral defense in adult Drosophila and demonstrates that viral-derived piRNA production depends on the biology of the host-virus combination rather than being part of a general antiviral process in insects.

Bacterial uracil modulates Drosophila DUOX-dependent gut immunity via Hedgehog-induced signaling endosomes.

Genetic studies in Drosophila have demonstrated that generation of microbicidal reactive oxygen species (ROS) through the NADPH dual oxidase (DUOX) is a first line of defense in the gut epithelia. Bacterial uracil acts as DUOX-activating ligand through poorly understood mechanisms. Here, we show that the Hedgehog (Hh) signaling pathway modulates uracil-induced DUOX activation. Uracil-induced Hh signaling is required for intestinal expression of the calcium-dependent cell adhesion molecule Cadherin 99C (Cad99C) and subsequent Cad99C-dependent formation of endosomes. These endosomes play essential roles in uracil-induced ROS production by acting as signaling platforms for PLCβ/PKC/Ca2+-dependent DUOX activation. Animals with impaired Hh signaling exhibit abolished Cad99C-dependent endosome formation and reduced DUOX activity, resulting in high mortality during enteric infection. Importantly, endosome formation, DUOX activation, and normal host survival are restored by genetic reintroduction of Cad99C into enterocytes, demonstrating the important role for Hh signaling in host resistance to enteric infection.

The Drosophila IMD pathway in the activation of the humoral immune response

The IMD pathway signaling plays a pivotal role in the Drosophila defense against bacteria. During the last two decades, significant progress has been made in identifying the components and deciphering the molecular mechanisms underlying this pathway, including the means of bacterial sensing and signal transduction. While these findings have contributed to the understanding of the immune signaling in insects, they have also provided new insights in studying the mammalian NF-κB signaling pathways. Here, we summarize the current view of the IMD pathway focusing on how it regulates the humoral immune response of Drosophila.

RNAi and antiviral defense in Drosophila: Setting up a systemic immune response

RNA interference (RNAi) controls gene expression in eukaryotic cells and thus, cellular homeostasis. In addition, in plants, nematodes and arthropods it is a central antiviral effector mechanism. Antiviral RNAi has been well described as a cell autonomous response, which is triggered by double-stranded RNA (dsRNA) molecules. This dsRNA is the precursor for the silencing of viral RNA in a sequence-specific manner. In plants, systemic antiviral immunity has been demonstrated, however much less is known in animals. Recently, some evidence for a systemic antiviral response in arthropods has come to light. Cell autonomous RNAi may not be sufficient to reach an efficient antiviral response, and the organism might rely on the spread and uptake of an RNAi signal of unknown origin. In this review, we offer a perspective on how RNAi-mediated antiviral immunity could confer systemic protection in insects and we propose directions for future research to understand the mechanism of RNAi-immune signal sorting, spreading and amplification.

AP-1/Fos-TGase2 Axis Mediates Wounding-induced Plasmodium falciparum Killing in Anopheles gambiae

Anopheline mosquitoes are the only vectors of human malaria worldwide. It is now widely accepted that mosquito immune responses play a crucial role in restricting Plasmodium development within the vector; therefore, further dissection of the molecular mechanisms underlying these processes should inform new vector control strategies urgently needed to roll back the disease. Here, using genome-wide transcriptional profiling, bioinformatics, and functional gene analysis, we identify a new axis of mosquito resistance to monoclonal Plasmodium falciparum infections that includes the AP-1 transcription factor Fos and the transglutaminase 2 (TGase2), a cross-linking enzyme with known roles in wound responses. We demonstrate that Fos regulates induction of TGase2 expression after wounding but does not affect expression of the components of the well characterized complement-like system. Silencing of Fos or of TGase2 aborts the wounding-induced mosquito killing of P. falciparum. These results reveal multiple signaling pathways that are required for efficient Plasmodium killing in Anopheles gambiae.

Immunotherapeutic Applications of IL-18

To become active and extracellularly released, IL-18 needs post-translational processing by the cytoplasmic enzyme caspase-1, which has high sequence homology with apoptotic cell death-associated enzymes in Caenorhabditis elegans. Furthermore, the receptor for IL-18 shares the signal transduction pathway with the Toll-like receptor, which highly resembles that for the host defense in Drosophila. Since nonvertebrates utilize only innate immunity, it is plausible that IL-18 is an innate immune cytokine. IL-18 is produced by both immune and nonimmune cells, and influences both immunity and nonimmune biology with dual functions beneficial for health and causative of diseases. In this review, recently identified features of IL-18 will be focused upon, followed by discussion of IL-18 as a possible therapeutic target.

Recent and Recurrent Selective Sweeps of the Antiviral RNAi Gene Argonaute-2 in Three Species of Drosophila

Antagonistic host–parasite interactions can drive rapid adaptive evolution in genes of the immune system, and such arms races may be an important force shaping polymorphism in the genome. The RNA interference pathway gene Argonaute-2 (AGO2) is a key component of antiviral defense in Drosophila, and we have previously shown that genes in this pathway experience unusually high rates of adaptive substitution. Here we study patterns of genetic variation in a 100-kbp region around AGO2 in three different species of Drosophila. Our data suggest that recent independent selective sweeps in AGO2 have reduced genetic variation across a region of more than 50 kbp in Drosophila melanogaster, D. simulans, and D. yakuba, and we estimate that selection has fixed adaptive substitutions in this gene every 30–100 thousand years. The strongest signal of recent selection is evident in D. simulans, where we estimate that the most recent selective sweep involved an allele with a selective advantage of the order of 0.5–1% and occurred roughly 13–60 Kya. To evaluate the potential consequences of the recent substitutions on the structure and function of AGO2, we used fold-recognition and homology-based modeling to derive a structural model for the Drosophila protein, and this suggests that recent substitutions in D. simulans are overrepresented at the protein surface. In summary, our results show that selection by parasites can consistently target the same genes in multiple species, resulting in areas of the genome that have markedly reduced genetic diversity.

The POU transcription factor Drifter/Ventral veinless regulates expression of Drosophila immune defense genes.

Innate immunity operates as a first line of defense in multicellular organisms against infections caused by different classes of microorganisms. Antimicrobial peptides (AMPs) are synthesized constitutively in barrier epithelia to protect against microbial attack and are also upregulated in response to infection. Here, we implicate Drifter/Ventral veinless (Dfr/Vvl), a class III POU domain transcription factor, in tissue-specific regulation of the innate immune defense of Drosophila. We show that Dfr/Vvl is highly expressed in a range of immunocompetent tissues, including the male ejaculatory duct, where its presence overlaps with and drives the expression of cecropin, a potent broad-spectrum AMP. Dfr/Vvl overexpression activates transcription of several AMP genes in uninfected flies in a Toll pathway- and Imd pathway-independent manner. Dfr/Vvl activates a CecA1 reporter gene both in vitro and in vivo by binding to an upstream enhancer specific for the male ejaculatory duct. Further, Dfr/Vvl and the homeodomain protein Caudal (Cad) activate transcription synergistically via this enhancer. We propose that the POU protein Dfr/Vvl acts together with other regulators in a combinatorial manner to control constitutive AMP gene expression in a gene-, tissue-, and sex-specific manner, thus promoting a first-line defense against infection in tissues that are readily exposed to pathogens.

Invasive and indigenous microbiota impact intestinal stem cell activity through multiple pathways in Drosophila

Gut homeostasis is controlled by both immune and developmental mechanisms, and its disruption can lead to inflammatory disorders or cancerous lesions of the intestine. While the impact of bacteria on the mucosal immune system is beginning to be precisely understood, little is known about the effects of bacteria on gut epithelium renewal. Here, we addressed how both infectious and indigenous bacteria modulate stem cell activity in Drosophila. We show that the increased epithelium renewal observed upon some bacterial infections is a consequence of the oxidative burst, a major defense of the Drosophila gut. Additionally, we provide evidence that the JAK-STAT (Janus kinase-signal transducers and activators of transcription) and JNK (c-Jun NH(2) terminal kinase) pathways are both required for bacteria-induced stem cell proliferation. Similarly, we demonstrate that indigenous gut microbiota activate the same, albeit reduced, program at basal levels. Altered control of gut microbiota in immune-deficient or aged flies correlates with increased epithelium renewal. Finally, we show that epithelium renewal is an essential component of Drosophila defense against oral bacterial infection. Altogether, these results indicate that gut homeostasis is achieved by a complex interregulation of the immune response, gut microbiota, and stem cell activity.

The XX International Congress of Zoology, 26–29 August 2008, Paris

International Congresses of Zoology (ICZ) provide an opportunity for zoologists working in different fields of zoology to meet and exchange their research and ideas. It is also a venue where topical issues facing the science of zoology, such as the biodiversity crisis, the teaching of zoology and ethics can be discussed. These Congresses were resurrected in 2000 in Athens and held again in Beijing in 2004. In an age of increasing reductionism and complex information management, having a general meeting of zoologists to discuss the whole animal is of vital service to our science. The XX International Congress of Zoology was jointly organized by the University Pierre and Marie Curie (Paris 6), National Museum of Natural History and the University of Paris-South (Paris 11). It was also strongly supported by the Region Ile-de-France, Linnean Society of London, International Union of Biological Sciences, National Centre for Scientific Research and the French National Institute for Agricultural Research. The ICZ held in Paris gathered together 460 attendants from 50 countries and took place in the Jussieu Campus, around the university P6 and the historic Grand Amphitheatre of the National Museum of Natural History. There were four plenary lectures: Professor Jules Hoffmann, President of the French Academy of Sciences presented ‘The antimicrobial defense of Drosophila: a paradigm for innate immunity’; Professor Rosa Polymeni discussed ‘Aristotle, founder of Zoology, when art imitates nature’; Professor Denis Duboule described ‘The rise and fall of Hox gene clusters’; and Professor Claus Nielsen presented his ideas on ‘Zoological systematics and phylogeny at the beginning of the 21 century’. Through 26 symposia, 223 oral communications and 223 poster presentations were delivered. Each symposium consisted of two to four keynote addresses followed by oral and poster communications. These symposia were titled: contemporary approaches in systematic zoology, mechanisms of speciation, animal genitalia in evolution, paleozoology and comparative anatomy, paleontology and evolution, biodiversity, genomics and ecology of protists, sex differentiation in vertebrates, evolution and development, transitions from clonal to sexual reproduction, comparative immunology, venomous animals and their venoms, integrative biology of acoustic communication, current trends in social insects, phenotypical plasticity and behavior, interdisciplinary approaches in ecology, ecotoxicology, marine organisms and symbiotic systems in extreme environments, ecological and evolutionary consequences of global climate evolution, studies of invasive animal species, comparative organogenesis in animals, Lamarck’s Philosophie Zoologique 200 years, a tribute to Darwin, diversity in teaching zoology. Last but not least was a special symposium organized by the International Commission on Zoological Nomenclature titled ‘Systema Naturae 250’, with Professor E. O. Wilson as a special guest. All Abstracts presented at the Congress are posted on the homepage of the International Society of Zoological Sciences (www.globalzoology.org).

The anti-microbial defense of Drosophila: a paradigm for innate immunity

The anti-microbial defense of Drosophila: a paradigm for innate immunity

Drosomycin-Like Defensin, a Human Homologue ofDrosophila melanogasterDrosomycin with Antifungal Activity

Innate antifungal defense in Drosophila melanogaster relies on the activation of the Toll molecule and the release of drosomycin, a defensin-like molecule with antifungal properties. Ten human homologues of Toll have been described, with central roles in activation of the innate host defense. In the present study, we report a putative human homologue of the Drosophila-derived drosomycin, designated drosomycin-like defensin (DLD). Synthetic DLD displays a broad spectrum of activity against Aspergillus spp. and other clinically relevant filamentous fungi. These effects are specific for filamentous fungi; no activity has been found against yeasts or gram-positive or gram-negative bacteria. Synthetic DLD also displays immunomodulatory effects on Aspergillus-stimulated cytokine production. In addition, we show the expression of DLD mRNA in several human tissues, particularly in the skin, consistent with its putative role as a defensin against invading microorganisms. This is the first indication of an endogenous human peptide with specific antifungal activity, which is probably central in the defense against infections with molds.

Antifungal defense in drosophila

Innate immunity has come to the forefront in immunology, aided by the discovery of antifungal defense in drosophila. Here Jules Hoffmann recounts his team's pioneering work on insect immunity.