Anti-Fibrotic Activity of an Antimicrobial Peptide in a Drosophila Model

Fibrotic lesions accompany several pathological conditions, including tumors. We show that expression of a dominant-active form of the Ras oncogene in Drosophila salivary glands (SGs) leads to redistribution of components of the basement membrane (BM) and fibrotic lesions. Similar to several types of mammalian fibrosis, the disturbed BM attracts clot components, including insect transglutaminase and phenoloxidase. SG epithelial cells show reduced apicobasal polarity accompanied by a loss of secretory activity. Both the fibrotic lesions and the reduced cell polarity are alleviated by ectopic expression of the antimicrobial peptide drosomycin (Drs), which also restores the secretory activity of the SGs. In addition to extracellular matrix components, both Drs and F-actin localize to fibrotic lesions

SWI/SNF regulates the alternative processing of a specific subset of pre-mRNAs in Drosophila melanogaster

<p>Abstract</p> <p>Background</p> <p>The SWI/SNF chromatin remodeling factors have the ability to remodel nucleosomes and play essential roles in key developmental processes. SWI/SNF complexes contain one subunit with ATPase activity, which in <it>Drosophila melanogaster </it>is called Brahma (Brm). The regulatory activities of SWI/SNF have been attributed to its influence on chromatin structure and transcription regulation, but recent observations have revealed that the levels of Brm affect the relative abundances of transcripts that are formed by alternative splicing and/or polyadenylation of the same pre-mRNA.</p> <p>Results</p> <p>We have investigated whether the function of Brm in pre-mRNA processing in <it>Drosophila melanogaster </it>is mediated by Brm alone or by the SWI/SNF complex. We have analyzed the effects of depleting individual SWI/SNF subunits on pre-mRNA processing throughout the genome, and we have identified a subset of transcripts that are affected by depletion of the SWI/SNF core subunits Brm, Snr1 or Mor. The fact that depletion of different subunits targets a subset of common transcripts suggests that the SWI/SNF complex is responsible for the effects observed on pre-mRNA processing when knocking down Brm. We have also depleted Brm in larvae and we have shown that the levels of SWI/SNF affect the pre-mRNA processing outcome <it>in vivo</it>.</p> <p>Conclusions</p> <p>We have shown that SWI/SNF can modulate alternative pre-mRNA processing, not only in cultured cells but also <it>in vivo</it>. The effect is restricted to and specific for a subset of transcripts. Our results provide novel insights into the mechanisms by which SWI/SNF regulates transcript diversity and proteomic diversity in higher eukaryotes.</p

The Toll immune-regulated Drosophila protein Fondue is involved in hemolymph clotting and puparium formation

Clotting is critical in limiting hemolymph loss and initiating wound healing in insects as in vertebrates. It is also an important immune defense, quickly forming a secondary barrier to infection, immobilizing bacteria and thereby promoting their killing. However, hemolymph clotting is one of the least understood immune responses in insects. Here, we characterize fondue (fon; CG15825), an immune-responsive gene of Drosophila melanogaster that encodes an abundant hemolymph protein containing multiple repeat blocks. After knockdown of fon by RNAi, bead aggregation activity of larval hemolymph is strongly reduced, and wound closure is affected. fon is thus the second Drosophila gene after hemolectin (hml), for which a knockdown causes a clotting phenotype. In contrast to hml-RNAi larvae, clot fibers are still observed in samples from fon-RNAi larvae. However, clot fibers from fon-RNAi larvae are more ductile and longer than in wt hemolymph samples, indicating that Fondue might be involved in cross-linking of fiber proteins. In addition, fon-RNAi larvae exhibit melanotic tumors and constitutive expression of the antifungal peptide gene Drosomycin (Drs), while fon-RNAi pupae display an aberrant pupal phenotype. Altogether, our studies indicate that Fondue is a major hemolymph protein required for efficient clotting in Drosophila

Pathogen Entrapment by Transglutaminase—A Conserved Early Innate Immune Mechanism

Clotting systems are required in almost all animals to prevent loss of body fluids after injury. Here, we show that despite the risks associated with its systemic activation, clotting is a hitherto little appreciated branch of the immune system. We compared clotting of human blood and insect hemolymph to study the best-conserved component of clotting systems, namely the Drosophila enzyme transglutaminase and its vertebrate homologue Factor XIIIa. Using labelled artificial substrates we observe that transglutaminase activity from both Drosophila hemolymph and human blood accumulates on microbial surfaces, leading to their sequestration into the clot. Using both a human and a natural insect pathogen we provide functional proof for an immune function for transglutaminase (TG). Drosophila larvae with reduced TG levels show increased mortality after septic injury. The same larvae are also more susceptible to a natural infection involving entomopathogenic nematodes and their symbiotic bacteria while neither phagocytosis, phenoloxidase or—as previously shown—the Toll or imd pathway contribute to immunity. These results firmly establish the hemolymph/blood clot as an important effector of early innate immunity, which helps to prevent septic infections. These findings will help to guide further strategies to reduce the damaging effects of clotting and enhance its beneficial contribution to immune reactions

Hemostasis in Invertebrates and Vertebrates: An Evolutionary Excursion.

No abstract available

A polydnavirus-encoded protein of an endoparasitoid wasp is an immune suppressor

The molecular mechanism by which polydnaviruses of endoparasitoid wasps disrupt cell-mediated encapsulation reactions of host insects is largely unknown. Here we show that a polydnavirus-encoded protein, produced from baculovirus and plasmid expression vectors, prevents cell surface exposure of lectin-binding sites and microparticle formation during immune stimulation of haemocytes. The inactivation of immune-related cellular processes by this protein was analysed using a specific lectin and annexin V and shown to be virtually identical to polydnavirus-mediated effects on haemocytes. Cytochalasin D application has similar effects on haemocytes, suggesting that the immune suppression by the polydnavirus protein is caused by the destabilization of actin filaments. Since the exposure of cell surface glycoproteins and the formation of microparticles are part of an immune response to foreign objects or microorganisms and a prerequisite for cell-mediated encapsulation of microorganisms and parasites, the virusencoded protein may become an important tool for the inactivation of cellular immune reactions in insects and an essential component in understanding immune suppression in parasitized host insects.Sassan Asgari, Otto Schmidt and Ulrich Theopol

Digging Back in Evolution : Danger in Drosophila

Insects, including the fruit fly, Drosophila melanogaster are used to study a wide array of processes, many of which are known or are expected to be regulated by damage-associated molecular patterns (DAMPs). These include regenerative processes after wounding, replacement of cells by cell competition, induction of immunity and inflammation, responses against tumorous cells and neurodegeneration. Most, if not all of these processes have beneficial outcomes on organismal health but may also lead to pathologies, which often resemble those observed in humans. Drosophila offers unique opportunities to analyze and manipulate genes and pathways related to these immune consequences with high temporal and local resolution. Ultimately, such detailed analyses in the Drosophila model will aid in our understanding of the roles DAMPs play at the bifurcation between physiological and pathological outcomes in other animal species, including humans

Innate immunity and its evasion and suppression by hymenopteran endoparasitoids

The definitive version may be found at www.interscience.wiley.comRecent studies suggest that insects use pattern recognition molecules to distinguish prokaryotic pathogens and fungi from "self" structures. Less understood is how the innate immune system of insects recognizes endoparasitic Hymenoptera and other eukaryotic invaders as foreign. Here we discuss candidate recognition factors and the strategies used by parasitoids to overcome host defense responses. We suggest that host-parasitoid systems are important experimental models for studying how the innate immune system of insects recognizes foreign invaders that are phylogenetically more closely related to their hosts. The strategies used by parasitoids suggest that insects may employ "hidden-self" recognition molecules for attacking foreign objects intruding the open circulatory system.Otto Schmidt, Uli Theopold and Mike Stran