Eiger, a TNF superfamily ligand that triggers the Drosophila JNK pathway

Reactive oxygen species activate the Drosophila TNF receptor Wengen for damage-induced regeneration

Tumor necrosis factor receptors (TNFRs) control pleiotropic pro-inflammatory functions that range from apoptosis to cell survival. The ability to trigger a particular function will depend on the upstream cues, association with regulatory complexes, and downstream pathways. In Drosophila melanogaster, two TNFRs have been identified, Wengen (Wgn) and Grindelwald (Grnd). Although several reports associate these receptors with JNK-dependent apoptosis, it has recently been found that Wgn activates a variety of other functions. We demonstrate that Wgn is required for survival by protecting cells from apoptosis. This is mediated by dTRAF1 and results in the activation of p38 MAP kinase. Remarkably, Wgn is required for apoptosis-induced regeneration and is activated by the reactive oxygen species (ROS) produced following apoptosis. This ROS activation is exclusive for Wgn, but not for Grnd, and can occur after knocking down Eiger/TNFα. The extracellular cysteine-rich domain of Grnd is much more divergent than that of Wgn, which is more similar to TNFRs from other animals, including humans. Our results show a novel TNFR function that responds to stressors by ensuring p38-dependent regeneration.

Inter-cell type interactions that control JNK signaling in the Drosophila intestine

JNK signaling is a critical regulator of inflammation and regeneration, but how it is controlled in specific tissue contexts remains unclear. Here we show that, in the Drosophila intestine, the TNF-type ligand, Eiger (Egr), is expressed exclusively by intestinal stem cells (ISCs) and enteroblasts (EBs), where it is induced by stress and during aging. Egr preferentially activates JNK signaling in a paracrine fashion in differentiated enterocytes (ECs) via its receptor, Grindelwald (Grnd). N-glycosylation genes (Alg3, Alg9) restrain this activation, and stress-induced downregulation of Alg3 and Alg9 correlates with JNK activation, suggesting a regulatory switch. JNK activity in ECs induces expression of the intermembrane protease Rhomboid (Rho), driving secretion of EGFR ligands Keren (Krn) and Spitz (Spi), which in turn activate EGFR signaling in progenitor cells (ISCs and EBs) to stimulate their growth and division, as well as to produce more Egr. This study uncovers an N-glycosylation-controlled, paracrine JNK-EGFR-JNK feedforward loop that sustains ISC proliferation during stress-induced gut regeneration.

Local Ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

Kin17 regulates proper cortical localization of Miranda in Drosophila neuroblasts by regulating Flfl expression

During asymmetric division of Drosophila larval neuroblasts, the fate determinant Prospero (Pros) and its adaptor Miranda (Mira) are segregated to the basal cortex through atypical protein kinase C (aPKC) phosphorylation of Mira and displacement from the apical cortex, but Mira localization after aPKC phosphorylation is not well understood. We identify Kin17, a DNA replication and repair protein, as a regulator of Mira localization during asymmetric cell division. Loss of Kin17 leads to aberrant localization of Mira and Pros to the centrosome, cytoplasm, and nucleus. We provide evidence to show that the mislocalization of Mira and Pros is likely due to reduced expression of Falafel (Flfl), a component of protein phosphatase 4 (PP4), and defects in dephosphorylation of serine-96 of Mira. Our work reveals that Mira is likely dephosphorylated by PP4 at the centrosome to ensure proper basal localization of Mira after aPKC phosphorylation and that Kin17 regulates PP4 activity by regulating Flfl expression.

Xrp1 governs the stress response program to spliceosome dysfunction

Co-transcriptional processing of nascent pre-mRNAs by the spliceosome is vital to regulating gene expression and maintaining genome integrity. Here, we show that the deficiency of functional U5 small nuclear ribonucleoprotein particles (snRNPs) in Drosophila imaginal cells causes extensive transcriptome remodeling and accumulation of highly mutagenic R-loops, triggering a robust stress response and cell cycle arrest. Despite compromised proliferative capacity, the U5 snRNP-deficient cells increased protein translation and cell size, causing intra-organ growth disbalance before being gradually eliminated via apoptosis. We identify the Xrp1-Irbp18 heterodimer as the primary driver of transcriptional and cellular stress program downstream of U5 snRNP malfunction. Knockdown of Xrp1 or Irbp18 in U5 snRNP-deficient cells attenuated JNK and p53 activity, restored normal cell cycle progression and growth, and inhibited cell death. Reducing Xrp1-Irbp18, however, did not rescue the splicing defects, highlighting the requirement of accurate splicing for cellular and tissue homeostasis. Our work provides novel insights into the crosstalk between splicing and the DNA damage response and defines the Xrp1-Irbp18 heterodimer as a critical sensor of spliceosome malfunction and mediator of the stress-induced cellular senescence program.

Drosophila melanogaster Sting mediates Coxiella burnetii infection by reducing accumulation of reactive oxygen species

The Gram-negative bacterium Coxiella burnetii is the causative agent of query fever in humans and coxiellosis in livestock. C. burnetii infects a variety of cell types, tissues, and animal species including mammals and arthropods, but there is much left to be understood about the molecular mechanisms at play during infection in distinct species. Human stimulator of interferon genes (STING) induces an innate immune response through the induction of type I interferons (IFNs), and IFN promotes or suppresses C. burnetii replication, depending on tissue type. Drosophila melanogaster contains a functional STING ortholog (Sting) which activates NF-κB signaling and autophagy. Here, we sought to address the role of D. melanogaster Sting during C. burnetii infection to uncover how Sting regulates C. burnetii infection in flies. We show that Sting-null flies exhibit higher mortality and reduced induction of antimicrobial peptides following C. burnetii infection compared to control flies. Additionally, Sting-null flies induce lower levels of oxidative stress genes during infection, but the provision of N-acetyl-cysteine (NAC) in food rescues Sting-null host survival. Lastly, we find that reactive oxygen species levels during C. burnetii infection are higher in Drosophila S2 cells knocked down for Sting compared to control cells. Our results show that at the host level, NAC provides protection against C. burnetii infection in the absence of Sting, thus establishing a role for Sting in protection against oxidative stress during C. burnetii infection.

Senescent cells and macrophages cooperate through a multi-kinase signaling network to promote intestinal transformation in Drosophila

Cellular senescence is a conserved biological process that plays a crucial and context-dependent role in cancer. The highly heterogeneous and dynamic nature of senescent cells and their small numbers in tissues make in vivo mechanistic studies of senescence challenging. As a result, how multiple senescence-inducing signals are integrated in vivo to drive senescence in only a small number of cells is unclear. Here, we identify cells that exhibit multiple features of senescence in a Drosophila model of intestinal transformation, which emerge in response to concurrent activation of AKT, JNK, and DNA damage signaling within transformed tissue. Eliminating senescent cells, genetically or by treatment with senolytic compounds, reduces overgrowth and improves survival. We find that senescent cells promote tumorigenesis by recruiting Drosophila macrophages to the transformed tissue, which results in non-autonomous activation of JNK signaling. These findings identify senescent cell-macrophage interactions as an important driver of epithelial transformation.

Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

Antioxidant and Anti-Inflammatory Properties of Quail Yolk Oil via Upregulation of Superoxide Dismutase 1 and Catalase Genes and Downregulation of EIGER and Unpaired 2 Genes in a D. melanogaster Model

Quail egg yolk oil (QEYO) has a rich history of medicinal use, showcasing heightened antioxidant and bioactive properties in our prior studies. This positions QEYO as a promising candidate for therapeutic and cosmetic applications. In this investigation, QEYO was extracted using ethanol/chloroform and 2-propanol/hexane solvents. GC-MS and FTIR analyses quantified 14 major bioactive compounds in the ethanol/chloroform fraction and 12 in the 2-propanol/hexane fraction. Toxicity evaluations in fruit flies, spanning acute, sub chronic, and chronic exposures, revealed no adverse effects. Negative geotaxis assays assessed locomotor activity, while biochemical assays using fly hemolymph gauged antioxidant responses. Real-time PCR revealed the relative expression levels of the antioxidant and anti-inflammatory genes. FTIR spectra indicated diverse functional groups, and the GC-MS results associated bioactive compounds with the regulation of the anti-inflammatory genes EIGER and UPD2. While no significant change in SOD activities was noted, male flies treated with specific QEYO doses exhibited increased catalase activity and total antioxidant capacity, coupled with a significant decrease in their malondialdehyde levels. This study offers valuable insights into the bioactive compounds of QEYO and their potential regulatory roles in gene expression.

Innate immune and proinflammatory signals activate the Hippo pathway via a Tak1-STRIPAK-Tao axis

The Hippo pathway controls developmental, homeostatic and regenerative tissue growth, and is frequently dysregulated in various diseases. Although this pathway can be activated by innate immune/inflammatory stimuli, the underlying mechanism is not fully understood. Here, we identify a conserved signaling cascade that leads to Hippo pathway activation by innate immune/inflammatory signals. We show that Tak1, a key kinase in innate immune/inflammatory signaling, activates the Hippo pathway by inducing the lysosomal degradation of Cka, an essential subunit of the STRIPAK PP2A complex that suppresses Hippo signaling. Suppression of STRIPAK results in the activation of Hippo pathway through Tao-Hpo signaling. We further show that Tak1-mediated Hippo signaling is involved in processes ranging from cell death to phagocytosis and innate immune memory. Our findings thus reveal a molecular connection between innate immune/inflammatory signaling and the evolutionally conserved Hippo pathway, thus contributing to our understanding of infectious, inflammatory and malignant diseases.

Ubiquitin signalling in Drosophila innate immune responses

Cells respond to invading pathogens and danger signals from the environment by adapting gene expression to meet the need for protective effector molecules. While this innate immune response is required for the cell and the organism to recover, excess immune activation may lead to loss of homeostasis, thereby promoting chronic inflammation and cancer progression. The molecular basis of innate immune defence is comprised of factors promoting survival and proliferation, such as cytokines, antimicrobial peptides and anti-apoptotic proteins. As the molecular mechanisms regulating innate immune responses are conserved through evolution, the fruit fly Drosophila melanogaster serves as a convenient, affordable and ethical model organism to enhance understanding of immune signalling. Fly immunity against bacterial infection is built up by both cellular and humoral responses, where the latter is regulated by the Imd and Toll pathways activating NF-κB transcription factors Relish, Dorsal and Dif, as well as JNK activation and JAK/STAT signalling. As in mammals, the Drosophila innate immune signalling pathways are characterised by ubiquitination of signalling molecules followed by ubiquitin receptors binding to the ubiquitin chains, as well as by rapid changes in protein levels by ubiquitin-mediated targeted proteasomal and lysosomal degradation. In this review, we summarise the molecular signalling pathways regulating immune responses to pathogen infection in Drosophila, with a focus on ubiquitin-dependent control of innate immunity and inflammatory signalling.

Differential Ire1 determines loser cell fate in tumor-suppressive cell competition

Tumor-suppressive cell competition (TSCC) is a conserved surveillance mechanism in which neighboring cells actively eliminate oncogenic cells. Despite overwhelming studies showing that the unfolded protein response (UPR) is dysregulated in various tumors, it remains debatable whether the UPR restrains or promotes tumorigenesis. Here, using Drosophila eye epithelium as a model, we uncover a surprising decisive role of the Ire1 branch of the UPR in regulating cell polarity gene scribble (scrib) loss-induced TSCC. Both mutation and hyperactivation of Ire1 accelerate elimination of scrib clones via inducing apoptosis and autophagy, respectively. Unexpectedly, relative Ire1 activity is also crucial for determining loser cell fate, as dysregulating Ire1 signaling in the surrounding healthy cells reversed the "loser" status of scrib clones by decreasing their apoptosis. Furthermore, we show that Ire1 is required for cell competition in mammalian cells. Together, these findings provide molecular insights into scrib-mediated TSCC and highlight Ire1 as a key determinant of loser cell fate.

MicroRNA-Mediated Host Immune Genes Manipulation Benefits AcMNPV Proliferation in Spodoptera frugiperda

Spodoptera frugiperda is a highly destructive migratory pest that threatens various crops globally. Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is an effective biocontrol agent against lepidopteran pests. Here, we explored the molecular mechanisms underlying the immune response to AcMNPV infection in S. frugiperda. RNA-seq and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analyses identified the Toll, IMD, and apoptosis pathways as primary immune responses. Investigation into AcMNPV-induced apoptosis in the S. frugiperda cell line (Sf9) revealed that the Toll pathway activated the JNK via the TRAF6 (TNF receptor-associated factor 6) adapter. In addition, AcMNPV-induced the differential expression of several host-encoded microRNAs (miRNAs), with significant negative regulatory effects, on S. frugiperda antiviral immune genes. RNAi and miRNA-mimic mediated silencing of these genes resulted in increased AcMNPV proliferation. Our findings reinforce the potential of AcMNPV as a potent biocontrol agent and further our understanding of developing biotechnology-based targeted pest control agents.

A Drosophila model targets Eiger/TNFα to alleviate obesity-related insulin resistance and macrophage infiltration

Obesity is associated with various metabolic disorders, such as insulin resistance and adipose tissue inflammation (ATM), characterized by macrophage infiltration into adipose cells. This study presents a new Drosophila model to investigate the mechanisms underlying these obesity-related pathologies. We employed genetic manipulation to reduce ecdysone levels to prolong the larval stage. These animals are hyperphagic and exhibit features resembling obesity in mammals, including increased lipid storage, adipocyte hypertrophy and high circulating glucose levels. Moreover, we observed significant infiltration of immune cells (hemocytes) into the fat bodies, accompanied by insulin resistance. We found that attenuation of Eiger/TNFα signaling reduced ATM and improved insulin sensitivity. Furthermore, using metformin and the antioxidants anthocyanins, we ameliorated both phenotypes. Our data highlight evolutionarily conserved mechanisms allowing the development of Drosophila models for discovering therapeutic pathways in adipose tissue immune cell infiltration and insulin resistance. Our model can also provide a platform to perform genetic screens or test the efficacy of therapeutic interventions for diseases such as obesity, type 2 diabetes and non-alcoholic fatty liver disease.

Cholinergic neurons trigger epithelial Ca2+ currents to heal the gut

A fundamental and unresolved question in regenerative biology is how tissues return to homeostasis after injury. Answering this question is essential for understanding the aetiology of chronic disorders such as inflammatory bowel diseases and cancer1. We used the Drosophila midgut2 to investigate this and discovered that during regeneration a subpopulation of cholinergic3 neurons triggers Ca2+ currents among intestinal epithelial cells, the enterocytes, to promote return to homeostasis. We found that downregulation of the conserved cholinergic enzyme acetylcholinesterase4 in the gut epithelium enables acetylcholine from specific Egr5 (TNF in mammals)-sensing cholinergic neurons to activate nicotinic receptors in innervated enterocytes. This activation triggers high Ca2+, which spreads in the epithelium through Innexin2-Innexin7 gap junctions6, promoting enterocyte maturation followed by reduction of proliferation and inflammation. Disrupting this process causes chronic injury consisting of ion imbalance, Yki (YAP in humans) activation7, cell death and increase of inflammatory cytokines reminiscent of inflammatory bowel diseases8. Altogether, the conserved cholinergic pathway facilitates epithelial Ca2+ currents that heal the intestinal epithelium. Our findings demonstrate nerve- and bioelectric9-dependent intestinal regeneration and advance our current understanding of how a tissue returns to homeostasis after injury.

Glia instruct axon regeneration via a ternary modulation of neuronal calcium channels in Drosophila

A neuron's regenerative capacity is governed by its intrinsic and extrinsic environment. Both peripheral and central neurons exhibit cell-type-dependent axon regeneration, but the underlying mechanism is unclear. Glia provide a milieu essential for regeneration. However, the routes of glia-neuron signaling remain underexplored. Here, we show that regeneration specificity is determined by the axotomy-induced Ca2+ transients only in the fly regenerative neurons, which is mediated by L-type calcium channels, constituting the core intrinsic machinery. Peripheral glia regulate axon regeneration via a three-layered and balanced modulation. Glia-derived tumor necrosis factor acts through its neuronal receptor to maintain calcium channel expression after injury. Glia sustain calcium channel opening by enhancing membrane hyperpolarization via the inwardly-rectifying potassium channel (Irk1). Glia also release adenosine which signals through neuronal adenosine receptor (AdoR) to activate HCN channels (Ih) and dampen Ca2+ transients. Together, we identify a multifaceted glia-neuron coupling which can be hijacked to promote neural repair.

Slik maintains tissue homeostasis by preventing JNK-mediated apoptosis

BACKGROUND

The c-Jun N-terminal kinase (JNK) pathway is an evolutionarily conserved regulator of cell death, which is essential for coordinating tissue homeostasis. In this study, we have characterized the Drosophila Ste20-like kinase Slik as a novel modulator of JNK pathway-mediated apoptotic cell death.

RESULTS

First, ectopic JNK signaling-triggered cell death is enhanced by slik depletion whereas suppressed by Slik overexpression. Second, loss of slik activates JNK signaling, which results in enhanced apoptosis and impaired tissue homeostasis. In addition, genetic epistasis analysis suggests that Slik acts upstream of or in parallel to Hep to regulate JNK-mediated apoptotic cell death. Moreover, Slik is necessary and sufficient for preventing physiologic JNK signaling-mediated cell death in development. Furthermore, introduction of STK10, the human ortholog of Slik, into Drosophila restores slik depletion-induced cell death and compromised tissue homeostasis. Lastly, knockdown of STK10 in human cancer cells also leads to JNK activation, which is cancelled by expression of Slik.

CONCLUSIONS

This study has uncovered an evolutionarily conserved role of Slik/STK10 in blocking JNK signaling, which is required for cell death inhibition and tissue homeostasis maintenance in development.

Drosophila TNF/TNFRs: At the crossroad between metabolism, immunity, and tissue homeostasis

Tumor necrosis factor (TNF)-α is a highly conserved proinflammatory cytokine with important functions in immunity, tissue repair, and cellular homeostasis. Due to the simplicity of the Drosophila TNF-TNF receptor (TNFR) system and a broad genetic toolbox, the fly has played a pivotal role in deciphering the mechanisms underlying TNF-mediated physiological and pathological functions. In this review, we summarize the recent advances in our understanding of how local and systemic sources of Egr/TNF contribute to its antitumor and tumor-promoting properties, and its emerging functions in adaptive growth responses, sleep regulation, and adult tissue homeostasis. The recent annotation of TNF as an adipokine and its indisputable contribution to obesity- and cancer-associated metabolic diseases have provoked a new area of research focusing on its dual function in regulating immunity and energy homeostasis. Here, we discuss the role of TNFR signaling in coupling immune and metabolic processes and how this might be relevant in the adaption of host to environmental stresses, or, in the case of obesity, promote metabolic derangements and disease.

Immunometabolic regulation during the presence of microorganisms and parasitoids in insects

Multicellular organisms live in environments containing diverse nutrients and a wide variety of microbial communities. On the one hand, the immune response of organisms can protect from the intrusion of exogenous microorganisms. On the other hand, the dynamic coordination of anabolism and catabolism of organisms is a necessary factor for growth and reproduction. Since the production of an immune response is an energy-intensive process, the activation of immune cells is accompanied by metabolic transformations that enable the rapid production of ATP and new biomolecules. In insects, the coordination of immunity and metabolism is the basis for insects to cope with environmental challenges and ensure normal growth, development and reproduction. During the activation of insect immune tissues by pathogenic microorganisms, not only the utilization of organic resources can be enhanced, but also the activated immune cells can usurp the nutrients of non-immune tissues by generating signals. At the same time, insects also have symbiotic bacteria in their body, which can affect insect physiology through immune-metabolic regulation. This paper reviews the research progress of insect immune-metabolism regulation from the perspective of insect tissues, such as fat body, gut and hemocytes. The effects of microorganisms (pathogenic bacteria/non-pathogenic bacteria) and parasitoids on immune-metabolism were elaborated here, which provide guidance to uncover immunometabolism mechanisms in insects and mammals. This work also provides insights to utilize immune-metabolism for the formulation of pest control strategies.

The TNFR Wengen regulates the FGF pathway by an unconventional mechanism

Unveiling the molecular mechanisms of receptor activation has led to much understanding of development as well as the identification of important drug targets. We use the Drosophila tracheal system to study the activity of two families of widely used and conserved receptors, the TNFRs and the RTK-FGFRs. Breathless, an FGFR, controls the program of differentiation of the tracheal terminal cells in response to ligand activation. Here we identify a role for Wengen, a TNFR, in repressing the terminal cell program by regulating the MAPK pathway downstream of Breathless. We find that Wengen acts independently of both its canonical ligand and downstream pathway genes. Wengen does not stably localise at the membrane and is instead internalised-a trafficking that seems essential for activity. We show that Breathless and Wengen colocalise in intracellular vesicles and form a complex. Furthermore, Wengen regulates Breathless accumulation, possibly regulating Breathless trafficking and degradation. We propose that, in the tracheal context, Wengen interacts with Breathless to regulate its activity, and suggest that such unconventional mechanism, involving binding by TNFRs to unrelated proteins, may be a general strategy of TNFRs.

Epithelial Ca2+ waves triggered by enteric neurons heal the gut

A fundamental and unresolved question in regenerative biology is how tissues return to homeostasis after injury. Answering this question is essential for understanding the etiology of chronic disorders such as inflammatory bowel diseases and cancer. We used the Drosophila midgut to investigate this question and discovered that during regeneration a subpopulation of cholinergic enteric neurons triggers Ca2+ currents among enterocytes to promote return of the epithelium to homeostasis. Specifically, we found that down-regulation of the cholinergic enzyme Acetylcholinesterase in the epithelium enables acetylcholine from defined enteric neurons, referred as ARCENs, to activate nicotinic receptors in enterocytes found near ARCEN-innervations. This activation triggers high Ca2+ influx that spreads in the epithelium through Inx2/Inx7 gap junctions promoting enterocyte maturation followed by reduction of proliferation and inflammation. Disrupting this process causes chronic injury consisting of ion imbalance, Yki activation and increase of inflammatory cytokines together with hyperplasia, reminiscent of inflammatory bowel diseases. Altogether, we found that during gut regeneration the conserved cholinergic pathway facilitates epithelial Ca2+ waves that heal the intestinal epithelium. Our findings demonstrate nerve- and bioelectric-dependent intestinal regeneration which advance the current understanding of how a tissue returns to its homeostatic state after injury and could ultimately help existing therapeutics.

MicroRNA miR-274-5p Suppresses Found-in-Neurons Associated with Melanotic Mass Formation and Developmental Growth in Drosophila

The hematopoietic system plays a crucial role in immune defense response and normal development, and it is regulated by various factors from other tissues. The dysregulation of hematopoiesis is associated with melanotic mass formation; however, the molecular mechanisms underlying this process are poorly understood. Here, we observed that the overexpression of miR-274 in the fat body resulted in the formation of melanotic masses. Moreover, abnormal activation of the JNK and JAK/STAT signaling pathways was linked to these consequences. In addition to this defect, miR-274 overexpression in the larval fat body decreased the total tissue size, leading to a reduction in body weight. miR-274-5p was found to directly suppress the expression of found-in-neurons (fne), which encodes an RNA-binding protein. Similar to the effects of miR-274 overexpression, fne depletion led to melanotic mass formation and growth reduction. Collectively, miR-274 plays a regulatory role in the fne-JNK signaling axis in melanotic mass formation and growth control.

N-Acetyltransferase 9 ameliorates Aβ42-mediated neurodegeneration in the Drosophila eye

Alzheimer's disease (AD), a progressive neurodegenerative disorder, manifests as accumulation of amyloid-beta-42 (Aβ42) plaques and intracellular accumulation of neurofibrillary tangles (NFTs) that results in microtubule destabilization. Targeted expression of human Aβ42 (GMR > Aβ42) in developing Drosophila eye retinal neurons results in Aβ42 plaque(s) and mimics AD-like extensive neurodegeneration. However, there remains a gap in our understanding of the underlying mechanism(s) for Aβ42-mediated neurodegeneration. To address this gap in information, we conducted a forward genetic screen, and identified N-acetyltransferase 9 (Mnat9) as a genetic modifier of GMR > Aβ42 neurodegenerative phenotype. Mnat9 is known to stabilize microtubules by inhibiting c-Jun-N- terminal kinase (JNK) signaling. We found that gain-of-function of Mnat9 rescues GMR > Aβ42 mediated neurodegenerative phenotype whereas loss-of-function of Mnat9 exhibits the converse phenotype of enhanced neurodegeneration. Here, we propose a new neuroprotective function of Mnat9 in downregulating the JNK signaling pathway to ameliorate Aβ42-mediated neurodegeneration, which is independent of its acetylation activity. Transgenic flies expressing human NAT9 (hNAT9), also suppresses Aβ42-mediated neurodegeneration thereby suggesting functional conservation in the interaction of fly Mnat9 or hNAT9 with JNK-mediated neurodegeneration. These studies add to the repertoire of molecular mechanisms that mediate cell death response following accumulation of Aβ42 and may provide new avenues for targeting neurodegeneration.

The Drosophila tumor necrosis factor receptor, Wengen, couples energy expenditure with gut immunity

It is well established that tumor necrosis factor (TNF) plays an instrumental role in orchestrating the metabolic disorders associated with late stages of cancers. However, it is not clear whether TNF/TNF receptor (TNFR) signaling controls energy homeostasis in healthy individuals. Here, we show that the highly conserved Drosophila TNFR, Wengen (Wgn), is required in the enterocytes (ECs) of the adult gut to restrict lipid catabolism, suppress immune activity, and maintain tissue homeostasis. Wgn limits autophagy-dependent lipolysis by restricting cytoplasmic levels of the TNFR effector, TNFR-associated factor 3 (dTRAF3), while it suppresses immune processes through inhibition of the dTAK1/TAK1-Relish/NF-κB pathway in a dTRAF2-dependent manner. Knocking down dTRAF3 or overexpressing dTRAF2 is sufficient to suppress infection-induced lipid depletion and immune activation, respectively, showing that Wgn/TNFR functions as an intersection between metabolism and immunity allowing pathogen-induced metabolic reprogramming to fuel the energetically costly task of combatting an infection.

Senescent cells and macrophages cooperate through a multi-kinase signaling network to promote intestinal transformation in Drosophila

Cellular senescence is a conserved biological process essential for embryonic development, tissue remodeling, repair, and a key regulator of aging. Senescence also plays a crucial role in cancer, though this role can be tumor-suppressive or tumor-promoting, depending on the genetic context and the microenvironment. The highly heterogeneous, dynamic, and context-dependent nature of senescence-associated features and the relatively small numbers of senescent cells in tissues makes in vivo mechanistic studies of senescence challenging. As a result, which senescence-associated features are observed in which disease contexts and how they contribute to disease phenotypes remain largely unknown. Similarly, the specific mechanisms by which various senescence-inducing signals are integrated in vivo to induce senescence and why some cells become senescent while their immediate neighbors do not are unclear. Here, we identify a small number of cells that exhibit multiple features of senescence in a genetically complex model of intestinal transformation we recently established in the developing Drosophila larval hindgut epithelium. We demonstrate that these cells emerge in response to concurrent activation of AKT, JNK, and DNA damage response pathways within transformed tissue. Eliminating senescent cells, genetically or by treatment with senolytic compounds, reduces overgrowth and improves survival. We find that this tumor-promoting role is mediated by Drosophila macrophages recruited to the transformed tissue by senescent cells, which results in non-autonomous activation of JNK signaling within the transformed epithelium. These findings emphasize complex cell-cell interactions underlying epithelial transformation and identify senescent cell-macrophage interactions as a potential druggable node in cancer.

Regulating metabolism to shape immune function: Lessons from Drosophila

Infection with pathogenic microbes is a severe threat that hosts manage by activating the innate immune response. In Drosophila melanogaster, the Toll and Imd signaling pathways are activated by pathogen-associated molecular patterns to initiate cellular and humoral immune processes that neutralize and kill invaders. The Toll and Imd signaling pathways operate in organs such as fat body and gut that control host nutrient metabolism, and infections or genetic activation of Toll and Imd signaling also induce wide-ranging changes in host lipid, carbohydrate and protein metabolism. Metabolic regulation by immune signaling can confer resistance to or tolerance of infection, but it can also lead to pathology and susceptibility to infection. These immunometabolic phenotypes are described in this review, as are changes in endocrine signaling and gene regulation that mediate survival during infection. Future work in the field is anticipated to determine key variables such as sex, dietary nutrients, life stage, and pathogen characteristics that modify immunometabolic phenotypes and, importantly, to uncover the mechanisms used by the immune system to regulate metabolism.

Sas-Ptp10D shapes germ-line stem cell niche by facilitating JNK-mediated apoptosis

The function of the stem cell system is supported by a stereotypical shape of the niche structure. In Drosophila ovarian germarium, somatic cap cells form a dish-like niche structure that allows only two or three germ-line stem cells (GSCs) reside in the niche. Despite extensive studies on the mechanism of stem cell maintenance, the mechanisms of how the dish-like niche structure is shaped and how this structure contributes to the stem cell system have been elusive. Here, we show that a transmembrane protein Stranded at second (Sas) and its receptor Protein tyrosine phosphatase 10D (Ptp10D), effectors of axon guidance and cell competition via epidermal growth factor receptor (Egfr) inhibition, shape the dish-like niche structure by facilitating c-Jun N-terminal kinase (JNK)-mediated apoptosis. Loss of Sas or Ptp10D in gonadal apical cells, but not in GSCs or cap cells, during the pre-pupal stage results in abnormal shaping of the niche structure in the adult, which allows excessive, four to six GSCs reside in the niche. Mechanistically, loss of Sas-Ptp10D elevates Egfr signaling in the gonadal apical cells, thereby suppressing their naturally-occurring JNK-mediated apoptosis that is essential for the shaping of the dish-like niche structure by neighboring cap cells. Notably, the abnormal niche shape and resulting excessive GSCs lead to diminished egg production. Our data propose a concept that the stereotypical shaping of the niche structure optimizes the stem cell system, thereby maximizing the reproductive capacity.

Spoonbill positively regulates JNK signalling mediated apoptosis in Drosophila melanogaster

A-kinase anchoring protein (AKAP) comprises a family of scaffold proteins, which decides the subcellular localisation of a combination of signalling molecules. Spoonbill (Spoon) is a putative A-kinase anchoring protein in Drosophila. We have earlier reported that Spoon suppresses ribonuclear foci formed by trinucleotide repeat expanded transcripts associated with Spinocerebellar Ataxia 8 neurodegeneration in Drosophila. However, the role of Spoonbill in cellular signalling was unexplored. In this report, we have unravelled a novel function of Spoon protein in the regulation of the apoptotic pathway. The Drosophila TNFα homolog, Eiger, induces apoptosis via activation of the JNK pathway. We have shown here that Spoonbill is a positive regulator of the Eiger-induced JNK signalling. Further genetic interaction studies show that the spoon interacts with components of the JNK pathway, TGF-β activated kinase 1 (Tak1 - JNKKK), hemipterous (hep - JNKK) and basket (bsk - JNK). Interestingly, Spoonbill alone can also induce ectopic activation of the JNK pathway in a context-specific manner. To understand the molecular mechanism underlying Spoonbill-mediated modulation of the JNK pathway, the interaction between Spoon and Drosophila JNK was assessed. basket encodes the only known JNK in Drosophila. This serine/threonine-protein kinase phosphorylates Jra/Kay, which transcriptionally regulate downstream targets like Matrix metalloproteinase 1 (Mmp1), puckered (puc), and proapoptotic genes hid, reaper and grim. Interestingly, we found that Spoonbill colocalises and co-immunoprecipitates with the Basket protein in the developing photoreceptor neurons. Hence, we propose that Spoon plays a vital role in JNK-induced apoptosis. Furthermore, stress-induced JNK activation underlying Parkinson's Disease was also examined. In the Parkinson's Drosophila model of neurodegeneration, depletion of Spoonbill leads to a partial reduction of JNK pathway activation, along with improvement in adult motor activity. These observations suggest that the putative scaffold protein Spoonbill is a functional and physical interacting partner of the Drosophila JNK protein, Basket. Spoon protein is localised on the outer mitochondrial membrane (OMM), which may perhaps provide a suitable subcellular niche for activation of Drosophila Basket protein by its kinases which induce apoptosis.

Gene Set Enrichment Analysis and Genetic Experiment Reveal Changes in Cell Signaling Pathways Induced by α-Synuclein Overexpression

Abnormal accumulation of alpha synuclein (α-Syn) in sporadic and familial Parkinson's disease (PD) may be a key step in its pathogenesis. In this study, the expression matrix of the GSE95427 dataset after α-Syn overexpression in human glioma cell line H4 was obtained from the GEO database. We used the Gene Set Enrichment Analysis (GSEA) method to reanalyze this dataset to evaluate the possible functions of α-Syn. The results showed that the tumor necrosis factor alpha (TNF-α) signal was significantly activated in α-Syn-overexpressing cells, and oxidative phosphorylation signal, extracellular matrix signal, cell cycle related signal and fatty acid metabolism signal were significantly inhibited. Moreover, we employed the α-Syn-expressing transgenic Drosophila model of Parkinson's disease and knocked-down eiger, a TNF superfamily ligand homologue, indicating that the TNF-α pathway plays a role in the common pathogenesis of synucleinopathies. Our analysis based on GSEA data provides more clues for a better understanding of α-Syn function.

TroTNFSF6, a tumor necrosis factor ligand superfamily member, promotes antibacterial immune response of golden pompano, Trachinotus ovatus

Tumor necrosis factor ligand superfamily member 6 (TNFSF6), also known as FasL/CD95L, is essential for maintaining the body's immune homeostasis. However, the current reports on TNFSF6 in fish are relatively scarce. In the present study, we conducted functional analyses of a TNFSF6 (TroTNFSF6) from the teleost fish golden pompano (Trachinotus ovatus). TroTNFSF6 is composed of 228 amino acids and has a low similarity with other species (9.65%-58.79%). TroTNFSF6 was expressed in the 11 tissues tested and was significantly up-regulated after Edwardsiella tarda infection. In vivo, overexpression of TroTNFSF6 effectively stimulated the AKP and ACP activities, and reduced bacterial infection in fish tissues. Correspondingly, knockdown of TroTNFSF6 expression resulted in increasing bacterial dissemination and colonization in fish tissues. In vitro, recombinant TroTNFSF6 protein promoted the proliferation of T. ovatus head kidney lymphocytes (HKLs), and promoted the apoptosis of murine liver cancer cells (Hepa1-6). The results indicated that TroTNFSF6 plays an important role in the T. ovatus antibacterial immunity. These observations will facilitate the future in-depth study of teleost TNFSF6.

Oxidative stress mediates end-organ damage in a novel model of acetaminophen-toxicity in Drosophila

Acetaminophen is the most common cause of acute drug-induced liver injury in the United States. However, research into the mechanisms of acetaminophen toxicity and the development of novel therapeutics is hampered by the lack of robust, reproducible, and cost-effective model systems. Herein, we characterize a novel Drosophila-based model of acetaminophen toxicity. We demonstrate that acetaminophen treatment of Drosophila results in similar pathophysiologic alterations as those observed in mammalian systems, including a robust production of reactive oxygen species, depletion of glutathione, and dose-dependent mortality. Moreover, these effects are concentrated in the Drosophila fat body, an organ analogous to the mammalian liver. Utilizing this system, we interrogated the influence of environmental factors on acetaminophen toxicity which has proven difficult in vertebrate models due to cost and inter-individual variability. We find that both increasing age and microbial depletion sensitize Drosophila to acetaminophen toxicity. These environmental influences both alter oxidative stress response pathways in metazoans. Indeed, genetic and pharmacologic manipulations of the antioxidant response modify acetaminophen toxicity in our model. Taken together, these data demonstrate the feasibility of Drosophila for the study of acetaminophen toxicity, bringing with it an ease of genetic and microbiome manipulation, high-throughput screening, and availability of transgenic animals.

Identification of a TNF-TNFR-like system in malaria vectors (Anopheles stephensi) likely to influence Plasmodium resistance

Identification of Plasmodium-resistance genes in malaria vectors remains an elusive goal despite the recent availability of high-quality genomes of several mosquito vectors. Anopheles stephensi, with its three distinctly-identifiable forms at the egg stage, correlating with varying vector competence, offers an ideal species to discover functional mosquito genes implicated in Plasmodium resistance. Recently, the genomes of several strains of An. stephensi of the type-form, known to display high vectorial capacity, were reported. Here, we report a chromosomal-level assembly of an intermediate-form of An. stephensi strain (IndInt), shown to have reduced vectorial capacity relative to a strain of type-form (IndCh). The contig level assembly with a L50 of 4 was scaffolded into chromosomes by using the genome of IndCh as the reference. The final assembly shows a heterozygous paracentric inversion, 3Li, involving 8 Mbp, which is syntenic to the extensively-studied 2La inversion implicated in Plasmodium resistance in An. gambiae involving 21 Mbp. Deep annotation of genes within the 3Li region in the IndInt assembly using the state-of-the-art protein-fold prediction and other annotation tools reveals the presence of a tumor necrosis factor-alpha (TNF-alpha) like gene, which is the homolog of the Eiger gene in Drosophila. Subsequent chromosome-wide searches revealed homologs of Wengen (Wgn) and Grindelwald (Grnd) genes, which are known to be the receptors for Eiger in Drosophila. We have identified all the genes in IndInt required for Eiger-mediated signaling by analogy to the TNF-alpha system, suggesting the presence of a functionally-active Eiger signaling pathway in IndInt. Comparative genomics of the three type-forms with that of IndInt, reveals structurally disruptive mutations in Eiger gene in all three strains of the type-form, suggesting compromised innate immunity in the type-form as the likely cause of high vectorial capacity in these strains. This is the first report of the presence of a homolog of Eiger in malaria vectors, known to be involved in cell death in Drosophila, within an inversion region in IndInt syntenic to an inversion associated with Plasmodium resistance in An. gambiae.

WASH activation controls endosomal recycling and EGFR and Hippo signaling during tumor-suppressive cell competition

Cell competition is a conserved homeostatic mechanism whereby epithelial cells eliminate neighbors with lower fitness. Cell communication at the interface of wild-type "winner" cells and polarity-deficient (scrib^-/-) "losers" is established through Sas-mediated Ptp10D activation in polarity-deficient cells. This tumor-suppressive cell competition restrains EGFR and Hippo signaling and enables Eiger-JNK mediated apoptosis in scrib^-/- clones. Here, we show that the activation state of the endosomal actin regulator WASH is a central node linking EGFR and Hippo signaling activation. The tyrosine kinase Btk29A and its substrate WASH are required downstream of Ptp10D for "loser" cell elimination. Constitutively active, phosphomimetic WASH is sufficient to induce both EGFR and Yki activation leading to overgrowth. On the mechanistic level we show that Ptp10D is recycled by the WASH/retromer complex, while EGFR is recycled by the WASH/retriever complex. Constitutive WASH activation selectively interferes with retromer function leading to Ptp10D mistargeting while promoting EGFR recycling and signaling activation. Phospho-WASH also activates aberrant Arp2/3 actin polymerization, leading to cytoskeletal imbalance, Yki activation and reduced apoptosis. Selective manipulation of WASH phosphorylation on sorting endosomes may restrict epithelial tumorous growth.

Ayurvedic formulations Guduchi and Madhuyashti triggers JNK signaling mediated immune response and adversely affects Huntington phenotype

BACKGROUND

Huntington's disease manifests due to abnormal CAG trinucleotide expansion, in the first exon of the Huntingtin gene and disease progression involves genetic, immune, and environmental components. The pathogenesis is characterized by the formation of Inclusion Bodies, disruption of neuronal circuitry, cellular machinery, and apoptosis, resulting in gradual and progressive loss of neuronal cells, ultimately leading to nervous system dysfunction. Thus, the present study was conducted to assess the effect of two Ayurvedic formulations, Guduchi and Madhuyashti, on Huntington's phenotype, using Drosophila as a model system.

METHOD

The Huntington phenotype was ectopically induced in the Drosophila eye using the UAS-GAL4 binary system and the effect of the two Ayurvedic formulations were assessed by feeding the progenies on them. Degeneration was observed microscopically and Real Time-PCR was done to assay the alterations in the different transcripts of the innate immune pathways and JNK signaling pathway. Immunostaining was performed to assay different gene expression patterns.

RESULT

The present study shows that Guduchi and Madhuyashti, endowed with immunomodulatory and intellect promoting properties, aggravates polyQ mediated neurodegeneration. We provide evidence that these formulations enhance JNK signaling by activating the MAP 3 K, dTAK1, which regulates the expression of Drosophila homologue for JNK. Sustained, rather than a transient expression of JNK leads to excessive production of Anti-Microbial Peptides without involving the canonical transcription factors of the Toll or IMD pathways, NF-κB. Enhanced JNK expression also increases caspase levels, with a concomitant reduction in cell proliferation, which may further contribute to increased degeneration.

CONCLUSION

This is a report linking the functional relevance of Guduchi and Madhuyashti with molecular pathways, which can be important for understanding their use in therapeutic applications and holds promise for mechanistic insight into the mammalian counterpart.

Drosophila as a Model Organism to Study Basic Mechanisms of Longevity

The spatio-temporal regulation of gene expression determines the fate and function of various cells and tissues and, as a consequence, the correct development and functioning of complex organisms. Certain mechanisms of gene activity regulation provide adequate cell responses to changes in environmental factors. Aside from gene expression disorders that lead to various pathologies, alterations of expression of particular genes were shown to significantly decrease or increase the lifespan in a wide range of organisms from yeast to human. Drosophila fruit fly is an ideal model system to explore mechanisms of longevity and aging due to low cost, easy handling and maintenance, large number of progeny per adult, short life cycle and lifespan, relatively low number of paralogous genes, high evolutionary conservation of epigenetic mechanisms and signalling pathways, and availability of a wide range of tools to modulate gene expression in vivo. Here, we focus on the organization of the evolutionarily conserved signaling pathways whose components significantly influence the aging process and on the interconnections of these pathways with gene expression regulation.

Molecular identification and functional analysis of a tumor necrosis factor superfamily gene from Chinese mitten crab (Eriocheir sinensis)

Tumor necrosis factor (TNF) is one of the most important cytokines involved in various biological processes in vertebrates and invertebrates. In the present study, a new member of the TNF superfamily (named EsTNFSF) was identified from the Chinese mitten crab (Eriocheir sinensis). The full-length cDNA of EsTNFSF is 2462 bp and encodes a polypeptide with 499 amino acids. The deduced EsTNFSF protein contained a transmembrane region and a conserved extracellular C-terminal TNF domain. Phylogenetic analysis indicated that EsTNFSF was closely related to other TNFSFs from crustaceans. Quantitative real-time PCR analysis showed that EsTNFSF was expressed in all the tissues examined, and the highest expression was found in the hepatopancreas. The mRNA levels of EsTNFSF in hemocytes underwent a time-dependent and variable degree of enhancement after stimulation with lipopolysaccharide, peptidoglycan, Staphylococcus aureus, and Vibrio parahaemolyticus. Functionally, EsTNFSF knockdown by siRNA suppressed the transcriptional levels of c-Jun N-terminal kinase and two antimicrobial peptides, anti-lipopolysaccharide factor and crustin. Furthermore, purified recombinant EsTNFSF protein accelerated the bacterial clearance in vivo and inhibited the growth of V. parahaemolyticus and S. aureus in vitro. The results revealed that EsTNFSF, as an inducible immune response gene, plays a crucial role in the antibacterial immune defense of E. sinensis.

Drosophila Innate Immunity Involves Multiple Signaling Pathways and Coordinated Communication Between Different Tissues

The innate immune response provides the first line of defense against invading pathogens, and immune disorders cause a variety of diseases. The fruit fly Drosophila melanogaster employs multiple innate immune reactions to resist infection. First, epithelial tissues function as physical barriers to prevent pathogen invasion. In addition, macrophage-like plasmatocytes eliminate intruders through phagocytosis, and lamellocytes encapsulate large particles, such as wasp eggs, that cannot be phagocytosed. Regarding humoral immune responses, the fat body, equivalent to the mammalian liver, secretes antimicrobial peptides into hemolymph, killing bacteria and fungi. Drosophila has been shown to be a powerful in vivo model for studying the mechanism of innate immunity and host-pathogen interactions because Drosophila and higher organisms share conserved signaling pathways and factors. Moreover, the ease with which Drosophila genetic and physiological characteristics can be manipulated prevents interference by adaptive immunity. In this review, we discuss the signaling pathways activated in Drosophila innate immunity, namely, the Toll, Imd, JNK, JAK/STAT pathways, and other factors, as well as relevant regulatory networks. We also review the mechanisms by which different tissues, including hemocytes, the fat body, the lymph gland, muscles, the gut and the brain coordinate innate immune responses. Furthermore, the latest studies in this field are outlined in this review. In summary, understanding the mechanism underlying innate immunity orchestration in Drosophila will help us better study human innate immunity-related diseases.

Integrins Cooperate With the EGFR/Ras Pathway to Preserve Epithelia Survival and Architecture in Development and Oncogenesis

Adhesion to the extracellular matrix (ECM) is required for normal epithelial cell survival. Disruption of this interaction leads to a specific type of apoptosis known as anoikis. Yet, there are physiological and pathological situations in which cells not connected to the ECM are protected from anoikis, such as during cell migration or metastasis. The main receptors transmitting signals from the ECM are members of the integrin family. However, although integrin-mediated cell-ECM anchorage has been long recognized as crucial for epithelial cell survival, the in vivo significance of this interaction remains to be weighed. In this work, we have used the Drosophila wing imaginal disc epithelium to analyze the importance of integrins as survival factors during epithelia morphogenesis. We show that reducing integrin expression in the wing disc induces caspase-dependent cell death and basal extrusion of the dead cells. In this case, anoikis is mediated by the activation of the JNK pathway, which in turn triggers expression of the proapoptotic protein Hid. In addition, our results strongly suggest that, during wing disc morphogenesis, the EGFR pathway protects cells undergoing cell shape changes upon ECM detachment from anoikis. Furthermore, we show that oncogenic activation of the EGFR/Ras pathway in integrin mutant cells rescues them from apoptosis while promoting their extrusion from the epithelium. Altogether, our results support the idea that integrins promote cell survival during normal tissue morphogenesis and prevent the extrusion of transformed cells.

Interorgan communication through peripherally derived peptide hormones in Drosophila

In multicellular organisms, endocrine factors such as hormones and cytokines regulate development and homoeostasis through communication between different organs. For understanding such interorgan communications through endocrine factors, the fruit fly Drosophila melanogaster serves as an excellent model system due to conservation of essential endocrine systems between flies and mammals and availability of powerful genetic tools. In Drosophila and other insects, functions of neuropeptides or peptide hormones from the central nervous system have been extensively studied. However, a series of recent studies conducted in Drosophila revealed that peptide hormones derived from peripheral tissues also play critical roles in regulating multiple biological processes, including growth, metabolism, reproduction, and behaviour. Here, we summarise recent advances in understanding target organs/tissues and functions of peripherally derived peptide hormones in Drosophila and describe how these hormones contribute to various biological events through interorgan communications.

Non-apoptotic activation of Drosophila caspase-2/9 modulates JNK signaling, the tumor microenvironment, and growth of wound-like tumors

Resistance to apoptosis due to caspase deregulation is considered one of the main hallmarks of cancer. However, the discovery of novel non-apoptotic caspase functions has revealed unknown intricacies about the interplay between these enzymes and tumor progression. To investigate this biological problem, we capitalized on a Drosophila tumor model with human relevance based on the simultaneous overactivation of the EGFR and the JAK/STAT signaling pathways. Our data indicate that widespread non-apoptotic activation of initiator caspases limits JNK signaling and facilitates cell fate commitment in these tumors, thus preventing the overgrowth and exacerbation of malignant features of transformed cells. Intriguingly, caspase activity also reduces the presence of macrophage-like cells with tumor-promoting properties in the tumor microenvironment. These findings assign tumor-suppressing activities to caspases independent of apoptosis, while providing molecular details to better understand the contribution of these enzymes to tumor progression.

Epithelial monitoring through ligand-receptor segregation ensures malignant cell elimination

Animals have evolved mechanisms, such as cell competition, to remove dangerous or nonfunctional cells from a tissue. Tumor necrosis factor signaling can eliminate clonal malignancies from Drosophila imaginal epithelia, but why this pathway is activated in tumor cells but not normal tissue is unknown. We show that the ligand that drives elimination is present in basolateral circulation but remains latent because it is spatially segregated from its apically localized receptor. Polarity defects associated with malignant transformation cause receptor mislocalization, allowing ligand binding and subsequent apoptotic signaling. This process occurs irrespective of the neighboring cells' genotype and is thus distinct from cell competition. Related phenomena at epithelial wound sites are required for efficient repair. This mechanism of polarized compartmentalization of ligand and receptor can generally monitor epithelial integrity to promote tissue homeostasis.

Phagocytosis Is the Sole Arm of Drosophila melanogaster Known Host Defenses That Provides Some Protection Against Microsporidia Infection

Microsporidia are obligate intracellular parasites able to infest specifically a large range of species, including insects. The knowledge about the biology of microsporidial infections remains confined to mostly descriptive studies, including molecular approaches such as transcriptomics or proteomics. Thus, functional data to understand insect host defenses are currently lacking. Here, we have undertaken a genetic analysis of known host defenses of the Drosophila melanogaster using an infection model whereby Tubulinosema ratisbonensis spores are directly injected in this insect. We find that phagocytosis does confer some protection in this infection model. In contrast, the systemic immune response, extracellular reactive oxygen species, thioester proteins, xenophagy, and intracellular antiviral response pathways do not appear to be involved in the resistance against this parasite. Unexpectedly, several genes such as PGRP-LE seem to promote this infection. The prophenol oxidases that mediate melanization have different functions; PPO1 presents a phenotype similar to that of PGRP-LE whereas that of PPO2 suggests a function in the resilience to infection. Similarly, eiger and Unpaired3, which encode two cytokines secreted by hemocytes display a resilience phenotype with a strong susceptibility to T. ratisbonensis.

A role for Flower and cell death in controlling morphogen gradient scaling

During development, morphogen gradients encode positional information to pattern morphological structures during organogenesis¹. Some gradients, like that of Dpp in the fly wing, remain proportional to the size of growing organs-that is, they scale. Gradient scaling keeps morphological patterns proportioned in organs of different sizes^2,3. Here we show a mechanism of scaling that ensures that, when the gradient is smaller than the organ, cell death trims the developing tissue to match the size of the gradient. Scaling is controlled by molecular associations between Dally and Pentagone, known factors involved in scaling, and a key factor that mediates cell death, Flower^4-6. We show that Flower activity in gradient expansion is not dominated by cell death, but by the activity of Dally/Pentagone on scaling. Here we show a potential connection between scaling and cell death that may uncover a molecular toolbox hijacked by tumours.

Cancer cachexia: lessons from Drosophila

Cachexia, a wasting syndrome that is often associated with cancer, is one of the primary causes of death in cancer patients. Cancer cachexia occurs largely due to systemic metabolic alterations stimulated by tumors. Despite the prevalence of cachexia, our understanding of how tumors interact with host tissues and how they affect metabolism is limited. Among the challenges of studying tumor-host tissue crosstalk are the complexity of cancer itself and our insufficient knowledge of the factors that tumors release into the blood. Drosophila is emerging as a powerful model in which to identify tumor-derived factors that influence systemic metabolism and tissue wasting. Strikingly, studies that are characterizing factors derived from different fly tumor cachexia models are identifying both common and distinct cachectic molecules, suggesting that cachexia is more than one disease and that fly models can help identify these differences. Here, we review what has been learned from studies of tumor-induced organ wasting in Drosophila and discuss the open questions.

Variation of TNF modulates cellular immunity of gregarious and solitary locusts against fungal pathogen Metarhizium anisopliae

Ecological immunology addresses the interactions between host immunity and the environment. Locusts display density-dependent phase transitions between solitary and gregarious locusts. In control practices and laboratory bioassays, gregarious locusts always exhibit stronger resistance to fungal pathogens than solitary locusts. However, few studies have investigated the mechanism of altered immune switch in locusts. Here, we combined mathematical simulation and experimental studies to show that gregarious locusts inhibit tumor necrosis factor (TNF) to alter immune defense by enhancing humoral defense and reducing cellular defense, and high levels of TNF reduce the survival of solitary locusts. Our study provides an important cue for understanding cellular immunity variations in response to different population densities and for improving the control efficacy of locust plagues.

Changes in population density lead to phenotypic differentiation of solitary and gregarious locusts, which display different resistance to fungal pathogens; however, how to regulate their cellular immune strategies remains unknown. Here, our stochastic simulation of pathogen proliferation suggested that humoral defense always enhanced resistance to fungal pathogens, while phagocytosis sometimes reduced defense against pathogens. Further experimental data proved that gregarious locusts had significantly decreased phagocytosis of hemocytes compared to solitary locusts. Additionally, transcriptional analysis showed that gregarious locusts promoted immune effector expression (gnbp1 and dfp) and reduced phagocytic gene expression (eater) and the cytokine tumor necrosis factor (TNF). Interestingly, higher expression of the cytokine TNF in solitary locusts simultaneously promoted eater expression and inhibited gnbp1 and dfp expression. Moreover, inhibition of TNF increased the survival of solitary locusts, and injection of TNF decreased the survival of gregarious locusts after fungal infection. Therefore, our results indicate that the alerted expression of TNF regulated the immune strategy of locusts to adapt to environmental changes.

Drosophila Trachea as a Novel Model of COPD

COPD, a chronic obstructive pulmonary disease, is one of the leading causes of death worldwide. Clinical studies and research in rodent models demonstrated that failure of repair mechanisms to cope with increased ROS and inflammation in the lung leads to COPD. Despite this progress, the molecular mechanisms underlying the development of COPD remain poorly understood, resulting in a lack of effective treatments. Thus, an informative, simple model is highly valued and desired. Recently, the cigarette smoke-induced Drosophila COPD model showed a complex set of pathological phenotypes that resemble those seen in human COPD patients. The Drosophila trachea has been used as a premier model to reveal the mechanisms of tube morphogenesis. The association of these mechanisms to structural changes in COPD can be analyzed by using Drosophila trachea. Additionally, the timeline of structural damage, ROS, and inflammation can be studied in live organisms using fluorescently-tagged proteins. The related function of human COPD genes identified by GWAS can be screened using respective fly homologs. Finally, the Drosophila trachea can be used as a high-throughput drug screening platform to identify novel treatments for COPD. Therefore, Drosophila trachea is an excellent model that is complementary to rodent COPD models.

A Blueprint for Cancer-Related Inflammation and Host Innate Immunity

Both in situ and allograft models of cancer in juvenile and adult Drosophila melanogaster fruit flies offer a powerful means for unravelling cancer gene networks and cancer-host interactions. They can also be used as tools for cost-effective drug discovery and repurposing. Moreover, in situ modeling of emerging tumors makes it possible to address cancer initiating events-a black box in cancer research, tackle the innate antitumor immune responses to incipient preneoplastic cells and recurrent growing tumors, and decipher the initiation and evolution of inflammation. These studies in Drosophila melanogaster can serve as a blueprint for studies in more complex organisms and help in the design of mechanism-based therapies for the individualized treatment of cancer diseases in humans. This review focuses on new discoveries in Drosophila related to the diverse innate immune responses to cancer-related inflammation and the systemic effects that are so detrimental to the host.

JNK and Yorkie drive tumor malignancy by inducing L-amino acid transporter 1 in Drosophila

Identifying a common oncogenesis pathway among tumors with different oncogenic mutations is critical for developing anti-cancer strategies. Here, we performed transcriptome analyses on two different models of Drosophila malignant tumors caused by Ras activation with cell polarity defects (RasV12/scrib-/-) or by microRNA bantam overexpression with endocytic defects (bantam/rab5-/-), followed by an RNAi screen for genes commonly essential for tumor growth and malignancy. We identified that Juvenile hormone Inducible-21 (JhI-21), a Drosophila homolog of the L-amino acid transporter 1 (LAT1), is upregulated in these malignant tumors with different oncogenic mutations and knocking down of JhI-21 strongly blocked their growth and invasion. JhI-21 expression was induced by simultaneous activation of c-Jun N-terminal kinase (JNK) and Yorkie (Yki) in these tumors and thereby contributed to tumor growth and progression by activating the mTOR-S6 pathway. Pharmacological inhibition of LAT1 activity in Drosophila larvae significantly suppressed growth of RasV12/scrib-/- tumors. Intriguingly, LAT1 inhibitory drugs did not suppress growth of bantam/rab5-/- tumors and overexpression of bantam rendered RasV12/scrib-/- tumors unresponsive to LAT1 inhibitors. Further analyses with RNA sequencing of bantam-expressing clones followed by an RNAi screen suggested that bantam induces drug resistance against LAT1 inhibitors via downregulation of the TMEM135-like gene CG31157. Our observations unveil an evolutionarily conserved role of LAT1 induction in driving Drosophila tumor malignancy and provide a powerful genetic model for studying cancer progression and drug resistance.

The Duality of Caspases in Cancer, as Told through the Fly

Caspases, a family of cysteine-aspartic proteases, have an established role as critical components in the activation and initiation of apoptosis. Alongside this a variety of non-apoptotic caspase functions in proliferation, differentiation, cellular plasticity and cell migration have been reported. The activity level and context are important factors in determining caspase function. As a consequence of their critical role in apoptosis and beyond, caspases are uniquely situated to have pathological roles, including in cancer. Altered caspase function is a common trait in a variety of cancers, with apoptotic evasion defined as a "hallmark of cancer". However, the role that caspases play in cancer is much more complex, acting both to prevent and to promote tumourigenesis. This review focuses on the major findings in Drosophila on the dual role of caspases in tumourigenesis. This has major implications for cancer treatments, including chemotherapy and radiotherapy, with the activation of apoptosis being the end goal. However, such treatments may inadvertently have adverse effects on promoting tumour progression and acerbating the cancer. A comprehensive understanding of the dual role of caspases will aid in the development of successful cancer therapeutic approaches.