Characterisation of Upd2, a Drosophila JAK/STAT pathway ligand

Wnt signaling couples G2 phase control with differentiation during hematopoiesis in Drosophila

During homeostasis, a critical balance is maintained between myeloid-like progenitors and their differentiated progeny, which function to mitigate stress and innate immune challenges. The molecular mechanisms that help achieve this balance are not fully understood. Using genetic dissection in Drosophila, we show that a Wnt6/EGFR-signaling network simultaneously controls progenitor growth, proliferation, and differentiation. Unlike G1-quiescence of stem cells, hematopoietic progenitors are blocked in G2 phase by a β-catenin-independent (Wnt/STOP) Wnt6 pathway that restricts Cdc25 nuclear entry and promotes cell growth. Canonical β-catenin-dependent Wnt6 signaling is spatially confined to mature progenitors through localized activation of the tyrosine kinases EGFR and Abelson kinase (Abl), which promote nuclear entry of β-catenin and facilitate exit from G2. This strategy combines transcription-dependent and -independent forms of both Wnt6 and EGFR pathways to create a direct link between cell-cycle control and differentiation. This unique combinatorial strategy employing conserved components may underlie homeostatic balance and stress response in mammalian hematopoiesis.

Transcriptome study reveals tick immune genes restrict Babesia microti infection

A systems biology approach was employed to gain insight into tick biology and interactions between vectors and pathogens. Haemaphysalis longicornis serves as one of the primary vectors of Babesia microti, significantly impacting human and animal health. Obtaining more information about their relationship is crucial for a comprehensive understanding of tick and pathogen biology, pathogen transmission dynamics, and potential control strategies. RNA sequencing of uninfected and B. microti-infected ticks resulted in the identification of 15 056 unigenes. Among these, 1 051 were found to be differentially expressed, with 796 being upregulated and 255 downregulated (P < 0.05). Integrated transcriptomics datasets revealed the pivotal role of immune-related pathways, including the Toll, Janus kinase/signal transducer and activator of transcription (JAK-STAT), immunodeficiency, and RNA interference (RNAi) pathways, in response to infection. Consequently, 3 genes encoding critical transcriptional factor Dorsal, Relish, and STAT were selected for RNAi experiments. The knockdown of Dorsal, Relish, and STAT resulted in a substantial increase in Babesia infection levels compared to the respective controls. These findings significantly advanced our understanding of tick-Babesia molecular interactions and proposed novel tick antigens as potential vaccine targets against tick infestations and pathogen transmission.

Leptin- and cytokine-like unpaired signaling in Drosophila

Animals have evolved a multitude of signaling pathways that enable them to orchestrate diverse physiological processes to tightly regulate systemic homeostasis. This signaling is mediated by various families of peptide hormones and cytokines that are conserved across the animal kingdom. In this review, we primarily focus on the unpaired (Upd) family of proteins in Drosophila which are evolutionarily related to mammalian leptin and the cytokine interleukin 6. We summarize expression patterns of Upd in Drosophila and discuss the parallels in structure, signaling pathway, and functions between Upd and their mammalian counterparts. In particular, we focus on the roles of Upd in governing metabolic homeostasis, growth and development, and immune responses. We aim to stimulate future studies on leptin-like signaling in other phyla which can help bridge the evolutionary gap between insect Upd and vertebrate leptin and cytokines like interleukin 6.

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.

Interlocking of co-opted developmental gene networks in Drosophila and the evolution of pre-adaptive novelty

The re-use of genes in new organs forms the base of many evolutionary novelties. A well-characterised case is the recruitment of the posterior spiracle gene network to the Drosophila male genitalia. Here we find that this network has also been co-opted to the testis mesoderm where is required for sperm liberation, providing an example of sequentially repeated developmental co-options. Associated to this co-option event, an evolutionary expression novelty appeared, the activation of the posterior segment determinant Engrailed to the anterior A8 segment controlled by common testis and spiracle regulatory elements. Enhancer deletion shows that A8 anterior Engrailed activation is not required for spiracle development but only necessary in the testis. Our study presents an example of pre-adaptive developmental novelty: the activation of the Engrailed transcription factor in the anterior compartment of the A8 segment where, despite having no specific function, opens the possibility of this developmental factor acquiring one. We propose that recently co-opted networks become interlocked, so that any change to the network because of its function in one organ, will be mirrored by other organs even if it provides no selective advantage to them.

Exposure to high-sugar diet induces transgenerational changes in sweet sensitivity and feeding behavior via H3K27me3 reprogramming

Human health is facing a host of new threats linked to unbalanced diets, including high-sugar diet (HSD), which contributes to the development of both metabolic and behavioral disorders. Studies have shown that diet-induced metabolic dysfunctions can be transmitted to multiple generations of offspring and exert long-lasting health burden. Meanwhile, whether and how diet-induced behavioral abnormalities can be transmitted to the offspring remains largely unclear. Here, we showed that ancestral HSD exposure suppressed sweet sensitivity and feeding behavior in the offspring in Drosophila. These behavioral deficits were transmitted through the maternal germline and companied by the enhancement of H3K27me3 modifications. PCL-PRC2 complex, a major driver of H3K27 trimethylation, was upregulated by ancestral HSD exposure, and disrupting its activity eliminated the transgenerational inheritance of sweet sensitivity and feeding behavior deficits. Elevated H3K27me3 inhibited the expression of a transcriptional factor Cad and suppressed sweet sensitivity of the sweet-sensing gustatory neurons, reshaping the sweet perception and feeding behavior of the offspring. Taken together, we uncovered a novel molecular mechanism underlying behavioral abnormalities spanning multiple generations of offspring upon ancestral HSD exposure, which would contribute to the further understanding of long-term health risk of unbalanced diet.

Anti-Tumor Effect of Turandot Proteins Induced via the JAK/STAT Pathway in the mxc Hematopoietic Tumor Mutant in Drosophila

Several antimicrobial peptides suppress the growth of lymph gland (LG) tumors in Drosophila multi sex comb (mxc) mutant larvae. The activity of another family of polypeptides, called Turandots, is also induced via the JAK/STAT pathway after bacterial infection; however, their influence on Drosophila tumors remains unclear. The JAK/STAT pathway was activated in LG tumors, fat body, and circulating hemocytes of mutant larvae. The mRNA levels of Turandot (Tot) genes increased markedly in the mutant fat body and declined upon silencing Stat92E in the fat body, indicating the involvement of the JAK/STAT pathway. Furthermore, significantly enhanced tumor growth upon a fat-body-specific silencing of the mRNAs demonstrated the antitumor effects of these proteins. The proteins were found to be incorporated into small vesicles in mutant circulating hemocytes (as previously reported for several antimicrobial peptides) but not normal cells. In addition, more hemocytes containing these proteins were found to be associated with tumors. The mutant LGs contained activated effector caspases, and a fat-body-specific silencing of Tots inhibited apoptosis and increased the number of mitotic cells in the LG, thereby suggesting that the proteins inhibited tumor cell proliferation. Thus, Tot proteins possibly exhibit antitumor effects via the induction of apoptosis and inhibition of cell proliferation.

Kinetics of blood cell differentiation during hematopoiesis revealed by quantitative long-term live imaging

Stem cells typically reside in a specialized physical and biochemical environment that facilitates regulation of their behavior. For this reason, stem cells are ideally studied in contexts that maintain this precisely constructed microenvironment while still allowing for live imaging. Here, we describe a long-term organ culture and imaging strategy for hematopoiesis in flies that takes advantage of powerful genetic and transgenic tools available in this system. We find that fly blood progenitors undergo symmetric cell divisions and that their division is both linked to cell size and is spatially oriented. Using quantitative imaging to simultaneously track markers for stemness and differentiation in progenitors, we identify two types of differentiation that exhibit distinct kinetics. Moreover, we find that infection-induced activation of hematopoiesis occurs through modulation of the kinetics of cell differentiation. Overall, our results show that even subtle shifts in proliferation and differentiation kinetics can have large and aggregate effects to transform blood progenitors from a quiescent to an activated state.

The Drosophila AWP1 ortholog Doctor No regulates JAK/STAT signaling for left-right asymmetry in the gut by promoting receptor endocytosis

Many organs of Drosophila show stereotypical left-right (LR) asymmetry; however, the underlying mechanisms remain elusive. Here, we have identified an evolutionarily conserved ubiquitin-binding protein, AWP1/Doctor No (Drn), as a factor required for LR asymmetry in the embryonic anterior gut. We found that drn is essential in the circular visceral muscle cells of the midgut for JAK/STAT signaling, which contributes to the first known cue for anterior gut lateralization via LR asymmetric nuclear rearrangement. Embryos homozygous for drn and lacking its maternal contribution showed phenotypes similar to those with depleted JAK/STAT signaling, suggesting that Drn is a general component of JAK/STAT signaling. Absence of Drn resulted in specific accumulation of Domeless (Dome), the receptor for ligands in the JAK/STAT signaling pathway, in intracellular compartments, including ubiquitylated cargos. Dome colocalized with Drn in wild-type Drosophila. These results suggest that Drn is required for the endocytic trafficking of Dome, which is a crucial step for activation of JAK/STAT signaling and the subsequent degradation of Dome. The roles of AWP1/Drn in activating JAK/STAT signaling and in LR asymmetric development may be conserved in various organisms.

dSmad2 differentially regulates dILP2 and dILP5 in insulin producing and circadian pacemaker cells in unmated adult females

Much is known about environmental influences on metabolism and systemic insulin levels. Less is known about how those influences are translated into molecular mechanisms regulating insulin production. To better understand the molecular mechanisms we generated marked cells homozygous for a null mutation in the Drosophila TGF-β signal transducer dSmad2 in unmated adult females. We then conducted side-by-side single cell comparisons of the pixel intensity of two Drosophila insulin-like peptides (dILP2 and dILP5) in dSmad2- mutant and wild type insulin producing cells (IPCs). The analysis revealed multiple features of dSmad2 regulation of dILPs. In addition, we discovered that dILP5 is expressed and regulated by dSmad2 in circadian pacemaker cells (CPCs). Outcomes of regulation by dSmad2 differ between dILP2 and dILP5 within IPCs and differ for dILP5 between IPCs and CPCs. Modes of dSmad2 regulation differ between dILP2 and dILP5. dSmad2 antagonism of dILP2 in IPCs is robust but dSmad2 regulation of dILP5 in IPCs and CPCs toggles between antagonism and agonism depending upon dSmad2 dosage. Companion studies of dILP2 and dILP5 in the IPCs of dCORL mutant (fussel in Flybase and SKOR in mammals) and upd2 mutant unmated adult females showed no significant difference from wild type. Taken together, the data suggest that dSmad2 regulates dILP2 and dILP5 via distinct mechanisms in IPCs (antagonist) and CPCs (agonist) and in unmated adult females that dSmad2 acts independently of dCORL and upd2.

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.

A conserved function of Human DLC3 and Drosophila Cv-c in testis development

The identification of genes affecting gonad development is essential to understand the mechanisms causing Variations/Differences in Sex Development (DSD). Recently, a DLC3 mutation was associated with male gonadal dysgenesis in 46,XY DSD patients. We have studied the requirement of Cv-c, the Drosophila ortholog of DLC3, in Drosophila gonad development, as well as the functional capacity of DLC3 human variants to rescue cv-c gonad defects. We show that Cv-c is required to maintain testis integrity during fly development. We find that Cv-c and human DLC3 can perform the same function in fly embryos, as flies carrying wild type but not patient DLC3 variations can rescue gonadal dysgenesis, suggesting functional conservation. We also demonstrate that the StART domain mediates Cv-c's function in the male gonad independently from the GAP domain's activity. This work demonstrates a role for DLC3/Cv-c in male gonadogenesis and highlights a novel StART domain mediated function required to organize the gonadal mesoderm and maintain its interaction with the germ cells during testis development.

Intrinsic and damage-induced JAK/STAT signaling regulate developmental timing by the Drosophila prothoracic gland

Development involves tightly paced, reproducible sequences of events, yet it must adjust to conditions external to it, such as resource availability and organismal damage. A major mediator of damage-induced immune responses in vertebrates and insects is JAK/STAT signaling. At the same time, JAK/STAT activation by the Drosophila Upd cytokines is pleiotropically involved in normal development of multiple organs. Whether inflammatory and developmental JAK/STAT roles intersect is unknown. Here, we show that JAK/STAT is active during development of the prothoracic gland (PG), which controls metamorphosis onset through ecdysone production. Reducing JAK/STAT signaling decreased PG size and advanced metamorphosis. Conversely, JAK/STAT hyperactivation by overexpression of pathway components or SUMOylation loss caused PG hypertrophy and metamorphosis delay. Tissue damage and tumors, known to secrete Upd cytokines, also activated JAK/STAT in the PG and delayed metamorphosis, at least in part by inducing expression of the JAK/STAT target Apontic. JAK/STAT damage signaling, therefore, regulates metamorphosis onset by co-opting its developmental role in the PG. Our findings in Drosophila provide insights on how systemic effects of damage and cancer can interfere with hormonally controlled development and developmental transitions.

Summary: Damage signaling from tumors mediated by JAK/STAT-activating Upd cytokines delays the Drosophila larva–pupa transition through co-option of a JAK/STAT developmental role in the prothoracic gland.

Body-fat sensor triggers ribosome maturation in the steroidogenic gland to initiate sexual maturation in Drosophila

Fat stores are critical for reproductive success and may govern maturation initiation. Here, we report that signaling and sensing fat sufficiency for sexual maturation commitment requires the lipid carrier apolipophorin in fat cells and Sema1a in the neuroendocrine prothoracic gland (PG). Larvae lacking apolpp or Sema1a fail to initiate maturation despite accruing sufficient fat stores, and they continue gaining weight until death. Mechanistically, sensing peripheral body-fat levels via the apolipophorin/Sema1a axis regulates endocytosis, endoplasmic reticulum remodeling, and ribosomal maturation for the acquisition of the PG cells' high biosynthetic and secretory capacity. Downstream of apolipophorin/Sema1a, leptin-like upd2 triggers the cessation of feeding and initiates sexual maturation. Human Leptin in the insect PG substitutes for upd2, preventing obesity and triggering maturation downstream of Sema1a. These data show how peripheral fat levels regulate the control of the maturation decision-making process via remodeling of endomembranes and ribosomal biogenesis in gland cells.

Thermal stress induces tissue damage and a broad shift in regenerative signaling pathways in the honey bee digestive tract

Honey bee colonies in the USA have suffered from increased die-off in the last few years with a complex set of interacting stresses playing a key role. With changing climate, an increase in the frequency of severe weather events, such as heat waves, is anticipated. Understanding how these changes may contribute to stress in honey bees is crucial. Individual honey bees appear to have a high capacity to endure thermal stress. One reason for this high-level endurance is likely their robust heat shock response (HSR), which contributes to thermotolerance at the cellular level. However, less is known about other mechanisms of thermotolerance, especially those operating at the tissue level. To elucidate other determinants of resilience in this species, we used thermal stress coupled with RNAseq and identified broad transcriptional remodeling of a number of key signaling pathways in the honey bee, including those pathways known to be involved in digestive tract regeneration in the fruit fly such as the Hippo and JAK/STAT pathways. We also observed cell death and shedding of epithelial cells, which likely leads to induction of this regenerative transcriptional program. We found that thermal stress affects many of these pathways in other tissues, suggesting a shared program of damage response. This study provides important foundational characterization of the tissue damage response program in this key pollinating species. In addition, our data suggest that a robust regeneration program may also be a critical contributor to thermotolerance at the tissue level, a possibility which warrants further exploration in this and other species.

Unravelling the broader complexity of IL-6 involvement in health and disease

The classification of interleukin-6 (IL-6) as a pro-inflammatory cytokine undervalues the biological impact of this cytokine in health and disease. With broad activities affecting the immune system, tissue homeostasis and metabolic processes, IL-6 displays complex biology. The significance of these involvements has become increasingly important in clinical settings where IL-6 is identified as a prominent target for therapy. Here, clinical experience with IL-6 antagonists emphasises the need to understand the context-dependent properties of IL-6 within an inflammatory environment and the anticipated or unexpected consequences of IL-6 blockade. In this review, we will describe the immunobiology of IL-6 and explore the gamut of IL-6 bioactivity affecting the clinical response to biological drugs targeting this cytokine pathway.

Genetic determinants of antiviral immunity in dipteran insects - Compiling the experimental evidence

The genetic basis of antiviral immunity in dipteran insects is extensively studied in Drosophila melanogaster and advanced technologies for genetic manipulation allow a better characterization of immune responses also in non-model insect species. Especially, immunity in vector mosquitoes is recently in the spotlight, due to the medical impact that these insects have by transmitting viruses and other pathogens. Here, we review the current state of experimental evidence that supports antiviral functions for immune genes acting in different cellular pathways. We discuss the well-characterized RNA interference mechanism along with the less well-defined JAK-STAT, Toll, and IMD signaling pathways. Furthermore, we highlight the initial evidence for antiviral activity observed for the autophagy pathway, transcriptional pausing, as well as piRNA production from endogenous viral elements. We focus our review on studies from Drosophila and mosquito species from the lineages Aedes, Culex, and Anopheles, which contain major vector species responsible for virus transmission.

The Impact of Age on Response to Infection in Drosophila

This review outlines the known cellular pathways and mechanisms involved in Drosophila age-dependent immunity to pathogenic microorganisms such as bacteria and fungi. We discuss the implication of host signaling pathways such as the Toll, Immune Deficiency (IMD), Janus kinase signal transducer and activator of transcription (JAK/STAT), and Insulin/Insulin Growth Factor/Target of Rapamycin (IIS/TOR) on immune function with aging. Additionally, we review the effects that factors such as sexual dimorphism, environmental stress, and cellular physiology exert on age-dependent immunity in Drosophila. We discuss potential tradeoffs between heightened immune function and longevity in the absence of infection, and we provide detailed tables outlining the various assays and pathogens used in the cited studies, as well as the age, sex, and strains of Drosophila used. We also discuss the overlapping effects these pathways and mechanisms have on one another. We highlight the great utility of Drosophila as a model organism and the importance of a greater focus on age-dependent antiviral immunity for future studies.

Regulators and signalling in insect antimicrobial innate immunity: Functional molecules and cellular pathways

Insects possess an immune system that protects them from attacks by various pathogenic microorganisms that would otherwise threaten their survival. Immune mechanisms may deal directly with the pathogens by eliminating them from the host organism or disarm them by suppressing the synthesis of toxins and virulence factors that promote the invasion and destructive action of the intruder within the host. Insects have been established as outstanding models for studying immune system regulation because innate immunity can be explored as an integrated system at the level of the whole organism. Innate immunity in insects consists of basal immunity that controls the constitutive synthesis of effector molecules such as antimicrobial peptides, and inducible immunity that is activated after detection of a microbe or its product(s). Activation and coordination of innate immune defenses in insects involve evolutionary conserved immune factors. Previous research in insects has led to the identification and characterization of distinct immune signalling pathways that modulate the response to microbial infections. This work has not only advanced the field of insect immunology, but it has also rekindled interest in the innate immune system of mammals. Here we review the current knowledge on key molecular components of insect immunity and discuss the opportunities they present for confronting infectious diseases in humans.

Sensing and signalling viral infection in drosophila

The fruitfly Drosophila melanogaster is a valuable model to unravel mechanisms of innate immunity, in particular in the context of viral infections. RNA interference, and more specifically the small interfering RNA pathway, is a major component of antiviral immunity in drosophila. In addition, the contribution of inducible transcriptional responses to the control of viruses in drosophila and other invertebrates is increasingly recognized. In particular, the recent discovery of a STING-IKKβ-Relish signalling cassette in drosophila has confirmed that NF-κB transcription factors play an important role in the control of viral infections, in addition to bacterial and fungal infections. Here, we review recent developments in the field, which begin to shed light on the mechanisms involved in sensing of viral infections and in signalling leading to production of antiviral effectors.

Differential activation of JAK-STAT signaling reveals functional compartmentalization in Drosophila blood progenitors

Blood cells arise from diverse pools of stem and progenitor cells. Understanding progenitor heterogeneity is a major challenge. The Drosophila larval lymph gland is a well-studied model to understand blood progenitor maintenance and recapitulates several aspects of vertebrate hematopoiesis. However in-depth analysis has focused on the anterior lobe progenitors (AP), ignoring the posterior progenitors (PP) from the posterior lobes. Using in situ expression mapping and developmental and transcriptome analysis, we reveal PP heterogeneity and identify molecular-genetic tools to study this abundant progenitor population. Functional analysis shows that PP resist differentiation upon immune challenge, in a JAK-STAT-dependent manner. Upon wasp parasitism, AP downregulate JAK-STAT signaling and form lamellocytes. In contrast, we show that PP activate STAT92E and remain undifferentiated, promoting survival. Stat92E knockdown or genetically reducing JAK-STAT signaling permits PP lamellocyte differentiation. We discuss how heterogeneity and compartmentalization allow functional segregation in response to systemic cues and could be widely applicable.

Insulin and Leptin/Upd2 Exert Opposing Influences on Synapse Number in Fat-Sensing Neurons

Energy-sensing neural circuits decide to expend or conserve resources based, in part, on the tonic, steady-state, energy-store information they receive. Tonic signals, in the form of adipose tissue-derived adipokines, set the baseline level of activity in the energy-sensing neurons, thereby providing context for interpretation of additional inputs. However, the mechanism by which tonic adipokine information establishes steady-state neuronal function has heretofore been unclear. We show here that under conditions of nutrient surplus, Upd2, a Drosophila leptin ortholog, regulates actin-based synapse reorganization to reduce bouton number in an inhibitory circuit, thus establishing a neural tone that is permissive for insulin release. Unexpectedly, we found that insulin feeds back on these same inhibitory neurons to conversely increase bouton number, resulting in maintenance of negative tone. Our results point to a mechanism by which two surplus-sensing hormonal systems, Upd2/leptin and insulin, converge on a neuronal circuit with opposing outcomes to establish energy-store-dependent neuron activity.

The Microbiota and Gut-Related Disorders: Insights from Animal Models

Over the past decade, the scientific committee has called for broadening our horizons in understanding host–microbe interactions and infectious disease progression. Owing to the fact that the human gut harbors trillions of microbes that exhibit various roles including the production of vitamins, absorption of nutrients, pathogen displacement, and development of the host immune system, particular attention has been given to the use of germ-free (GF) animal models in unraveling the effect of the gut microbiota on the physiology and pathophysiology of the host. In this review, we discuss common methods used to generate GF fruit fly, zebrafish, and mice model systems and highlight the use of these GF model organisms in addressing the role of gut-microbiota in gut-related disorders (metabolic diseases, inflammatory bowel disease, and cancer), and in activating host defense mechanisms and amending pathogenic virulence.

A cytokine receptor domeless promotes white spot syndrome virus infection via JAK/STAT signaling pathway in red claw crayfish Cherax quadricarinatus

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway is pivotal in immune responses for a variety of pathogens in both vertebrates and invertebrates. Domeless (Dome), as a unique cytokine receptor, involves in the upstream JAK/STAT pathway in invertebrates. In this study, the full-length cDNA sequence of a cytokine receptor Dome was identified from red claw crayfish Cherax quadricarinatus (named as CqDome), which contained an open reading frame of 4251 bp, encoding 1416 amino acids. The CqDome contained extracellular conservative domains of a signal peptide, two cytokine binding modules (CBM), three fibronectin-type-III-like (FN3) domains and a transmembrane region. Tissue distribution analysis showed that CqDome generally expressed in all the tissues selected with a high expression in hemocyte. The gene expression of both the viral immediately early gene (IE1) and a late gene envelope protein VP28 of white spot syndrome virus (WSSV) were significantly decreased after gene silencing of CqDome in crayfish haematopoietic tissue (Hpt) cells, indicating a key role of CqDome in promoting WSSV infection. Furthermore, the phosphorylation level of CqSTAT was significantly inhibited by gene silencing of CqDome in Hpt cells, indicating that CqDome participated in signal transduction of JAK/STAT pathway in red claw crayfish. These data together suggest that CqDome is likely to promote WSSV infection via JAK/STAT pathway, which sheds new light on further elucidation of the pathogenesis of WSSV.

Single-cell transcriptome maps of myeloid blood cell lineages in Drosophila

The Drosophila lymph gland, the larval hematopoietic organ comprised of prohemocytes and mature hemocytes, has been a valuable model for understanding mechanisms underlying hematopoiesis and immunity. Three types of mature hemocytes have been characterized in the lymph gland: plasmatocytes, lamellocytes, and crystal cells, which are analogous to vertebrate myeloid cells, yet molecular underpinnings of the lymph gland hemocytes have been less investigated. Here, we use single-cell RNA sequencing to comprehensively analyze heterogeneity of developing hemocytes in the lymph gland, and discover previously undescribed hemocyte types including adipohemocytes, stem-like prohemocytes, and intermediate prohemocytes. Additionally, we identify the developmental trajectory of hemocytes during normal development as well as the emergence of the lamellocyte lineage following active cellular immunity caused by wasp infestation. Finally, we establish similarities and differences between embryonically derived- and larval lymph gland hemocytes. Altogether, our study provides detailed insights into the hemocyte development and cellular immune responses at single-cell resolution.

How the Drosophila lymph gland hemocytes develop and are regulated at a single-cell level is unclear. Here, the authors use single-cell RNA sequencing to show heterogeneity of developing hemocytes in the lymph gland and how they react to wasp infestation, and compare hemocytes from two independent origins.

Rosy Beginnings: Studying Peroxisomes in Drosophila

Research using the fruit fly Drosophila melanogaster has traditionally focused on understanding how mutations affecting gene regulation or function affect processes linked to animal development. Accordingly, flies have become an essential foundation of modern medical research through repeated contributions to our fundamental understanding of how their homologs of human genes function. Peroxisomes are organelles that metabolize lipids and reactive oxygen species like peroxides. However, despite clear linkage of mutations in human genes affecting peroxisomes to developmental defects, for many years fly models were conspicuously absent from the study of peroxisomes. Now, the few early studies linking the Rosy eye color phenotype to peroxisomes in flies have been joined by a growing body of research establishing novel roles for peroxisomes during the development or function of specific tissues or cell types. Similarly, unique properties of cultured fly Schneider 2 cells have advanced our understanding of how peroxisomes move on the cytoskeleton. Here, we profile how those past and more recent Drosophila studies started to link specific effects of peroxisome dysfunction to organ development and highlight the utility of flies as a model for human peroxisomal diseases. We also identify key differences in the function and proliferation of fly peroxisomes compared to yeast or mammals. Finally, we discuss the future of the fly model system for peroxisome research including new techniques that should support identification of additional tissue specific regulation of and roles for peroxisomes.

Down-regulation of a cytokine secreted from peripheral fat bodies improves visual attention while reducing sleep in Drosophila

Sleep is vital for survival. Yet under environmentally challenging conditions, such as starvation, animals suppress their need for sleep. Interestingly, starvation-induced sleep loss does not evoke a subsequent sleep rebound. Little is known about how starvation-induced sleep deprivation differs from other types of sleep loss, or why some sleep functions become dispensable during starvation. Here, we demonstrate that down-regulation of the secreted cytokine unpaired 2 (upd2) in Drosophila flies may mimic a starved-like state. We used a genetic knockdown strategy to investigate the consequences of upd2 on visual attention and sleep in otherwise well-fed flies, thereby sidestepping the negative side effects of undernourishment. We find that knockdown of upd2 in the fat body (FB) is sufficient to suppress sleep and promote feeding-related behaviors while also improving selective visual attention. Furthermore, we show that this peripheral signal is integrated in the fly brain via insulin-expressing cells. Together, these findings identify a role for peripheral tissue-to-brain interactions in the simultaneous regulation of sleep quality and attention, to potentially promote adaptive behaviors necessary for survival in hungry animals.

-Omic Analysis of the Sepia officinalis White Body: New Insights into Multifunctionality and Haematopoiesis Regulation

Cephalopods, like other protostomes, lack an adaptive immune system and only rely on an innate immune system. The main immune cells are haemocytes (Hcts), which are able to respond to pathogens and external attacks. First reports based on morphological observations revealed that the white body (WB) located in the optic sinuses of cuttlefish was the origin of Hcts. Combining transcriptomic and proteomic analyses, we identified several factors known to be involved in haematopoiesis in vertebrate species in cuttlefish WB. Among these factors, members of the JAK-STAT signaling pathway were identified, some of them for the first time in a molluscan transcriptome and proteome. Immune factors, such as members of the Toll/NF-κB signaling pathway, pattern recognition proteins and receptors, and members of the oxidative stress responses, were also identified, and support an immune role of the WB. Both transcriptome and proteome analyses revealed that the WB harbors an intense metabolism concurrent with the haematopoietic function. Finally, a comparative analysis of the WB and Hct proteomes revealed many proteins in common, confirming previous morphological studies on the origin of Hcts in cuttlefish. This molecular work demonstrates that the WB is multifunctional and provides bases for haematopoiesis regulation in cuttlefish.

The Pupal Ectoparasitoid Pachycrepoideus vindemmiae Regulates Cellular and Humoral Immunity of Host Drosophila melanogaster

The immunological interaction between Drosophila melanogaster and its larval parasitoids has been thoroughly investigated, however, little is known about the interaction between the host and its pupal parasitoids. Pachycrepoideus vindemmiae, a pupal ectoparasitoid of D. melanogaster, injects venom into its host while laying eggs on the puparium, which regulates host immunity and interrupts host development. To resist the invasion of parasitic wasps, various immune defense strategies have been developed in their hosts as a consequence of co-evolution. In this study, we mainly focused on the host immunomodulation by P. vindemmiae and thoroughly investigated cellular and humoral immune response, including cell adherence, cell viability, hemolymph melanization and the Toll, Imd, and JAK/STAT immune pathways. Our results indicated that venom had a significant inhibitory effect on lamellocyte adherence and induced plasmatocyte cell death. Venom injection and in vitro incubation strongly inhibited hemolymph melanization. More in-depth investigation revealed that the Toll and Imd immune pathways were immediately activated upon parasitization, followed by the JAK/STAT pathway, which was activated within the first 24 h post-parasitism. These regulatory effects were further validated by qPCR. Our present study manifested that P. vindemmiae regulated the cellular and humoral immune system of host D. melanogaster in many aspects. These findings lay the groundwork for studying the immunological interaction between D. melanogaster and its pupal parasitoid.

In vivo Hox binding specificity revealed by systematic changes to a single cis regulatory module

Hox proteins belong to a family of transcription factors with similar DNA binding specificities that control animal differentiation along the antero-posterior body axis. Hox proteins are expressed in partially overlapping regions where each one is responsible for the formation of particular organs and structures through the regulation of specific direct downstream targets. Thus, explaining how each Hox protein can selectively control its direct targets from those of another Hox protein is fundamental to understand animal development. Here we analyse a cis regulatory module directly regulated by seven different Drosophila Hox proteins and uncover how different Hox class proteins differentially control its expression. We find that regulation by one or another Hox protein depends on the combination of three modes: Hox-cofactor dependent DNA-binding specificity; Hox-monomer binding sites; and interaction with positive and negative Hox-collaborator proteins. Additionally, we find that similar regulation can be achieved by Amphioxus orthologs, suggesting these three mechanisms are conserved from insects to chordates.

Hox proteins are expressed in partially overlapping regions to inform development along the embryo’s head-tail axis. Here the authors analyse a cis regulatory module directly regulated by seven different Drosophila Hox proteins to uncover how different Hox class proteins differentially control its expression.

Drosophila Peptide Hormones Allatostatin A and Diuretic Hormone 31 Exhibiting Complementary Gradient Distribution in Posterior Midgut Antagonistically Regulate Midgut Senescence and Adult Lifespan

Enteroendocrine cells (EEs) are evolutionarily conserved gastrointestinal secretory cells that show scattered distribution in the intestinal epithelium. These cells classified into several subtypes based on the hormones they produce in both mammals and insects. In the fruit fly Drosophila, it has been suggested that nearly equal numbers of two subtypes of EEs (Allatostatin A: AstA and Diuretic hormone 31 : Dh31) are alternately produced from the intestinal stem cells in the posterior midgut. However, we found that these two subtypes are not always present in this manner, but are rather distributed in a complementary frequency gradient along the posterior midgut. We show that midgut-preferential RNA knockdown of the peptide hormones AstA or Dh31 respectively results in decreased or increased adult lifespan. This effect on longevity is apparently correlated with the midgut senescence phenotypes as a result of direct hormone action through both hormone receptors expressed in the enteroblasts or other midgut cell types. However, gut senescence does not appear to be the direct cause for longevity regulation, as knockdown of both hormone receptors did not affect adult lifespan. Furthermore, these senescence phenotypes appear to be independent of insulin signaling and manifest in an organ-specific manner. These results indicate that the two intestinal secretory peptides antagonistically regulate adult lifespan and intestinal senescence through multiple pathways, irrespective of insulin, which implicates a complementary gradient distribution of each of the hormone-producing EEs, consistent with local requirements for cell activity along the posterior midgut.

A high-fat diet impacts memory and gene expression of the head in mated female Drosophila melanogaster

Obesity predisposes humans to a range of life-threatening comorbidities, including type 2 diabetes and cardiovascular disease. Obesity also aggravates neural pathologies, such as Alzheimer's disease, but this class of comorbidity is less understood. When Drosophila melanogaster (flies) are exposed to high-fat diet (HFD) by supplementing a standard medium with coconut oil, they adopt an obese phenotype of decreased lifespan, increased triglyceride storage, and hindered climbing ability. The latter development has been previously regarded as a potential indicator of neurological decline in fly models of neurodegenerative disease. Our objective was to establish the obesity phenotype in Drosophila and identify a potential correlation, if any, between obesity and neurological decline through behavioral assays and gene expression microarray. We found that mated female w1118 flies exposed to HFD maintained an obese phenotype throughout adult life starting at 7 days, evidenced by increased triglyceride stores, diminished life span, and impeded climbing ability. While climbing ability worsened cumulatively between 7 and 14 days of exposure to HFD, there was no corresponding alteration in triglyceride content. Microarray analysis of the mated female w1118 fly head revealed HFD-induced changes in expression of genes with functions in memory, metabolism, olfaction, mitosis, cell signaling, and motor function. Meanwhile, an Aversive Phototaxis Suppression assay in mated female flies indicated reduced ability to recall an entrained memory 6 h after training. Overall, our results support the suitability of mated female flies for examining connections between diet-induced obesity and nervous or neurobehavioral pathology, and provide many directions for further investigation.

JAK/STAT signaling is involved in air sac primordium development of Drosophila melanogaster

The dorsal thoracic air sacs in fruit flies (Drosophila melanogaster) are functionally and developmentally comparable to human lungs. The progenitors of these structures, air sac primordia (ASPs), invasively propagate into wing imaginal disks, employing mechanisms similar to those that promote metastasis in malignant tumors. We investigated whether Janus kinase/signal transducer and activator of transcription JAK/STAT signaling plays a role in the directed morphogenesis of ASPs. We find that JAK/STAT signaling occurs in ASP tip cells and misexpression of core components in the JAK/STAT signaling cascade significantly impedes ASP development. We further identify Upd2 as an activating ligand for JAK/STAT activity in the ASP. Together, these data constitute a considerable step forward in understanding the role of JAK/STAT signaling in ASPs and similar structures in mammalian models.

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.

Commensal microbiota-induced redox signaling activates proliferative signals in the intestinal stem cell microenvironment

A distinct taxon of the Drosophila microbiota, Lactobacillus plantarum, is capable of stimulating the generation of reactive oxygen species (ROS) within cells, and inducing epithelial cell proliferation. Here, we show that microbial-induced ROS generation within Drosophila larval stem cell compartments exhibits a distinct spatial distribution. Lactobacilli-induced ROS is strictly excluded from defined midgut compartments that harbor adult midgut progenitor (AMP) cells, forming a functional 'ROS sheltered zone' (RSZ). The RSZ is undiscernible in germ-free larvae, but forms following monocolonization with L. plantarum L. plantarum is a strong activator of the ROS-sensitive CncC/Nrf2 signaling pathway within enterocytes. Enterocyte-specific activation of CncC stimulated the proliferation of AMPs, which demonstrates that pro-proliferative signals are transduced from enterocytes to AMPs. Mechanistically, we show that the cytokine Upd2 is expressed in the gut following L. plantarum colonization in a CncC-dependent fashion, and may function in lactobacilli-induced AMP proliferation and intestinal tissue growth and development.

JAK/STAT signaling in stem cells and regeneration: from Drosophila to vertebrates

The JAK/STAT pathway is a conserved metazoan signaling system that transduces cues from extracellular cytokines into transcriptional changes in the nucleus. JAK/STAT signaling is best known for its roles in immunity. However, recent work has demonstrated that it also regulates critical homeostatic processes in germline and somatic stem cells, as well as regenerative processes in several tissues, including the gonad, intestine and appendages. Here, we provide an overview of JAK/STAT signaling in stem cells and regeneration, focusing on Drosophila and highlighting JAK/STAT pathway functions in proliferation, survival and cell competition that are conserved between Drosophila and vertebrates.

Drosophila Jak/STAT Signaling: Regulation and Relevance in Human Cancer and Metastasis

Over the past three-decades, Janus kinase (Jak) and signal transducer and activator of transcription (STAT) signaling has emerged as a paradigm to understand the involvement of signal transduction in development and disease pathology. At the molecular level, cytokines and interleukins steer Jak/STAT signaling to transcriptional regulation of target genes, which are involved in cell differentiation, migration, and proliferation. Jak/STAT signaling is involved in various types of blood cell disorders and cancers in humans, and its activation is associated with carcinomas that are more invasive or likely to become metastatic. Despite immense information regarding Jak/STAT regulation, the signaling network has numerous missing links, which is slowing the progress towards developing drug therapies. In mammals, many components act in this cascade, with substantial cross-talk with other signaling pathways. In Drosophila, there are fewer pathway components, which has enabled significant discoveries regarding well-conserved regulatory mechanisms. Work across species illustrates the relevance of these regulators in humans. In this review, we showcase fundamental Jak/STAT regulation mechanisms in blood cells, stem cells, and cell motility. We examine the functional relevance of key conserved regulators from Drosophila to human cancer stem cells and metastasis. Finally, we spotlight less characterized regulators of Drosophila Jak/STAT signaling, which stand as promising candidates to be investigated in cancer biology. These comparisons illustrate the value of using Drosophila as a model for uncovering the roles of Jak/STAT signaling and the molecular means by which the pathway is controlled.

Ixodes Immune Responses Against Lyme Disease Pathogens

Although Ixodes scapularis and other related tick species are considered prolific vectors for a number of important human diseases, many aspects of their biology, microbial interactions, and immunity are largely unknown; in particular, how these ancient vectors recognize invading pathogens like Borrelia burgdorferi and influence their persistence. The analysis of the Ixodes genome and a limited set of transcriptomic data have established that ticks encode many components of classical immune pathways; yet at the same time, they lack many key orthologs of these recognition networks. Therefore, whether a given immune pathway is active in Ixodes ticks and how precisely they exert its microbicidal functions are only incompletely delineated. A few recent studies have suggested that classical pathways like the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) as well as immunodeficiency (IMD) pathways are fully functional in I. scapularis, and upon challenge with microbes, generate potent microbicidal responses against diverse tick-borne pathogens including B. burgdorferi. These studies also highlight novel concepts of vector immunity that include both a direct and an indirect mode of recognition of pathogens, as well as the influence of the gut microbiome, which ultimately dictates the outcome of a robust microbicidal response. Further understanding of how Ixodes ticks recognize and suppress invading microbes like B. burgdorferi will enrich our fundamental knowledge of vector immunobiology, thereby contributing to the development of future interventions to better control the tick-borne pathogen.

JAK/STAT signaling prevents excessive apoptosis to ensure maintenance of the interfollicular stalk critical for Drosophila oogenesis

Apoptosis not only eliminates cells that are damaged or dangerous but also cells whose function during development in patterning or organogenesis is complete. The successful formation of germ cells is essential for the perpetuation of a species. The production of an oocyte often depends on signaling between germline and somatic cells, but also between specialized types of somatic cells. In Drosophila, each developing egg chamber is separated from the next by a single file of interfollicular somatic cells. Little is known about the function of the interfollicular stalk, although its presumed role in separating egg chambers is to ensure that patterning cues from one egg chamber do not impact or disrupt the development of adjacent egg chambers. We found that cells comprising the stalk undergo a progressive decrease in number during oogenesis through an apoptotic-dependent loss. The extent of programmed cell death is restricted by JAK/STAT signaling in a cell-autonomous manner to ensure that the stalk is maintained. Both a failure to undergo the normal reduction in stalk cell number, or to prevent excessive stalk cell apoptosis results in a decrease in fecundity. Thus, activation of JAK/STAT signaling in the Drosophila interfollicular stalk emerges as a model to study the tight regulation of signaling-dependent apoptosis.

A Mechanism Coupling Systemic Energy Sensing to Adipokine Secretion

Adipocytes sense systemic nutrient status and systemically communicate this information by releasing adipokines. The mechanisms that couple nutritional state to adipokine release are unknown. Here, we investigated how Unpaired 2 (Upd2), a structural and functional ortholog of the primary human adipokine leptin, is released from Drosophila fat cells. We find that Golgi reassembly stacking protein (GRASP), an unconventional secretion pathway component, is required for Upd2 secretion. In nutrient-rich fat cells, GRASP clusters in close proximity to the apical side of lipid droplets (LDs). During nutrient deprivation, glucagon-mediated increase in calcium (Ca²⁺) levels, via calmodulin kinase II (CaMKII) phosphorylation, inhibits proximal GRASP localization to LDs. Using a heterologous cell system, we show that human leptin secretion is also regulated by Ca²⁺ and CaMKII. In summary, we describe a mechanism by which increased cytosolic Ca²⁺ negatively regulates adipokine secretion and have uncovered an evolutionarily conserved molecular link between intracellular Ca²⁺ levels and energy homeostasis.

dOCRL maintains immune cell quiescence by regulating endosomal traffic

Lowe Syndrome is a developmental disorder characterized by eye, kidney, and neurological pathologies, and is caused by mutations in the phosphatidylinositol-5-phosphatase OCRL. OCRL plays diverse roles in endocytic and endolysosomal trafficking, cytokinesis, and ciliogenesis, but it is unclear which of these cellular functions underlie specific patient symptoms. Here, we show that mutation of Drosophila OCRL causes cell-autonomous activation of hemocytes, which are macrophage-like cells of the innate immune system. Among many cell biological defects that we identified in docrl mutant hemocytes, we pinpointed the cause of innate immune cell activation to reduced Rab11-dependent recycling traffic and concomitantly increased Rab7-dependent late endosome traffic. Loss of docrl amplifies multiple immune-relevant signals, including Toll, Jun kinase, and STAT, and leads to Rab11-sensitive mis-sorting and excessive secretion of the Toll ligand Spåtzle. Thus, docrl regulation of endosomal traffic maintains hemocytes in a poised, but quiescent state, suggesting mechanisms by which endosomal misregulation of signaling may contribute to symptoms of Lowe syndrome.

Lowe syndrome is a developmental disorder characterized by severe kidney, eye, and neurological symptoms, and is caused by mutations in the gene OCRL. OCRL has been shown to control many steps of packaging and transport of materials within cells, though it remains unclear which of these disrupted transport steps cause each of the many symptoms in Lowe syndrome patients. We found that in fruit flies, loss of OCRL caused transport defects at specific internal compartments in innate immune cells, resulting in amplification of multiple critical inflammatory signals. Similar inflammatory signals have been implicated in forms of epilepsy, which is a primary symptom in Lowe syndrome patients. Thus, our work uncovers a new function for OCRL in animals, and opens an exciting new avenue of investigation into how loss of OCRL causes the symptoms of Lowe syndrome.

Growth control in the Drosophila eye disc by the cytokine Unpaired

A fundamental question in developmental biology is how organ size is controlled. We have previously shown that the area growth rate in the Drosophila eye primordium declines inversely proportionally to the increase in its area. How the observed reduction in the growth rate is achieved is unknown. Here, we explore the dilution of the cytokine Unpaired (Upd) as a possible candidate mechanism. In the developing eye, upd expression is transient, ceasing at the time when the morphogenetic furrow first emerges. We confirm experimentally that the diffusion and stability of the JAK/STAT ligand Upd are sufficient to control eye disc growth via a dilution mechanism. We further show that sequestration of Upd by ectopic expression of an inactive form of the receptor Domeless (Dome) results in a substantially lower growth rate, but the area growth rate still declines inversely proportionally to the area increase. This growth rate-to-area relationship is no longer observed when Upd dilution is prevented by the continuous, ectopic expression of Upd. We conclude that a mechanism based on the dilution of the growth modulator Upd can explain how growth termination is controlled in the eye disc.

Modulation of occluding junctions alters the hematopoietic niche to trigger immune activation

Stem cells are regulated by signals from their microenvironment, or niche. During Drosophila hematopoiesis, a niche regulates prohemocytes to control hemocyte production. Immune challenges activate cell-signalling to initiate the cellular and innate immune response. Specifically, certain immune challenges stimulate the niche to produce signals that induce prohemocyte differentiation. However, the mechanisms that promote prohemocyte differentiation subsequent to immune challenges are poorly understood. Here we show that bacterial infection induces the cellular immune response by modulating occluding-junctions at the hematopoietic niche. Occluding-junctions form a permeability barrier that regulates the accessibility of prohemocytes to niche derived signals. The immune response triggered by infection causes barrier breakdown, altering the prohemocyte microenvironment to induce immune cell production. Moreover, genetically induced barrier ablation provides protection against infection by activating the immune response. Our results reveal a novel role for occluding-junctions in regulating niche-hematopoietic progenitor signalling and link this mechanism to immune cell production following infection.

Optimized strategy for in vivo Cas9-activation in Drosophila

While several large-scale resources are available for in vivo loss-of-function studies in Drosophila, an analogous resource for overexpressing genes from their endogenous loci does not exist. We describe a strategy for generating such a resource using Cas9 transcriptional activators (CRISPRa). First, we compare a panel of CRISPRa approaches and demonstrate that, for in vivo studies, dCas9-VPR is the most optimal activator. Next, we demonstrate that this approach is scalable and has a high success rate, as >75% of the lines tested activate their target gene. We show that CRISPRa leads to physiologically relevant levels of target gene expression capable of generating strong gain-of-function (GOF) phenotypes in multiple tissues and thus serves as a useful platform for genetic screening. Based on the success of this CRISRPa approach, we are generating a genome-wide collection of flies expressing single-guide RNAs (sgRNAs) for CRISPRa. We also present a collection of more than 30 Gal4 > UAS:dCas9-VPR lines to aid in using these sgRNA lines for GOF studies in vivo.

Chronic activation of JNK JAK/STAT and oxidative stress signalling causes the loser cell status

Cell competition is a form of cell interaction that causes the elimination of less fit cells, or losers, by wild-type (WT) cells, influencing overall tissue health. Several mutations can cause cells to become losers; however, it is not known how. Here we show that Drosophila wing disc cells carrying functionally unrelated loser mutations (Minute and mahjong) display the common activation of multiple stress signalling pathways before cell competition and find that these pathways collectively account for the loser status. We find that JNK signalling inhibits the growth of losers, while JAK/STAT signalling promotes competition-induced winner cell proliferation. Furthermore, we show that losers display oxidative stress response activation and, strikingly, that activation of this pathway alone, by Nrf2 overexpression, is sufficient to prime cells for their elimination by WT neighbours. Since oxidative stress and Nrf2 are linked to several diseases, cell competition may occur in a number of pathological conditions.Cell competition causes the removal of less fit cells ('losers') but why some gene mutations turn cells into losers is unclear. Here, the authors show that Drosophila wing disc cells carrying some loser mutations activate Nrf2 and JNK signalling, which contribute to the loser status.

Screening and Analysis of Janelia FlyLight Project Enhancer-Gal4 Strains Identifies Multiple Gene Enhancers Active During Hematopoiesis in Normal and Wasp-Challenged Drosophila Larvae

A GFP expression screen has been conducted on >1000 Janelia FlyLight Project enhancer-Gal4 lines to identify transcriptional enhancers active in the larval hematopoietic system. A total of 190 enhancers associated with 87 distinct genes showed activity in cells of the third instar larval lymph gland and hemolymph. That is, gene enhancers were active in cells of the lymph gland posterior signaling center (PSC), medullary zone (MZ), and/or cortical zone (CZ), while certain of the transcriptional control regions were active in circulating hemocytes. Phenotypic analyses were undertaken on 81 of these hematopoietic-expressed genes, with nine genes characterized in detail as to gain- and loss-of-function phenotypes in larval hematopoietic tissues and blood cells. These studies demonstrated the functional requirement of the cut gene for proper PSC niche formation, the hairy, Btk29A, and E2F1 genes for blood cell progenitor production in the MZ domain, and the longitudinals lacking, dFOXO, kayak, cap-n-collar, and delilah genes for lamellocyte induction and/or differentiation in response to parasitic wasp challenge and infestation of larvae. Together, these findings contribute substantial information to our knowledge of genes expressed during the larval stage of Drosophila hematopoiesis and newly identify multiple genes required for this developmental process.

Actin is an evolutionarily-conserved damage-associated molecular pattern that signals tissue injury in Drosophila melanogaster

Damage-associated molecular patterns (DAMPs) are molecules released by dead cells that trigger sterile inflammation and, in vertebrates, adaptive immunity. Actin is a DAMP detected in mammals by the receptor, DNGR-1, expressed by dendritic cells (DCs). DNGR-1 is phosphorylated by Src-family kinases and recruits the tyrosine kinase Syk to promote DC cross-presentation of dead cell-associated antigens. Here we report that actin is also a DAMP in invertebrates that lack DCs and adaptive immunity. Administration of actin to Drosophila melanogaster triggers a response characterised by selective induction of STAT target genes in the fat body through the cytokine Upd3 and its JAK/STAT-coupled receptor, Domeless. Notably, this response requires signalling via Shark, the Drosophila orthologue of Syk, and Src42A, a Drosophila Src-family kinase, and is dependent on Nox activity. Thus, extracellular actin detection via a Src-family kinase-dependent cascade is an ancient means of detecting cell injury that precedes the evolution of adaptive immunity.

Human NUP98-HOXA9 promotes hyperplastic growth of hematopoietic tissues in Drosophila

Acute myeloid leukemia (AML) is a complex malignancy with poor prognosis. Several genetic lesions can lead to the disease. One of these corresponds to the NUP98-HOXA9 (NA9) translocation that fuses sequences encoding the N-terminal part of NUP98 to those encoding the DNA-binding domain of HOXA9. Despite several studies, the mechanism underlying NA9 ability to induce leukemia is still unclear. To bridge this gap, we sought to functionally dissect NA9 activity using Drosophila. For this, we generated transgenic NA9 fly lines and expressed the oncoprotein during larval hematopoiesis. This markedly enhanced cell proliferation and tissue growth, but did not alter cell fate specification. Moreover, reminiscent to NA9 activity in mammals, strong cooperation was observed between NA9 and the MEIS homolog HTH. Genetic characterization of NA9-induced phenotypes suggested interference with PVR (Flt1-4 RTK homolog) signaling, which is similar to functional interactions observed in mammals between Flt3 and HOXA9 in leukemia. Finally, NA9 expression was also found to induce non-cell autonomous effects, raising the possibility that its leukemia-inducing activity also relies on this property. Together, our work suggests that NA9 ability to induce blood cell expansion is evolutionarily conserved. The amenability of NA9 activity to a genetically-tractable system should facilitate unraveling its molecular underpinnings.