A drosomycin-GFP reporter transgene reveals a local immune response in Drosophila that is not dependent on the Toll pathway.

A hallmark of the systemic antimicrobial response of Drosophila is the synthesis by the fat body of several antimicrobial peptides which are released into the hemolymph in response to a septic injury. One of these peptides, drosomycin, is active primarily against fungi. Using a drosomycin-green fluorescent protein (GFP) reporter gene, we now show that in addition to the fat body, a variety of epithelial tissues that are in direct contact with the external environment, including those of the respiratory, digestive and reproductive tracts, can express the antifungal peptide, suggesting a local response to infections affecting these barrier tissues. As is the case for vertebrate epithelia, insect epithelia appear to be more than passive physical barriers and are likely to constitute an active component of innate immunity. We also show that, in contrast to the systemic antifungal response, this local immune response is independent of the Toll pathway.     

Fungal peptide Destruxin A plays a specific role in suppressing the innate immune response in Drosophila melanogaster

Destruxins are a class of insecticidal, anti-viral, and phytotoxic cyclic depsipeptides that are also studied for their toxicity to cancer cells. They are produced by various fungi, and a direct relationship has been established between Destruxin production and the virulence of the entomopathogen Metarhizium anisopliae. Aside from opening calcium channels, their in vivo mode of action during pathogenesis remains largely uncharacterized. To better understand the effects of a Destruxin, we looked at changes in gene expression following injection of Destruxin A into the fruit fly Drosophila melanogaster. Microarray results revealed reduced expression of various antimicrobial peptides that play a major role in the humoral immune response of the fly. Flies co-injected with a non-lethal dose of Destruxin A and the normally innocuous Gram-negative bacteria Escherichia coli, showed increased mortality and an accompanying increase in bacterial titers. Mortality due to sepsis was rescued through ectopic activation of components in the IMD pathway, one of two signal transduction pathways that are responsible for antimicrobial peptide induction. These results demonstrate a novel role for Destruxin A in specific suppression of the humoral immune response in insects.     

RNAi is an antiviral immune response against a dsRNA virus in Drosophila melanogaster

Drosophila melanogaster has a robust and efficient innate immune system, which reacts to infections ranging from bacteria to fungi and, as discovered recently, viruses as well. The known Drosophila immune responses rely on humoral and cellular activities, similar to those found in the innate immune system of other animals. Recently, RNAi or 'RNA silencing' has arisen as a possible means by which Drosophila can react to a specific pathogens, transposons and retroviral elements, in a fashion similar to that of a traditional mammalian adaptive immune system instead of in a more generalized and genome encoded innate immune-based response. RNAi is a highly conserved regulation and defence mechanism, which suppresses gene expression via targeted RNA degradation directed by either exogenous dsRNA (cleaved into siRNAs) or endogenous miRNAs. In plants, RNAi has been found to act as an antiviral immune response system. Here we show that RNAi is an antiviral response used by Drosophila to combat infection by Drosophila X Virus, a birnavirus, as well. Additionally, we identify multiple core RNAi pathway genes, including piwi, vasa intronic gene (vig), aubergine (aub), armitage (armi), Rm62, r2d2 and Argonaute2 (AGO2) as having vital roles in this response in whole organisms. Our findings establish Drosophila as an ideal model for the study of antiviral RNAi responses in animals.     

Effect of ciprofloxacin on specific immune response in rabbits

Ciprofloxacin (10 mg/kg body weight, iv, twice daily for 4 days) failed to alter specific antibody titres, total immunoglobulin concentration, total serum protein concentration, total leukocyte count, lymphocyte percentage, phagocytic index and skin thickness in DNCB skin sensitivity test against Brucella plain killed antigen in New Zealand White rabbits. It can be concluded that ciprofloxacin at the dose and duration employed did not adversely affect specific immune response in normal rabbits.     

Drosophila innate immune response pathways moonlight in neurodegeneration

In this Extra View, we highlight recent Drosophila research that has uncovered a new role for the innate immune response. The research indicates that, in addition to combating infection, the innate immune response promotes neurodegeneration. Our publication (Petersen et al., 2012) reveals a correlative relationship between the innate immune response and neurodegeneration in a model of the human disease Ataxia-telangiectasia (A-T). We also found that glial cells are responsible for the innate immune response in the A-T model, and work by others implicates glial cells in neurodegeneration. Additionally, publications by Chinchore et al. (2012) and Tan et al. (2008) reveal a causative role for the innate immune response in models of human retinal degenerative disorders and Alzheimer disease, respectively. Collectively, these findings suggest that activation of the innate immune response is a shared cause of neurodegeneration in different human diseases.     

Exercise-induced angiogenesis is dependent on metabolically primed ATF3/4+ endothelial cells

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Discontinuous DNA replication of Drosophila melanogaster is primed by octaribonucleotide primer.

To investigate the precise structure of eucaryotic primer RNA made in vivo, short DNA chains isolated from nuclei of Drosophila melanogaster embryos were analyzed. Post-labeling of 5' ends of short DNA chains with polynucleotide kinase and [gamma-32P]ATP revealed that 7% of the DNA fragments were covalently linked with mono- to octaribonucleotide primers at their 5' ends. Octaribonucleotides, the major component (ca. 30%), formed the cap structure in the reaction with vaccinia guanylyltransferase and [alpha-32P]GTP, indicating that they were the intact primer RNA with tri- (or di-) phosphate termini, and the shorter ribooligomers were degradation intermediates. The intact primers started with purine (A/G ratio, 4:1), and the starting few ribonucleotide residues were rich in A.     

Drosophila strain specific response to cisplatin neurotoxicity

ABSTRACT

Drosophila melanogaster has recently been developed as a simple, in vivo, genetic model of chemotherapy-induced peripheral neuropathy. Flies treated with the chemotherapy agent cisplatin display both a neurodegenerative phenotype and cell death in rapidly dividing follicles, mimicking the cell specific responses seen in humans. Cisplatin induces climbing deficiencies and loss of fertility in a dose dependent manner. Drosophila sensitivity to cisplatin in both cell types is affected by genetic background. We show that mutation or RNAi-based knockdown of genes known to be associated with CIPN incidence in humans affect sensitivity of flies to CIPN. Drosophila is a promising model with which to study the effect of genetics on sensitivity to CIPN.     

A directed miniscreen for genes involved in the Drosophila anti-parasitoid immune response

Drosophila larvae react against eggs from the endoparasitoid wasp Leptopilina boulardi by surrounding them in a multilayered cellular capsule. Once a wasp egg is recognized as foreign, circulating macrophage-like cells, known as plasmatocytes, adhere to the invader. After spreading around the wasp egg, plasmatocytes form cellular junctions between the cells, effectively separating the egg from the hemocoel. Next, a second sub-type of circulating immunosurveillance cell (hemocyte), known as lamellocytes, adhere to either the wasp egg or more likely the plasmatocytes surrounding the egg. From these events, it is obvious that adhesion and cell shape change are an essential part of Drosophila's cellular immune response against parasitoid wasp eggs. To date, very few genes have been described as being necessary for a proper anti-parasitization response in Drosophila. With this in mind, we performed a directed genetic miniscreen to discover new genes required for this response. Many of the genes with an encapsulation defect have mammalian homologues involved in cellular adhesion, wound healing, and thrombosis, including extracellular matrix proteins, cellular adhesion molecules, and small GTPases.     

High-frequency P element loss in Drosophila is homolog dependent

P transposable elements in Drosophila melanogaster can undergo precise loss at a rate exceeding 13% per generation. The process is similar to gene conversion in its requirement for a homolog that is wild type at the insertion site and in its reduced frequency when pairing between the homologs is inhibited. However, it differs from classical gene conversion by its high frequency, its requirement for P transposase, its unidirectionality, and its occurrence in somatic and premeiotic cells. Our results suggest a model of P element transposition in which jumps occur by a "cut-and-paste" mechanism but are followed by double-strand gap repair to restore the P element at the donor site. The results also suggest a technique for site-directed mutagenesis in Drosophila.     

Drosophila serpin 27A is a likely target for immune suppression of the blood cell-mediated melanotic encapsulation response

Avirulent strains of the endoparasitoid Leptopilina boulardi succumb to a blood cell-mediated melanotic encapsulation response in host larvae of Drosophila melanogaster. Virulent wasp strains effectively abrogate the cellular response with substances introduced into the host that specifically target and effectively suppress one or more immune signaling pathways, including elements that control phenoloxidase-mediated melanotic encapsulation. The present study implicates involvement of the Drosophila Toll pathway in cellular innate immunity by regulating the serine protease inhibitor Serpin 27A (Spn27A), which normally functions as a negative regulator of phenoloxidase. The introduction of Spn27A into normally highly immune competent D. melanogaster larvae significantly reduced their ability to form melanotic capsules around eggs of L. boulardi. This study confirms the role of Spn27A in the melanization cascade and establishes that this pathway and associated blood cell responses can be activated by parasitization. The activation of phenoloxidase and the site-specific localization of the ensuing melanotic response are such critical components of the blood cell response that Spn27A and the signaling elements mediating its activity are likely to represent prime targets for immune suppression by L. boulardi.     

Tissue communication in a systemic immune response of Drosophila

Several signaling pathways, including the JAK/STAT and Toll pathways, are known to activate blood cells (hemocytes) in Drosophila melanogaster larvae. They are believed to regulate the immune response against infections by parasitoid wasps, such as Leptopilina boulardi, but how these pathways control the hemocytes is not well understood. Here, we discuss the recent discovery that both muscles and fat body take an active part in this response. Parasitoid wasp infection induces Upd2 and Upd3 secretion from hemocytes, leading to JAK/STAT activation mainly in hemocytes and in skeletal muscles. JAK/STAT activation in muscles, but not in hemocytes, is required for an efficient encapsulation of wasp eggs. This suggests that Upd2 and Upd3 are important cytokines, coordinating different tissues for the cellular immune response in Drosophila. In the fat body, Toll signaling initiates a systemic response in which hemocytes are mobilized and activated hemocytes (lamellocytes) are generated. However, the contribution of Toll signaling to the defense against wasps is limited, probably because the wasps inject inhibitors that prevent the activation of the Toll pathway. In conclusion, parasite infection induces a systemic response in Drosophila larvae involving major organ systems and probably the physiology of the entire organism.     

Fecundity in Drosophila following desiccation is dependent on nutrition and selection regime

Life-history trade-offs of populations of Drosophila melanogaster selected for enhanced desiccation resistance (D populations) include increased pupal mortality, retarded development, increased longevity, and decreased fecundity. We tested the effects of acute desiccation on fecundity and the effects of various nutritional regimes on fecundity following a bout of desiccation in the D populations and their control populations (C populations). Female flies were desiccated for 8 h (C populations) or 24 h (D populations) and then recovered on one of four treatments: distilled water, a saline solution, a saline and sucrose solution, or food. Each treatment was tested in the presence and absence of a yeast supplement. Fecundity was then measured on an oviposition medium over a 12-h period. Fecundity was also measured in flies that did not undergo a desiccation stress. Yeast increased fecundity under all conditions examined in the C populations but not in the D populations. There was an overall effect of recovery treatment on fecundity but no effect of desiccation stress.     

Wolbachia-mediated sperm modification is dependent on the host genotype in Drosophila.

Estimates of Wolbachia density in the eggs, testes and whole flies of drosophilid hosts have been unable to predict the lack of cytoplasmic incompatibility (CI) expression in so-called mod(-) variants. Consequently, the working hypothesis has been that CI expression, although related to Wolbachia density, is also governed by unknown factors that are influenced by both host and bacterial genomes. Here, we compare the behaviour of the mod(-) over-replicating Wolbachia popcorn strain in its native Drosophila melanogaster host to the same strain transinfected into a novel host, namely Drosophila simulans. We report that (i) the popcorn strain is a close relative of other D. melanogaster infections, (ii) the mod(-) status of popcorn in D. melanogaster appears to result from its inability to colonize sperm bundles, (iii) popcorn is present in the bundles in D. simulans and induces strong CI expression, which demonstrates that the bacterial strain does not lack the genetic machinery for inducing CI and that there is host-species-specific control over Wolbachia tissue tropism, and (iv) infection of sperm bundles by the mod(-) D. simulans wCof strain indicates that there are several independent routes by which a strain can be a CI non-expressor.     

Idiotype-restricted antibody response to specific immune complexes

In this report, we compared the immunogenicity of specific antigen/antibody complexes with that of free antigen. The complexes were prepared in antigen excess using the TEPC-15 myeloma protein and a phosphorylcholine-containing polysaccharide antigen (PnC), and the PnC-specific antibody response was measured using a hemolytic plaque assay 5 days after immunization. The results showed that the complexes were as immunogenic as the free antigen; however, the PnC-specific antibody response induced with the complexes was completely dominated by one particular idiotope (defined by plaque inhibition with the AB1-2 monoclonal antibody). On the other hand, the response of mice immunized with free antigen (PnC) was dominated to a lesser degree by the AB1-2 idiotope, and there was a great degree of variability in idiotope expression among individual mice. The results suggest that immunization with antigen/antibody complexes restricts the response to the expression of idiotopes that are present in the immune complex.     

CYFIP dependent actin remodeling controls specific aspects of Drosophila eye morphogenesis

Cell rearrangements shape organs and organisms using molecular pathways and cellular processes that are still poorly understood. Here we investigate the role of the Actin cytoskeleton in the formation of the Drosophila compound eye, which requires extensive remodeling and coordination between different cell types. We show that CYFIP/Sra-1, a member of the WAVE/SCAR complex and regulator of Actin remodeling, controls specific aspects of eye architecture: rhabdomere extension, rhabdomere terminal web organization, adherens junctions, retina depth and basement membrane integrity. We demonstrate that some phenotypes manifest independently, due to defects in different cell types. Mutations in WAVE/SCAR and in ARP2/3 complex subunits but not in WASP, another major regulator of Actin nucleation, phenocopy CYFIP defects. Thus, the CYFIP-SCAR-ARP2/3 pathway orchestrates specific tissue remodeling processes.     

Vascular injury response in mice is dependent on genetic background

Mouse models are employed to unravel the pathophysiology of vascular restenosis. Although much effort has been spent on how to apply an adequate arterial injury, the influence of the genetic background of mice has not yet received sufficient consideration. The study presented herein was designed to demonstrate the influence of the mouse strain on vascular injury response. Mice of a defined background (50% 129 strain and 50% DBA strain) were backcrossed into either the 129 strain or the DBA strain. Male offspring were subjected to a femoral artery injury model by applying an electric current. Morphometric analysis revealed that backcrossing into the 129 strain resulted in a significant (P < 0.001) 17-fold increase in neointima formation (n = 17 mice) compared with backcrossing into the DBA strain (n = 19). The values of neointima area were 9.18 x 10(3) +/- 2.13 x 10(3) and 0.54 x 10(3) +/- 0.39 x 10(3) microm2, respectively. In conjunction, the vessel wall area was enhanced by 1.8-fold (P < 0.001). In contrast, no significant differences were found for the areas of the lumen and the tunica media. Similarly, a significant increase in neointima formation was also found for mice of pure 129 strain compared with pure DBA strain. The results underline the importance of the genetic background for studies on vascular injury response. Furthermore, because the mouse genome of the various strains is well defined, serial testing of the genetic background of mice will provide candidate genes and/or genetic modifiers controlling vascular injury response.