Ras-oncogenic Drosophila hindgut but not midgut cells use an inflammation-like program to disseminate to distant sites

Prevalence of mouthpart sensilla and protease producing symbiotic gut bacteria in the forensic fly Chrysomya megacephala (Fabricius, 1794): Insight from foraging to digestion

The blow fly, Chrysomya megacephala (Fabricius, 1794) is a globally prevalent forensically important species that helps to estimate accurate postmortem interval since the death. This fly occasionally causes cutaneous myiasis and transmits several pathogenic bacteria. To understand their ability of corpse detection and digestion of protein-rich meal, the present study describes the mouthpart sensilla and assessment of protease producing symbiotic gut bacteria. Scanning electron microscopy (SEM) showed the prevalence of trichoid sensilla (Tr), basiconic sensilla (Ba) and microtrichia (Mr) on labellar lobes, haustellum and maxillary palps of mouthparts. Bacterial particles of both rod (small and large) and spherical shaped were detected in the gut of C. megacephala using SEM. The bacterial density was higher on the foregut and midgut in comparison to the hindgut. From 72 bacterial isolates, 10 isolates from the foregut region showed considerable protease-producing efficacy ranging between 3.98 - 6.83 GHR and 9.73 - 34.68 U/ml protease. Among these, the most promising protease-producing bacterial isolate showed 16S rDNA sequence similarity (99.85%) with Chryseobacterium artocarpi DNA. This bacterium was the first report from flies. The findings of the study might help in better understanding of the role of sensilla in host perception and foregut symbiotic bacterial association in protein digestion in C. megacephala.

Nutrient Sensing via Gut in Drosophila melanogaster

Nutrient-sensing mechanisms in animals' sense available nutrients to generate a physiological regulatory response involving absorption, digestion, and regulation of food intake and to maintain glucose and energy homeostasis. During nutrient sensing via the gastrointestinal tract, nutrients interact with receptors on the enteroendocrine cells in the gut, which in return respond by secreting various hormones. Sensing of nutrients by the gut plays a critical role in transmitting food-related signals to the brain and other tissues informing the composition of ingested food to digestive processes. These signals modulate feeding behaviors, food intake, metabolism, insulin secretion, and energy balance. The increasing significance of fly genetics with the availability of a vast toolbox for studying physiological function, expression of chemosensory receptors, and monitoring the gene expression in specific cells of the intestine makes the fly gut the most useful tissue for studying the nutrient-sensing mechanisms. In this review, we emphasize on the role of Drosophila gut in nutrient-sensing to maintain metabolic homeostasis and gut-brain cross talk using endocrine and neuronal signaling pathways stimulated by internal state or the consumption of various dietary nutrients. Overall, this review will be useful in understanding the post-ingestive nutrient-sensing mechanisms having a physiological and pathological impact on health and diseases.

Roles of matrix metalloproteinases in development, immunology, and ovulation in fruit Fly (Drosophila)

Matrix metalloproteinase (MMP), a protease enzyme, participates in proteolytic cleavage of extracellular matrix proteins from Drosophila and mammals. But, recent studies have revealed other physiologically important roles of MMP in Drosophila. MMP contributes to cardioblast movement and distribution of collagen proteins during cardiogenesis in developing Drosophila. Tissue remodeling, especially tracheal development is also maintained by MMP. MMP regulates certain immunological functions in Drosophila such as wound repairing, plasmatocyte assemblage at the injured site of the basement membrane and glial response to axon degeneration in Drosophila nervous system. But, the contribution of MMP to tumor formation and metastasis in Drosophila has made it an interesting topic among researchers. Ovulation and egg laying are also found to be affected positively by MMP in Drosophila.

Drosophila melanogaster as a Model System to Assess the Effect of Epstein-Barr Virus DNA on Inflammatory Gut Diseases

The Epstein-Barr virus (EBV) commonly infects humans and is highly associated with different types of cancers and autoimmune diseases. EBV has also been detected in inflamed gastrointestinal mucosa of patients suffering from prolonged inflammation of the digestive tract such as inflammatory bowel disease (IBD) with no clear role identified yet for EBV in the pathology of such diseases. Since we have previously reported immune-stimulating capabilities of EBV DNA in various models, in this study we investigated whether EBV DNA may play a role in exacerbating intestinal inflammation through innate immune and regeneration responses using the Drosophila melanogaster model. We have generated inflamed gastrointestinal tracts in adult fruit flies through the administration of dextran sodium sulfate (DSS), a sulfated polysaccharide that causes human ulcerative colitis- like pathologies due to its toxicity to intestinal cells. Intestinal damage induced by inflammation recruited plasmatocytes to the ileum in fly hindguts. EBV DNA aggravated inflammation by enhancing the immune deficiency (IMD) pathway as well as further increasing the cellular inflammatory responses manifested upon the administration of DSS. The study at hand proposes a possible immunostimulatory role of the viral DNA exerted specifically in the fly hindgut hence further developing our understanding of immune responses mounted against EBV DNA in the latter intestinal segment of the D. melanogaster gut. These findings suggest that EBV DNA may perpetuate proinflammatory processes initiated in an inflamed digestive system. Our findings indicate that D. melanogaster can serve as a model to further understand EBV-associated gastroinflammatory pathologies. Further studies employing mammalian models may validate the immunogenicity of EBV DNA in an IBD context and its role in exacerbating the disease through inflammatory mediators.

Fly foregut and transmission of microbes

Two areas of research that have greatly increased in attention are: dipterans as vectors and the microbes they are capable of vectoring. Because it is the front-end of the fly that first encounters these microbes, this review focuses on the legs, mouthparts, and foregut, which includes the crop as major structures involved in dipteran vectoring ability. The legs and mouthparts are generally involved in mechanical transmission of microbes. However, the crop is involved in more than just mechanical transmission, for it is within the lumen of the crop that microbes are taken up with the meal of the fly, stored, and it is within the lumen that horizontal transmission of bacterial resistance has been demonstrated. In addition to storage of microbes, the crop is also involved in depositing the microbes via a process known as regurgitation. Various aspects of crop regulation are discussed and specific examples of crop involvement with microorganisms are discussed. The importance of biofilm and biofilm formation are presented, as well as, some physical parameters of the crop that might either facilitate or inhibit biofilm formation. Finally, there is a brief discussion of dipteran model systems for studying crop microbe interactions.

Drosophila melanogaster: A Model Organism to Study Cancer

Cancer is a multistep disease driven by the activation of specific oncogenic pathways concomitantly with the loss of function of tumor suppressor genes that act as sentinels to control physiological growth. The conservation of most of these signaling pathways in Drosophila, and the ability to easily manipulate them genetically, has made the fruit fly a useful model organism to study cancer biology. In this review we outline the basic mechanisms and signaling pathways conserved between humans and flies responsible of inducing uncontrolled growth and cancer development. Second, we describe classic and novel Drosophila models used to study different cancers, with the objective to discuss their strengths and limitations on their use to identify signals driving growth cell autonomously and within organs, drug discovery and for therapeutic approaches.

Grow With the Challenge - Microbial Effects on Epithelial Proliferation, Carcinogenesis, and Cancer Therapy

The eukaryotic host is in close contact to myriads of resident and transient microbes, which influence the crucial physiological pathways. Emerging evidence points to their role of host-microbe interactions for controlling tissue homeostasis, cell fate decisions, and regenerative capacity in epithelial barrier organs including the skin, lung, and gut. In humans and mice, it has been shown that the malignant tumors of these organs harbor an altered microbiota. Mechanistic studies have shown that the altered metabolic properties and secreted factors contribute to epithelial carcinogenesis and tumor progression. Exciting recent work points toward a crucial influence of the associated microbial communities on the response to chemotherapy and immune-check point inhibitors during cancer treatment, which suggests that the modulation of the microbiota might be a powerful tool for personalized oncology. In this article, we provide an overview of how the bacterial signals and signatures may influence epithelial homeostasis across taxa from cnidarians to vertebrates and delineate mechanisms, which might be potential targets for therapy of human diseases by either harnessing barrier integrity (infection and inflammation) or restoring uncontrolled proliferation (cancer).

Modelling Cooperative Tumorigenesis in Drosophila

The development of human metastatic cancer is a multistep process, involving the acquisition of several genetic mutations, tumour heterogeneity, and interactions with the surrounding microenvironment. Due to the complexity of cancer development in mammals, simpler model organisms, such as the vinegar fly, Drosophila melanogaster, are being utilized to provide novel insights into the molecular mechanisms involved. In this review, we highlight recent advances in modelling tumorigenesis using the Drosophila model, focusing on the cooperation of oncogenes or tumour suppressors, and the interaction of mutant cells with the surrounding tissue in epithelial tumour initiation and progression.

The Immune Phenotype of Three Drosophila Leukemia Models

Many leukemia patients suffer from dysregulation of their immune system, making them more susceptible to infections and leading to general weakening (cachexia). Both adaptive and innate immunity are affected. The fruit fly Drosophila melanogaster has an innate immune system, including cells of the myeloid lineage (hemocytes). To study Drosophila immunity and physiology during leukemia, we established three models by driving expression of a dominant-active version of the Ras oncogene (Ras^V12 ) alone or combined with knockdowns of tumor suppressors in Drosophila hemocytes. Our results show that phagocytosis, hemocyte migration to wound sites, wound sealing, and survival upon bacterial infection of leukemic lines are similar to wild type. We find that in all leukemic models the two major immune pathways (Toll and Imd) are dysregulated. Toll-dependent signaling is activated to comparable extents as after wounding wild-type larvae, leading to a proinflammatory status. In contrast, Imd signaling is suppressed. Finally, we notice that adult tissue formation is blocked and degradation of cell masses during metamorphosis of leukemic lines, which is akin to the state of cancer-dependent cachexia. To further analyze the immune competence of leukemic lines, we used a natural infection model that involves insect-pathogenic nematodes. We identified two leukemic lines that were sensitive to nematode infections. Further characterization demonstrates that despite the absence of behavioral abnormalities at the larval stage, leukemic larvae show reduced locomotion in the presence of nematodes. Taken together, this work establishes new Drosophila models to study the physiological, immunological, and behavioral consequences of various forms of leukemia.

Constructing personalized longitudinal holo'omes of colon cancer-prone humans and their modeling in flies and mice

Specific host genes and intestinal microbes, dysbiosis, aberrant immune responses and lifestyle may contribute to intestinal inflammation and cancer, but each of these parameters does not suffice to explain why sporadic colon cancer develops at an old age and only in some of the people with the same profile. To improve our understanding, longitudinal multi-omic and personalized studies will help to pinpoint combinations of host genetic, epigenetic, microbiota and lifestyle-shaped factors, such as blood factors and metabolites that change as we age. The intestinal holo’ome – defined as the combination of host and microbiota genomes, transcriptomes, proteomes, and metabolomes – may be imbalanced and shift to disease when the wrong host gene expression profile meets the wrong microbiota composition. These imbalances can be triggered by the dietary- or lifestyle-shaped intestinal environment. Accordingly, personalized human intestinal holo’omes will differ significantly among individuals and between two critical points in time: long before and upon the onset of disease. Detrimental combinations of factors could therefore be pinpointed computationally and validated using animal models, such as mice and flies. Finally, treatment strategies that break these harmful combinations could be tested in clinical trials. Herein we provide an overview of the literature and a roadmap to this end.

Damage signals in the insect immune response

Insects and mammals share an ancient innate immune system comprising both humoral and cellular responses. The insect immune system consists of the fat body, which secretes effector molecules into the hemolymph and several classes of hemocytes, which reside in the hemolymph and of protective border epithelia. Key features of wound- and immune responses are shared between insect and mammalian immune systems including the mode of activation by commonly shared microbial (non-self) patterns and the recognition of these patterns by dedicated receptors. It is unclear how metazoan parasites in insects, which lack these shared motifs, are recognized. Research in recent years has demonstrated that during entry into the insect host, many eukaryotic pathogens leave traces that alert potential hosts of the damage they have afflicted. In accordance with terminology used in the mammalian immune systems, these signals have been dubbed danger- or damage-associated signals. Damage signals are necessary byproducts generated during entering hosts either by mechanical or proteolytic damage. Here, we briefly review the current stage of knowledge on how wound closure and wound healing during mechanical damage is regulated and how damage-related signals contribute to these processes. We also discuss how sensors of proteolytic activity induce insect innate immune responses. Strikingly damage-associated signals are also released from cells that have aberrant growth, including tumor cells. These signals may induce apoptosis in the damaged cells, the recruitment of immune cells to the aberrant tissue and even activate humoral responses. Thus, this ensures the removal of aberrant cells and compensatory proliferation to replace lost tissue. Several of these pathways may have been co-opted from wound healing and developmental processes.

Drosophila as a model to study the role of blood cells in inflammation, innate immunity and cancer

Drosophila has a primitive yet effective blood system with three types of haemocytes which function throughout different developmental stages and environmental stimuli. Haemocytes play essential roles in tissue modeling during embryogenesis and morphogenesis, and also in innate immunity. The open circulatory system of Drosophila makes haemocytes ideal signal mediators to cells and tissues in response to events such as infection and wounding. The application of recently developed and sophisticated genetic tools to the relatively simple genome of Drosophila has made the fly a popular system for modeling human tumorigensis and metastasis. Drosophila is now used for screening and investigation of genes implicated in human leukemia and also in modeling development of solid tumors. This second line of research offers promising opportunities to determine the seemingly conflicting roles of blood cells in tumor progression and invasion. This review provides an overview of the signaling pathways conserved in Drosophila during haematopoiesis, haemostasis, innate immunity, wound healing and inflammation. We also review the most recent progress in the use of Drosophila as a cancer research model with an emphasis on the roles haemocytes can play in various cancer models and in the links between inflammation and cancer.

Human pathogenic bacteria, fungi, and viruses in Drosophila: disease modeling, lessons, and shortcomings

Drosophila has been the invertebrate model organism of choice for the study of innate immune responses during the past few decades. Many Drosophila-microbe interaction studies have helped to define innate immunity pathways, and significant effort has been made lately to decipher mechanisms of microbial pathogenesis. Here we catalog 68 bacterial, fungal, and viral species studied in flies, 43 of which are relevant to human health. We discuss studies of human pathogens in flies revealing not only the elicitation and avoidance of immune response but also mechanisms of tolerance, host tissue homeostasis, regeneration, and predisposition to cancer. Prominent among those is the emerging pattern of intestinal regeneration as a defense response induced by pathogenic and innocuous bacteria. Immunopathology mechanisms and many microbial virulence factors have been elucidated, but their relevance to human health conventionally necessitates validation in mammalian models of infection.

Drosophila melanogaster: a first step and a stepping-stone to anti-infectives

Following an expansion in the antibiotic drug discovery in the previous century, we now face a bottleneck in the production of new anti-infective drugs. Traditionally, chemical libraries are screened either using in vitro culture systems or in silico to identify and chemically modify small molecules with antimicrobial properties. Nevertheless, almost all compounds passing through in vitro screening fail to pass preclinical trials. Drug screening in Drosophila offers to fill the gap between in vitro and mammalian model host testing by eliminating compounds that are toxic or have reduced bioavailability and by identifying others that may boost innate host defence or selectively reduce microbial virulence in a whole-organism setting. Such alternative screening methods in Drosophila, while low-throughput, may reduce the cost and increase the success rate of preclinical trials.

Regenerative inflammation: lessons from Drosophila intestinal epithelium in health and disease

Intestinal inflammation is widely recognized as a pivotal player in health and disease. Defined cytologically as the infiltration of leukocytes in the lamina propria layer of the intestine, it can damage the epithelium and, on a chronic basis, induce inflammatory bowel disease and potentially cancer. The current view thus dictates that blood cell infiltration is the instigator of intestinal inflammation and tumor-promoting inflammation. This is based partially on work in humans and mice showing that intestinal damage during microbially mediated inflammation activates phagocytic cells and lymphocytes that secrete inflammatory signals promoting tissue damage and tumorigenesis. Nevertheless, extensive parallel work in the Drosophila midgut shows that intestinal epithelium damage induces inflammatory signals and growth factors acting mainly in a paracrine manner to induce intestinal stem cell proliferation and tumor formation when genetically predisposed. This is accomplished without any apparent need to involve Drosophila hemocytes. Therefore, recent work on Drosophila host defense to infection by expanding its main focus on systemic immunity signaling pathways to include the study of organ homeostasis in health and disease shapes a new notion that epithelially emanating cytokines and growth factors can directly act on the intestinal stem cell niche to promote “regenerative inflammation” and potentially cancer.