Functional exploration of colorectal cancer genomes using Drosophila

Nanoparticle Uptake in the Aging and Oncogenic Drosophila Midgut Measured with Surface-Enhanced Raman Spectroscopy

Colorectal cancer remains a major global health concern. Colonoscopy, the gold-standard colorectal cancer diagnostic, relies on the visual detection of lesions and necessitates invasive biopsies for confirmation. Alternative diagnostic methods, based on nanomedicine, can facilitate early detection of malignancies. Here, we examine the uptake of surface-enhanced Raman scattering nanoparticles (SERS NPs) as a marker for intestinal tumor detection and imaging using an established Drosophila melanogaster model for gut disease. Young and old Oregon-R and w1118 flies were orally administered SERS NPs and scanned without and upon gut lumen clearance to assess nanoparticle retention as a function of aging. Neither young nor old flies showed significant NP retention in their body after gut lumen clearance. Moreover, tumorigenic flies of the esg-Gal4/UAS-RasV12 genotype were tested for SERS NP retention 2, 4 and 6 days after RasV12 oncogene induction in their midgut progenitor cells. Tumorigenic flies showed a statistically significant NP retention signal at 2 days, well before midgut epithelium impairment. The signal was then visualized in scans of dissected guts revealing areas of NP uptake in the posterior midgut region of high stem cell activity.

Functional exploration of copy number alterations in a Drosophila model of triple-negative breast cancer

Accounting for 10-20% of breast cancer cases, triple-negative breast cancer (TNBC) is associated with a disproportionate number of breast cancer deaths. One challenge in studying TNBC is its genomic profile: with the exception of TP53 loss, most breast cancer tumors are characterized by a high number of copy number alterations (CNAs), making modeling the disease in whole animals challenging. We computationally analyzed 186 CNA regions previously identified in breast cancer tumors to rank genes within each region by likelihood of acting as a tumor driver. We then used a Drosophila p53-Myc TNBC model to identify 48 genes as functional drivers. To demonstrate the utility of this functional database, we established six 3-hit models; altering candidate genes led to increased aspects of transformation as well as resistance to the chemotherapeutic drug fluorouracil. Our work provides a functional database of CNA-associated TNBC drivers, and a template for an integrated computational/whole-animal approach to identify functional drivers of transformation and drug resistance within CNAs in other tumor types.

Oncogenic signaling in the adult Drosophila prostate-like accessory gland leads to activation of a conserved pro-tumorigenic program, in the absence of proliferation

Drosophila models for tumorigenesis and metastasis have revealed conserved mechanisms of signaling that are also involved in mammalian cancer. Many of these models use the proliferating tissues of the larval stages of Drosophila development, when tissues are highly mitotically active, or stem cells are abundant. Fewer Drosophila tumorigenesis models use adult animals to initiate tumor formation when many tissues are largely terminally differentiated and postmitotic. The Drosophila accessory glands are prostate-like tissues and a model for some aspects of prostate tumorigenesis using this tissue has been explored. In this model, oncogenic signaling was induced during the proliferative stage of accessory gland development, raising the question of how oncogenic activity would impact the terminally differentiated and postmitotic adult tissue. Here, we show that oncogenic signaling in the adult Drosophila accessory gland leads to activation of a conserved pro-tumorigenic program, similar to that observed in mitotic larval tissues, but in the absence of proliferation. Oncogenic signaling in the adult postmitotic gland leads to tissue hyperplasia with nuclear anaplasia and aneuploidy through endoreduplication, which increases polyploidy and occasionally results in non-mitotic neoplastic-like extrusions. We compare gene expression changes in our Drosophila model with that of endocycling prostate cancer cells induced by chemotherapy, which potentially mediate tumor recurrence after treatment. Similar signaling pathways are activated in the Drosophila gland and endocycling cancer cells, suggesting the adult accessory glands provide a useful model for aspects of prostate cancer progression that do not involve cellular proliferation.

Cholesterol Dietary Intake and Tumor Cell Homeostasis Drive Early Epithelial Tumorigenesis: A Potential Modelization of Early Prostate Tumorigenesis

Epidemiological studies point to cholesterol as a possible key factor for both prostate cancer incidence and progression. It could represent a targetable metabolite as the most aggressive tumors also appear to be sensitive to therapies designed to decrease hypercholesterolemia, such as statins. However, it remains unknown whether and how cholesterol, through its dietary uptake and its metabolism, could be important for early tumorigenesis. Oncogene clonal induction in the Drosophila melanogaster accessory gland allows us to reproduce tumorigenesis from initiation to early progression, where tumor cells undergo basal extrusion to form extra-epithelial tumors. Here we show that these tumors accumulate lipids, and especially esterified cholesterol, as in human late carcinogenesis. Interestingly, a high-cholesterol diet has a limited effect on accessory gland tumorigenesis. On the contrary, cell-specific downregulation of cholesterol uptake, intracellular transport, or metabolic response impairs the formation of such tumors. Furthermore, in this context, a high-cholesterol diet suppresses this impairment. Interestingly, expression data from primary prostate cancer tissues indicate an early signature of redirection from cholesterol de novo synthesis to uptake. Taken together, these results reveal that during early tumorigenesis, tumor cells strongly increase their uptake and use of dietary cholesterol to specifically promote the step of basal extrusion. Hence, these results suggest the mechanism by which a reduction in dietary cholesterol could lower the risk and slow down the progression of prostate cancer.

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.

Modeling childhood cancer in Drosophila melanogaster

Childhood cancer is a major cause of death in developed countries, and while treatments and survival rates have improved, long-term side effects remain a challenge. The genetic component of pediatric tumors and their aggressive progression, makes the study of childhood cancer a complex area of research. Here, we introduce the fruit fly Drosophila melanogaster as study model. We emphasize its numerous advantages, including binary gene expression systems that enable precise control over the timing and location of gene expression manipulation, the capacity to combine multiple genes associated with cancer or the testing of human cancer variants within a live, intact animal. As an illustrative example, we focus on the Drosophila cancer paradigm which involves medically relevant genes, the Notch and PI3K/Akt signaling pathways. We describe how this cancer paradigm allows assessing two critical aspects of tumorigenesis during juvenile stages: (1) viability (do animals with particular cancer mutations survive into adulthood?), and (2) tumor burden (what percentage of animals bearing the cancer mutations actually develop cancer and what is the extent of the tumor?). We highlight the potential of Drosophila as a molecular therapeutic tool for drug screening and drug repurposing of medicines already approved to treat other diseases in children, thereby accelerating the potential translation of results into humans. This preclinical animal model sustains huge potential and is cost-effective. It allows screening of thousands of compounds and genes at a relatively low cost and human efforts, opening innovative venues to explore more effective and safer treatments of childhood cancer.

Colon Cancer Cells Evade Drug Action by Enhancing Drug Metabolism

Colorectal cancer (CRC) is the second most deadly cancer worldwide. One key reason is the failure of therapies that target RAS proteins, which represent approximately 40% of CRC cases. Despite the recent discovery of multiple alternative signalling pathways that contribute to resistance, durable therapies remain an unmet need. Here, we use liquid chromatography/mass spectrometry (LC/MS) analyses on Drosophila CRC tumour models to identify multiple metabolites in the glucuronidation pathway-a toxin clearance pathway-as upregulated in trametinib-resistant RAS/APC/P53 ("RAP") tumours compared to trametinib-sensitive RASG12V tumours. Elevating glucuronidation was sufficient to direct trametinib resistance in RASG12V animals while, conversely, inhibiting different steps along the glucuronidation pathway strongly reversed RAP resistance to trametinib. For example, blocking an initial HDAC1-mediated deacetylation step with the FDA-approved drug vorinostat strongly suppressed trametinib resistance in Drosophila RAP tumours. We provide functional evidence that pairing oncogenic RAS with hyperactive WNT activity strongly elevates PI3K/AKT/GLUT signalling, which in turn directs elevated glucose and subsequent glucuronidation. Finally, we show that this mechanism of trametinib resistance is conserved in an KRAS/APC/TP53 mouse CRC tumour organoid model. Our observations demonstrate a key mechanism by which oncogenic RAS/WNT activity promotes increased drug clearance in CRC. The majority of targeted therapies are glucuronidated, and our results provide a specific path towards abrogating this resistance in clinical trials.

WNT Signalling Promotes NF-κB Activation and Drug Resistance in KRAS-Mutant Colorectal Cancer

Approximately 40% of colorectal cancer (CRC) cases are characterized by KRAS mutations, rendering them insensitive to most CRC therapies. While the reasons for this resistance remain incompletely understood, one key aspect is genetic complexity: in CRC, oncogenic KRAS is most commonly paired with mutations that alter WNT and P53 activities ("RAP"). Here, we demonstrate that elevated WNT activity upregulates canonical (NF-κB) signalling in both Drosophila and human RAS mutant tumours. This upregulation required Toll-1 and Toll-9 and resulted in reduced efficacy of RAS pathway targeted drugs such as the MEK inhibitor trametinib. Inhibiting WNT activity pharmacologically significantly suppressed trametinib resistance in RAP tumours and more genetically complex RAP-containing 'patient avatar' models. WNT/MEK drug inhibitor combinations were further improved by targeting brm, shg, ago, rhoGAPp190 and upf1, highlighting these genes as candidate biomarkers for patients sensitive to this duel approach. These findings shed light on how genetic complexity impacts drug resistance and proposes a therapeutic strategy to reverse this resistance.

Disruptions in cell fate decisions and transformed enteroendocrine cells drive intestinal tumorigenesis in Drosophila

Most epithelial tissues are maintained by stem cells that produce the different cell lineages required for proper tissue function. Constant communication between different cell types ensures precise regulation of stem cell behavior and cell fate decisions. These cell-cell interactions are often disrupted during tumorigenesis, but mechanisms by which they are co-opted to support tumor growth in different genetic contexts are poorly understood. Here, we introduce PromoterSwitch, a genetic platform we established to generate large, transformed clones derived from individual adult Drosophila intestinal stem/progenitor cells. We show that cancer-driving genetic alterations representing common colon tumor genome landscapes disrupt cell fate decisions within transformed tissue and result in the emergence of abnormal cell fates. We also show that transformed enteroendocrine cells, a differentiated, hormone-secreting cell lineage, support tumor growth by regulating intestinal stem cell proliferation through multiple genotype-dependent mechanisms, which represent potential vulnerabilities that could be exploited for therapy.

Intestinal stem cells and their niches in homeostasis and disease

Tissues such as the intestine harbor stem cells that have remarkable functional plasticity in response to a dynamic environment. To adapt to the environment, stem cells constantly receive information from their surrounding microenvironment (also called the 'niche') that instructs them how to adapt to changes. The Drosophila midgut shows morphological and functional similarities to the mammalian small intestine and has been a useful model system to study signaling events in stem cells and tissue homeostasis. In this review, we summarize the current understanding of the Drosophila midgut regarding how stem cells communicate with microenvironmental niches including enteroblasts, enterocytes, enteroendocrine cells and visceral muscles to coordinate tissue regeneration and homeostasis. In addition, distant cells such as hemocytes or tracheal cells have been shown to interact with stem cells and influence the development of intestinal diseases. We discuss the contribution of stem cell niches in driving or counteracting disease progression, and review conceptual advances derived from the Drosophila intestine as a model for stem cell biology.

The Comet Assay in Drosophila: A Tool to Study Interactions between DNA Repair Systems in DNA Damage Responses In Vivo and Ex Vivo

The comet assay in Drosophila has been used in the last few years to study DNA damage responses (DDR) in different repair-mutant strains and to compare them to analyze DNA repair. We have used this approach to study interactions between DNA repair pathways in vivo. Additionally, we have implemented an ex vivo comet assay, in which nucleoids from treated and untreated cells were incubated ex vivo with cell-free protein extracts from individuals with distinct repair capacities. Four strains were used: wild-type OregonK (OK), nucleotide excision repair mutant mus201, dmPolQ protein mutant mus308, and the double mutant mus201;mus308. Methyl methanesulfonate (MMS) was used as a genotoxic agent. Both approaches were performed with neuroblasts from third-instar larvae; they detected the effects of the NER and dmPolQ pathways on the DDR to MMS and that they act additively in this response. Additionally, the ex vivo approach quantified that mus201, mus308, and the double mutant mus201;mus308 strains presented, respectively, 21.5%, 52.9%, and 14.8% of OK strain activity over MMS-induced damage. Considering the homology between mammals and Drosophila in repair pathways, the detected additive effect might be extrapolated even to humans, demonstrating that Drosophila might be an excellent model to study interactions between repair pathways.

Regulation of intestinal stem cell activity by a mitotic cell cycle regulator Polo in Drosophila

Maintaining a definite and stable pool of dividing stem cells plays an important role in organ development. This process requires an appropriate progression of mitosis for proper spindle orientation and polarity to ensure the ability of stem cells to proliferate and differentiate correctly. Polo-like kinases (Plks)/Polo are the highly conserved serine/threonine kinases involved in the initiation of mitosis as well as in the progression of the cell cycle. Although numerous studies have investigated the mitotic defects upon loss of Plks/Polo in cells, little is known about the in vivo consequences of stem cells with abnormal Polo activity in the context of tissue and organism development. The current study aimed to investigate this question using the Drosophila intestine, an organ dynamically maintained by the intestinal stem cells (ISCs). The results indicated that the polo depletion caused a reduction in the gut size due to a gradual decrease in the number of functional ISCs. Interestingly, the polo-deficient ISCs showed an extended G2/M phase and aneuploidy and were subsequently eliminated by premature differentiation into enterocytes (ECs). In contrast, the constitutively active Polo (poloT182D) suppressed ISC proliferation, induced abnormal accumulation of β-tubulin in cells, and drove ISC loss via apoptosis. Therefore, Polo activity should be properly maintained for optimal stem cell function. Further analysis suggested that polo was a direct target gene of Sox21a, a Sox transcription factor that critically regulates stem cell activity. Together, this study provided a novel perspective on the correlation between the progression of mitosis and the ISC function in Drosophila.

A polycistronic transgene design for combinatorial genetic perturbations from a single transcript in Drosophila

Experimental models that capture the genetic complexity of human disease and allow mechanistic explorations of the underlying cell, tissue, and organ interactions are crucial to furthering our understanding of disease biology. Such models require combinatorial manipulations of multiple genes, often in more than one tissue at once. The ability to perform complex genetic manipulations in vivo is a key strength of Drosophila, where many tools for sophisticated and orthogonal genetic perturbations exist. However, combining the large number of transgenes required to establish more representative disease models and conducting mechanistic studies in these already complex genetic backgrounds is challenging. Here we present a design that pushes the limits of Drosophila genetics by allowing targeted combinatorial ectopic expression and knockdown of multiple genes from a single inducible transgene. The polycistronic transcript encoded by this transgene includes a synthetic short hairpin cluster cloned within an intron placed at the 5' end of the transcript, followed by two protein-coding sequences separated by the T2A sequence that mediates ribosome skipping. This technology is particularly useful for modeling genetically complex diseases like cancer, which typically involve concurrent activation of multiple oncogenes and loss of multiple tumor suppressors. Furthermore, consolidating multiple genetic perturbations into a single transgene further streamlines the ability to perform combinatorial genetic manipulations and makes it readily adaptable to a broad palette of transgenic systems. This flexible design for combinatorial genetic perturbations will also be a valuable tool for functionally exploring multigenic gene signatures identified from omics studies of human disease and creating humanized Drosophila models to characterize disease-associated variants in human genes. It can also be adapted for studying biological processes underlying normal tissue homeostasis and development that require simultaneous manipulation of many genes.

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.

A targeted genetic modifier screen in Drosophila uncovers vulnerabilities in a genetically complex model of colon cancer

Received on 16 January 2023; accepted on 21 February 2023Kinases are key regulators of cellular signal transduction pathways. Many diseases, including cancer, are associated with global alterations in protein phosphorylation networks. As a result, kinases are frequent targets of drug discovery efforts. However, target identification and assessment, a critical step in targeted drug discovery that involves identifying essential genetic mediators of disease phenotypes, can be challenging in complex, heterogeneous diseases like cancer, where multiple concurrent genomic alterations are common. Drosophila is a particularly useful genetic model system to identify novel regulators of biological processes through unbiased genetic screens. Here, we report 2 classic genetic modifier screens focusing on the Drosophila kinome to identify kinase regulators in 2 different backgrounds: KRAS TP53 PTEN APC, a multigenic cancer model that targets 4 genes recurrently mutated in human colon tumors and KRAS alone, a simpler model that targets one of the most frequently altered pathways in cancer. These screens identified hits unique to each model and one shared by both, emphasizing the importance of capturing the genetic complexity of human tumor genome landscapes in experimental models. Our follow-up analysis of 2 hits from the KRAS-only screen suggests that classical genetic modifier screens in heterozygous mutant backgrounds that result in a modest, nonlethal reduction in candidate gene activity in the context of a whole animal-a key goal of systemic drug treatment-may be a particularly useful approach to identify the most rate-limiting genetic vulnerabilities in disease models as ideal candidate drug targets.

Modelling Cancer Metastasis in Drosophila melanogaster

Cancer metastasis, the process by which tumour cells spread throughout the body and form secondary tumours at distant sites, is the leading cause of cancer-related deaths. The metastatic cascade is a highly complex process encompassing initial dissemination from the primary tumour, travel through the blood stream or lymphatic system, and the colonisation of distant organs. However, the factors enabling cells to survive this stressful process and adapt to new microenvironments are not fully characterised. Drosophila have proven a powerful system in which to study this process, despite important caveats such as their open circulatory system and lack of adaptive immune system. Historically, larvae have been used to model cancer due to the presence of pools of proliferating cells in which tumours can be induced, and transplanting these larval tumours into adult hosts has enabled tumour growth to be monitored over longer periods. More recently, thanks largely to the discovery that there are stem cells in the adult midgut, adult models have been developed. We focus this review on the development of different Drosophila models of metastasis and how they have contributed to our understanding of important factors determining metastatic potential, including signalling pathways, the immune system and the microenvironment.

Drosophila as a toolkit to tackle cancer and its metabolism

Cancer is one of the most severe health problems worldwide accounting for the second leading cause of death. Studies have indicated that cancers utilize different metabolic systems as compared with normal cells to produce extra energy and substances required for their survival, which contributes to tumor formation and progression. Recently, the fruit fly Drosophila has been attracting significant attention as a whole-body model for elucidating the cancer mechanisms including metabolism. This tiny organism offers a valuable toolkit with various advantages such as high genetic conservation and similar drug response to mammals. In this review, we introduce flies modeling for cancer patient genotypes which have pinpointed novel therapeutic targets and drug candidates in the salivary gland, thyroid, colon, lung, and brain. Furthermore, we introduce fly models for metabolic diseases such as diabetes mellitus, obesity, and cachexia. Diabetes mellitus and obesity are widely acknowledged risk factors for cancer, while cachexia is a cancer-related metabolic condition. In addition, we specifically focus on two cancer metabolic alterations: the Warburg effect and redox metabolism. Indeed, flies proved useful to reveal the relationship between these metabolic changes and cancer. Such accumulating achievements indicate that Drosophila offers an efficient platform to clarify the mechanisms of cancer as a systemic disease.

Drosophila melanogaster: A platform for anticancer drug discovery and personalized therapies

Cancer is a complex disease whereby multiple genetic aberrations, epigenetic modifications, metabolic reprogramming, and the microenvironment contribute to the development of a tumor. In the traditional anticancer drug discovery pipeline, drug candidates are usually screened in vitro using two-dimensional or three-dimensional cell culture. However, these methods fail to accurately mimic the human disease state. This has led to the poor success rate of anticancer drugs in the preclinical stages since many drugs are abandoned due to inefficacy or toxicity when transitioned to whole-organism models. The common fruit fly, Drosophila melanogaster, has emerged as a beneficial system for modeling human cancers. Decades of fundamental research have shown the evolutionary conservation of key genes and signaling pathways between flies and humans. Moreover, Drosophila has a lower genetic redundancy in comparison to mammals. These factors, in addition to the advancement of genetic toolkits for manipulating gene expression, allow for the generation of complex Drosophila genotypes and phenotypes. Numerous studies have successfully created Drosophila models for colorectal, lung, thyroid, and brain cancers. These models were utilized in the high-throughput screening of FDA-approved drugs which led to the identification of several compounds capable of reducing proliferation and rescuing phenotypes. More noteworthy, Drosophila has also unlocked the potential for personalized therapies. Drosophila ‘avatars’ presenting the same mutations as a patient are used to screen multiple therapeutic agents targeting multiple pathways to find the most appropriate combination of drugs. The outcomes of these studies have translated to significant responses in patients with adenoid cystic carcinoma and metastatic colorectal cancers. Despite not being widely utilized, the concept of in vivo screening of drugs in Drosophila is making significant contributions to the current drug discovery pipeline. In this review, we discuss the application of Drosophila as a platform in anticancer drug discovery; with special focus on the cancer models that have been generated, drug libraries that have been screened and the status of personalized therapies. In addition, we elaborate on the biological and technical limitations of this system.

What we have learnt from Drosophila model organism: the coordination between insulin signaling pathway and tumor cells

Cancer development is related to a variety of signaling pathways which mediate various cellular processes including growth, survival, division and competition of cells, as well as cell-cell interaction. The insulin signaling pathway interacts with different pathways and plays a core role in the regulations of all these processes. In this study, we reviewed recent studies on the relationship between the insulin signaling pathway and tumors using the Drosophila melanogaster model. We found that on one hand, the insulin pathway is normally hyperactive in tumor cells, which promotes tumor growth, and on the other hand, tumor cells can suppress the growth of healthy tissues via inhibition of their insulin pathway. Moreover, systematic disruption in glucose homeostasis also facilitates cancer development by different mechanisms. The studies on how the insulin network regulates the behaviors of cancer cells may help to discover new therapeutic treatments for cancer.

The MicroRNA miR-277 Controls Physiology and Pathology of the Adult Drosophila Midgut by Regulating the Expression of Fatty Acid β-Oxidation-Related Genes in Intestinal Stem Cells

Cell division, growth, and differentiation are energetically costly and dependent processes. In adult stem cell-based epithelia, cellular identity seems to be coupled with a cell's metabolic profile and vice versa. It is thus tempting to speculate that resident stem cells have a distinct metabolism, different from more committed progenitors and differentiated cells. Although investigated for many stem cell types in vitro, in vivo data of niche-residing stem cell metabolism is scarce. In adult epithelial tissues, stem cells, progenitor cells, and their progeny have very distinct functions and characteristics. In our study, we hypothesized and tested whether stem and progenitor cell types might have a distinctive metabolic profile in the intestinal lineage. Here, taking advantage of the genetically accessible adult Drosophila melanogaster intestine and the availability of ex vivo single cell sequencing data, we tested that hypothesis and investigated the metabolism of the intestinal lineage from stem cell (ISC) to differentiated epithelial cell in their native context under homeostatic conditions. Our initial in silico analysis of single cell RNAseq data and functional experiments identify the microRNA miR-277 as a posttranscriptional regulator of fatty acid β-oxidation (FAO) in the intestinal lineage. Low levels of miR-277 are detected in ISC and progressively rising miR-277 levels are found in progenitors during their growth and differentiation. Supporting this, miR-277-regulated fatty acid β-oxidation enzymes progressively declined from ISC towards more differentiated cells in our pseudotime single-cell RNAseq analysis and in functional assays on RNA and protein level. In addition, in silico clustering of single-cell RNAseq data based on metabolic genes validates that stem cells and progenitors belong to two independent clusters with well-defined metabolic characteristics. Furthermore, studying FAO genes in silico indicates that two populations of ISC exist that can be categorized in mitotically active and quiescent ISC, of which the latter relies on FAO genes. In line with an FAO dependency of ISC, forced expression of miR-277 phenocopies RNAi knockdown of FAO genes by reducing ISC size and subsequently resulting in stem cell death. We also investigated miR-277 effects on ISC in a benign and our newly developed CRISPR-Cas9-based colorectal cancer model and found effects on ISC survival, which as a consequence affects tumor growth, further underlining the importance of FAO in a pathological context. Taken together, our study provides new insights into the basal metabolic requirements of intestinal stem cell on β-oxidation of fatty acids evolutionarily implemented by a sole microRNA. Gaining knowledge about the metabolic differences and dependencies affecting the survival of two central and cancer-relevant cell populations in the fly and human intestine might reveal starting points for targeted combinatorial therapy in the hope for better treatment of colorectal cancer in the future.

Embracing complexity in Drosophila cancer models

Cancer continues to be a leading cause of death worldwide, largely due to metastases and cachexia. It is a complex disease that is commonly associated with a variety of comorbidities. With global increases in ageing populations and obesity, multimorbidity is a rapidly growing clinical issue in the context of cancer. Cancer is also genetically heterogeneous, with a tumour's unique profile determining its incidence of metastasis, degree of cachexia and response to therapeutics. These complexities of human cancer are difficult to replicate in animal models and are, in part, responsible for the failures in translational cancer research. In this Perspective, we highlight the fruit fly, Drosophila melanogaster, as a powerful model organism to investigate multimorbidity and tumour diversity. We also highlight how harnessing these complexities in Drosophila can, potentially, enhance cancer research and advance therapeutic discoveries.

Rational Design and Identification of Harmine-Inspired, N-Heterocyclic DYRK1A Inhibitors Employing a Functional Genomic In Vivo Drosophila Model System

Deregulation of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) plays a significant role in developmental brain defects, early-onset neurodegeneration, neuronal cell loss, dementia, and several types of cancer. Herein, we report the discovery of three new classes of N-heterocyclic DYRK1A inhibitors based on the potent, yet toxic kinase inhibitors, harmine and harmol. An initial in vitro evaluation of the small molecule library assembled revealed that the core heterocyclic motifs benzofuranones, oxindoles, and pyrrolones, showed statistically significant DYRK1A inhibition. Further, the utilization of a low cost, high-throughput functional genomic in vivo model system to identify small molecule inhibitors that normalize DYRK1A overexpression phenotypes is described. This in vivo assay substantiated the in vitro results, and the resulting correspondence validates generated classes as architectural motifs that serve as potential DYRK1A inhibitors. Further expansion and analysis of these core compound structures will allow discovery of safe, more effective chemical inhibitors of DYRK1A to ameliorate phenotypes caused by DYRK1A overexpression.

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.

Conditional CRISPR-Cas Genome Editing in Drosophila to Generate Intestinal Tumors

CRISPR-Cas has revolutionized genetics and extensive efforts have been made to enhance its editing efficiency by developing increasingly more elaborate tools. Here, we evaluate the CRISPR-Cas9 system in Drosophila melanogaster to assess its ability to induce stem cell-derived tumors in the intestine. We generated conditional tissue-specific CRISPR knockouts using different Cas9 expression vectors with guide RNAs targeting the BMP, Notch, and JNK pathways in intestinal progenitors such as stem cells (ISCs) and enteroblasts (EBs). Perturbing Notch and BMP signaling increased the proliferation of ISCs/EBs and resulted in the formation of intestinal tumors, albeit with different efficiencies. By assessing both the anterior and posterior regions of the midgut, we observed regional differences in ISC/EB proliferation and tumor formation upon mutagenesis. Surprisingly, high continuous expression of Cas9 in ISCs/EBs blocked age-dependent increase in ISCs/EBs proliferation and when combined with gRNAs targeting tumor suppressors, it prevented tumorigenesis. However, no such effects were seen when temporal parameters of Cas9 were adjusted to regulate its expression levels or with a genetically modified version, which expresses Cas9 at lower levels, suggesting that fine-tuning Cas9 expression is essential to avoid deleterious effects. Our findings suggest that modifications to Cas9 expression results in differences in editing efficiency and careful considerations are required when choosing reagents for CRISPR-Cas9 mutagenesis studies. In summary, Drosophila can serve as a powerful model for context-dependent CRISPR-Cas based perturbations and to test genome-editing systems in vivo.

Low-protein diet applied as part of combination therapy or stand-alone normalizes lifespan and tumor proliferation in a model of intestinal cancer

Tumors of the intestinal tract are among the most common tumor diseases in humans, but, like many other tumor entities, show an unsatisfactory prognosis with a need for effective therapies. To test whether nutritional interventions and a combination with a targeted therapy can effectively cure these cancers, we used the fruit fly Drosophila as a model. In this system, we induced tumors by EGFR overexpression in intestinal stem cells. Limiting the amount of protein in the diet restored life span to that of control animals. In combination with a specific EGFR inhibitor, all major tumor-associated phenotypes could be rescued. This form of treatment was also successful in a real treatment scenario, which means when they started after the full tumor phenotype was expressed. In conclusion, reduced protein administration can be a very promising form of adjuvant cancer therapy.

Tumor models in various Drosophila tissues

The development of cancer is a complex multistage process. Over the past few decades, the model organism Drosophila melanogaster has been crucial in identifying cancer-related genes and pathways and elucidating mechanisms underlying growth regulation in development. Investigations using Drosophila has yielded new insights into the molecular mechanisms involved in tumor initiation and progression. In this review, we describe various tumor models that have been developed in recent years using different Drosophila tissues, such as the imaginal tissue, the neural tissue, the gut, the ovary, and hematopoietic cells. We discuss underlying genetic alterations, cancer-like characteristics, as well as similarities and key differences among these models. We also discuss how disruptions in stem cell division and differentiation result in tumor formation in diverse tissues, and highlight new concepts developed using the fly model to understand context-dependent tumorigenesis. We further discuss the progress made in Drosophila to explore tumor-host interactions that involve the innate immune response to tumor growth and the cachexia wasting phenotype. This article is categorized under: Cancer > Genetics/Genomics/Epigenetics Cancer > Stem Cells and Development Cancer > Molecular and Cellular Physiology.

Tumour-host interactions through the lens of Drosophila

There is a large gap between the deep understanding of mechanisms driving tumour growth and the reasons why patients ultimately die of cancer. It is now appreciated that interactions between the tumour and surrounding non-tumour (sometimes referred to as host) cells play critical roles in mortality as well as tumour progression, but much remains unknown about the underlying molecular mechanisms, especially those that act beyond the tumour microenvironment. Drosophila has a track record of high-impact discoveries about cell-autonomous growth regulation, and is well suited to now probe mysteries of tumour - host interactions. Here, we review current knowledge about how fly tumours interact with microenvironmental stroma, circulating innate immune cells and distant organs to influence disease progression. We also discuss reciprocal regulation between tumours and host physiology, with a particular focus on paraneoplasias. The fly's simplicity along with the ability to study lethality directly provide an opportunity to shed new light on how cancer actually kills.

Drosophila Accessory Gland: A Complementary In Vivo Model to Bring New Insight to Prostate Cancer

Prostate cancer is the most common cancer in aging men. Despite recent progress, there are still few effective treatments to cure its aggressive and metastatic stages. A better understanding of the molecular mechanisms driving disease initiation and progression appears essential to support the development of more efficient therapies and improve patient care. To do so, multiple research models, such as cell culture and mouse models, have been developed over the years and have improved our comprehension of the biology of the disease. Recently, a new model has been added with the use of the Drosophila accessory gland. With a high level of conservation of major signaling pathways implicated in human disease, this functional equivalent of the prostate represents a powerful, inexpensive, and rapid in vivo model to study epithelial carcinogenesis. The purpose of this review is to quickly overview the existing prostate cancer models, including their strengths and limitations. In particular, we discuss how the Drosophila accessory gland can be integrated as a convenient complementary model by bringing new understanding in the mechanisms driving prostate epithelial tumorigenesis, from initiation to metastatic formation.

Precision Medicine on the Fly: Using Drosophila to Decipher Gene-Environment Interactions in Parkinson's Disease

Big data approaches have profoundly influenced state-of-the-art in many fields of research, with toxicology being no exception. Here, we use Parkinson's disease as a window through which to explore the challenges of a dual explosion of metabolomic data addressing the myriad environmental exposures individuals experience and genetic analyses implicating many different loci as risk factors for disease. We argue that new experimental approaches are needed to convert the growing body of omics data into molecular mechanisms of disease that can be therapeutically targeted in specific patients. We outline one attractive strategy, which capitalizes on the rapid generation time and advanced molecular tools available in the fruit fly, Drosophila, to provide a platform for mechanistic dissection and drug discovery.

Sensitive High-Throughput Assays for Tumour Burden Reveal the Response of a Drosophila melanogaster Model of Colorectal Cancer to Standard Chemotherapies

Drosophila melanogaster (Drosophila) models of cancer are emerging as powerful tools to investigate the basic mechanisms underlying tumour progression and identify novel therapeutics. Rapid and inexpensive, it is possible to carry out genetic and drug screens at a far larger scale than in vertebrate organisms. Such whole-organism-based drug screens permits assessment of drug absorption and toxicity, reducing the possibility of false positives. Activating mutations in the Wnt and Ras signalling pathways are common in many epithelial cancers, and when driven in the adult Drosophila midgut, it induces aggressive intestinal tumour-like outgrowths that recapitulate many aspects of human colorectal cancer (CRC). Here we have taken a Drosophila CRC model in which tumourous cells are marked with both GFP and luciferase reporter genes, and developed novel high-throughput assays for quantifying tumour burden. Leveraging these assays, we find that the Drosophila CRC model responds rapidly to treatment with standard CRC-drugs, opening the door to future rapid genetic and drug screens.

A Drosophila platform identifies a novel, personalized therapy for a patient with adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a rare cancer type that originates in the salivary glands. Tumors commonly invade along nerve tracks in the head and neck, making surgery challenging. Follow-up treatments for recurrence or metastasis including chemotherapy and targeted therapies have shown limited efficacy, emphasizing the need for new therapies. Here, we report a Drosophila-based therapeutic approach for a patient with advanced ACC disease. A patient-specific Drosophila transgenic line was developed to model the five major variants associated with the patient's disease. Robotics-based screening identified a three-drug cocktail—vorinostat, pindolol, tofacitinib—that rescued transgene-mediated lethality in the Drosophila patient-specific line. Patient treatment led to a sustained stabilization and a partial metabolic response of 12 months. Subsequent resistance was associated with new genomic amplifications and deletions. Given the lack of options for patients with ACC, our data suggest that this approach may prove useful for identifying novel therapeutic candidates.

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Personalized therapy was developed for patient with Adenoid Cystic Carcinoma

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Genomics analysis was leveraged to establish a Drosophila ‘personalized patient avatar’

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A robotics-based screen identified a novel three drug therapeutic cocktail

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12 months response was followed by relapse and significant tumor genomic re-wiring

Tiny Drosophila makes giant strides in cancer research

Cancer burden has been increasing worldwide, making cancer the second leading cause of death in the world. Over the past decades, various experimental models have provided important insights into the nature of cancer. Among them, the fruit fly Drosophila as a whole-animal toolkit has made a decisive contribution to our understanding of fundamental mechanisms of cancer development including loss of cell polarity. In recent years, scalable Drosophila platforms have proven useful also in developing anti-cancer regimens that are effective not only in mammalian models but also in patients. Here, we review studies using Drosophila as a tool to advance cancer study by complementing other traditional research systems.

Amalgam regulates the receptor tyrosine kinase pathway through Sprouty in glial cell development in the Drosophila larval brain

The receptor tyrosine kinase (RTK) pathway plays an essential role in development and disease by controlling cell proliferation and differentiation. Here, we profile the Drosophila larval brain by single-cell RNA-sequencing and identify Amalgam (Ama), which encodes a cell adhesion protein of the immunoglobulin IgLON family, as regulating the RTK pathway activity during glial cell development. Depletion of Ama reduces cell proliferation, affects glial cell type composition and disrupts the blood-brain barrier (BBB), which leads to hemocyte infiltration and neuronal death. We show that Ama depletion lowers RTK activity by upregulating Sprouty (Sty), a negative regulator of the RTK pathway. Knockdown of Ama blocks oncogenic RTK signaling activation in the Drosophila glioma model and halts malignant transformation. Finally, knockdown of a human ortholog of Ama, LSAMP, results in upregulation of SPROUTY2 in glioblastoma cell lines, suggesting that the relationship between Ama and Sty is conserved.

Interorgan communication in development and cancer

Studies in model organisms have demonstrated that extensive communication occurs between distant organs both during development and in diseases such as cancer. Organs communicate with each other to coordinate growth and reach the correct size, while the fate of tumor cells depend on the outcome of their interaction with the immune system and peripheral tissues. In this review, we outline recent studies in Drosophila, which have enabled an improved understanding of the complex crosstalk between organs in the context of both organismal and tumor growth. We argue that Drosophila is a powerful model organism for studying these interactions, and these studies have the potential for improving our understanding of signaling pathways and candidate factors that mediate this conserved interorgan crosstalk. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Early Embryonic Development > Development to the Basic Body Plan Invertebrate Organogenesis > Flies.

A Drosophila model of oral peptide therapeutics for adult intestinal stem cell tumors

Peptide therapeutics, unlike small-molecule drugs, display crucial advantages of target specificity and the ability to block large interacting interfaces, such as those of transcription factors. The transcription co-factor of the Hippo pathway, YAP/Yorkie (Yki), has been implicated in many cancers, and is dependent on its interaction with the DNA-binding TEAD/Sd proteins via a large Ω-loop. In addition, the mammalian vestigial-like (VGLL) proteins, specifically their TONDU domain, competitively inhibit YAP-TEAD interaction, resulting in arrest of tumor growth. Here, we show that overexpression of the TONDU peptide or its oral uptake leads to suppression of Yki-driven intestinal stem cell tumors in the adult Drosophila midgut. In addition, comparative proteomic analyses of peptide-treated and untreated tumors, together with chromatin immunoprecipitation analysis, reveal that integrin pathway members are part of the Yki-oncogenic network. Collectively, our findings establish Drosophila as a reliable in vivo platform to screen for cancer oral therapeutic peptides and reveal a tumor suppressive role for integrins in Yki-driven tumors.This article has an associated First Person interview with the first author of the paper.

Dissemination of RasV12-transformed cells requires the mechanosensitive channel Piezo

Dissemination of transformed cells is a key process in metastasis. Despite its importance, how transformed cells disseminate from an intact tissue and enter the circulation is poorly understood. Here, we use a fully developed tissue, Drosophila midgut, and describe the morphologically distinct steps and the cellular events occurring over the course of Ras^V12-transformed cell dissemination. Notably, Ras^V12-transformed cells formed the Actin- and Cortactin-rich invasive protrusions that were important for breaching the extracellular matrix (ECM) and visceral muscle. Furthermore, we uncovered the essential roles of the mechanosensory channel Piezo in orchestrating dissemination of Ras^V12-transformed cells. Collectively, our study establishes an in vivo model for studying how transformed cells migrate out from a complex tissue and provides unique insights into the roles of Piezo in invasive cell behavior.

Drosophila tumours can be utilised to study the mechanisms of cell dissemination. Here, the authors use Drosophila midgut to examine the course of Ras^V12-transformed cell dissemination from midgut into circulation, which requires the actions of invasive protrusions and the mechanosensitive channel Piezo.

Rounding up the Usual Suspects: Assessing Yorkie, AP-1, and Stat Coactivation in Tumorigenesis

Can hyperactivation of a few key signaling effectors be the underlying reason for the majority of epithelial cancers despite different driver mutations? Here, to address this question, we use the Drosophila model, which allows analysis of gene expression from tumors with known initiating mutations. Furthermore, its simplified signaling pathways have numerous well characterized targets we can use as pathway readouts. In Drosophila tumor models, changes in the activities of three pathways, Jun N-terminal Kinase (JNK), Janus Kinase / Signal Transducer and Activator of Transcription (JAK/STAT), and Hippo, mediated by AP-1 factors, Stat92E, and Yorkie, are reported frequently. We hypothesized this may indicate that these three pathways are commonly deregulated in tumors. To assess this, we mined the available transcriptomic data and evaluated the activity levels of eight pathways in various tumor models. Indeed, at least two out of our three suspects contribute to tumor development in all Drosophila cancer models assessed, despite different initiating mutations or tissues of origin. Surprisingly, we found that Notch signaling is also globally activated in all models examined. We propose that these four pathways, JNK, JAK/STAT, Hippo, and Notch, are paid special attention and assayed for systematically in existing and newly developed models.

Drug discovery and chemical probing in Drosophila

Flies are increasingly utilized in drug discovery and chemical probing in vivo, which are novel technologies complementary to genetic probing in fundamental biological studies. Excellent genetic conservation, small size, short generation time, and over one hundred years of genetics make Drosophila an attractive model for rapid assay readout and use of analytical amounts of compound, enabling the experimental iterations needed in early drug development at a fraction of time and costs. Here, we describe an effective drug-testing pipeline using adult flies that can be easily implemented to study several disease models and different genotypes to discover novel molecular insight, probes, quality lead compounds, and develop novel prototype drugs.

Strategies for Functional Interrogation of Big Cancer Data Using Drosophila Cancer Models

Rapid development of high throughput genome analysis technologies accompanied by significant reduction in costs has led to the accumulation of an incredible amount of data during the last decade. The emergence of big data has had a particularly significant impact in biomedical research by providing unprecedented, systems-level access to many disease states including cancer, and has created promising opportunities as well as new challenges. Arguably, the most significant challenge cancer research currently faces is finding effective ways to use big data to improve our understanding of molecular mechanisms underlying tumorigenesis and developing effective new therapies. Functional exploration of these datasets and testing predictions from computational approaches using experimental models to interrogate their biological relevance is a key step towards achieving this goal. Given the daunting scale and complexity of the big data available, experimental systems like Drosophila that allow large-scale functional studies and complex genetic manipulations in a rapid, cost-effective manner will be of particular importance for this purpose. Findings from these large-scale exploratory functional studies can then be used to formulate more specific hypotheses to be explored in mammalian models. Here, I will discuss several strategies for functional exploration of big cancer data using Drosophila cancer models.

Sequential Ras/MAPK and PI3K/AKT/mTOR pathways recruitment drives basal extrusion in the prostate-like gland of Drosophila

One of the most important but less understood step of epithelial tumourigenesis occurs when cells acquire the ability to leave their epithelial compartment. This phenomenon, described as basal epithelial cell extrusion (basal extrusion), represents the first step of tumour invasion. However, due to lack of adequate in vivo model, implication of emblematic signalling pathways such as Ras/Mitogen-Activated Protein Kinase (MAPK) and phosphoinositide 3 kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signalling pathways, is scarcely described in this phenomenon. We have developed a unique model of basal extrusion in the Drosophila accessory gland. There, we demonstrate that both Ras/MAPK and PI3K/AKT/mTOR pathways are necessary for basal extrusion. Furthermore, as in prostate cancer, we show that these pathways are co-activated. This occurs through set up of Epidermal Growth Factor Receptor (EGFR) and Insulin Receptor (InR) dependent autocrine loops, a phenomenon that, considering human data, could be relevant for prostate cancer.

JNK-dependent intestinal barrier failure disrupts host-microbe homeostasis during tumorigenesis

The intestinal epithelium forms a tight barrier to the environment and is constantly regenerated. Precise control of barrier function and tissue renewal is important to maintain homeostasis. Using an inducible tumor model in the Drosophila intestine, this study shows that tumor progression disrupts the intestinal barrier and leads to commensal dysbiosis, thereby further fueling tumor growth. This reenforcing feedback loop can be interrupted by treatments with JNK inhibitor or antibiotics.

In all animals, the intestinal epithelium forms a tight barrier to the environment. The epithelium regulates the absorption of nutrients, mounts immune responses, and prevents systemic infections. Here, we investigate the consequences of tumorigenesis on the microbiome using a Drosophila intestinal tumor model. We show that upon loss of BMP signaling, tumors lead to aberrant activation of JNK/Mmp2 signaling, followed by intestinal barrier dysfunction and commensal imbalance. In turn, the dysbiotic microbiome triggers a regenerative response and stimulates tumor growth. We find that inhibiting JNK signaling or depletion of the microbiome restores barrier function of the intestinal epithelium, leading to a reestablishment of host–microbe homeostasis, and organismic lifespan extension. Our experiments identify a JNK-dependent feedback amplification loop between intestinal tumors and the microbiome. They also highlight the importance of controlling the activity level of JNK signaling to maintain epithelial barrier function and host–microbe homeostasis.

Outcompeting cancer

The tumour microenvironment plays a critical role in determining tumour fate. Within that environment, and indeed throughout epithelial tissues, cells experience competition with their neighbours, with those less fit being eliminated by fitter adjacent cells. Herein we discuss evidence suggesting that mutations in cancer cells may be selected for their ability to exploit cell competition to kill neighbouring host cells, thereby facilitating tumour expansion. In some instances, cell competition may help host tissues to defend against cancer, by removing neoplastic and aneuploid cells. Cancer risk factors, such as high-sugar or high-fat diet and inflammation, impact cell competition-based host defences, suggesting that their effect on tumour risk may in part be accounted for by their influence on cell competition. We propose that interventions aimed at modifying the strength and direction of cell competition could induce cancer cell killing and form the basis for novel anticancer therapies.

Drosophila as a model to understand autophagy deregulation in human disorders

Autophagy has important functions in normal physiology to maintain homeostasis and protect against cellular stresses by the removal of harmful cargos such as dysfunctional organelles, protein aggregates and invading pathogens. The deregulation of autophagy is a hallmark of many diseases and therapeutic targeting of autophagy is highly topical. With the complex role of autophagy in disease it is essential to understand the genetic and molecular basis of the contribution of autophagy to pathogenesis. The model organism, Drosophila, provides a genetically amenable system to dissect out the contribution of autophagy to human disease models. Here we review the roles of autophagy in human disease and how autophagy studies in Drosophila have contributed to the understanding of pathophysiology.

Two-Faced: Roles of JNK Signalling During Tumourigenesis in the Drosophila Model

The highly conserved c-Jun N-terminal Kinase (JNK) signalling pathway has many functions, regulating a diversity of processes: from cell movement during embryogenesis to the stress response of cells after environmental insults. Studies modelling cancer using the vinegar fly, Drosophila melanogaster, have identified both pro- and anti-tumourigenic roles for JNK signalling, depending on context. As a tumour suppressor, JNK signalling commonly is activated by conserved Tumour Necrosis Factor (TNF) signalling, which promotes the caspase-mediated death of tumourigenic cells. JNK pathway activation can also occur via actin cytoskeleton alterations, and after cellular damage inflicted by reactive oxygen species (ROS). Additionally, JNK signalling frequently acts in concert with Salvador-Warts-Hippo (SWH) signalling – either upstream of or parallel to this potent growth-suppressing pathway. As a tumour promoter, JNK signalling is co-opted by cells expressing activated Ras-MAPK signalling (among other pathways), and used to drive cell morphological changes, induce invasive behaviours, block differentiation, and enable persistent cell proliferation. Furthermore, JNK is capable of non-autonomous influences within tumour microenvironments by effecting the transcription of various cell growth- and proliferation-promoting molecules. In this review, we discuss these aspects of JNK signalling in Drosophila tumourigenesis models, and highlight recent publications that have expanded our knowledge of this important and versatile pathway.

Physiology, Development, and Disease Modeling in the Drosophila Excretory System

The insect excretory system contains two organ systems acting in concert: the Malpighian tubules and the hindgut perform essential roles in excretion and ionic and osmotic homeostasis. For over 350 years, these two organs have fascinated biologists as a model of organ structure and function. As part of a recent surge in interest, research on the Malpighian tubules and hindgut of Drosophila have uncovered important paradigms of organ physiology and development. Further, many human disease processes can be modeled in these organs. Here, focusing on discoveries in the past 10 years, we provide an overview of the anatomy and physiology of the Drosophila excretory system. We describe the major developmental events that build these organs during embryogenesis, remodel them during metamorphosis, and repair them following injury. Finally, we highlight the use of the Malpighian tubules and hindgut as accessible models of human disease biology. The Malpighian tubule is a particularly excellent model to study rapid fluid transport, neuroendocrine control of renal function, and modeling of numerous human renal conditions such as kidney stones, while the hindgut provides an outstanding model for processes such as the role of cell chirality in development, nonstem cell-based injury repair, cancer-promoting processes, and communication between the intestine and nervous system.

Cytoneme-mediated signaling essential for tumorigenesis

Communication between neoplastic cells and cells of their microenvironment is critical to cancer progression. To investigate the role of cytoneme-mediated signaling as a mechanism for distributing growth factor signaling proteins between tumor and tumor-associated cells, we analyzed EGFR and RET Drosophila tumor models and tested several genetic loss-of-function conditions that impair cytoneme-mediated signaling. Neuroglian, capricious, Irk2, SCAR, and diaphanous are genes that cytonemes require during normal development. Neuroglian and Capricious are cell adhesion proteins, Irk2 is a potassium channel, and SCAR and Diaphanous are actin-binding proteins, and the only process to which they are known to contribute jointly is cytoneme-mediated signaling. We observed that diminished function of any one of these genes suppressed tumor growth and increased organism survival. We also noted that EGFR-expressing tumor discs have abnormally extensive tracheation (respiratory tubes) and ectopically express Branchless (Bnl, a FGF) and FGFR. Bnl is a known inducer of tracheation that signals by a cytoneme-mediated process in other contexts, and we determined that exogenous over-expression of dominant negative FGFR suppressed tumor growth. Our results are consistent with the idea that cytonemes move signaling proteins between tumor and stromal cells and that cytoneme-mediated signaling is required for tumor growth and malignancy.

The growth of many types of tumors depend on productive interactions with stromal, non-tumor neighbors, and although there is evidence that tumor and stromal cells exchange signaling proteins and growth factors that they produce, the mechanism by which these proteins move between the signaling cells has not been investigated and is not known. Our previous work has shown that normal cells make transient chemical synapses at sites where specialized filopodia called cytonemes contact signaling partners, and in this work we explore the possibility that tumors use the same mechanism to communicate with stromal cells. We show that cytoneme-mediated signaling is essential for growth of Drosophila tumors that model human EGFR over-expression and RET-driven disease. Remarkably, inhibition of cytonemes cures flies of lethal tumors.

Using Drosophila Models and Tools to Understand the Mechanisms of Novel Human Cancer Driver Gene Function

The formation, overgrowth and metastasis of tumors comprise a complex series of cellular and molecular events resulting from the combined effects of a variety of aberrant signaling pathways, mutations, and epigenetic alterations. Modeling this complexity in vivo requires multiple genes to be manipulated simultaneously, which is technically challenging. Here, we analyze how Drosophila research can further contribute to identifying pathways and elucidating mechanisms underlying novel cancer driver (risk) genes associated with tumor growth and metastasis in humans.