Of flies and men--studying human disease in Drosophila

Hazard Assessment of the Effects of Acute and Chronic Exposure to Permethrin, Copper Hydroxide, Acephate, and Validamycin Nanopesticides on the Physiology of Drosophila: Novel Insights into the Cellular Internalization and Biological Effects

New insights into the interactions between nanopesticides and edible plants are required in order to elucidate their impacts on human health and agriculture. Nanopesticides include formulations consisting of organic/inorganic nanoparticles. Drosophila melanogaster has become a powerful model in genetic research thanks to its genetic similarity to mammals. This project mainly aimed to generate new evidence for the toxic/genotoxic properties of different nanopesticides (a nanoemulsion (permethrin nanopesticides, 20 ± 5 nm), an inorganic nanoparticle as an active ingredient (copper(II) hydroxide [Cu(OH)₂] nanopesticides, 15 ± 6 nm), a polymer-based nanopesticide (acephate nanopesticides, 55 ± 25 nm), and an inorganic nanoparticle associated with an organic active ingredient (validamycin nanopesticides, 1177 ± 220 nm)) and their microparticulate forms (i.e., permethrin, copper(II) sulfate pentahydrate (CuSO₄·5H₂O), acephate, and validamycin) widely used against agricultural pests, while also showing the merits of using Drosophila—a non-target in vivo eukaryotic model organism—in nanogenotoxicology studies. Significant biological effects were noted at the highest doses of permethrin (0.06 and 0.1 mM), permethrin nanopesticides (1 and 2.5 mM), CuSO₄·5H₂O (1 and 5 mM), acephate and acephate nanopesticides (1 and 5 mM, respectively), and validamycin and validamycin nanopesticides (1 and 2.5 mM, respectively). The results demonstrating the toxic/genotoxic potential of these nanopesticides through their impact on cellular internalization and gene expression represent significant contributions to future nanogenotoxicology studies.

Effects of Chlorophyll a and b in Reducing Genotoxicity of 2-Amino-3,8-dimethylimidazo[4,5-F]quinoxaline (MeIQx)

In this study, the protective effects of chlorophyll a and chlorophyll b (0.5 and 1 µM) against the heterocyclic amine compound 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx, 4.69 µM, 9.38 µM, 23.45 µM) with somatic mutation and recombination test in Drosophila melanogaster are investigated. Chronic applications are performed to transheterozygous larvae with respect to two recessive genes, mwh (multiple wing hair) and flr3 (flare), by using Drosophila strains. The genotoxic effects of MeIQx are primarily determined for third instars larvae. In antigenotoxicity studies, two different application groups are constituted. While for the first group doses of chlorophyll a, b, and MeIQx are given to the third instars larvae simultaneously, for the second group doses of MeIQx are applied at the third instars after doses of chlorophyll a and b are given to at the second instars larvae. Chlorophyll a and b are effective in reducing genotoxic effects of MeIQx by both applications on individuals and it is observed that the pretreatment method is much more effective than the simultaneous one. There are similar results for chlorophyll a and b in efficacy.

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.

Integrative developmental biology in the age of anthropogenic change

Humans are changing and challenging nature in many ways. Conservation Biology seeks to limit human impacts on nature and preserve biological diversity. Traditionally, Developmental Biology and Conservation Biology have had nonoverlapping objectives, operating in distinct spheres of biological science. However, this chasm can and should be filled to help combat the emerging challenges of the 21st century. The means by which to accomplish this goal were already established within the conceptual framework of evo- and eco-devo and can be further expanded to address the ways that anthropogenic disturbance affect embryonic development. Herein, I describe ways that these approaches can be used to advance the study of reptilian embryos. More specifically, I explore the ways that a developmental perspective can advance ongoing studies of embryonic physiology in the context of global warming and chemical pollution, both of which are known stressors of reptilian embryos. I emphasize ways that these developmental perspectives can inform conservation biologists trying to develop management practices that will address the complexity of challenges facing reptilian embryos.

Zika virus non-structural protein NS4A restricts eye growth in Drosophila through regulation of JAK/STAT signaling

To gain a comprehensive view of the changes in host gene expression underlying Zika virus (ZIKV) pathogenesis, we performed whole-genome RNA sequencing (RNA-seq) of ZIKV-infected Drosophila adult flies. RNA-seq analysis revealed that ZIKV infection alters several and diverse biological processes, including stress, locomotion, lipid metabolism, imaginal disc morphogenesis and regulation of JAK/STAT signaling. To explore the interaction between ZIKV infection and JAK/STAT signaling regulation, we generated genetic constructs overexpressing ZIKV-specific non-structural proteins NS2A, NS2B, NS4A and NS4B. We found that ectopic expression of non-structural proteins in the developing Drosophila eye significantly restricts growth of the larval and adult eye and correlates with considerable repression of the in vivo JAK/STAT reporter, 10XStat92E-GFP At the cellular level, eye growth defects are associated with reduced rate of proliferation without affecting the overall rate of apoptosis. In addition, ZIKV NS4A genetically interacts with the JAK/STAT signaling components; co-expression of NS4A along with the dominant-negative form of domeless or StatRNAi results in aggravated reduction in eye size, while co-expression of NS4A in HopTuml (also known as hopTum ) mutant background partially rescues the hop-induced eye overgrowth phenotype. The function of ZIKV NS4A in regulating growth is maintained in the wing, where ZIKV NS4A overexpression in the pouch domain results in reduced growth linked with diminished expression of Notch targets, Wingless (Wg) and Cut, and the Notch reporter, NRE-GFP Thus, our study provides evidence that ZIKV infection in Drosophila results in restricted growth of the developing eye and wing, wherein eye phenotype is induced through regulation of JAK/STAT signaling, whereas restricted wing growth is induced through regulation of Notch signaling. The interaction of ZIKV non-structural proteins with the conserved host signaling pathways further advance our understanding of ZIKV-induced pathogenesis.This article has an associated First Person interview with the first author of the paper.

Gene-Diet Interactions: Dietary Rescue of Metabolic Effects in spen-Depleted Drosophila melanogaster

Obesity and its comorbidities are a growing health epidemic. Interactions between genetic background, the environment, and behavior (i.e., diet) greatly influence organismal energy balance. Previously, we described obesogenic mutations in the gene Split ends (Spen) in Drosophila melanogaster, and roles for Spen in fat storage and metabolic state. Lipid catabolism is impaired in Spen-deficient fat storage cells, accompanied by a compensatory increase in glycolytic flux and protein catabolism. Here, we investigate gene-diet interactions to determine if diets supplemented with specific macronutrients can rescue metabolic dysfunction in Spen-depleted animals. We show that a high-yeast diet partially rescues adiposity and developmental defects. High sugar partially improves developmental timing as well as longevity of mated females. Gene-diet interactions were heavily influenced by developmental-stage-specific organismal needs: extra yeast provides benefits early in development (larval stages) but becomes detrimental in adulthood. High sugar confers benefits to Spen-depleted animals at both larval and adult stages, with the caveat of increased adiposity. A high-fat diet is detrimental according to all tested criteria, regardless of genotype. Whereas Spen depletion influenced phenotypic responses to supplemented diets, diet was the dominant factor in directing the whole-organism steady-state metabolome. Obesity is a complex disease of genetic, environmental, and behavioral inputs. Our results show that diet customization can ameliorate metabolic dysfunction underpinned by a genetic factor.

Invertebrate and vertebrate models in aging research

Therapeutic interventions that can delay age associated diseases and ensure a longer health-span is a major goal of aging research. Consequent to understanding that aging is a modifiable trait, a large number of studies are currently being undertaken to elucidate the mechanism(s) of the aging process. Research on human aging and longevity is difficult, due to longer time frame, ethical concerns and environmental variables. Most of the present day understanding about the aging process comes through studies conducted on model organisms. These provide suitable platforms for understanding underlying mechanism(s) which control aging and have led to major discoveries that emphasize the evolutionarily conserved molecular pathways as key players that respond to extra and intracellular signals. This is a review of various invertebrate and vertebrate models including yeast, Drosophila, C. elegans, rodents, naked mole rat, and birds, currently used in aging research with emphasis on how well they can mimic aging in higher animals and humans.

Drosophila Model in Cancer: An Introduction

Cancer is a cumulative manifestation of several complicated disease states that affect multiple organs. Over the last few decades, the fruit fly Drosophila melanogaster, has become a successful model for studying human cancers. The genetic simplicity and vast arsenal of genetic tools available in Drosophila provides a unique opportunity to address questions regarding cancer initiation and progression that would be extremely challenging in other model systems. In this chapter we provide a historical overview of Drosophila as a model organism for cancer research, summarize the multitude of genetic tools available, offer a brief comparison between different model organisms and cell culture platforms used in cancer studies and briefly discuss some of the latest models and concepts in recent Drosophila cancer research.

Surprising conservation of schizophrenia risk genes in lower organisms reflects their essential function and the evolution of genetic liability

Schizophrenia is a devastating psychiatric illness that affects approximately 1% of the population. Genetic variation in multiple genes causes elevated risk for the disorder, but the molecular basis is inadequately understood and it is not clear how risk genes have evolved and persisted in the genome. To address these issues, we have identified orthologs/homologs of 344 schizophrenia risk genes (from the Psychiatric Genomics Consortium dataset) in lower organisms, including C. elegans, Drosophila and zebrafish, along with phenotypes produced by genetic disruption in C. elegans. Schizophrenia risk genes were evolutionarily conserved at significantly higher rates in C. elegans (81%) and zebrafish (88%) than genes in general for these two species (40-70%). The risk-gene equivalents were highly (~3-fold) enriched for essential genes consistent with polygenic mutation threshold models, which propose that genetic susceptibility results from the inevitable expression of harmful combinations of risk variants in the population. Most notably, numerous examples of cross-species synteny revealed how blocks of risk genes geared toward a shared biological purpose coalesced into proximity during evolution. We obtained initial evidence that schizophrenia risk genes affected different stages of development, potentially allowing differential modulation by the environment. Taken together, studies of the conservation of schizophrenia risk genes in simple model organisms provided novel insights into the molecular basis for genetic susceptibility to a complex human psychiatric disorder.

Rare Genetic Blood Disease Modeling in Zebrafish

Hematopoiesis results in the correct formation of all the different blood cell types. In mammals, it starts from specific hematopoietic stem and precursor cells residing in the bone marrow. Mature blood cells are responsible for supplying oxygen to every cell of the organism and for the protection against pathogens. Therefore, inherited or de novo genetic mutations affecting blood cell formation or the regulation of their activity are responsible for numerous diseases including anemia, immunodeficiency, autoimmunity, hyper- or hypo-inflammation, and cancer. By definition, an animal disease model is an analogous version of a specific clinical condition developed by researchers to gain information about its pathophysiology. Among all the model species used in comparative medicine, mice continue to be the most common and accepted model for biomedical research. However, because of the complexity of human diseases and the intrinsic differences between humans and other species, the use of several models (possibly in distinct species) can often be more helpful and informative than the use of a single model. In recent decades, the zebrafish (Danio rerio) has become increasingly popular among researchers, because it represents an inexpensive alternative compared to mammalian models, such as mice. Numerous advantages make it an excellent animal model to be used in genetic studies and in particular in modeling human blood diseases. Comparing zebrafish hematopoiesis to mammals, it is highly conserved with few, significant differences. In addition, the zebrafish model has a high-quality, complete genomic sequence available that shows a high level of evolutionary conservation with the human genome, empowering genetic and genomic approaches. Moreover, the external fertilization, the high fecundity and the transparency of their embryos facilitate rapid, in vivo analysis of phenotypes. In addition, the ability to manipulate its genome using the last genome editing technologies, provides powerful tools for developing new disease models and understanding the pathophysiology of human disorders. This review provides an overview of the different approaches and techniques that can be used to model genetic diseases in zebrafish, discussing how this animal model has contributed to the understanding of genetic diseases, with a specific focus on the blood disorders.

Anti-cancer drug discovery: update and comparisons in yeast, Drosophila, and zebrafish

Discovery of novel cancer chemotherapeutics focuses on screening and identifying compounds that can target 'cancer-specific' biological processes while causing minimal toxicity to non-tumor cells. Alternatively, model organisms with highly conserved cancer-related cellular processes relative to human cells may offer new opportunities for anticancer drug discovery when combined with chemical screening. Some organisms used for chemotherapeutic discovery include yeast, Drosophila, and zebrafish which are similar in important ways relevant to cancer study but offer distinct advantages as well. Here, we describe these model attributes and the rationale for using them in cancer drug screening research.

The study of Priapulus caudatus reveals conserved molecular patterning underlying different gut morphogenesis in the Ecdysozoa

Background

The digestive systems of animals can become highly specialized in response to their exploration and occupation of new ecological niches. Although studies on different animals have revealed commonalities in gut formation, the model systems Caenorhabditis elegans and Drosophila melanogaster, which belong to the invertebrate group Ecdysozoa, exhibit remarkable deviations in how their intestines develop. Their morphological and developmental idiosyncrasies have hindered reconstructions of ancestral gut characters for the Ecdysozoa, and limit comparisons with vertebrate models. In this respect, the phylogenetic position, and slow evolving morphological and molecular characters of marine priapulid worms advance them as a key group to decipher evolutionary events that occurred in the lineages leading to C. elegans and D. melanogaster.

Results

In the priapulid Priapulus caudatus, the gut consists of an ectodermal foregut and anus, and a mid region of at least partial endodermal origin. The inner gut develops into a 16-cell primordium devoid of visceral musculature, arranged in three mid tetrads and two posterior duplets. The mouth invaginates ventrally and shifts to a terminal anterior position as the ventral anterior ectoderm differentially proliferates. Contraction of the musculature occurs as the head region retracts into the trunk and resolves the definitive larval body plan. Despite obvious developmental differences with C. elegans and D. melanogaster, the expression in P. caudatus of the gut-related candidate genes NK2.1, foxQ2, FGF8/17/18, GATA456, HNF4, wnt1, and evx demonstrate three distinct evolutionarily conserved molecular profiles that correlate with morphologically identified sub-regions of the gut.

Conclusions

The comparative analysis of priapulid development suggests that a midgut formed by a single endodermal population of vegetal cells, a ventral mouth, and the blastoporal origin of the anus are ancestral features in the Ecdysozoa. Our molecular data on P. caudatus reveal a conserved ecdysozoan gut-patterning program and demonstrates that extreme morphological divergence has not been accompanied by major molecular innovations in transcriptional regulators during digestive system evolution in the Ecdysozoa. Our data help us understand the origins of the ecdysozoan body plan, including those of C. elegans and D. melanogaster, and this is critical for comparisons between these two prominent model systems and their vertebrate counterparts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0139-z) contains supplementary material, which is available to authorized users.

Intercellular cooperation and competition in brain cancers: lessons from Drosophila and human studies

Glioblastoma (GBM) is a primary brain cancer with an extremely poor prognosis. GBM tumors contain heterogeneous cellular components, including a small subpopulation of tumor cells termed glioma stem cells (GSCs). GSCs are characterized as chemotherapy- and radiotherapy-resistant cells with prominent tumorigenic ability. Studies in Drosophila cancer models demonstrated that interclonal cooperation and signaling from apoptotic clones provokes aggressive growth of neighboring tumorigenic clones, via compensatory proliferation or apoptosis induced proliferation. Mechanistically, these aggressive tumors depend on activation of Jun-N-terminal kinase (upstream of c-JUN), and Drosophila Wnt (Wg) in the apoptotic clones. Consistent with these nonmammalian studies, data from several mammalian studies have shown that c-JUN and Wnt are hyperactivated in aggressive tumors (including GBM). However, it remains elusive whether compensatory proliferation is an evolutionarily conserved mechanism in cancers. In the present report, we summarize recent studies in Drosophila models and mammalian models (e.g., xenografts of human cancer cells into small animals) to elucidate the intercellular interactions between the apoptosis-prone cancer cells (e.g., non-GSCs) and the hyperproliferative cancer cells (e.g., GSCs). These evolving investigations will yield insights about molecular signaling interactions in the context of post-therapeutic phenotypic changes in human cancers. Furthermore, these studies are likely to revise our understanding of the genetic changes and post-therapeutic cell-cell interactions, which is a vital area of cancer biology with wide applications to many cancer types in humans.

Mutagenic/recombinogenic effects of four lipid peroxidation products in Drosophila

The human diet is an important factor in the development of different diseases. Lipid peroxidation during frying in edible vegetable liquid oils of food components is a mechanism leading to the formation of free radicals. Such radicals induce tissue damage and are implicated in diverse pathological conditions, including aging, atherosclerosis, brain disorders, cancer, lung disorders and various liver disorders. In the present study, we decided to investigate the genotoxic effects of four lipid peroxidation products in the in vivo Drosophila wing somatic mutation and recombination test. In this test, point mutation, chromosome breakage and mitotic recombination produce single spots; while twin spots are produced only by mitotic recombination. Drosophila is a suitable eukaryotic organism for mutagenicity studies and also its metabolism is quite similar to that of mammalians. Since conflicting data exist on the possible risk of several lipid peroxidation products for humans, we have selected four of them, namely acrolein, crotonaldehyde, 4-hydroxy-hexenal (4-HHE) and 4-oxo-2-nonenal (4-ONE). Especially at the highest concentrations tested all exert both mutagenic and recombinogenic effects in the Drosophila SMART assay, showing a direct dose-effect relationship. This is the first study reporting genotoxicity data in Drosophila for these compounds.

The Drosophila melanogaster host model

The deleterious and sometimes fatal outcomes of bacterial infectious diseases are the net result of the interactions between the pathogen and the host, and the genetically tractable fruit fly, Drosophila melanogaster, has emerged as a valuable tool for modeling the pathogen-host interactions of a wide variety of bacteria. These studies have revealed that there is a remarkable conservation of bacterial pathogenesis and host defence mechanisms between higher host organisms and Drosophila. This review presents an in-depth discussion of the Drosophila immune response, the Drosophila killing model, and the use of the model to examine bacterial-host interactions. The recent introduction of the Drosophila model into the oral microbiology field is discussed, specifically the use of the model to examine Porphyromonas gingivalis-host interactions, and finally the potential uses of this powerful model system to further elucidate oral bacterial-host interactions are addressed.

High-throughput screening and small animal models, where are we?

Current high-throughput screening methods for drug discovery rely on the existence of targets. Moreover, most of the hits generated during screenings turn out to be invalid after further testing in animal models. To by-pass these limitations, efforts are now being made to screen chemical libraries on whole animals. One of the most commonly used animal model in biology is the murine model Mus musculus. However, its cost limit its use in large-scale therapeutic screening. In contrast, the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the fish Danio rerio are gaining momentum as screening tools. These organisms combine genetic amenability, low cost and culture conditions that are compatible with large-scale screens. Their main advantage is to allow high-throughput screening in a whole-animal context. Moreover, their use is not dependent on the prior identification of a target and permits the selection of compounds with an improved safety profile. This review surveys the versatility of these animal models for drug discovery and discuss the options available at this day.

At the crossroads of polarity, proliferation and apoptosis: the use of Drosophila to unravel the multifaceted role of endocytosis in tumor suppression

Endocytosis is an important regulator of cell-cell signaling and endocytic trafficking has been increasingly implicated in control of tumor suppression. Recent insights from Drosophila indicate that impairment of multiple trafficking steps which lead to receptor degradation can cause tumor formation in epithelial organs. These tumors are characterized by sustained activation of a number of mitogenic signaling pathways, and by subversion of epithelial polarity and the apoptotic response. Cooperation between such alterations, as well as tumor-host interactions, is also observed. The recapitulation of several hallmarks of human cancers in fly tumors provides a framework to understand the role of defective endocytosis in cancer.

Autophagy in Drosophila melanogaster

Macroautophagy (autophagy) is a bulk cytoplasmic degradation process that is conserved from yeast to mammals. Autophagy is an important cellular response to starvation and stress, and plays critical roles in development, cell death, aging, immunity, and cancer. The fruit fly Drosophila melanogaster provides an excellent model system to study autophagy in vivo, in the context of a developing organism. Autophagy (atg) genes and their regulators are conserved in Drosophila, and autophagy is induced in response to nutrient starvation and hormones during development. In this review we provide an overview of how Drosophila research has contributed to our understanding of the role and regulation of autophagy in cell survival, growth, nutrient utilization, and cell death. Recent Drosophila research has also provided important mechanistic information about the role of autophagy in protein aggregation disorders, neurodegeneration, aging, and innate immunity. Differences in the role of autophagy in specific contexts and/or cell types suggest that there may be cell-context-specific regulators of autophagy, and studies in Drosophila are well-suited to yield discoveries about this specificity.

WDTC1, the ortholog of Drosophila adipose gene, associates with human obesity, modulated by MUFA intake

Adipose (adp) is an obesity gene in Drosophila and mice with crucial functions in fat metabolism. We investigated the correlation between genetic variation of the WDTC1 locus, the ortholog of adp, and human obesity. Five WDTC1 single-nucleotide polymorphisms (SNPs) were genotyped in 935 and 1,115 adults of two ethnically diverse US populations. In the Boston Puerto Rican population, we demonstrated that two WDTC1 SNPs strongly associated with obesity. Homozygote and heterozygote carriers of the major allele i22835A, representing approximately 96% of the population, had significantly higher mean BMI (31.5 and 31.0 kg/m(2), respectively) than noncarriers (28.6 kg/m(2)). Conversely, homozygotes of the minor allele i22835G were leaner and were 74% less likely to be overweight or obese (odds ratio (OR) = 0.26, P = 0.003) compared to homozygote carriers of the major allele. Haplotype analyses based on two SNPs further supported these findings. In addition, we found a strong interaction of monounsaturated fatty acid (MUFA) intake by genotype in this population. As dietary MUFA intake increased, minor allele carriers of SNP i22835A>G had higher BMIs, whereas major allele carriers had lower BMIs. A white population also exhibited a pattern of association between WDTC1 genotypes and obesity although of a different nature. Those WDTC1 variants which associated with obesity likely have experienced strong positive selection in human history, when food supply was unpredictable. Given the high frequency of the major alleles in both populations, we suggest that WDTC1 variation may be an important risk factor contributing to obesity in these populations.

Endocrine regulation of aging and reproduction in Drosophila

Hormonal signals can modulate lifespan and reproductive capacity across the animal kingdom. The use of model organisms such as worms, flies and mice has been fundamentally important for aging research in the discovery of genetic alterations that can extend healthy lifespan. The effects of mutations in the insulin and insulin-like growth factor-like signaling (IIS) pathways are evolutionarily conserved in that they can increase lifespan in all three animal models. Additionally, steroids and other lipophilic signaling molecules modulate lifespan in diverse organisms. Here we shall review how major hormonal pathways in the fruit fly Drosophila melanogaster interact to influence reproductive capacity and aging.

RNAi and RNAa--the yin and yang of RNAome

RNA interference (RNAi) is a powerful technology with huge applications for functional genomics, target identification in drug discovery and elucidation of molecular signaling pathways. Current RNAi studies have demonstrated the clinical potential of small interfering RNAs (siRNAs) in metabolic diseases, cancer, AIDS, malaria, neurodegenerative disorders, dental diseases and other illnesses. Interestingly, recent studies have shown that the small RNA molecules, either indigenously produced as microRNAs (miRNAs) or exogenously administered synthetic dsRNAs could effectively activate a particular gene in a sequence specific manner instead of silencing it. This novel, but still uncharacterized, phenomenon has been termed as RNA activation (RNAa). The paradoxical concept of Yin and Yang, which describe two primal opposing but complementary principles, can potentially be applied to elucidate the complex phenomenon of RNAa/RNAi in the RNAome. This warrants a proper understanding of the RNAi/RNAa molecular pathways in living organisms before any of the small dsRNAs can potentially be exploited for therapeutics in human beings.

Drosophila melanogaster neurobiology, neuropharmacology, and how the fly can inform central nervous system drug discovery

Central nervous system (CNS) drug discovery in the post-genomic era is rapidly evolving. Older empirical methods are giving way to newer technologies that include bioinformatics, structural biology, genetics, and modern computational approaches. In the search for new medical therapies, and in particular treatments for disorders of the central nervous system, there has been increasing recognition that identification of a single biological target is unlikely to be a recipe for success; a broad perspective is required. Systems biology is one such approach, and has been increasingly recognized as a very important area of research, as it places specific molecular targets within a context of overall biochemical action. Understanding the complex interactions between the components within a given biological system that lead to modifications in output, such as changes in behavior or development, may be important avenues of discovery to identify new therapies. One avenue to drug discovery that holds tremendous potential is the use of model genetic organisms such as the fruit fly, Drosophila melanogaster. The similarity between mode of drug action, behavior, and gene response in D. melanogaster and mammalian systems, combined with the power of genetics, have recently made the fly a very attractive system to study fundamental neuropharmacological processes relevant to human diseases. The promise that the use of model organisms such as the fly offers is speed, high throughput, and dramatically reduced overall costs that together should result in an enhanced rate of discovery.

p53 ubiquitination: Mdm2 and beyond

Although early studies have suggested that the oncoprotein Mdm2 is the primary E3 ubiquitin ligase for the p53 tumor suppressor, an increasing amount of data suggests that p53 ubiquitination and degradation are more complex than once thought. The discoveries of MdmX, HAUSP, ARF, COP1, Pirh2, and ARF-BP1 continue to uncover the multiple facets of this pathway. There is no question that Mdm2 plays a pivotal role in downregulating p53 activities in numerous cellular settings. Nevertheless, growing evidence challenges the conventional view that Mdm2 is essential for p53 turnover.

Tumor suppressor properties of the ESCRT-II complex component Vps25 in Drosophila

We have found that the Drosophila gene vps25 possesses several properties of a tumor suppressor. First, vps25 mutant cells activate Notch and Dpp receptor signaling, inducing ectopic organizers in developing eyes and limbs and consequent overproliferation of both mutant and nearby wild-type cells. Second, as the mutant cells proliferate, they lose their epithelial organization and undergo apoptosis. Strikingly, when apoptosis of mutant cells is blocked, tumor-like overgrowths are formed that are capable of metastasis. vps25 encodes a component of the ESCRT-II complex, which sorts membrane proteins into multivesicular bodies during endocytic trafficking to the lysosome. Activation of Notch and Dpp receptor signaling in mutant cells results from an endocytic blockage that causes accumulation of these receptors and other signaling components in endosomes. These results highlight the importance of endocytic trafficking in regulating signaling and epithelial organization and suggest a possible role for ESCRT components in human cancer.

A novel forward genetic screen for identifying mutations affecting larval neuronal dendrite development in Drosophila melanogaster

Vertebrate and invertebrate dendrites are information-processing compartments that can be found on both central and peripheral neurons. Elucidating the molecular underpinnings of information processing in the nervous system ultimately requires an understanding of the genetic pathways that regulate dendrite formation and maintenance. Despite the importance of dendrite development, few forward genetic approaches have been used to analyze the latest stages of dendrite development, including the formation of F-actin-rich dendritic filopodia or dendritic spines. We developed a forward genetic screen utilizing transgenic Drosophila second instar larvae expressing an actin, green fluorescent protein (GFP) fusion protein (actin::GFP) in subsets of sensory neurons. Utilizing this fluorescent transgenic reporter, we conducted a forward genetic screen of >4000 mutagenized chromosomes bearing lethal mutations that affected multiple aspects of larval dendrite development. We isolated 13 mutations on the X and second chromosomes composing 11 complementation groups affecting dendrite outgrowth/branching, dendritic filopodia formation, or actin::GFP localization within dendrites in vivo. In a fortuitous observation, we observed that the structure of dendritic arborization (da) neuron dendritic filopodia changes in response to a changing environment.

Modeling early Epstein-Barr virus infection in Drosophila melanogaster: the BZLF1 protein

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis and is associated with several forms of cancer, including lymphomas and nasopharyngeal carcinoma. The EBV immediate-early protein BZLF1 functions as a transcriptional activator of EBV early gene expression and is essential for the viral transition between latent and lytic replication. In addition to its role in the EBV life cycle, BZLF1 (Z) also has profound effects upon the host cellular environment, including disruption of cell cycle regulation, signal transduction pathways, and transcription. In an effort to understand the nature of Z interactions with the host cellular environment, we have developed a Drosophila model of early EBV infection, where we have expressed Z in the Drosophila eye. Using this system, we have identified a highly conserved interaction between the Epstein-Barr virus Z protein and shaven, a Drosophila homolog of the human Pax2/5/8 family of genes. Pax5 is a well-characterized human gene involved with B-cell development. The B-cell-specific Pax5 also promotes the transcription of EBV latent genes from the EBV Wp promoter. Our work clearly demonstrates that the Drosophila system is an appropriate and powerful tool for identifying the underlying genetic networks involved in human infectious disease.

Functional replacement ofDrosophilaBtk29A with human Btk in male genital development and survival

Drosophila type 2 Btk29A reveals the highest homology to Btk among mammalian Tec kinases. In Btk29A(ficP) mutant males, the apodeme holding the penis split into two pieces. Human Btk rescued this phenotype in 39% of Btk29A(ficP) males, while the Drosophila transgenes did so in 90-100% of mutants. The Btk29A(ficP) mutation reduced adult longevity to 11% that of wild-type. This effect was counteracted by Drosophila type 2, yielding 76% of the wild-type lifespan. Human Btk extended the lifespan of Btk29A(ficP) mutants only to 20% that of wild-type. Thus human Btk can partially replace Drosophila Btk29A+ in male genital development and survival.

The genetics of cell death: approaches, insights and opportunities in Drosophila

Cell death is ubiquitous in metazoans and involves the action of an evolutionarily conserved process known as programmed cell death or apoptosis. In Drosophila melanogaster, it is now uniquely possible to screen for genes that determine the fate - life or death - of any cell or population of cells during development and in the adult. This review describes these genetic approaches and the key insights into cell-death mechanisms that have been obtained, as well as the outstanding questions that these techniques can help to answer.

Epithelial polarity and proliferation control: links from the Drosophila neoplastic tumor suppressors

Mammalian epithelial tumors lose polarity as they progress toward malignancy, but whether polarity loss might causally contribute to cancer has remained unclear. In Drosophila, mutations in the "neoplastic tumor suppressor genes" (nTSGs) scribble, discs-large, and lethal giant larvae disrupt polarity of epithelia and neuroblasts, and simultaneously induce extensive overproliferation of these cells, which exhibit malignant-like characteristics. Herein I review what is known about the role of the fly nTSGs in controlling cell polarity and cell proliferation. Incorporating data from mammalian studies, I consider how polarity and proliferation can be coupled, and how disruption of polarity could promote cancer.

Of flies and men; p53, a tumour suppressor

The completion of the Drosophila genome sequencing project [Science 287 (2000) 2185] has reconfirmed the fruit fly as a model organism to study human disease. Comparison studies have shown that two thirds of genes implicated in human cancers have counterparts in the fly [Curr. Opin. Genet. Dev. 11 (2001) 274; J. Cell Biol. 150 (2000) F23], including the tumour suppressor, p53. The suitability of the fruit fly to study the function of the tumour suppressor p53 is further exemplified by the lack of p53 family members within the fly genome, i.e., no homologues to p63 and p73 have been identified. Hence, there is no redundancy between family members greatly facilitating the analysis of p53 function. In addition, studying p53 in Drosophila provides an opportunity to learn about the evolution of tumour suppressors. Here, we will discuss what is known about Drosophila p53 in relation to human p53.

Tumour suppressors--a fly's perspective

For a century, the little fruitfly Drosophila melanogaster has taught generations of geneticists about how genes control the development of a multicellular organism. More recently, Drosophila has begun to contribute more directly towards our understanding of human disease [Bernards A, Hariharan IK. Of flies and men-studying human disease in Drosophila. Curr Opin Genet Dev 2001, 11, 274-278]. It is capable of doing this because it shares many disease-related genes with us. For example, the Drosophila genome sequencing project has revealed that two thirds of the genes implicated in human cancers have a counterpart in the fly genome [Adams MD, Celniker SE, Holt RA, et al. The genome sequence of Drosophila melanogaster. Science 2000, 287, 2185-2195, Fortini ME, Skupski MP, Boguski MS, Hariharan IK. A survey of human disease gene counterparts in the Drosophila genome. J Cell Biol 2000, 150, F23-30]. In particular, the fly has homologues of the Retinoblastoma protein (pRb) and of p53, two prototypical tumour suppressors which are inactivated in the majority of human tumours. Here, we will compare the fly's tumour suppressors with their human counterparts and we will review recent advances in our understanding of how these factors function in the fly.

GAPs galore! A survey of putative Ras superfamily GTPase activating proteins in man and Drosophila

Typical members of the Ras superfamily of small monomeric GTP-binding proteins function as regulators of diverse processes by cycling between biologically active GTP- and inactive GDP-bound conformations. Proteins that control this cycling include guanine nucleotide exchange factors or GEFs, which activate Ras superfamily members by catalyzing GTP for GDP exchange, and GTPase activating proteins or GAPs, which accelerate the low intrinsic GTP hydrolysis rate of typical Ras superfamily members, thus causing their inactivation. Two among the latter class of proteins have been implicated in common genetic disorders associated with an increased cancer risk, neurofibromatosis-1, and tuberous sclerosis. To facilitate genetic analysis, I surveyed Drosophila and human sequence databases for genes predicting proteins related to GAPs for Ras superfamily members. Remarkably, close to 0.5% of genes in both species (173 human and 64 Drosophila genes) predict proteins related to GAPs for Arf, Rab, Ran, Rap, Ras, Rho, and Sar family GTPases. Information on these genes has been entered into a pair of relational databases, which can be used to identify evolutionary conserved proteins that are likely to serve basic biological functions, and which can be updated when definitive information on the coding potential of both genomes becomes available.

Dying for a cause: invertebrate genetics takes on human neurodegeneration

If invertebrate neurons are injured by hostile environments or aberrant proteins they die much like human neurons, indicating that the powerful advantages of invertebrate molecular genetics might be successfully used for testing specific hypotheses about human neurological diseases, for drug discovery and for non-biased screens for suppressors and enhancers of neurodegeneration. Recent molecular dissection of the genetic requirements for hypoxia, excitotoxicity and death in models of Alzheimer disease, polyglutamine-expansion disorders, Parkinson disease and more, is providing mechanistic insights into neurotoxicity and suggesting new therapeutic interventions. An emerging theme is that neuronal crises of distinct origins might converge to disrupt common cellular functions, such as protein folding and turnover.

Dystroglycan is required for polarizing the epithelial cells and the oocyte in Drosophila

The transmembrane protein Dystroglycan is a central element of the dystrophin-associated glycoprotein complex, which is involved in the pathogenesis of many forms of muscular dystrophy. Dystroglycan is a receptor for multiple extracellular matrix (ECM) molecules such as Laminin, agrin and perlecan, and plays a role in linking the ECM to the actin cytoskeleton; however, how these interactions are regulated and their basic cellular functions are poorly understood. Using mosaic analysis and RNAi in the model organism Drosophila melanogaster, we show that Dystroglycan is required cell-autonomously for cellular polarity in two different cell types, the epithelial cells (apicobasal polarity) and the oocyte (anteroposterior polarity). Loss of Dystroglycan function in follicle and disc epithelia results in expansion of apical markers to the basal side of cells and overexpression results in a reduced apical localization of these same markers. In Dystroglycan germline clones early oocyte polarity markers fail to be localized to the posterior, and oocyte cortical F-actin organization is abnormal. Dystroglycan is also required non-cell-autonomously to organize the planar polarity of basal actin in follicle cells, possibly by organizing the Laminin ECM. These data suggest that the primary function of Dystroglycan in oogenesis is to organize cellular polarity; and this study sets the stage for analyzing the Dystroglycan complex by using the power of Drosophila molecular genetics.

The methods to generate transgenic animals and to control transgene expression

Transgenic animals have been used for years to study gene function and to create models for the study of human diseases. This approach has become still more justified after the complete sequencing of several genomes. Transgenic animals are ready to become industrial bioreactors for the preparation of pharmaceuticals in milk and probably in the future in egg white. Improvement of animal production by transgenesis is still in infancy. Despite its intensive use, animal transgenesis is still suffering from technical limitations. The generation of transgenics has recently become easier or possible for different species thanks to the use of transposons or retrovirus, to incubation of sperm which DNA followed by fertilization by intracellular sperm injection or not and to the use of the cloning technique using somatic cells in which genes have been added or inactivated. The Cre-LoxP system is more and more used to withdraw a given sequence from the genome or to target the integration of a foreign DNA. The tetracycline system has been improved and can more and more frequently be used to obtain faithful expression of transgenes. Several tools: RNA forming a triple helix with DNA, antisense RNA including double strand RNA inducing RNA interference and ribozymes, and also expression of proteins having a negative transdominant effect, are tentatively being improved to inhibit specifically the expression of host or viral genes.All these techniques are expected to offer experimenters new and more precise models to study gene function even in large animals. Improvement of breeding by transgenesis has become more plausible including through the precise allele replacement in farm animals.