Adenosine deaminase-related growth factors stimulate cell proliferation in Drosophila by depleting extracellular adenosine

A Pvr-AP-1-Mmp1 signaling pathway is activated in astrocytes upon traumatic brain injury

Traumatic brain injury (TBI) caused by external mechanical forces is a major health burden worldwide, but the underlying mechanism in glia remains largely unclear. We report herein that Drosophila adults exhibit a defective blood-brain barrier, elevated innate immune responses, and astrocyte swelling upon consecutive strikes with a high-impact trauma device. RNA sequencing (RNA-seq) analysis of these astrocytes revealed upregulated expression of genes encoding PDGF and VEGF receptor-related (Pvr, a receptor tyrosine kinase), adaptor protein complex 1 (AP-1, a transcription factor complex of the c-Jun N-terminal kinase pathway) composed of Jun-related antigen (Jra) and kayak (kay), and matrix metalloproteinase 1 (Mmp1) following TBI. Interestingly, Pvr is both required and sufficient for AP-1 and Mmp1 upregulation, while knockdown of AP-1 expression in the background of Pvr overexpression in astrocytes rescued Mmp1 upregulation upon TBI, indicating that Pvr acts as the upstream receptor for the downstream AP-1-Mmp1 transduction. Moreover, dynamin-associated endocytosis was found to be an important regulatory step in downregulating Pvr signaling. Our results identify a new Pvr-AP-1-Mmp1 signaling pathway in astrocytes in response to TBI, providing potential targets for developing new therapeutic strategies for TBI.

ADA2 regulates inflammation and hematopoietic stem cell emergence via the A2bR pathway in zebrafish

Deficiency of adenosine deaminase 2 (DADA2) is an inborn error of immunity caused by loss-of-function mutations in the adenosine deaminase 2 (ADA2) gene. Clinical manifestations of DADA2 include vasculopathy and immuno-hematological abnormalities, culminating in bone marrow failure. A major gap exists in our knowledge of the regulatory functions of ADA2 during inflammation and hematopoiesis, mainly due to the absence of an ADA2 orthologue in rodents. Exploring these mechanisms is essential for understanding disease pathology and developing new treatments. Zebrafish possess two ADA2 orthologues, cecr1a and cecr1b, with the latter showing functional conservation with human ADA2. We establish a cecr1b-loss-of-function zebrafish model that recapitulates the immuno-hematological and vascular manifestations observed in humans. Loss of Cecr1b disrupts hematopoietic stem cell specification, resulting in defective hematopoiesis. This defect is caused by induced inflammation in the vascular endothelium. Blocking inflammation, pharmacological modulation of the A2r pathway, or the administration of the recombinant human ADA2 corrects these defects, providing insights into the mechanistic link between ADA2 deficiency, inflammation and immuno-hematological abnormalities. Our findings open up potential therapeutic avenues for DADA2 patients.

Deficiency of Adenosine Deaminase 2: Clinical Manifestations, Diagnosis, and Treatment

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic vasculitis syndrome caused by biallelic mutations in the adenosine deaminase 2 gene. The diagnosis of DADA2 is confirmed by decreased enzymatic activity of ADA2 and genetic testing. Symptoms range from cutaneous vasculitis and polyarteritis nodosa-like lesions to stroke. The vasculopathy of DADA2 can affect many organ systems, including the gastrointestinal and renal systems. Hematologic manifestations occur early with hypogammaglobulinemia, lymphopenia, pure red cell aplasia, or pancytopenia. Treatment can be challenging. Tumor necrosis factor inhibitors are helpful to control inflammatory symptoms. Hematopoietic stem cell transplant may be needed to treat refractory cytopenias, vasculopathy, or immunodeficiency.

Delineating Purinergic Signaling in Drosophila

Simplistic models can aid in discovering what is important in the context of normal and pathological behavior. First recognized as a genetic model more than 100 years ago, to date, fruit flies (Drosophila melanogaster) still remain an astonishingly good laboratory stand-in for scientists to study development and physiology and to investigate the molecular mechanisms of human diseases. This is because fruit flies indeed represent a simplistic model. Furthermore, about 75% of human disease-related genes have their counterparts in the Drosophila genome, added to the fact that fruit flies are inexpensive and extremely easy to maintain, being invertebrates and, moreover, lacking any ethical concern issues. Purinergic signaling is, by definition, mediated by extracellular purinergic ligands, among which ATP represents the prototype molecule. A key feature that has progressively emerged when dissecting the purinergic mechanisms is the multilayer and dynamic nature of the signaling sustained by purinergic ligands. Indeed, these last are sequentially metabolized by several different ectonucleotidases, which generate the ligands that simultaneously activate several different purinergic receptors. Since significant purinergic actions have also been described in Drosophila, the aim of the present work is to provide a comprehensive picture of the purinergic events occurring in fruit flies.

Internal sensory neurons regulate stage-specific growth in Drosophila

Animals control their developmental schedule in accordance with internal states and external environments. In Drosophila larvae, it is well established that nutrient status is sensed by different internal organs, which in turn regulate production of insulin-like peptides and thereby control growth. In contrast, the impact of the chemosensory system on larval development remains largely unclear. Here, we performed a genetic screen to identify gustatory receptor (Gr) neurons regulating growth and development, and found that Gr28a-expressing neurons are required for proper progression of larval growth. Gr28a is expressed in a subset of peripheral internal sensory neurons, which directly extend their axons to insulin-producing cells (IPCs) in the central nervous system. Silencing of Gr28a-expressing neurons blocked insulin-like peptide release from IPCs and suppressed larval growth during the mid-larval period. These results indicate that Gr28a-expressing neurons promote larval development by directly regulating growth-promoting endocrine signaling in a stage-specific manner.

Characterization and Expression Analysis of Mollusk-like Growth Factor: A Secreted Protein Involved in Pacific Abalone Embryonic and Larval Development

Growth factors are mostly secreted proteins that play key roles in an organism's biophysical processes through binding to specific receptors on the cell surface. The mollusk-like growth factor (MLGF) is a novel cell signaling protein in the adenosine deaminase-related growth factor (ADGF) subfamily. In this study, the MLGF gene was cloned and characterized from the digestive gland tissue of Pacific abalone and designated as Hdh-MLGF. The transcribed full-length sequence of Hdh-MLGF was 1829 bp long with a 1566 bp open reading frame (ORF) encoding 521 amino acids. The deduced amino acid sequence contained a putative signal peptide and two conserved adenosine deaminase domains responsible for regulating molecular function. Fluorescence in situ hybridization localized Hdh-MLGF in the submucosa layer of digestive tubules in the digestive gland. The mRNA expression analysis indicated that Hdh-MLGF expression was restricted to the digestive gland in the adult Pacific abalone. However, Hdh-MLGF mRNA expressions were observed in all stages of embryonic and larval development, suggesting Hdh-MLGF might be involved in the Pacific abalone embryonic and larval development. This is the first study describing Hdh-MLGF and its involvement in the Pacific abalone embryonic and larval development.

Identification and Functional Characterization of Adenosine Deaminase in Mucor circinelloides: A Novel Potential Regulator of Nitrogen Utilization and Lipid Biosynthesis

Adenosine deaminase (ADA) is an enzyme distributed in a wide variety of organisms that cleaves adenosine into inosine. Since inosine plays an important role in nitrogen metabolism, ADA may have a critical function in the regulation of fatty acid synthesis. However, the role of ADA in oleaginous fungi has not been reported so far. Therefore, in this study, we identified one ada gene encoding ADA (with ID scaffold0027.9) in the high lipid-producing fungus, Mucor circinelloides WJ11, and investigated its role in cell growth, lipid production, and nitrogen metabolism by overexpressing and knockout of this gene. The results showed that knockout of the ada altered the efficiency of nitrogen consumption, which led to a 20% increment in the lipid content (25% of cell dry weight) of the engineered strain, while overexpression of the ada showed no significant differences compared with the control strain at the final growth stage; however, interestingly, it increased lipid accumulation at the early growth stage. Additionally, transcriptional analysis was conducted by RT-qPCR and our findings indicated that the deletion of ada activated the committed steps of lipid biosynthesis involved in acetyl-CoA carboxylase (acc1 gene), cytosolic malic acid enzyme (cme1 gene), and fatty acid synthases (fas1 gene), while it suppressed the expression of AMP-activated protein kinase (ampk α1 and ampk β genes), which plays a role in lipolysis, whereas the ada-overexpressed strain displayed reverse trends. Conclusively, this work unraveled a novel role of ADA in governing lipid biosynthesis and nitrogen metabolism in the oleaginous fungus, M. circinelloides.

Mechanisms of vascular inflammation in deficiency of adenosine deaminase 2 (DADA2)

Deficiency of adenosine deaminase 2 (DADA2) was first described as a monogenic form of systemic vasculitis that closely resembles polyarteritis nodosa (PAN). The phenotypic spectrum of DADA2 has vastly expanded in recent years and now includes pure red cell aplasia, bone marrow failure syndrome, lymphoproliferative disease, and humoral immunodeficiency. Vasculitis remains the most common presentation of DADA2, and treatment with tumor necrosis factor inhibitors (TNFi) has shown remarkable efficacy in preventing stroke and ameliorating features of systemic inflammation. The precise function of ADA2 has not been elucidated, and how absence of ADA2 ignites inflammation is an active area of research. In this review, we will discuss the current understanding of DADA2 from research and clinical perspectives. We will evaluate several proposed functions of ADA2, including polarization of monocyte phenotype, regulation of neutrophil extracellular trap formation, and modulation of innate immunity. We will also review the role of inflammatory cytokines including TNF and type I interferons. Lastly, we will provide future perspectives on understanding the phenotypic heterogeneity of DADA2 and discuss potential treatment options.

Proteomics of purified lamellocytes from Drosophila melanogaster HopTum-l identifies new membrane proteins and networks involved in their functions

In healthy Drosophila melanogaster larvae, plasmatocytes and crystal cells account for 95% and 5% of the hemocytes, respectively. A third type of hemocytes, lamellocytes, are rare, but their number increases after oviposition by parasitoid wasps. The lamellocytes form successive layers around the parasitoid egg, leading to its encapsulation and melanization, and finally the death of this intruder. However, the total number of lamellocytes per larva remains quite low even after parasitoid infestation, making direct biochemical studies difficult. Here, we used the Hop^Tum-l mutant strain that constitutively produces large numbers of lamellocytes to set up a purification method and analyzed their major proteins by 2D gel electrophoresis and their plasma membrane surface proteins by 1D SDS-PAGE after affinity purification. Mass spectrometry identified 430 proteins from 2D spots and 344 affinity-purified proteins from 1D bands, for a total of 639 unique proteins. Known lamellocyte markers such as PPO3 and the myospheroid integrin were among the components identified with specific chaperone proteins. Affinity purification detected other integrins, as well as a wide range of integrin-associated proteins involved in the formation and function of cell-cell junctions. Overall, the newly identified proteins indicate that these cells are highly adapted to the encapsulation process (recognition, motility, adhesion, signaling), but may also have several other physiological functions (such as secretion and internalization of vesicles) under different signaling pathways. These results provide the basis for further in vivo and in vitro studies of lamellocytes, including the development of new markers to identify coexisting populations and their respective origins and functions in Drosophila immunity.

Control Release of Adenosine Potentiate Osteogenic Differentiation within a Bone Integrative EGCG-g-NOCC/Collagen Composite Scaffold toward Guided Bone Regeneration in a Critical-Sized Calvarial Defect

The regeneration of critical-sized bone defects with biomimetic scaffolds remains clinically challenging due to avascular necrosis, chronic inflammation, and altered osteogenic activity. Two confounding mechanisms, efficacy manipulation, and temporal regulation dictate the scaffold's bone regenerative ability. Equally critical is the priming of the mesenchymal stromal cells (MSCs) toward lineage-specific differentiation into bone-forming osteoblast, which particularly depends on varied mechanochemical and biological cues during bone tissue regeneration. This study sought to design and develop an optimized osteogenic scaffold, adenosine/epigallocatechin gallate-N,O-carboxymethyl chitosan/collagen type I (AD/EGCG-g-NOCC@clgn I), having osteoinductive components toward swift bone regeneration in a calvarial defect BALB/c mice model. The ex vivo findings distinctly establish the pro-osteogenic potential of adenosine and EGCG, stimulating MSCs toward osteoblast differentiation with significantly increased expression of alkaline phosphatase, calcium deposits, and enhanced osteocalcin expression. Moreover, the 3D matrix recapitulates extracellular matrix (ECM) properties, provides a favorable microenvironment, structural support against mechanical stress, and acts as a reservoir for sustained release of osteoinductive molecules for cell differentiation, proliferation, and migration during matrix osteointegration observed. Evidence from in vivo experiments, micro-CT analyses, histology, and histomorphometry signify accelerated osteogenesis both qualitatively and quantitatively: effectual bone union with enhanced bone formation and new ossified tissue in 4 mm sized defects. Our results suggest that the optimized scaffold serves as an adjuvant to guide bone tissue regeneration in critical-sized calvarial defects with promising therapeutic efficacy.

Adenosine Receptor and Its Downstream Targets, Mod(mdg4) and Hsp70, Work as a Signaling Pathway Modulating Cytotoxic Damage in Drosophila

Adenosine (Ado) is an important signaling molecule involved in stress responses. Studies in mammalian models have shown that Ado regulates signaling mechanisms involved in “danger-sensing” and tissue-protection. Yet, little is known about the role of Ado signaling in Drosophila. In the present study, we observed lower extracellular Ado concentration and suppressed expression of Ado transporters in flies expressing mutant huntingtin protein (mHTT). We altered Ado signaling using genetic tools and found that the overexpression of Ado metabolic enzymes, as well as the suppression of Ado receptor (AdoR) and transporters (ENTs), were able to minimize mHTT-induced mortality. We also identified the downstream targets of the AdoR pathway, the modifier of mdg4 (Mod(mdg4)) and heat-shock protein 70 (Hsp70), which modulated the formation of mHTT aggregates. Finally, we showed that a decrease in Ado signaling affects other Drosophila stress reactions, including paraquat and heat-shock treatments. Our study provides important insights into how Ado regulates stress responses in Drosophila.

Polyarteritis nodosa and deficiency of adenosine deaminase 2 - Shared genealogy, generations apart

Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis that predominantly affects medium-sized arteries. With the establishment and refinement of vasculitis nomenclature and diagnostic criteria, clinical findings of PAN and distinguishing features from other vasculitides are now well characterized. Although PAN typically manifests in adulthood, cohort studies in paediatric patients have shaped our understanding of childhood-onset PAN. The paradigm of childhood-onset PAN changed considerably with the landmark discovery of deficiency of ADA2 (DADA2), a monogenic cause of vasculitis that is often indistinguishable from PAN. Testing for DADA2 has provided an explanation to numerous challenging cases of familial PAN and early-onset PAN around the world. The ability to distinguish DADA2 from classic PAN have important therapeutic implications as tumor necrosis factor inhibitors have demonstrated remarkable efficacy in the treatment of DADA2. In this review, we will discuss our current understanding of PAN and DADA2 and highlight similarities and differences between these vasculitides.

Loss of Histone Locus Bodies in the Mature Hemocytes of Larval Lymph Gland Result in Hyperplasia of the Tissue in mxc Mutants of Drosophila

Mutations in the multi sex combs (mxc) gene in Drosophila results in malignant hyperplasia in larval hematopoietic tissues, called lymph glands (LG). mxc encodes a component of the histone locus body (HLB) that is essential for cell cycle-dependent transcription and processing of histone mRNAs. The mammalian nuclear protein ataxia-telangiectasia (NPAT) gene, encoded by the responsible gene for ataxia telangiectasia, is a functional Mxc orthologue. However, their roles in tumorigenesis are unclear. Genetic analyses of the mxc mutants and larvae having LG-specific depletion revealed that a reduced activity of the gene resulted in the hyperplasia, which is caused by hyper-proliferation of immature LG cells. The depletion of mxc in mature hemocytes of the LG resulted in the hyperplasia. Furthermore, the inhibition of HLB formation was required for LG hyperplasia. In the mutant larvae, the total mRNA levels of the five canonical histones decreased, and abnormal forms of polyadenylated histone mRNAs, detected rarely in normal larvae, were generated. The ectopic expression of the polyadenylated mRNAs was sufficient for the reproduction of the hyperplasia. The loss of HLB function, especially 3-end processing of histone mRNAs, is critical for malignant LG hyperplasia in this leukemia model in Drosophila. We propose that mxc is involved in the activation to induce adenosine deaminase-related growth factor A (Adgf-A), which suppresses immature cell proliferation in LG.

Snellenius manilae bracovirus suppresses the host immune system by regulating extracellular adenosine levels in Spodoptera litura

Sufficient energy supply to the host immune system is important for resisting pathogens. Therefore, during pathogen infection, the host metabolism is reassigned from storage, growth, and development to the immune system. Previous studies in Drosophila melanogaster have demonstrated that systemic metabolic switching upon an immune challenge is activated by extracellular adenosine signaling, modulating carbohydrate mobilization and redistributing energy to the hemocytes. In the present study, we discovered that symbiotic virus (SmBV) of the parasitoid wasp Snellenius manilae is able to down-regulate the extracellular adenosine of its host, Spodoptera litura, to inhibit metabolism switching. The decreased carbohydrate mobilization, glycogenolysis, and ATP synthesis upon infection results in the host being unable to supply energy to its immune system, thus benefitting the development of wasp larvae. When we added adenosine to the infected S. litura larvae, we observed enhanced host immune responses that decreased the pupation rate of S. manilae. Previous studies showed that after pathogen infection, the host activates its adenosine pathway to trigger immune responses. However, our results suggest a different model: we found that in S. manilae, SmBV modulates the host adenosine pathway such that wasp eggs and larvae can evade the host immune response.

An in vivo RNAi screen uncovers the role of AdoR signaling and adenosine deaminase in controlling intestinal stem cell activity

Metabolites are increasingly appreciated for their roles as signaling molecules. To dissect the roles of metabolites, it is essential to understand their signaling pathways and their enzymatic regulations. From an RNA interference (RNAi) screen for regulators of intestinal stem cell (ISC) activity in the Drosophila midgut, we identified adenosine receptor (AdoR) as a top candidate gene required for ISC proliferation. We demonstrate that Ras/MAPK and Protein Kinase A (PKA) signaling act downstream of AdoR and that Ras/MAPK mediates the major effect of AdoR on ISC proliferation. Extracellular adenosine, the ligand for AdoR, is a small metabolite that can be released by various cell types and degraded in the extracellular space by secreted adenosine deaminase. Interestingly, down-regulation of adenosine deaminase-related growth factor A (Adgf-A) from enterocytes is necessary for extracellular adenosine to activate AdoR and induce ISC overproliferation. As Adgf-A expression and its enzymatic activity decrease following tissue damage, our study provides important insights into how the enzymatic regulation of extracellular adenosine levels under tissue-damage conditions facilitates ISC proliferation.

Human adenosine deaminase 2 deficiency: A multi-faceted inborn error of immunity

Human adenosine deaminase 1 deficiency was described in the 1970s to cause severe combined immunodeficiency. The residual adenosine deaminase activity in these patients was attributed to adenosine deaminase 2. Human adenosine deaminase type 2 deficiency (DADA2), due to biallelic deleterious mutations in the ADA2 gene, is the first described monogenic type of small- and medium-size vessel vasculitis. The phenotype of DADA2 also includes lymphoproliferation, cytopenia, and variable degrees of immunodeficiency. The physiological role of ADA2 is still enigmatic hence the pathophysiology of the condition is unclear. Preliminary data showed that in the absence of ADA2, macrophage differentiation is skewed to a pro-inflammatory M1 subset, which is detrimental for endothelial integrity. The inflammatory phenotype responds well to anti-TNF therapy with etanercept and that is the first-line treatment for prevention of severe vascular events including strokes. The classic immunosuppressive drugs are not successful in controlling the disease activity. However, hematopoietic stem cell transplantation (HSCT) has been shown to be a definitive cure in DADA2 patients who present with a severe cytopenia. HSCT can also cure the vascular phenotype and is the treatment modality for patients' refractory to anti-cytokine therapies. In this review, we describe what is currently known about the molecular mechanisms of DADA2. Further research on the pathophysiology of this multifaceted condition is needed to fine-tune and steer future therapeutic strategies.

Structure of Arabidopsis thaliana N6-methyl-AMP deaminase ADAL with bound GMP and IMP and implications for N6-methyl-AMP recognition and processing

Arabidopsis thaliana aminohydrolase (AtADAL) has been shown to be involved in the metabolism of N⁶-methyl-AMP, a proposed intermediate during m⁶A-modified RNA metabolism, which can be subsequently incorporated into newly synthesized RNA by Pol II. It has been proposed that AtADAL will prevent N⁶-methyl-AMP reuse and catabolize it to inosine monophosphate (IMP). Here, we have solved the crystal structures of AtADAL in the apo form and in complex with GMP and IMP in the presence of Zn²⁺. We have identified the substrate-binding pocket of AtADAL and compared it with that for adenosine deaminase (ADA), adenine deaminase (ADE) and AMP deaminase (AMPD) from multiple species. The comparisons reveal that plant ADAL1 may have the potential ability to catalyze different alkyl-group substituted substrates.

Drosophila as a Genetic Model for Hematopoiesis

In this FlyBook chapter, we present a survey of the current literature on the development of the hematopoietic system in Drosophila The Drosophila blood system consists entirely of cells that function in innate immunity, tissue integrity, wound healing, and various forms of stress response, and are therefore functionally similar to myeloid cells in mammals. The primary cell types are specialized for phagocytic, melanization, and encapsulation functions. As in mammalian systems, multiple sites of hematopoiesis are evident in Drosophila and the mechanisms involved in this process employ many of the same molecular strategies that exemplify blood development in humans. Drosophila blood progenitors respond to internal and external stress by coopting developmental pathways that involve both local and systemic signals. An important goal of these Drosophila studies is to develop the tools and mechanisms critical to further our understanding of human hematopoiesis during homeostasis and dysfunction.

Generating and working with Drosophila cell cultures: Current challenges and opportunities

The use of Drosophila cell cultures has positively impacted both fundamental and biomedical research. The most widely used cell lines: Schneider, Kc, the CNS and imaginal disc lines continue to be the choice for many applications. Drosophila cell lines provide a homogenous source of cells suitable for biochemical experimentations, transcriptomics, functional genomics, and biomedical applications. They are amenable to RNA interference and serve as a platform for high-throughput screens to identify relevant candidate genes or drugs for any biological process. Currently, CRISPR-based functional genomics are also being developed for Drosophila cell lines. Even though many uniquely derived cell lines exist, cell genetic techniques such the transgenic UAS-GAL4-based Ras^V12 oncogene expression, CRISPR-Cas9 editing and recombination mediated cassette exchange are likely to drive the establishment of many more lines from specific tissues, cells, or genotypes. However, the pace of creating new lines is hindered by several factors inherent to working with Drosophila cell cultures: single cell cloning, optimal media formulations and culture conditions capable of supporting lines from novel tissue sources or genotypes. Moreover, even though many Drosophila cell lines are morphologically and transcriptionally distinct it may be necessary to implement a standard for Drosophila cell line authentication, ensuring the identity and purity of each cell line. Altogether, recent advances and a standardized authentication effort should improve the utility of Drosophila cell cultures as a relevant model for fundamental and biomedical research. This article is categorized under: Technologies > Analysis of Cell, Tissue, and Animal Phenotypes.

Deficiency of Adenosine Deaminase 2 (DADA2): Updates on the Phenotype, Genetics, Pathogenesis, and Treatment

Deficiency of ADA2 (DADA2) is the first molecularly described monogenic vasculitis syndrome. DADA2 is caused by biallelic hypomorphic mutations in the ADA2 gene that encodes the adenosine deaminase 2 (ADA2) protein. Over 60 disease-associated mutations have been identified in all domains of ADA2 affecting the catalytic activity, protein dimerization, and secretion. Vasculopathy ranging from livedo reticularis to polyarteritis nodosa (PAN) and life-threatening ischemic and/or hemorrhagic stroke dominate the clinical features of DADA2. Vasculitis and inflammation can affect many organs, explaining the intestinal, hepatological, and renal manifestations. DADA2 should be primarily considered in patients with early-onset fevers, rashes, and strokes even in the absence of positive family history. Hematological manifestations include most commonly hypogammaglobulinemia, although pure red cell aplasia (PRCA), immune thrombocytopenia, and neutropenia have been increasingly reported. Thus, DADA2 may unify a variety of syndromes previously not thought to be related. The first-line treatment consists of TNF-inhibitors and is effective in controlling inflammation and in preserving vascular integrity. Hematopoietic stem cell transplantation (HSCT) has been successful in a group of patients presenting with hematological manifestations. ADA2 is highly expressed in myeloid cells and plays a role in the differentiation of macrophages; however, its function is still largely undetermined. Deficiency of ADA2 has been linked to an imbalance in differentiation of monocytes towards proinflammatory M1 macrophages. Future research on the function of ADA2 and on the pathophysiology of DADA2 will improve our understanding of the condition and promote early diagnosis and targeted treatment.

Hormonal control of growth in the wing imaginal disks of Junonia coenia: the relative contributions of insulin and ecdysone

The wing imaginal disks of Lepidoptera can be grown in tissue culture, but require both insulin and ecdysone to grow normally. Here we investigate the contributions the two hormones make to growth. Ecdysone is required to maintain mitoses, whereas in the presence of insulin alone mitoses stop. Both ecdysone and insulin stimulate protein synthesis, but only ecdysone stimulates DNA synthesis. Insulin stimulates primarily cytoplasmic growth and an increase in cell size, whereas ecdysone, by virtue of its stimulation of DNA synthesis and mitosis, stimulates growth by an increase in cell number. Although both hormones stimulate protein synthesis they do so in different spatial patterns. Both hormones stimulate protein synthesis in the inter-vein regions, but ecdysone stimulates synthesis more strongly in the veins and in the margin of the wing disk. We propose that the balance of insulin and ecdysone signaling must be regulated to maintain normal growth, and when growth appears to be due primarily to an increase in cell number, or an increase in cell size, this may indicate growth occurred under conditions that favored a stronger role for ecdysone, or insulin, respectively.

Vasculopathy, Immunodeficiency, and Bone Marrow Failure: The Intriguing Syndrome Caused by Deficiency of Adenosine Deaminase 2

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic form of systemic vasculopathy that often presents during early childhood. Linked to biallelic mutations in ADA2 (previously CECR1), DADA2 was initially described as a syndrome of recurrent fever, livedo racemosa, early-onset strokes, and peripheral vasculopathy that resembles polyarteritis nodosum. However, the wide spectrum of clinical findings and heterogeneity of disease, even among family members with identical mutations, is increasingly recognized. Evidence of systemic inflammation and vasculopathy is not uniformly present in DADA2 patients and some can remain asymptomatic through adulthood. Humoral immunodeficiency characterized by low immunoglobulin levels and increased risk of infection is another common feature of DADA2. Variable cytopenias including pure red cell aplasia that mimics Diamond-Blackfan anemia can also be primary manifestations of DADA2. How defects in a single gene translate into these heterogeneous presentations remains to be answered. In this review, we will summarize lessons learned from the pleiotropic clinical manifestations of DADA2.

Oxygenation and adenosine deaminase support growth and proliferation of ex vivo cultured Drosophila wing imaginal discs

The Drosophila wing imaginal disc has been an important model system over past decades for discovering novel biology related to development, signaling and epithelial morphogenesis. Novel experimental approaches have been enabled using a culture setup that allows ex vivo cultures of wing discs. Current setups, however, are not able to sustain both growth and cell-cycle progression of wing discs ex vivo We discover here a setup that requires both oxygenation of the tissue and adenosine deaminase activity in the medium, and supports both growth and proliferation of wing discs for 9 h. Nonetheless, further work will be required to extend the duration of the culturing and to enable live imaging of the cultured discs in the future.

Drosophila imaginal disc growth factor 2 is a trophic factor involved in energy balance, detoxification, and innate immunity

Drosophila imaginal disc growth factor 2 (IDGF2) is a member of chitinase-like protein family (CLPs) able to induce the proliferation of imaginal disc cells in vitro. In this study we characterized physiological concentrations and expression of IDGF2 in vivo as well as its impact on the viability and transcriptional profile of Drosophila cells in vitro. We show that IDGF2 is independent of insulin and protects cells from death caused by serum deprivation, toxicity of xenobiotics or high concentrations of extracellular adenosine (Ado) and deoxyadenosine (dAdo). Transcriptional profiling suggested that such cytoprotection is connected with the induction of genes involved in energy metabolism, detoxification and innate immunity. We also show that IDGF2 is an abundant haemolymph component, which is further induced by injury in larval stages. The highest IDGF2 accumulation was found at garland and pericardial nephrocytes supporting its role in organismal defence and detoxification. Our findings provide evidence that IDGF2 is an important trophic factor promoting cellular and organismal survival.

Targeted genetics in Drosophila cell lines: Inserting single transgenes in vitro

A long-standing problem with analyzing transgene expression in tissue-culture cells is the variation caused by random integration of different copy numbers of transfected transgenes. In mammalian cells, single transgenes can be inserted by homologous recombination but this process is inefficient in Drosophila cells. To tackle this problem, our group, and the Cherbas group, used recombination-mediated cassette exchange (RMCE) to introduce single-copy transgenes into specific locations in the Drosophila genome. In both cases, ϕC31 was used to catalyze recombination between its target sequences attP in the genome, and attB flanking the donor sequence. We generated cell lines de novo with a single attP-flanked cassette for recombination, whereas, Cherbas et al. introduced a single attP-flanked cassette into existing cell lines. In both approaches, a 2-drug selection scheme was used to select for cells with a single copy of the donor sequence inserted by RMCE and against cells with random integration of multiple copies. Here we describe the general advantages of using RMCE to introduce genes into fly cells, the different attributes of the 2 methods, and how future work could make use of other recombinases and CRISPR/Cas9 genome editing to further enable genetic manipulation of Drosophila cells in vitro.

Tools for Targeted Genome Engineering of Established Drosophila Cell Lines

We describe an adaptation of φC31 integrase-mediated targeted cassette exchange for use in Drosophila cell lines. Single copies of an attP-bounded docking platform carrying a GFP-expression marker, with or without insulator elements flanking the attP sites, were inserted by P-element transformation into the Kc167 and Sg4 cell lines; each of the resulting docking-site lines carries a single mapped copy of one of the docking platforms. Vectors for targeted substitution contain a cloning cassette flanked by attB sites. Targeted substitution occurs by integrase-mediated substitution between the attP sites (integrated) and the attB sites (vector). We describe procedures for isolating cells carrying the substitutions and for eliminating the products of secondary off-target events. We demonstrate the technology by integrating a cassette containing a Cu(2+)-inducible mCherry marker, and we report the expression properties of those lines. When compared with clonal lines made by traditional transformation methods, which lead to the illegitimate insertion of tandem arrays, targeted insertion lines give more uniform expression, lower basal expression, and higher induction ratios. Targeted substitution, though intricate, affords results that should greatly improve comparative expression assays-a major emphasis of cell-based studies.

Immunogenicity and Serological Cross-Reactivity of Saliva Proteins among Different Tsetse Species

Tsetse are vectors of pathogenic trypanosomes, agents of human and animal trypanosomiasis in Africa. Components of tsetse saliva (sialome) are introduced into the mammalian host bite site during the blood feeding process and are important for tsetse’s ability to feed efficiently, but can also influence disease transmission and serve as biomarkers for host exposure. We compared the sialome components from four tsetse species in two subgenera: subgenus Morsitans: Glossina morsitans morsitans (Gmm) and Glossina pallidipes (Gpd), and subgenus Palpalis: Glossina palpalis gambiensis (Gpg) and Glossina fuscipes fuscipes (Gff), and evaluated their immunogenicity and serological cross reactivity by an immunoblot approach utilizing antibodies from experimental mice challenged with uninfected flies. The protein and immune profiles of sialome components varied with fly species in the same subgenus displaying greater similarity and cross reactivity. Sera obtained from cattle from disease endemic areas of Africa displayed an immunogenicity profile reflective of tsetse species distribution. We analyzed the sialome fractions of Gmm by LC-MS/MS, and identified TAg5, Tsal1/Tsal2, and Sgp3 as major immunogenic proteins, and the 5'-nucleotidase family as well as four members of the Adenosine Deaminase Growth Factor (ADGF) family as the major non-immunogenic proteins. Within the ADGF family, we identified four closely related proteins (TSGF-1, TSGF-2, ADGF-3 and ADGF-4), all of which are expressed in tsetse salivary glands. We describe the tsetse species-specific expression profiles and genomic localization of these proteins. Using a passive-immunity approach, we evaluated the effects of rec-TSGF (TSGF-1 and TSGF-2) polyclonal antibodies on tsetse fitness parameters. Limited exposure of tsetse to mice with circulating anti-TSGF antibodies resulted in a slight detriment to their blood feeding ability as reflected by compromised digestion, lower weight gain and less total lipid reserves although these results were not statistically significant. Long-term exposure studies of tsetse flies to antibodies corresponding to the ADGF family of proteins are warranted to evaluate the role of this conserved family in fly biology.

Insect saliva contains many proteins that are injected into the mammalian host during the blood feeding process. Saliva proteins enhance the blood feeding ability of insects, but they can also induce mammalian immune responses that inhibit successful feeding, or modulate the bite site to benefit pathogen transmission. Here we studied saliva from four different tsetse species that belong to two distant species groups. We show that the saliva protein profiles of different species groups vary. Experimental mice subjected to fly bites display varying immunological responses against the abundant saliva proteins and the antigenicity of the shared saliva proteins in different tsetse species differs. We show that one member of the ADGF family with adenosine deaminase motifs, TSGF-2, is non-immunogenic in Glossina morsitans in mice, while the same protein from Glossina fuscipes is highly immunogenic. Such species-specific immune responses could be exploited as biomarkers of host exposures in the field. We also show that short-term exposure of G. morsitans to mice passively immunized by anti-TSGF antibodies leads to slight but not statistically significant negative fitness effects. Thus, future investigations with non-antigenic saliva proteins are warranted as they can lead to novel mammalian vaccine targets to reduce tsetse populations in the field.

MicroRNA miR-8 regulates multiple growth factor hormones produced from Drosophila fat cells

Metabolic organs such as the liver and adipose tissue produce several peptide hormones that influence metabolic homeostasis. Fat bodies, the Drosophila counterpart of liver and adipose tissues, have been thought to analogously secrete several hormones that affect organismal physiology, but their identity and regulation remain poorly understood. Previous studies have indicated that microRNA miR-8, functions in the fat body to non-autonomously regulate organismal growth, suggesting that fat body-derived humoral factors are regulated by miR-8. Here, we found that several putative peptide hormones known to have mitogenic effects are regulated by miR-8 in the fat body. Most members of the imaginal disc growth factors and two members of the adenosine deaminase-related growth factors are up-regulated in the absence of miR-8. Drosophila insulin-like peptide 6 (Dilp6) and imaginal morphogenesis protein-late 2 (Imp-L2), a binding partner of Dilp, are also up-regulated in the fat body of miR-8 null mutant larvae. The fat body-specific reintroduction of miR-8 into the miR-8 null mutants revealed six peptides that showed fat-body organ-autonomous regulation by miR-8. Amongst them, only Imp-L2 was found to be regulated by U-shaped, the miR-8 target for body growth. However, a rescue experiment by knockdown of Imp-L2 indicated that Imp-L2 alone does not account for miR-8's control over the insect's growth. Our findings suggest that multiple peptide hormones regulated by miR-8 in the fat body may collectively contribute to Drosophila growth.

Extracellular adenosine mediates a systemic metabolic switch during immune response

Immune defense is energetically costly, and thus an effective response requires metabolic adaptation of the organism to reallocate energy from storage, growth, and development towards the immune system. We employ the natural infection of Drosophila with a parasitoid wasp to study energy regulation during immune response. To combat the invasion, the host must produce specialized immune cells (lamellocytes) that destroy the parasitoid egg. We show that a significant portion of nutrients are allocated to differentiating lamellocytes when they would otherwise be used for development. This systemic metabolic switch is mediated by extracellular adenosine released from immune cells. The switch is crucial for an effective immune response. Preventing adenosine transport from immune cells or blocking adenosine receptor precludes the metabolic switch and the deceleration of development, dramatically reducing host resistance. Adenosine thus serves as a signal that the “selfish” immune cells send during infection to secure more energy at the expense of other tissues.

A study of the fruit fly's response to parasitoid wasp eggs reveals that immune cells selfishly release adenosine as a signal to trigger a systemic metabolic switch, thereby suppressing nonimmune processes and securing energy and nutrients for immune activity. Read the Primer.

The immune response is energetically costly and often requires adaption of the whole organism to ensure it receives enough energy. It is not well understood how distribution of energy resources within the organism is regulated during an immune response. To understand this better, we used parasitoid wasp infection of fruit fly larvae—the host larvae have 48 h before they pupate to destroy the infecting “alien” or face destruction by the parasitoid that will consume the developing pupa. Here we find a signal, generated by the host immune cells, which mediates a systemic energy switch. This signal—adenosine—suppresses processes driving larval to pupal development of the host, thereby freeing up energy for the immune system. We show that the resulting developmental delay in the fruit fly larvae is crucial for an efficient immune response; without the adenosine signal, resistance to the parasitoid drops drastically. Generation of this signal by immune cells demonstrates that in response to external stressors, the immune system can mobilize reallocation to itself of energy and nutrients from the rest of the organism.

Mutation in the Drosophila melanogaster adenosine receptor gene selectively decreases the mosaic hyperplastic epithelial outgrowth rates in wts or dco heterozygous flies

Adenosine (Ado) is a ubiquitous metabolite that plays a prominent role as a paracrine homeostatic signal of metabolic imbalance within tissues. It quickly responds to various stress stimuli by adjusting energy metabolism and influencing cell growth and survival. Ado is also released by dead or dying cells and is present at significant concentrations in solid tumors. Ado signaling is mediated by Ado receptors (AdoR) and proteins modulating its concentration, including nucleoside transporters and Ado deaminases. We examined the impact of genetic manipulations of three Drosophila genes involved in Ado signaling on the incidence of somatic mosaic clones formed by the loss of heterozygosity (LOH) of tumor suppressor and marker genes. We show here that genetic manipulations with the AdoR, equilibrative nucleoside transporter 2 (Ent2), and Ado deaminase growth factor-A (Adgf-A) cause dramatic changes in the frequency of hyperplastic outgrowth clones formed by LOH of the warts (wts) tumor suppressor, while they have almost no effect on control yellow (y) clones. In addition, the effect of AdoR is dose-sensitive and its overexpression leads to the increase in wts hyperplastic epithelial outgrowth rates. Consistently, the frequency of mosaic hyperplastic outgrowth clones generated by the LOH of another tumor suppressor, discs overgrown (dco), belonging to the wts signaling pathway is also dependent on AdoR. Our results provide interesting insight into the maintenance of tissue homeostasis at a cellular level.

Injury and immune response: applying the danger theory to mosquitoes

The insect immune response can be activated by the recognition of both non-self and molecular by-products of tissue damage. Since pathogens and tissue damage usually arise at the same time during infection, the specific mechanisms of the immune response to microorganisms, and to tissue damage have not been unraveled. Consequently, some aspects of damage caused by microorganisms in vector-borne arthropods have been neglected. We herein reassess the Anopheles-Plasmodium interaction, incorporating Matzinger's danger/damage hypothesis and George Salt's injury assumptions. The invasive forms of the parasite cross the peritrophic matrix and midgut epithelia to reach the basal lamina and differentiate into an oocyst. The sporozoites produced in the oocyst are released into the hemolymph, and from there enter the salivary gland. During parasite development, wounds to midgut tissue and the basement membrane are produced. We describe the response of the different compartments where the parasite interacts with the mosquito. In the midgut, the response includes the expression of antimicrobial peptides, production of reactive oxygen species, and possible activation of midgut regenerative cells. In the basal membrane, wound repair mainly involves the production of molecules and the recruitment of hemocytes. We discuss the susceptibility to damage in tissues, and how the place and degree of damage may influence the differential response and the expression of damage associated molecular patterns (DAMPs). Knowledge about damage caused by parasites may lead to a deeper understanding of the relevance of tissue damage and the immune response it generates, as well as the origins and progression of infection in this insect-parasite interaction.

Functions of the Drosophila JAK-STAT pathway: Lessons from stem cells

JAK-STAT signaling has been proposed to act in numerous stem cells in a variety of organisms. Here we provide an overview of its roles in three well characterized stem cell populations in Drosophila, in the intestine, lymph gland and testis. In flies, there is a single JAK and a single STAT, which has made the genetic dissection of pathway function considerably easier and facilitated the analysis of communication between stem cells, their niches and offspring. Studies in flies have revealed roles for this pathway as diverse as regulating bona fide intrinsic self-renewal, integrating response to environmental cues that control quiescence and promoting mitogenic responses to stress.

Comparative metatranscriptomic signatures of wood and paper feeding in the gut of the termite Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Termites are highly eusocial insects that thrive on recalcitrant materials like wood and soil and thus play important roles in global carbon recycling and also in damaging wooden structures. Termites, such as Reticulitermes flavipes (Rhinotermitidae), owe their success to their ability to extract nutrients from lignocellulose (a major component of wood) with the help of gut-dwelling symbionts. With the aim to gain new insights into this enzymatic process we provided R. flavipes with a complex lignocellulose (wood) or pure cellulose (paper) diet and followed the resulting differential gene expression on a custom oligonucleotide-microarray platform. We identified a set of expressed sequence tags (ESTs) with differential abundance between the two diet treatments and demonstrated the source (host/symbiont) of these genes, providing novel information on termite nutritional symbiosis. Our results reveal: (1) the majority of responsive wood- and paper-abundant ESTs are from host and symbionts, respectively; (2) distinct pathways are associated with lignocellulose and cellulose feeding in both host and symbionts; and (3) sets of diet-responsive ESTs encode putative digestive and wood-related detoxification enzymes. Thus, this study illuminates the dynamics of termite nutritional symbiosis and reveals a pool of genes as potential targets for termite control and functional studies of termite-symbiont interactions.

A high-throughput template for optimizing Drosophila organ culture with response-surface methods

The Drosophila wing imaginal disc is a key model organ for molecular developmental genetics. Wing disc studies are generally restricted to end-point analyses of fixed tissues. Recently several studies have relied on limited data from discs cultured in uncharacterized conditions. Systematic efforts towards developing Drosophila organ culture techniques are becoming crucial for further progress. Here, we have designed a multi-tiered, high-throughput pipeline that employs design-of-experiment methods to design a culture medium for wing discs. The resulting formula sustains high levels of proliferation for more than 12 hours. This approach results in a statistical model of proliferation as a function of extrinsic growth supplements and identifies synergies that improve insulin-stimulated growth. A more dynamic view of organogenesis emerges from the optimized culture system that highlights important facets of growth: spatiotemporal clustering of cell divisions and cell junction rearrangements. The same approach could be used to improve culture conditions for other organ systems.

Characterization of a gene coding for a putative adenosine deaminase-related growth factor by RNA interference in the basidiomycete Flammulina velutipes

A full-length cDNA coding for a putative adenosine deaminase (Fv-ada) was isolated from the basidiomycete Flammulina velutipes. Fv-ada encodes a polypeptide consisting of 537 amino acid residues, which has a consensus sequence conserved among adenosine deaminase-related growth factors (ADGF) found in several metazoa, including chordates and insects. Fv-ada transcript was detected at all stages of growth in dikaryotic F. velutipes cells, with a peak at the primordial stage. Heterologous expression of Fv-ada in the yeast Pichia pastoris produced recombinant Fv-ADA that catalyzed the conversion of adenosine to inosine. Dikaryotic mycelia from F. velutipes were transformed with the binary plasmid pFungiway-Fv-ada, which was designed to suppress the expression of Fv-ada through RNA interference. The growth rates of the resulting transformants were retarded in response to the degree of suppression, indicating that Fv-ada plays an important role in the mycelial growth of F. velutipes. These results suggested that ADGF could function as growth factors in fungi, as is seen in other eukaryotes.

Differential response of Drosophila cell lines to extracellular adenosine

Adenosine (Ado) is a crucial metabolite that affects a wide range of physiological processes. Key proteins regulating Ado signaling, transport and metabolism are conserved among vertebrates and invertebrates. It is well known that Ado influences proliferation of several vertebrate and invertebrate cells. Here we show that Ado negatively influences viability, changes morphology and mitochondrial polarity of the Drosophila imaginal disc cell line (Cl.8+) via a mechanism exclusively dependent on cellular Ado uptake. High transport of Ado is followed by phosphorylation and ATP production as a part of Ado salvation, which at higher concentrations may interfere with cellular homeostasis. In contrast, hematopoietic cell line Mbn2, which grows well in high Ado concentration, preferentially uses adenosine deaminase as a part of the purine catabolic pathway. Our results show that different types of Drosophila cell lines use different pathways for Ado conversion and suggest that such differences may be an important part of complex mechanisms maintaining energy homeostasis in the body.

Characterization of the Drosophila adenosine receptor: the effect of adenosine analogs on cAMP signaling in Drosophila cells and their utility for in vivo experiments

Adenosine receptors (AR) belonging to the G protein-coupled receptor family influence a wide range of physiological processes. Recent elucidation of the structure of human A2AR revealed the conserved amino acids necessary for contact with the Ado moiety. However, the selectivity of Ado analogs for AR subtypes is still not well understood. We have shown previously that the Drosophila adenosine receptor (DmAdoR) evokes an increase in cAMP and calcium concentration in heterologous cells. In this study, we have characterized the second-messenger stimulation by endogenous DmAdoR in a Drosophila neuroblast cell line and examined a number of Ado analogs for their ability to interact with DmAdoR. We show that Ado can stimulate cAMP but not calcium levels in Drosophila cells. We found one full and four partial DmAdoR agonists, as well as four antagonists. The employment of the full agonist, 2-chloroadenosine, in flies mimicked in vivo the phenotype of DmAdoR over-expression, whereas the antagonist, SCH58261, rescued the flies from the lethality caused by DmAdoR over-expression. Differences in pharmacological effect of the tested analogs between DmAdoR and human A2AR can be partially explained by the dissimilarity of specific key amino acid residues disclosed by the alignment of these receptors.

Interaction between differentiating cell- and niche-derived signals in hematopoietic progenitor maintenance

Maintenance of a hematopoietic progenitor population requires extensive interaction with cells within a microenvironment or niche. In the Drosophila hematopoietic organ, niche-derived Hedgehog signaling maintains the progenitor population. Here, we show that the hematopoietic progenitors also require a signal mediated by Adenosine deaminase growth factor A (Adgf-A) arising from differentiating cells that regulates extracellular levels of adenosine. The adenosine signal opposes the effects of Hedgehog signaling within the hematopoietic progenitor cells and the magnitude of the adenosine signal is kept in check by the level of Adgf-A secreted from differentiating cells. Our findings reveal signals arising from differentiating cells that are required for maintaining progenitor cell quiescence and that function with the niche-derived signal in maintaining the progenitor state. Similar homeostatic mechanisms are likely to be utilized in other systems that maintain relatively large numbers of progenitors that are not all in direct contact with the cells of the niche.

Functional characterization of ecto-5'-nucleotidases and apyrases in Drosophila melanogaster

Ecto-5'-nucleotidases are glycosyl phosphatidylinositol (GPI)-linked membrane-bound glycoproteins that convert extracellular AMP to adenosine. They play important roles in the inflammatory response where they modulate levels of pro-inflammatory extracellular ATP and anti-inflammatory extracellular adenosine. They are found in the saliva of blood feeding insects and also have a role in male reproduction. Drosophila possesses five genes with eight alternative transcripts encoding proteins with sequence homology to mammalian ecto-5'-nucleotidases. Here we show that two of them - NT5E-1 (CG4827) and NT5E-2 (CG30104) - are GPI-linked proteins with ecto-5'-nucleotidase activity but that they can also be released from the GPI anchor and exhibit secreted 5'-nucleotidase activity in growth media. The third locus in the cluster, CG30103, most likely also encodes a GPI-anchored membrane-bound protein but without 5'-nucleotidase activity, possibly due to the numerous substitutions in the amino acid sequence. Together with NT5E-2, CG30103 is also expressed in the testis offering an interesting model to investigate ecto-5'-nucleotidase enzymatic and extra-enzymatic function in male reproduction. CG42249 locus encoding two alternative transcripts is sequentially similar to family of apyrases related to 5'-nucleotidases and we show here that together with CG5276 belonging to another family of calcium-activated nucleotidases function as apyrases converting extracellular ATP to ADP and AMP. The last locus, CG11883, encodes most likely a cytoplasmic/mitochondrial protein.

Expression of Drosophila adenosine deaminase in immune cells during inflammatory response

Extra-cellular adenosine is an important regulator of inflammatory responses. It is generated from released ATP by a cascade of ectoenzymes and degraded by adenosine deaminase (ADA). There are two types of enzymes with ADA activity: ADA1 and ADGF/ADA2. ADA2 activity originates from macrophages and dendritic cells and is associated with inflammatory responses in humans and rats. Drosophila possesses a family of six ADGF proteins with ADGF-A being the main regulator of extra-cellular adenosine during larval stages. Herein we present the generation of a GFP reporter for ADGF-A expression by a precise replacement of the ADGF-A coding sequence with GFP using homologous recombination. We show that the reporter is specifically expressed in aggregating hemocytes (Drosophila immune cells) forming melanotic capsules; a characteristic of inflammatory response. Our vital reporter thus confirms ADA expression in sites of inflammation in vivo and demonstrates that the requirement for ADA activity during inflammatory response is evolutionary conserved from insects to vertebrates. Our results also suggest that ADA activity is achieved specifically within sites of inflammation by an uncharacterized post-transcriptional regulation based mechanism. Utilizing various mutants that induce melanotic capsule formation and also a real immune challenge provided by parasitic wasps, we show that the acute expression of the ADGF-A protein is not driven by one specific signaling cascade but is rather associated with the behavior of immune cells during the general inflammatory response. Connecting the exclusive expression of ADGF-A within sites of inflammation, as presented here, with the release of energy stores when the ADGF-A activity is absent, suggests that extra-cellular adenosine may function as a signal for energy allocation during immune response and that ADGF-A/ADA2 expression in such sites of inflammation may regulate this role.

Increased extracellular adenosine in Drosophila that are deficient in adenosine deaminase activates a release of energy stores leading to wasting and death

Extracellular adenosine is an important signaling molecule in neuromodulation, immunomodulation and hypoxia. Adenosine dysregulation can cause various pathologies, exemplified by a deficiency in adenosine deaminase in severe combined immunodeficiency. We have established a Drosophila model to study the effects of increased adenosine in vivo by mutating the main Drosophila adenosine deaminase-related growth factor (ADGF-A). Using a genetic screen, we show here that the increased extracellular adenosine in the adgf-a mutant is associated with hyperglycemia and impairment in energy storage. The adenosine works in this regard through the adenosine receptor as an anti-insulin hormone in parallel to adipokinetic hormone, a glucagon counterpart in flies. If not regulated properly, this action can lead to a loss of energy reserves (wasting) and death of the organism. Because adenosine signaling is associated with the immune response and the response to stress in general, our results mark extracellular adenosine as a good candidate signal involved in the wasting syndrome that accompanies various human pathologies.

Bowman-Birk inhibitor affects pathways associated with energy metabolism in Drosophila melanogaster

Bowman-Birk inhibitor (BBI) is toxic when fed to certain insects, including the fruit fly, Drosophila melanogaster. Dietary BBI has been demonstrated to slow growth and increase insect mortality by inhibiting the digestive enzymes trypsin and chymotrypsin, resulting in a reduced supply of amino acids. In mammals, BBI influences cellular energy metabolism. Therefore, we tested the hypothesis that dietary BBI affects energy-associated pathways in the D. melanogaster midgut. Through microarray and metabolomic analyses, we show that dietary BBI affects energy utilization pathways in the midgut cells of D. melanogaster. In addition, ultrastructure studies indicate that microvilli are significantly shortened in BBI-fed larvae. These data provide further insights into the complex cellular response of insects to dietary protease inhibitors.

Equilibrative nucleoside transporter 2 regulates associative learning and synaptic function in Drosophila

Nucleoside transporters are evolutionarily conserved proteins that are essential for normal cellular function. In the present study, we examined the role of equilibrative nucleoside transporter 2 (ent2) in Drosophila. Null mutants of ent2 are lethal during late larval/early pupal stages, indicating that ent2 is essential for normal development. Hypomorphic mutant alleles of ent2, however, are viable and exhibit reduced associative learning. We additionally used RNA interference to knock down ent2 expression in specific regions of the CNS and show that ent2 is required in the alpha/beta lobes of the mushroom bodies and the antennal lobes. To determine whether the observed behavioral defects are attributable to defects in synaptic transmission, we examined transmitter release at the larval neuromuscular junction (NMJ). Excitatory junction potentials were significantly elevated in ent2 mutants, whereas paired-pulse plasticity was reduced. We also observed an increase in stimulus dependent calcium influx in the presynaptic terminal. The defects observed in calcium influx and transmitter release probability at the NMJ were rescued by introducing an adenosine receptor mutant allele (AdoR(1)) into the ent2 mutant background. The results of the present study provide the first evidence of a role for ent2 function in Drosophila and suggest that the observed defects in associative learning and synaptic function may be attributable to changes in adenosine receptor activation.

Structural basis for the growth factor activity of human adenosine deaminase ADA2

Two distinct adenosine deaminases, ADA1 and ADA2, are found in humans. ADA1 has an important role in lymphocyte function and inherited mutations in ADA1 result in severe combined immunodeficiency. The recently isolated ADA2 belongs to the novel family of adenosine deaminase growth factors (ADGFs), which play an important role in tissue development. The crystal structures of ADA2 and ADA2 bound to a transition state analogue presented here reveal the structural basis of the catalytic/signaling activity of ADGF/ADA2 proteins. In addition to the catalytic domain, the structures discovered two ADGF/ADA2-specific domains of novel folds that mediate the protein dimerization and binding to the cell surface receptors. This complex architecture is in sharp contrast with that of monomeric single domain ADA1. An extensive glycosylation and the presence of a conserved disulfide bond and a signal peptide in ADA2 strongly suggest that ADA2, in contrast to ADA1, is specifically designed to act in the extracellular environment. The comparison of catalytic sites of ADA2 and ADA1 demonstrates large differences in the arrangement of the substrate-binding pockets. These structural differences explain the substrate and inhibitor specificity of adenosine deaminases and provide the basis for a rational design of ADA2-targeting drugs to modulate the immune system responses in pathophysiological conditions.