Drosophila hemopoiesis and cellular immunity

A novel method for infecting Drosophila adult flies with insect pathogenic nematodes

Drosophila has been established as an excellent genetic and genomic model to investigate host-pathogen interactions and innate immune defense mechanisms. To date, most information on the Drosophila immune response derives from studies that involve bacterial, fungal or viral pathogens. However, immune reactions to insect parasitic nematodes are still not well characterized. The nematodes Heterorhabditis bacteriophora live in symbiosis with the entomopathogenic bacteria Photorhabdus luminescens, and they are able to invade and kill insects. Interestingly, Heterorhabditis nematodes are viable in the absence of Photorhabdus. Techniques for infecting Drosophila larvae with these nematodes have been previously reported. Here, we have developed a method for infecting Drosophila adult flies with Heterorhabditis nematodes carrying (symbiotic worms) or lacking (axenic worms) their associated bacteria. The protocol we present can be readily adapted for studying parasitic strategies of other insect nematodes using Drosophila as the host infection model.

Large-scale RNAi screens add both clarity and complexity to Drosophila NF-κB signaling

NF-κB signaling is an immune response mechanism remarkably conserved through phylogeny. The genetically tractable model animal Drosophila melanogaster is an important model organism for studying NF-κB signaling in the immune response. Fruit flies have two NF-κB signaling pathways: the Toll and the Imd pathway. Traditional genetic screens have revealed many important aspects about the regulation of Drosophila NF-κB signaling and have helped us to also understand the immune response in humans. For example, the discovery that Toll like receptors are the main immune signaling molecules in mammals was based on work in flies. During the past decade high throughput RNA interference (RNAi)-based screening in cultured Drosophila cells has become a common method for identifying novel genes required for numerous cellular processes including NF-κB signaling. These screens have identified many novel positive and negative regulators of Drosophila NF-κB signaling thus enhancing our understanding of these signaling cascades.

Healthy aging - insights from Drosophila

Human life expectancy has nearly doubled in the past century due, in part, to social and economic development, and a wide range of new medical technologies and treatments. As the number of elderly increase it becomes of vital importance to understand what factors contribute to healthy aging. Human longevity is a complex process that is affected by both environmental and genetic factors and interactions between them. Unfortunately, it is currently difficult to identify the role of genetic components in human longevity. In contrast, model organisms such as C. elegans, Drosophila, and rodents have facilitated the search for specific genes that affect lifespan. Experimental evidence obtained from studies in model organisms suggests that mutations in a single gene may increase longevity and delay the onset of age-related symptoms including motor impairments, sexual and reproductive and immune dysfunction, cardiovascular disease, and cognitive decline. Furthermore, the high degree of conservation between diverse species in the genes and pathways that regulate longevity suggests that work in model organisms can both expand our theoretical knowledge of aging and perhaps provide new therapeutic targets for the treatment of age-related disorders.

Identification of putative miRNA involved in Drosophila melanogaster immune response

MicroRNAs (miRNAs) are small endogenous non-coding RNAs that post-transcriptionally regulate gene expression in eukaryotes. They are known to play diverse roles in physiological processes such as homeostasis, development, cancer and immune response. In Drosophila melanogaster up to 176 miRNAs have been identified; yet, their biological functions remain unknown. Here, we describe an in silico screening strategy to identify miRNAs involved in a specific immune signaling pathway that is based on: (i) the potential capability of miRNAs to target mRNAs of a given pathway; (ii) the sequence conservation of miRNAs across species and (iii) the expression profile of miRNAs. Using this strategy, we have defined a subset of seven Drosophila miRNAs that are likely to participate in the immune response. Interestingly, some of these miRNAs target peptidoglycan receptor proteins (PGRPs) for which no regulators are known yet. miRNA-mediated regulation may explain how PGRPs are controlled in the immune signaling pathway.

Structural and functional characterization of pseudopodocyte, a shaggy immune cell produced by two Drosophila species of the obscura group

We recently reported that most of the Drosophila species of the obscura group were unable to mount cellular capsules and no lamellocyte was ever found in the hemolymph of any of the tested species. Only three species were able to encapsulate, despite lacking lamellocytes. Their encapsulation ability was always associated with the presence of an unpreviously described kind of capsule-forming immunocytes designated as "atypical hemocytes". Here, we describe the ultrastructural and functional characteristics of this type of hemocyte. We show that these cells share many ultrastructural and morphological features with Drosophila melanogaster plasmatocytes, although they are involved in the formation of the external layers of the cellular capsule, a functional property exhibited by lamellocytes in D. melanogaster. Due to the high number of pseudopodes in these cells, we suggest to name them "pseudopodocytes". After structural and functional characterization of these atypical hemocytes, their ambiguous status between plasmatocytes and lamellocytes is discussed.

Prion-induced toxicity in PrP transgenic Drosophila

Prion diseases are fatal transmissible neurodegenerative diseases of humans and various vertebrate species. In their natural hosts these conditions are characterised by prolonged incubation times prior to the onset of clinical signs of terminal disease. Accordingly, tractable models of mammalian prion disease are required in order to better understand the mechanisms of prion replication and prion-induced neurotoxicity. Transmission of prion diseases can occur across a species barrier and this is facilitated in recipients transgenic for the same PrP gene as the individual from which the infectious prions are derived. Here we have tested the hypothesis that exogenous ovine prions can induce neurotoxicity in Drosophila melanogaster transgenic for ovine PrP. Drosophila that expressed ovine PrP pan neuronally and inoculated with ovine prions at the larval stage by oral exposure to scrapie-infected sheep brain homogenate showed markedly accelerated locomotor and survival defects. ARQ PrP transgenic Drosophila exposed to scrapie-infected brain homogenate showed a significant and progressive reduction in locomotor activity compared to similar flies exposed to normal sheep brain homogenate. The prion-induced locomotor defect was accompanied by the accumulation of potentially misfolded PrP in the brains of prion-inoculated flies. VRQ PrP transgenic Drosophila, which expressed less ovine PrP than ARQ flies, showed a reduced median survival compared to similar flies exposed to normal sheep brain homogenate. These prion-induced phenotypic effects were PrP-mediated since ovine prions were not toxic in non-PrP transgenic control flies. Our observations provide the basis of an invertebrate model of transmissible mammalian prion disease.

Protocol for ex vivo incubation of Drosophila primary post-embryonic haemocytes for real-time analyses

The cellular branch of the Drosophila larval innate immune system consists of three immunosurveillance (haemocyte) cell types: plasmatocytes, crystal cells, and lamellocytes. In order to examine haemocyte cytoskeletal dynamics or migration, most researchers use embryos or in vitro cell culture systems, but very little is known about the behaviour of post-embryonic haemocytes. The current method employs an ex vivo system, in which post-embryonic haemocytes are isolated for short-term analysis, in order to investigate various aspects of their behaviour during events requiring cytoskeleton dynamics and Rho GTPase signalling.

Drosophila cellular immunity: a story of migration and adhesion

Research during the past 15 years has led to significant breakthroughs, providing evidence of a high degree of similarity between insect and mammalian innate immune responses, both humoural and cellular, and highlighting Drosophila melanogaster as a model system for studying the evolution of innate immunity. In a manner similar to cells of the mammalian monocyte and macrophage lineage, Drosophila immunosurveillance cells (haemocytes) have a number of roles. For example, they respond to wound signals, are involved in wound healing and contribute to the coagulation response. Moreover, they participate in the phagocytosis and encapsulation of invading pathogens, are involved in the removal of apoptotic bodies and produce components of the extracellular matrix. There are several reasons for using the Drosophila cellular immune response as a model to understand cell signalling during adhesion and migration in vivo: many genes involved in the regulation of Drosophila haematopoiesis and cellular immunity have been maintained across taxonomic groups ranging from flies to humans, many aspects of Drosophila and mammalian innate immunity seem to be conserved, and Drosophila is a simplified and well-studied genetic model system. In the present Commentary, we will discuss what is known about cellular adhesion and migration in the Drosophila cellular immune response, during both embryonic and larval development, and where possible compare it with related mechanisms in vertebrates.

Contribution of the caspase gene sequence diversification to the specifically antiviral defense in invertebrate

Vertebrates achieve adaptive immunity of all sorts against pathogens through the diversification of antibodies. However the mechanism of invertebrates' innate immune defense against various pathogens remains largely unknown. Our study used shrimp and white spot syndrome virus (WSSV) to show that PjCaspase, a caspase gene of shrimp that is crucial in apoptosis, possessed gene sequence diversity. At present, the role of gene sequence diversity in immunity has not been characterized. To address this issue, we compared the PjCaspase gene sequence diversities from WSSV-free and WSSV-resistant shrimp. The sequence analysis indicated that the PjCaspase gene from the WSSV-resistant shrimp contained a special fragment, designated as fragment 3 (221-229 aa). Down-regulation or overexpression of the PjCaspase gene containing fragment 3 led to significant inhibition or enhancement of virus-induced apoptosis, but had no effect on bacterium challenge. We found evidence that the silencing or overexpression of this gene led to a 7-fold increase or 11-fold decrease of WSSV copies, respectively. Our results suggested that the PjCaspase gene containing fragment 3 provided the molecular basis for the antiviral defense of shrimp. This study represented the first report of the role of gene sequence diversity in the immunity of an invertebrate against virus infection. Invertebrates may employ this gene sequence diversity as a system to avoid pathogen interference with their immune response.

The extended loop of the C-terminal carbohydrate-recognition domain of Manduca sexta immulectin-2 is important for ligand binding and functions

Our previous research showed that immulectin-2 (IML-2), a C-type lectin from the tobacco hornworn, Manduca sexta, is a pattern recognition receptor (PRR) that can bind to pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS), peptidoglycan (PG) and β-1,3-glucan, and IML-2 plays an important role in cellular encapsulation, melanization, phagocytosis, and prophenoloxidase (proPO) activation. Unlike most mammalian C-type lectins that contain a single carbohydrate-recognition domain (CRD), IML-2 is composed of tandem CRDs, and the C-terminal CRD2 contains an extended loop, which is not present in most C-type CRDs. We hypothesize that the extended loop may participate in ligand binding, encapsulation, melanization, phagocytosis and/or proPO activation in M. sexta. To test this hypothesis, two deletion mutant proteins (IML-2Δ220-244 and IML-2Δ220-257), in which the extended loop of the CRD2 was partially or completely deleted, were expressed and purified. By comparing the characteristics of recombinant IML-2, IML-2Δ220-244 and IML-2Δ220-257, we found that deletion of the extended loop in CRD2 impaired the ability of IML-2 to bind microbial PAMPs and to stimulate proPO activation, indicating that the extended loop of IML-2 plays an important role in ligand binding and biological functions.

Senescence of the cellular immune response in Drosophila melanogaster

Immune system effectiveness generally declines as animals age, compromising disease resistance. In Drosophila, expression of a variety of immune-related genes elevates during ageing; however how this is linked to increasing pathogen susceptibility in older flies has remained unclear. We investigated whether changes in the Drosophila cellular immune response might contribute to immunosenescence. Experiments studied fly cohorts of different ages and compared the numbers and activity of the circulating haemocytes involved in pathogen defence. In female wildtype Samarkand and Oregon R flies the haemocyte population fell by 31.8% and 10.2% respectively during the first four weeks of adulthood. Interestingly we detected no such decline in male flies. The impact of ageing on the phagocytic activity of haemocytes was investigated by injecting flies with fluorescently labelled microbes or latex beads and assessing the ability of haemocytes to engulf them. For all immune challenges the proportion of actively phagocytosing haemocytes decreased as flies aged. Whilst 24.3%±1.15% of haemocytes in one-week-old flies phagocytosed Escherichia coli bacteria or Beauveria bassiana fungal spores, this decreased to 16.7%±0.99% in four-week-old flies. This clear senescence of the Drosophila cellular immune response may underpin increased disease susceptibility in older flies.

Drosophila phagocytosis - still many unknowns under the surface

In mammals, phagocytosis coordinates host defence on two levels: It acts both as an effector of the innate immunity, as well as an initiator of the adaptive immunity. The fruit fly Drosophila melanogaster (D. melanogaster) lacks the adaptive immune response, and the role of Drosophila plasmatocytes, cells that resemble phagocytosing mammalian macrophages, is limited to innate immune responses. During the past years, several studies have shed light on the role of phagocytosis in the Drosophila host defence. At least in some infection models, the systemic production of potent antimicrobial peptides (AMPs) does not completely compensate for the need for cellular immune responses. As a model, Drosophila offers powerful tools for studying phagocytosis including, large-scale RNA interference (RNAi) based in vitro screens that can be combined with classical Drosophila genetics. These kinds of approaches have led to important discoveries related especially to microbial recognition by Drosophila plasmatocytes. Events following initial recognition, however, have remained more elusive. This review summarizes the current knowledge on Drosophila phagocytosis focusing on the most recent advancements in the field, and highlighting the benefits the Drosophila system has to offer for research on phagocytosis.

Distinct role of Hsp70 in Drosophila hemocytes during severe hypoxia

Severe hypoxia can lead to injury and mortality in vertebrate or invertebrate organisms. Our research is focused on understanding the molecular mechanisms that lead to injury or adaptation to hypoxic stress using Drosophila as a model system. In this study, we employed the UAS-Gal4 system to dissect the protective role of Hsp70 in specific tissues in vivo under severe hypoxia. In contrast to overexpression in tissues such as muscles, heart, and brain, we found that overexpression of Hsp70 in hemocytes of flies provides a remarkable survival benefit to flies exposed to severe hypoxia for days. Furthermore, these flies were tolerant not only to severe hypoxia but also to other stresses such as oxidant stress (e.g., paraquat feeding or hyperoxia). Interestingly we observed that the better survival with Hsp70 overexpression in hemocytes under hypoxia or oxidant stress is causally linked to reactive oxygen species (ROS) reduction in whole flies. We also show that hemocytes are a major source of ROS generation, leading to injury during hypoxia, and their elimination results in a better survival under hypoxia. Hence, our study identified a protective role for Hsp70 in Drosophila hemocytes, which is linked to ROS reduction in the whole flies and thus helps in their remarkable survival during oxidant or hypoxic stress.

Losing the battle against fungal infection: suppression of termite immune defenses during mycosis

The dampwood termite, Zootermopsis angusticollis is known to generate humoral immune responses to the entomopathogenic fungus Metarhizium anisopliae. However, little is known about how the termite's cellular immune system reacts to fungal infection. To test the effect of conidia exposure on cellular immunity, we quantified the number and types of hemocytes in the hemolymph of naïve nymphs and compared their circulating counts with those of nestmates exposed to 0, 2×10(3), 2×10(6) or 2×10(8) conidia/ml doses. These termites were then bled and their hemocytes counted on days 1, 2, 3, 4, 7 post-exposure. Our results show, first, that naïve Z. angusticollis nymphs have three different blood cell types tentatively identified as granular hemocytes, prohemocytes and plasmatocytes. In these individuals, plasmatocytes were on average 13.5 and 3.3 times more numerous than granular hemocytes and prohemocytes, respectively. Second, a full factorial general linear analysis indicated that hemocyte type, time elapsed since conidia exposure and conidia dosage as well as all their interactions explained 43% of the variability in hemocyte density. The numbers of prohemocytes and particularly plasmatocytes, but not granular hemocytes, appear to be affected by the progression of disease. The decline in hemocyte numbers coincided with the appearance of hyphal bodies and the onset of "sluggish" termite behavior that culminated in the insect's death. Hemocyte counts of infected males and females were affected to the same extent. Hence, M. anisopliae overtakes the cellular immune responses of Z. angusticollis mainly by destroying the host's most abundant hemocyte types.

Bacteria-Induced Dscam Isoforms of the Crustacean, Pacifastacus leniusculus

The Down syndrome cell adhesion molecule, also known as Dscam, is a member of the immunoglobulin super family. Dscam plays an essential function in neuronal wiring and appears to be involved in innate immune reactions in insects. The deduced amino acid sequence of Dscam in the crustacean Pacifastacus leniusculus (PlDscam), encodes 9(Ig)-4(FNIII)-(Ig)-2(FNIII)-TM and it has variable regions in the N-terminal half of Ig2 and Ig3 and the complete Ig7 and in the transmembrane domain. The cytoplasmic tail can generate multiple isoforms. PlDscam can generate more than 22,000 different unique isoforms. Bacteria and LPS injection enhanced the expression of PlDscam, but no response in expression occurred after a white spot syndrome virus (WSSV) infection or injection with peptidoglycans. Furthermore, PlDscam silencing did not have any effect on the replication of the WSSV. Bacterial specific isoforms of PlDscam were shown to have a specific binding property to each tested bacteria, E. coli or S. aureus. The bacteria specific isoforms of PlDscam were shown to be associated with bacterial clearance and phagocytosis in crayfish.

Invertebrate animals lack an adaptive immune system and have no antibodies. Vertebrate antibodies belong to the immunoglobulin super family of proteins, and one other member of this large family is the Down syndrome cell adhesion molecule or Dscam. Of specific interest is that Dscam proteins in invertebrates show a great diversity of isoforms, and its gene structure in Drosophila melanogaster and other insect species allow for more than 30,000 different isoforms. Dscam proteins are important for the interaction between neurons in insects, but recently a role for this hypervariable protein in immune defense has been shown. Here, we show that Dscam proteins with similar highly variable structures are present in a crustacean, the freshwater crayfish Pacifastacus leniusculus. We also found that specific isoforms could be induced in the animal after injection of different bacteria. The Dscam isoforms induced by Escherichia coli were found to cluster together in a phylogenetic analysis. Furthermore we produced recombinant proteins of the different isoforms that were induced by E. coli and Staphylococcus aureus and we could demonstrate that these proteins can bind specifically to their corresponding bacteria. The bacteria specific isoforms of Dscam were also shown to be associated with bacterial clearance and phagocytosis in crayfish. Our study therefore provides new insights into the function of invertebrate Dscams in immunity.

Differentially expressed genes in silkworm cell cultures in response to infection by Wolbachia and Cardinium endosymbionts

Wolbachia and Cardinium are bacterial endosymbionts that are widely distributed amongst arthropods. Both cause reproductive alterations, such as cytoplasmic incompatibility, parthenogenesis and feminization. Here we studied differentially expressed genes in Wolbachia- and Cardinium-infected Bm-aff3 silkworm cells using a silkworm microarray. Wolbachia infection did not alter gene expression or induce or suppress immune responses. In contrast, Cardinium infection induced many immune-related genes, including antimicrobial peptides, pattern recognition receptors and a serine protease. Host immune responses differed, possibly because of the different cell wall structures of Wolbachia and Cardinium because the former lacks genes encoding lipopolysaccharide components and two racemases for peptidoglycan formation. A few possibly non-immune-related genes were differentially expressed, but their involvement in host reproductive alteration was unclear.

Effects of heavy metals on insect immunocompetent cells

The influence of the following heavy metals, copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb), on haemocytes of the house fly Musca domestica L. was studied under laboratory conditions. House fly larvae were exposed to low or high, semi-lethal concentrations of metals. These particular metals were selected because they are present in polluted environments in Poland. In addition, we studied expression of the stress proteins HSP70 and HSP72 in haemocytes collected from larvae that had been exposed to heavy metal. The obtained results showed changes in haemocytes morphology and phagocytotic plasticity in the experimental flies in comparison to control. The number of prohaemocytes, regarded as stem cells, increased, while granulocytes, responsible for phagocytosis, decreased. However, we have not detected any clear changes in expression of HSP70 or HSP72 in flies treated with low or high concentrations of the heavy metals.

The Rho-family GTPase Rac1 regulates integrin localization in Drosophila immunosurveillance cells

Background

When the parasitoid wasp Leptopilina boulardi lays an egg in a Drosophila larva, phagocytic cells called plasmatocytes and specialized cells known as lamellocytes encapsulate the egg. The Drosophila β-integrin Myospheroid (Mys) is necessary for lamellocytes to adhere to the cellular capsule surrounding L. boulardi eggs. Integrins are heterodimeric adhesion receptors consisting of α and β subunits, and similar to other plasma membrane receptors undergo ligand-dependent endocytosis. In mammalian cells it is known that integrin binding to the extracellular matrix induces the activation of Rac GTPases, and we have previously shown that Rac1 and Rac2 are necessary for a proper encapsulation response in Drosophila larvae. We wanted to test the possibility that Myospheroid and Rac GTPases interact during the Drosophila anti-parasitoid immune response.

Results

In the current study we demonstrate that Rac1 is required for the proper localization of Myospheroid to the cell periphery of haemocytes after parasitization. Interestingly, the mislocalization of Myospheroid in Rac1 mutants is rescued by hyperthermia, involving the heat shock protein Hsp83. From these results we conclude that Rac1 and Hsp83 are required for the proper localization of Mys after parasitization.

Significance

We show for the first time that the small GTPase Rac1 is required for Mysopheroid localization. Interestingly, the necessity of Rac1 in Mys localization was negated by hyperthermia. This presents a problem, in Drosophila we quite often raise larvae at 29°C when using the GAL4/UAS misexpression system. If hyperthermia rescues receptor endosomal recycling defects, raising larvae in hyperthermic conditions may mask potentially interesting phenotypes.

Fraternal twins: Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1, two homologous EF-hand containing calcium binding adaptor proteins with distinct functions

Changes in the intracellular calcium concentration govern cytoskeletal rearrangement, mitosis, apoptosis, transcriptional regulation or synaptic transmission, thereby, regulating cellular effector and organ functions. Calcium binding proteins respond to changes in the intracellular calcium concentration with structural changes, triggering enzymatic activation and association with downstream proteins. One type of calcium binding proteins are EF-hand super family proteins. Here, we describe two recently discovered homologous EF-hand containing adaptor proteins, Swiprosin-1/EF-hand domain containing 2 (EFhd2) and Swiprosin-2/EF-hand domain containing 1 (EFhd1), which are related to allograft inflammatory factor-1 (AIF-1). For reasons of simplicity and concision we propose to name Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 from now on EFhd2 and EFhd1, according to their respective gene symbols. AIF-1 and Swiprosin-1/EFhd2 are already present in Bilateria, for instance in Drosophila melanogaster and Caenhorhabditis elegans. Swiprosin-2/EFhd1 arose later from gene duplication in the tetrapodal lineage. Secondary structure prediction of AIF-1 reveals disordered regions and one functional EF-hand. Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 exhibit a disordered region at the N-terminus, followed by two EF-hands and a coiled-coil domain. Whereas both proteins are similar in their predicted overall structure they differ in a non-homologous stretch of 60 amino acids just in front of the EF-hands. AIF-1 controls calcium-dependent cytoskeletal rearrangement in innate immune cells by means of its functional EF-hand. We propose that Swiprosin-1/EFhd2 as well is a cytoskeleton associated adaptor protein involved in immune and brain cell function. Pro-inflammatory conditions are likely to modulate expression and function of Swiprosin-1/EFhd2. Swiprosin-2/EFhd1, on the other hand, modulates apoptosis and differentiation of neuronal and muscle precursor cells, probably through an association with mitochondria. We suggest furthermore that Swiprosin-2/EFhd1 is part of a cellular response to oxidative stress, which could explain its pro-survival activity in neuronal, muscle and perhaps some malignant tissues.

Innate immune responses of Drosophila melanogaster are altered by spaceflight

Alterations and impairment of immune responses in humans present a health risk for space exploration missions. The molecular mechanisms underpinning innate immune defense can be confounded by the complexity of the acquired immune system of humans. Drosophila (fruit fly) innate immunity is simpler, and shares many similarities with human innate immunity at the level of molecular and genetic pathways. The goals of this study were to elucidate fundamental immune processes in Drosophila affected by spaceflight and to measure host-pathogen responses post-flight. Five containers, each containing ten female and five male fruit flies, were housed and bred on the space shuttle (average orbit altitude of 330.35 km) for 12 days and 18.5 hours. A new generation of flies was reared in microgravity. In larvae, the immune system was examined by analyzing plasmatocyte number and activity in culture. In adults, the induced immune responses were analyzed by bacterial clearance and quantitative real-time polymerase chain reaction (qPCR) of selected genes following infection with E. coli. The RNA levels of relevant immune pathway genes were determined in both larvae and adults by microarray analysis. The ability of larval plasmatocytes to phagocytose E. coli in culture was attenuated following spaceflight, and in parallel, the expression of genes involved in cell maturation was downregulated. In addition, the level of constitutive expression of pattern recognition receptors and opsonins that specifically recognize bacteria, and of lysozymes, antimicrobial peptide (AMP) pathway and immune stress genes, hallmarks of humoral immunity, were also reduced in larvae. In adults, the efficiency of bacterial clearance measured in vivo following a systemic infection with E. coli post-flight, remained robust. We show that spaceflight altered both cellular and humoral immune responses in Drosophila and that the disruption occurs at multiple interacting pathways.

Drosophila Mtm and class II PI3K coregulate a PI(3)P pool with cortical and endolysosomal functions

Turnover of endosomal PI(3)P by mtm maintains endolysosomal homeostasis and cortical remodeling in Drosophila hemocytes during migration.

Reversible phosphoinositide phosphorylation provides a dynamic membrane code that balances opposing cell functions. However, in vivo regulatory relationships between specific kinases, phosphatases, and phosphoinositide subpools are not clear. We identified myotubularin (mtm), a Drosophila melanogaster MTM1/MTMR2 phosphoinositide phosphatase, as necessary and sufficient for immune cell protrusion formation and recruitment to wounds. Mtm-mediated turnover of endosomal phosphatidylinositol 3-phosphate (PI(3)P) pools generated by both class II and III phosphatidylinositol 3-kinases (Pi3K68D and Vps34, respectively) is needed to down-regulate membrane influx, promote efflux, and maintain endolysosomal homeostasis. Endocytosis, but not endolysosomal size, contributes to cortical remodeling by mtm function. We propose that Mtm-dependent regulation of an endosomal PI(3)P pool has separable consequences for endolysosomal homeostasis and cortical remodeling. Pi3K68D depletion (but not Vps34) rescues protrusion and distribution defects in mtm-deficient immune cells and restores functions in other tissues essential for viability. The broad interactions between mtm and class II Pi3K68D suggest a novel strategy for rebalancing PI(3)P-mediated cell functions in MTM-related human disease.

Analysis of expressed sequence tags for Frankliniella occidentalis, the western flower thrips

Thrips are members of the insect order Thysanoptera and Frankliniella occidentalis (the western flower thrips) is the most economically important pest within this order. F. occidentalis is both a direct pest of crops and an efficient vector of plant viruses, including Tomato spotted wilt virus (TSWV). Despite the world-wide importance of thrips in agriculture, there is little knowledge of the F. occidentalis genome or gene functions at this time. A normalized cDNA library was constructed from first instar thrips and 13 839 expressed sequence tags (ESTs) were obtained. Our EST data assembled into 894 contigs and 11 806 singletons (12 700 nonredundant sequences). We found that 31% of these sequences had significant similarity (E< or = 10(-10)) to protein sequences in the National Center for Biotechnology Information nonredundant (nr) protein database, and 25% were functionally annotated using Blast 2GO. We identified 74 sequences with putative homology to proteins associated with insect innate immunity. Sixteen sequences had significant similarity to proteins associated with small RNA-mediated gene silencing pathways (RNA interference; RNAi), including the antiviral pathway (short interfering RNA-mediated pathway). Our EST collection provides new sequence resources for characterizing gene functions in F. occidentalis and other thrips species with regards to vital biological processes, studying the mechanism of interactions with the viruses harboured and transmitted by the vector, and identifying new insect gene-centred targets for plant disease and insect control.

Two hemocyte lineages exist in silkworm larval hematopoietic organ

Background

Insects have multiple hemocyte morphotypes with different functions as do vertebrates, however, their hematopoietic lineages are largely unexplored with the exception of Drosophila melanogaster.

Methodology/Principal Findings

To study the hematopoietic lineage of the silkworm, Bombyx mori, we investigated in vivo and in vitro differentiation of hemocyte precursors in the hematopoietic organ (HPO) into the four mature hemocyte subsets, namely, plasmatocytes, granulocytes, oenocytoids, and spherulocytes. Five days after implantation of enzymatically-dispersed HPO cells from a GFP-expressing transgenic line into the hemocoel of normal larvae, differentiation into plasmatocytes, granulocytes and oenocytoids, but not spherulocytes, was observed. When the HPO cells were cultured in vitro, plasmatocytes appeared rapidly, and oenocytoids possessing prophenol oxidase activity appeared several days later. HPO cells were also able to differentiate into a small number of granulocytes, but not into spherulocytes. When functionally mature plasmatocytes were cultured in vitro, oenocytoids were observed 10 days later. These results suggest that the hemocyte precursors in HPO first differentiate into plasmatocytes, which further change into oenocytoids.

Conclusions/Significance

From these results, we propose that B. mori hemocytes can be divided into two major lineages, a granulocyte lineage and a plasmatocyte-oenocytoid lineage. The origins of the spherulocytes could not be determined in this study. We construct a model for the hematopoietic lineages at the larval stage of B. mori.

Effects of zinc on programmed cell death of Musca domestica and Drosophila melanogaster blood cells

Programmed cell death (PCD) and phagocytotic activity of immune cells play a pivotal role in insect development. We examined the influence of Zn(2+), an important element to fundamental biological processes, on phagocytosis and apoptosis of hemocytes in two fly species: Musca domestica and Drosophila melanogaster. Hemocytes were isolated from the third instar larvae of both species and treated for 3h with zinc chloride solutions, containing 0.35 mM or 1.7 mM of Zn(2+), and untreated as control. Phagocytotic activity of hemocytes was examined by flow cytometry after adding latex fluorescent beads to the medium, while apoptosis was evaluated by application of annexinV-FITC and pan-caspase-FITC inhibitor. Mitochondrial viability was determined by measuring resazurin absorbancy in the cell medium. The obtained results showed that Zn(2+) increases phagocytosis and affects PCD of both species hemocytes but each in a different way. Zinc decreases fraction of annexin-positive hemocytes in M. domestica but increases it in D. melanogaster. The pan-caspase analysis revealed low and high activity of caspases in hemocytes of M. domestica and D. melanogaster, respectively. Zn(2+) also decreased the viability of hemocyte mitochondria but only in D. melanogaster. It suggests that flies use different pathways of PCD, or that Zn plays a different role in this process in M. domestica than in D. melanogaster.

The strepsipteran endoparasite Xenos vesparum alters the immunocompetence of its host, the paper wasp Polistes dominulus

It is unexplained how strepsipteran insects manipulate the physiology of their hosts in order to undergo endoparasitic development without being entrapped by the innate immune defences of the host. Here we present pioneering work that aimed to explore for the first time several components of the cellular and humoral immune response among immature stages of the paper wasp Polistes dominulus, in both unparasitized insects and after infection by the strepsipteran endoparasite Xenos vesparum. We carried out hemocyte counts, phagocytosis assays in vitro and antibacterial response in vivo. On the whole, hemocyte load does not seem to be drastically affected by parasitization: a non-significant increase in hemocyte numbers was observed in parasitized wasps as respect to control, while the two dominant hemocyte types were present with similar proportions in both groups. On the other hand, phagocytosis was significantly reduced in hemocytes from parasitized wasps while the antibacterial response seemed to be less effective in control. These somewhat unexpected results are discussed, along with the implications of a multiple approach in immune response studies.

Swiprosin-1/EFhd2 controls B cell receptor signaling through the assembly of the B cell receptor, Syk, and phospholipase C gamma2 in membrane rafts

Compartmentalization of the BCR in membrane rafts is important for its signaling capacity. Swiprosin-1/EFhd2 (Swip-1) is an EF-hand and coiled-coil-containing adaptor protein with predicted Src homology 3 (SH3) binding sites that we identified in membrane rafts. We showed previously that Swip-1 amplifies BCR-induced apoptosis; however, the mechanism of this amplification was unknown. To address this question, we overexpressed Swip-1 and found that Swip-1 amplified the BCR-induced calcium flux in WEHI231, B62.1, and Bal17 cells. Conversely, the BCR-elicited calcium flux was strongly attenuated in Swip-1-silenced WEHI231 cells, and this was due to a decreased calcium mobilization from intracellular stores. Complementation of Swip-1 expression in Swip-1-silenced WEHI231 cells restored the BCR-induced calcium flux and enhanced spleen tyrosine kinase (Syk) tyrosine phosphorylation and activity as well as SLP65/BLNK/BASH and phospholipase C gamma2 (PLCgamma2) tyrosine phosphorylation. Furthermore, Swip-1 induced the constitutive association of the BCR itself, Syk, and PLCgamma2 with membrane rafts. Concomitantly, Swip-1 stabilized the association of BCR with tyrosine-phosphorylated proteins, specifically Syk and PLCgamma2, and enhanced the constitutive interaction of Syk and PLCgamma2 with Lyn. Interestingly, Swip-1 bound to the rSH3 domains of the Src kinases Lyn and Fgr, as well as to that of PLCgamma. Deletion of the predicted SH3-binding region in Swip-1 diminished its association and that of Syk and PLCgamma2 with membrane rafts, reduced its interaction with the SH3 domain of PLCgamma, and diminished the BCR-induced calcium flux. Hence, Swip-1 provides a membrane scaffold that is required for the Syk-, SLP-65-, and PLCgamma2-dependent BCR-induced calcium flux.

The role of lysozyme in the prophenoloxidase activation system of Manduca sexta: an in vitro approach

Activation of the prophenoloxidase (proPO) system and synthesis of antimicrobial peptides (including lysozyme) are two key defense mechanisms in arthropods. Activation of proPO involves a cascade of serine proteinases that eventually converts proPO to active phenoloxidase (PO). However, a trade-off between lysozyme/antibacterial activity and PO activity has been observed in some insects, and a mosquito lysozyme can inhibit melanization. It is not clear whether lysozyme can inhibit PO activity and/or proPO activation. In this study, we used in vitro assays to investigate the role of lysozyme in proPO activation in the tobacco hornworm Manduca sexta. We showed that lysozymes from M. sexta, human milk and hen egg white did not inhibit PO activity in the pre-activated naïve plasma of M. sexta larvae, but significantly inhibited proPO activation in the naïve plasma. Western blot analysis showed that direct incubation of M. sexta lysozyme with the naïve plasma prevented conversion of proPO to PO, but stimulated degradation of precursor proteins for serine proteinase homolog-2 (SPH2) and proPO-activating proteinase-1 (PAP1), two key components required for proPO activation. Far-western blot analysis showed that M. sexta lysozyme and proPO interacted with each other. Altogether, our results suggest that lysozymes may inhibit the proPO activation system by preventing conversion of proPO to PO via direct protein interaction with proPO.

Two-color photoactivatable probe for selective tracking of proteins and cells

We report the development and application of photoactivatable Green Cherry (G(PA)C), the first genetically encoded "continuously red-photoactivatable green" two-color probe for live cell imaging. G(PA)C is unique in that it enables real-time tracking of selected subpopulations of proteins and organelles in the cell or of cells within tissues and whole organisms, with constant reference to the entire population of the probe. Using G(PA)C-zyxin as proof of utility, we obtained new insights into the dynamic movement of the cytoskeletal protein zyxin. We show that zyxin is continuously and rapidly recruited from the cytosol into established focal adhesions. It can also move rapidly within a given focal adhesion and "hop" between adjacent focal adhesions, emphasizing the dynamic nature of proteins within these structures. The in vivo utility of G(PA)C is exemplified by tracking hemocyte movements using a versatile transgenic Drosophila model engineered to express G(PA)C in tissues and cells of interest under the control of the GAL4-inducible promoter.

Formins in development: orchestrating body plan origami

Formins, proteins defined by the presence of an FH2 domain and their ability to nucleate linear F-actin de novo, play a key role in the regulation of the cytoskeleton. Initially thought to primarily regulate actin, recent studies have highlighted a role for formins in the regulation of microtubule dynamics, and most recently have uncovered the ability of some formins to coordinate the organization of both the microtubule and actin cytoskeletons. While biochemical analyses of this family of proteins have yielded many insights into how formins regulate diverse cytoskeletal reorganizations, we are only beginning to appreciate how and when these functional properties are relevant to biological processes in a developmental or organismal context. Developmental genetic studies in fungi, Dictyostelium, vertebrates, plants and other model organisms have revealed conserved roles for formins in cell polarity, actin cable assembly and cytokinesis. However, roles have also been discovered for formins that are specific to particular organisms. Thus, formins perform both global and specific functions, with some of these roles concurring with previous biochemical data and others exposing new properties of formins. While not all family members have been examined across all organisms, the analyses to date highlight the significance of the flexibility within the formin family to regulate a broad spectrum of diverse cytoskeletal processes during development.

Changes in the proteomes of the hemocytes and fat bodies of the flesh fly Sarcophaga bullata larvae after infection by Escherichia coli

Background

Insects have an efficient self-defense system that is based on innate immunity. Recent findings have disclosed many parallels between human and insect innate immunity, and simultaneously fine differences in the processes between various species have been revealed. Studies on the immune systems of various insect species may uncover the differences in their host defense strategies.

Results

We analyzed the proteomes of the hemocytes and fat bodies of Sarcophaga bullata larvae after infection by Escherichia coli. The 2-DE gels of the hemocytes and fat bodies of infected larvae were compared with those of aseptically injured larvae. Our analysis included the construction of protein maps of the hemocyte cells and cells from fat bodies, the identification of the changed proteins, in response to infection, using LC-MS/MS, and the estimation of the trends in expression of these proteins at three time points (30 min, 6 hours and 22 hours) after infection. In total, seven changed spots were found in the hemocytes, and four changed spots were found in the fat bodies. Three types of trends in protein expression were observed. Cofilin and transgelin were undetectable at 30 min after infection but were continuously up-regulated in the induced larvae after 22 hours. A prophenoloxidase isoform and lectin subunit α were slightly up-regulated at 30 min after infection, and their protein levels reached the highest points after 6 hours but decreased after 22 hours. T-Complex subunit α, GST, ferritin-like protein and an anterior fat body protein (regucalcin homologue) were down-regulated at 22 hours after infection.

Conclusions

Many proteins identified in our study corresponded to the proteins identified in other insects. Compared to the former studies performed in insects, we presented 2-D protein maps of the hemocytes and fat bodies and showed the trends in expression of the immune-elicited proteins.

RNAi knock-down of the Litopenaeus vannamei Toll gene (LvToll) significantly increases mortality and reduces bacterial clearance after challenge with Vibrio harveyi

In this study, we used real-time PCR to simultaneously monitor the responses of 12 key genes of the shrimp innate immune system in Litopenaeus vannamei after challenge with Vibrio harveyi. In the proPO activating system, we found that proPO was up-regulated (3.3x control at 36hpi). The hemolymph clotting genes transglutaminase (TGase) and clotting protein were also up-regulated, as were 5 genes in the antimicrobial peptide system (ALF, Crustin, Lyz, PEN2 and PEN4), with only PEN3 showing no significant changes. In the antioxidant defense system, SOD was slightly elevated while GPx was substantially down-regulated. In the pattern recognition receptor system, at 24hpi, the Toll gene (LvToll) showed the highest relative increase in expression level of all the investigated genes (15x greater than the sterile seawater control). In the second part of this study, when LvToll was knocked down by RNAi silencing, there was no effect on either survival rates or bacterial number in unchallenged shrimp. There was also no difference in mortality rates between control shrimp and LvToll-silenced shrimp when these two groups were challenged with a viral pathogen (white spot syndrome virus; WSSV). However, when LvToll-silenced shrimp were challenged by V. harveyi, there was a significant increase in mortality and bacterial CFU counts. We note that the increase in bacterial CFU count occurred even though treatment with EGFP dsRNA had the opposite effect of reducing the CFU counts. We conclude that LvToll is an important factor in the shrimp innate immune response to acute V. harveyi infection, but not to WSSV.

The role of melanization and cytotoxic by-products in the cellular immune responses of Drosophila against parasitic wasps

The cellular innate immune response of several species of Drosophila terminates with the encasement of large foreign objects within melanotic capsules comprised of several layers of adhering blood cells or hemocytes. This reaction is manifested by various Drosophila hosts in response to infection by endoparasitic wasps (i.e., parasitoids). Creditable assessments of the factor(s) causing, or contributing to, parasite mortality have long been considered as cytotoxic elements certain molecules associated with enzyme-mediated melanogenesis. However, observations that warrant additional or alternative considerations are those documenting parasitoid survival despite melanotic encapsulation, and those where parasitoids are destroyed with no evidence of this host response. Recent studies of the production of some reactive intermediates of oxygen and nitrogen during infection provide a basis for proposing that these molecules constitute important components of the immune arsenal of Drosophila. Studies of the virulence factors injected by female wasps during oviposition that suppress the host response will likely facilitate identification of the cytotoxic molecules as well as the cell-signaling pathways that regulate their synthesis.

Socialized medicine: individual and communal disease barriers in honey bees

Honey bees are attacked by numerous parasites and pathogens toward which they present a variety of individual and group-level defenses. In this review, we briefly introduce the many pathogens and parasites afflicting honey bees, highlighting the biology of specific taxonomic groups mainly as they relate to virulence and possible defenses. Second, we describe physiological, immunological, and behavioral responses of individual bees toward pathogens and parasites. Third, bees also show behavioral mechanisms for reducing the disease risk of their nestmates. Accordingly, we discuss the dynamics of hygienic behavior and other group-level behaviors that can limit disease. Finally, we conclude with several avenues of research that seem especially promising for understanding host-parasite relationships in bees and for developing breeding or management strategies for enhancing honey bee health. We discuss how human efforts to maintain healthy colonies intersect with similar efforts by the bees, and how bee management and breeding protocols can affect disease traits in the short and long term.

Sequence variants in three loci influence monocyte counts and erythrocyte volume

Blood cells participate in vital physiological processes, and their numbers are tightly regulated so that homeostasis is maintained. Disruption of key regulatory mechanisms underlies many blood-related Mendelian diseases but also contributes to more common disorders, including atherosclerosis. We searched for quantitative trait loci (QTL) for hematology traits through a whole-genome association study, because these could provide new insights into both hemopoeitic and disease mechanisms. We tested 1.8 million variants for association with 13 hematology traits measured in 6015 individuals from the Australian and Dutch populations. These traits included hemoglobin composition, platelet counts, and red blood cell and white blood cell indices. We identified three regions of strong association that, to our knowledge, have not been previously reported in the literature. The first was located in an intergenic region of chromosome 9q31 near LPAR1, explaining 1.5% of the variation in monocyte counts (best SNP rs7023923, p=8.9x10(-14)). The second locus was located on chromosome 6p21 and associated with mean cell erythrocyte volume (rs12661667, p=1.2x10(-9), 0.7% variance explained) in a region that spanned five genes, including CCND3, a member of the D-cyclin gene family that is involved in hematopoietic stem cell expansion. The third region was also associated with erythrocyte volume and was located in an intergenic region on chromosome 6q24 (rs592423, p=5.3x10(-9), 0.6% variance explained). All three loci replicated in an independent panel of 1543 individuals (p values=0.001, 9.9x10(-5), and 7x10(-5), respectively). The identification of these QTL provides new opportunities for furthering our understanding of the mechanisms regulating hemopoietic cell fate.

Unraveling the protective effect of a Drosophila phosphatidylethanolamine-binding protein upon bacterial infection by means of proteomics

This study addresses the biological function of CG18594, a Drosophila melanogaster phosphatidylethanolamine-binding protein (PEBP) that we named PEBP1, by combining fly genetics, survival experiments and differential proteomics. We demonstrate that transgenic flies overexpressing PEBP1 are highly protected against bacterial infection due to the release of immunity-related proteins in their hemolymph. Apart from proteins that have been reported earlier to participate in insect immunity, we also identify proteins involved in metabolism and signaling, and, in addition, twelve (hypothetical) proteins with unknown function. This is the first report demonstrating an immune function for a Drosophila PEBP protein.

Drosophila lamin mutations cause melanotic mass formation and lamellocyte differentiation

The fruit fly immune system is a valuable model for invertebrate and innate immunity. Cellular immune reactions in Drosophila are of great interest, especially the molecular genetic mechanisms of hemocyte differentiation and the encapsulation of foreign bodies. Here we report that changes in the lamin gene cause melanotic masses. These darkened clusters of cells result from autoimmune-like encapsulation of self-tissue, as shown by the presence in lam larvae of lamellocytes, effector hemocytes that appear in larvae following wounding or parasitization. Lamins thus affect immunity in Drosophila, and lam mutations can serve as genetic tools to dissect cellular immune signaling and effector pathways.

Preclinical testing on insects predicts human haematotoxic potentials

The substitution of insects for laboratory animals in toxicity testing is likely to become a reality in the framework of prescreening. Haematotoxicological studies of newly developed chemicals, such as food components, drugs, etc. performed on insects can offer advantages in, for example, environmental toxicology. Reliable routine predictions should produce an increase in our knowledge of haemocyte physiology. Although the differences between human physiology and morphology and those of insects are great, the basic functions of insect haemocytes and mammalian leukocytes appear not to have changed during evolution. The use of insects in haematotoxicity assays represents a preclinical testing strategy which will lower costs, accelerate screening and offer ethical benefits.

Genome-wide transcriptomic profiling of Anopheles gambiae hemocytes reveals pathogen-specific signatures upon bacterial challenge and Plasmodium berghei infection

Background

The mosquito Anopheles gambiae is a major vector of human malaria. Increasing evidence indicates that blood cells (hemocytes) comprise an essential arm of the mosquito innate immune response against both bacteria and malaria parasites. To further characterize the role of hemocytes in mosquito immunity, we undertook the first genome-wide transcriptomic analyses of adult female An. gambiae hemocytes following infection by two species of bacteria and a malaria parasite.

Results

We identified 4047 genes expressed in hemocytes, using An. gambiae genome-wide microarrays. While 279 transcripts were significantly enriched in hemocytes relative to whole adult female mosquitoes, 959 transcripts exhibited immune challenge-related regulation. The global transcriptomic responses of hemocytes to challenge with different species of bacteria and/or different stages of malaria parasite infection revealed discrete, minimally overlapping, pathogen-specific signatures of infection-responsive gene expression; 105 of these represented putative immunity-related genes including anti-Plasmodium factors. Of particular interest was the specific co-regulation of various members of the Imd and JNK immune signaling pathways during malaria parasite invasion of the mosquito midgut epithelium.

Conclusion

Our genome-wide transcriptomic analysis of adult mosquito hemocytes reveals pathogen-specific signatures of gene regulation and identifies several novel candidate genes for future functional studies.

Blood monocytes: development, heterogeneity, and relationship with dendritic cells

Monocytes are circulating blood leukocytes that play important roles in the inflammatory response, which is essential for the innate response to pathogens. But inflammation and monocytes are also involved in the pathogenesis of inflammatory diseases, including atherosclerosis. In adult mice, monocytes originate in the bone marrow in a Csf-1R (MCSF-R, CD115)-dependent manner from a hematopoietic precursor common for monocytes and several subsets of macrophages and dendritic cells (DCs). Monocyte heterogeneity has long been recognized, but in recent years investigators have identified three functional subsets of human monocytes and two subsets of mouse monocytes that exert specific roles in homeostasis and inflammation in vivo, reminiscent of those of the previously described classically and alternatively activated macrophages. Functional characterization of monocytes is in progress in humans and rodents and will provide a better understanding of the pathophysiology of inflammation.

Purification and characterization of silkworm hemocytes by flow cytometry

Hemocyte functions are well-investigated in the silkworm, Bombyx mori, however, detailed analysis of each hemocyte subset has been hampered by the lack of appropriate separation method. Here we use an array of flow cytometric analyses to characterize silkworm hemocytes with various molecular probes, such as propidium iodide, green fluorescence protein, monoclonal antibodies, and fluorescent lectins. Of these, separation using propidium iodide was the simplest and provided most reliable results for the isolation of the hemocyte subsets. cDNAs were then synthesized from these sorted populations and subset-specific gene expression was examined by RT-PCR. Granulocytes, plasmatocytes, and oenocytoids expressed different classes of immune genes, suggesting that they have multiple roles in silkworm immunity. In contrast, a contribution of spherulocytes to immunity was not documented in that they failed to express most of the genes. The functions of spherulocytes are thus likely to be distinct from those of the other three hemocyte subsets.

The Drosophila cell adhesion molecule Neuroglian regulates Lissencephaly-1 localisation in circulating immunosurveillance cells

Background

When the parasitoid wasp Leptopilina boulardi lays its eggs in Drosophila larvae phagocytic cells called plasmatocytes and specialized cells known as lamellocytes encapsulate the egg. This requires these circulating immunosurveillance cells (haemocytes) to change from a non-adhesive to an adhesive state enabling them to bind to the invader. Interestingly, attachment of leukocytes, platelets, and insect haemocytes requires the same adhesion complexes as epithelial and neuronal cells.

Results

Here evidence is presented showing that the Drosophila L1-type cell adhesion molecule Neuroglian (Nrg) is required for haemocytes to encapsulate L. boulardi wasp eggs. The amino acid sequence FIGQY containing a conserved phosphorylated tyrosine is found in the intracellular domain of all L1-type cell adhesion molecules. This conserved tyrosine is phosphorylated at the cell periphery of plasmatocytes and lamellocytes prior to parasitisation, but dephosphorylated after immune activation. Intriguingly, another pool of Nrg located near the nucleus of plasmatocytes remains phosphorylated after parasitisation. In mammalian neuronal cells phosphorylated neurofascin, another L1-type cell adhesion molecule interacts with a nucleokinesis complex containing the microtubule binding protein lissencephaly-1 (Lis1) [1]. Interestingly in plasmatocytes from Nrg mutants the nucleokinesis regulating protein Lissencephaly-1 (Lis1) fails to localise properly around the nucleus and is instead found diffuse throughout the cytoplasm and at unidentified perinuclear structures. After attaching to the wasp egg control plasmatocytes extend filopodia laterally from their cell periphery; as well as extending lateral filopodia plasmatocytes from Nrg mutants also extend many filopodia from their apical surface.

Conclusion

The Drosophila cellular adhesion molecule Neuroglian is expressed in haemocytes and its activity is required for the encapsulation of L. boularli eggs. At the cell periphery of haemocytes Neuroglian may be involved in cell-cell interactions, while at the cell centre Neuroglian regulates the localisation of the nucleokinesis complex protein lissencephaly-1.

Tissue damage-induced intestinal stem cell division in Drosophila

Stem cell division is essential for tissue integrity during growth, aging, and pathogenic assaults. Adult gastrointestinal tract encounters numerous stimulations, and impaired tissue regeneration may lead to inflammatory diseases and cancer. Intestinal stem cells in adult Drosophila have recently been identified and shown to replenish the various cell types within the midgut. However, it is not known whether these intestinal stem cells can respond to environmental challenges. By feeding dextran sulfate sodium and bleomycin to flies and by expressing apoptotic proteins, we show that Drosophila intestinal stem cells can increase the rate of division in response to tissue damage. Moreover, if tissue damage results in epithelial cell loss, the newly formed enteroblasts can differentiate into mature epithelial cells. By using this newly established system of intestinal stem cell proliferation and tissue regeneration, we find that the insulin receptor signaling pathway is required for intestinal stem cell division.

TM9SF4 is required for Drosophila cellular immunity via cell adhesion and phagocytosis

Nonaspanins are characterised by a large N-terminal extracellular domain and nine putative transmembrane domains. This evolutionarily conserved family comprises three members in Dictyostelium discoideum (Phg1A, Phg1B and Phg1C) and Drosophila melanogaster, and four in mammals (TM9SF1-TM9SF4), the function of which is essentially unknown. Genetic studies in Dictyostelium demonstrated that Phg1A is required for cell adhesion and phagocytosis. We created Phg1A/TM9SF4-null mutant flies and showed that they were sensitive to pathogenic Gram-negative, but not Gram-positive, bacteria. This increased sensitivity was not due to impaired Toll or Imd signalling, but rather to a defective cellular immune response. TM9SF4-null larval macrophages phagocytosed Gram-negative E. coli inefficiently, although Gram-positive S. aureus were phagocytosed normally. Mutant larvae also had a decreased wasp egg encapsulation rate, a process requiring haemocyte-dependent adhesion to parasitoids. Defective cellular immunity was coupled to morphological and adhesion defects in mutant larval haemocytes, which had an abnormal actin cytoskeleton. TM9SF4, and its closest paralogue TM9SF2, were both required for bacterial internalisation in S2 cells, where they displayed partial redundancy. Our study highlights the contribution of phagocytes to host defence in an organism possessing a complex innate immune response and suggests an evolutionarily conserved function of TM9SF4 in eukaryotic phagocytes.

Stem cell regulation by JAK/STAT signaling in Drosophila

Stem cells have become one of the "buzz" topics in the last decade or so. One of the best systems to study adult stem cells in vivo is in the model organism, Drosophila melanogaster. One hundred years of genetic analysis, a sequenced and highly annotated genome and genomics makes this a difficult organism to avoid. The JAK/STAT pathway has been shown to regulate stem cells during haematopoiesis and gametogenesis in Drosophila. In this review we cover the current literature and contrast each group of stem cells with respect to JAK/STAT signaling.

Immune reactions of insects on bacterial pathogens and mutualists

In the past few years the knowledge of insect defense mechanisms against pathogenic microorganisms and parasites has significantly increased on both the molecular and the organismic level. These investigations have led to new concepts of immune protection also relevant for mammals with the identification of the Toll receptor family as an eminent example. This review provides a brief overview of insect strategies to on the one hand defeat bacterial pathogens while on the other hand cooperating with symbiotic bacteria beneficial for the insects.

Cuticular surface lipids are responsible for disguise properties of an entomoparasite against host cellular responses

Entomopathogenic nematodes are widely used as alternatives to chemicals for the biological control of insects. These endoparasites are symbiotically associated with bacteria that are lethal for the host; however, parasites need to overcome the host immune defences to complete a successful life cycle. The processes parasites employ to escape or depress host immunity are targeted at deceiving non-self recognition as well as inactivating defence reactions. The purpose of this paper is to investigate the interactions between the entomopathogenic nematode Steinernema feltiae and the lepidopteran Galleria mellonella, focusing on the role of the parasite's body-surface compounds in the immunoevasion of host cell-mediated responses. To evaluate host self/non-self discrimination and encapsulation efficiency, we carried out a series of interaction assays between cultured host hemocytes and parasites or isolated cuticles. The data obtained suggest that the parasite cuticular lipids (PCLs) are able to bind a variety of host hemolymph molecules; PCLs attract host proteins from the hemolymph creating a coat around the parasite, thus, enabling Steinernema to disguise itself against hemocytes recognition. The role of parasite lipids in the disguise process was also investigated by simulating the nematode body surface with agarose microbeads covered with purified cuticular components; when the beads were coated with cuticular lipids, host hemocytes were not able to recognize and encapsulate. Results suggest that by means of attracting host hemolymph components onto its cuticular surface, S. feltiae prevents hemocytes attachment to its cuticle and inhibits melanization by depleting hemolymph components.

Comparative genomic analysis of the Tribolium immune system

The annotation, and comparison with homologous genes in other species, of immunity-related genes in the Tribolium castaneum genome allowed the identification of around 300 candidate defense proteins, and revealed a framework of information on Tribolium immunity.

Background

Tribolium castaneum is a species of Coleoptera, the largest and most diverse order of all eukaryotes. Components of the innate immune system are hardly known in this insect, which is in a key phylogenetic position to inform us about genetic innovations accompanying the evolution of holometabolous insects. We have annotated immunity-related genes and compared them with homologous molecules from other species.

Results

Around 300 candidate defense proteins are identified based on sequence similarity to homologs known to participate in immune responses. In most cases, paralog counts are lower than those of Drosophila melanogaster or Anopheles gambiae but are substantially higher than those of Apis mellifera. The genome contains probable orthologs for nearly all members of the Toll, IMD, and JAK/STAT pathways. While total numbers of the clip-domain serine proteinases are approximately equal in the fly (29), mosquito (32) and beetle (30), lineage-specific expansion of the family is discovered in all three species. Sixteen of the thirty-one serpin genes form a large cluster in a 50 kb region that resulted from extensive gene duplications. Among the nine Toll-like proteins, four are orthologous to Drosophila Toll. The presence of scavenger receptors and other related proteins indicates a role of cellular responses in the entire system. The structures of some antimicrobial peptides drastically differ from those in other orders of insects.

Conclusion

A framework of information on Tribolium immunity is established, which may serve as a stepping stone for future genetic analyses of defense responses in a nondrosophiline genetic model insect.