Gustatory receptors required for sensing umbelliferone in Drosophila melanogaster

Studies of taste modality using the animal model Drosophila melanogaster have elucidated a number of uncharacterized mechanisms of sensory responses. Gustatory receptors expressed in taste organs are not only responsible for the acceptance and rejection of different foods, but are also involved in the process of selecting an oviposition site. This contact-chemosensation is essential for animals to discriminate between nutritious and contaminated foods. In this study, we characterized the function of gustatory receptors that play a dual role in feeding and oviposition using the plant metabolite umbelliferone. The combined electrophysiological and behavioral evidence demonstrated that two broadly tuned gustatory receptors, GR33a and GR66a, and one narrowly tuned gustatory receptor, GR93a, are all required to generate a functional umbelliferone receptor.     

Chemical genetics and drug screening in Drosophila cancer models

Drug candidates often fail in preclinical and clinical testing because of reasons of efficacy and/or safety.It would be time- and cost-efficient to have screening models that reduce the rate of such false positive candidates that appear promising at first but fail later.In this regard,it would be particularly useful to have a rapid and inexpensive whole animal model that can pre-select hits from high-throughput screens but before testing in costly rodent assays.Drosophila melanogaster has emerged as a potential whole animal model for drug screening.Of particular interest have been drugs that must act in the context of multi-cellularity such as those for neurological disorders and cancer.A recent review provides a comprehensive summary of drug screening in Drosophila,but with an emphasis on neurodegenerative disorders.Here,we review Drosophila screens in the literature aimed at cancer therapeutics.     

Chemical genetics and drug screening in Drosophila cancer models

Drug candidates often fail in preclinical and clinical testing because of reasons of efficacy and/or safety.It would be time- and cost-efficient to have screening models that reduce the rate of such false positive candidates that appear promising at first but fail later.In this regard,it would be particularly useful to have a rapid and inexpensive whole animal model that can pre-select hits from high-throughput screens but before testing in costly rodent assays.Drosophila melanogaster has emerged as a potential whole animal model for drug screening.Of particular interest have been drugs that must act in the context of multi-cellularity such as those for neurological disorders and cancer.A recent review provides a comprehensive summary of drug screening in Drosophila,but with an emphasis on neurodegenerative disorders.Here,we review Drosophila screens in the literature aimed at cancer therapeutics.     

Chemical Selection of Alcohol Dehydrogenase Negative Mutants in Drosophila

We describe a selection procedure which utilizes the vapor from an unsaturated alcohol, 1-pentene-3-ol, for the detection and isolation of mutant flies with little or no alcohol dehydrogenase activity. ADH-negative flies are unaffected by exposure to the unsaturated alcohol, but ADH positives (wild-types) die after short exposure. The technique can be used to select rare ADH-negative individuals from large populations of wild-type flies.     

Direct sensing of systemic and nutritional signals by haematopoietic progenitors in Drosophila

The Drosophila lymph gland is a haematopoietic organ in which progenitor cells, which are most akin to the common myeloid progenitor in mammals, proliferate and differentiate into three types of mature cell--plasmatocytes, crystal cells and lamellocytes--the functions of which are reminiscent of mammalian myeloid cells. During the first and early second instars of larval development, the lymph gland contains only progenitors, whereas in the third instar, a medial region of the primary lobe of the lymph gland called the medullary zone contains these progenitors, and maturing blood cells are found juxtaposed in a peripheral region designated the cortical zone. A third group of cells referred to as the posterior signalling centre functions as a haematopoietic niche. Similarly to mammalian myeloid cells, Drosophila blood cells respond to multiple stresses including hypoxia, infection and oxidative stress. However, how systemic signals are sensed by myeloid progenitors to regulate cell-fate determination has not been well described. Here, we show that the haematopoietic progenitors of Drosophila are direct targets of systemic (insulin) and nutritional (essential amino acid) signals, and that these systemic signals maintain the progenitors by promoting Wingless (WNT in mammals) signalling. We expect that this study will promote investigation of such possible direct signal sensing mechanisms by mammalian myeloid progenitors.     

Chemical cues influence pupation behavior of Drosophila simulans and Drosophila buzzatii in nature and in the laboratory

In the wild, larvae of several species of Drosophila develop in heterogeneous and rapidly changing environments sharing resources as food and space. In this scenario, sensory systems contribute to detect, localize and recognize congeners and heterospecifics, and provide information about the availability of food and chemical features of environments where animals live. We investigated the behavior of D. simulans and D. buzzatii larvae to chemicals emitted by conspecific and heterospecific larvae. Our goal was to understand the role of these substances in the selection of pupation sites in the two species that cohabit within decaying prickly pear fruits (Opuntia ficus-indica). In these breeding sites, larvae of D. simulans and D. buzzatii detect larvae of the other species changing their pupation site preferences. Larvae of the two species pupated in the part of the fruit containing no or few heterospecifics, and spent a longer time in/on spots marked by conspecifics rather than heterospecifics. In contrast, larvae of the two species reared in isolation from conspecifics pupated randomly over the substrate and spent a similar amount of time on spots marked by conspecifics and by heterospecifics. Our results indicate that early chemically-based experience with conspecific larvae is critical for the selection of the pupation sites in D. simulans and D. buzzatii, and that pupation site preferences of Drosophila larvae depend on species-specific chemical cues. These preferences can be modulate by the presence of larvae of the same or another species.     

Chemical Patterns, Compartments and a Binary Epigenetic Code in Drosophila

I propose a model which accounts for the geometries and sequencein which compartmental boundary lines arise on the differentimaginal discs, and on the blastoderm of Drosophila melanogaster;and propose that successive lines are recorded by differentbinary switches, to create a binary epigenetic code word specifyingeach disc, and disc compartment. I suppose a biochemical systemundergoing reaction and diffusion acts throughout development.As an imaginal disc grows, a succession of differently shapedchemical concentration patterns form at a discrete set of discsizes. I suppose a specific concentration of one chemical isa threshold. Concentrations above or below threshold switchcells to one or another of two commitments. Then the line acrossthe imaginal disc with the threshold concentration is a predictedcompartmental boundary. The sequence and geometries of suchlines predict the compartmental boundaries seen on the wingdisc, the other discs, and on the blastoderm stage egg. Thecompartmental lines on the wing disc suggest that a terminalcompartment is specified by a combination of binary names recordinga sequence of binary commitments: anterior, not posterior; dorsal,not ventral; wing, not thorax; proximal, not distal. Each combinationcomprises a binary epigenetic code word. Recently I constructedan independent model for transdetermination in Drosophila whichproposed a similar binary epigenetic code for the differentdiscs. The clone restriction lines predicted on the blastodermby my transdetermination model, the chemical pattern model,and analogy with the wing disc, are nearly identical. Severalare already confirmed. The resultant binary code scheme correctlypredicts many relative transdetermination frequencies and accountssimply for the action of most homeotic mutants as genes whichalter a single switch state in one or more discs.     

Gonadal Mosaicism Induced by Chemical Treatment of Sperm in Drosophila melanogaster

Accurate interpretation of forward genetic screens of chromosomes exposed in mature spermatozoa to a mutagenic chemical requires understanding—incomplete to date—of how exposed chromosomes and their replicas proceed through early development stages from the fertilized ovum to establishment of the germline of the treated male’s offspring. We describe a model for early embryonic development and establishment of the germline of Drosophila melanogaster and a model-validating experiment. Our model proposes that, barring repair, DNA strands modified by treatment with alkylating agents are stable and mutagenic. Each replication of an alkylated strand can result in misreplication and a mutant-bearing daughter nucleus. Daughter nuclei thenceforth replicate faithfully and their descendants comprise the embryonic syncytium. Of the 256 nuclei present after the eighth division, several migrate into the polar plasm at the posterior end of the embryo to found the germline. Based upon distribution of descendants of the alkylated strands, the misreplication rate, and the number of nuclei selected as germline progenitors, the frequency of gonadal mosaicism is predictable. Experimentally, we tracked chromosomes 2 and 3 from EMS-treated sperm through a number of generations, to characterize autosomal recessive lethal mutations and infer gonadal genetic content of the sons of treated males. Over 50% of 106 sons bore germlines that were singly, doubly, or triply mosaic for chromosome 2 or chromosome 3. These findings were consistent with our model, assuming a rate of misreplication between 0.65 and 0.80 at each replication of an alkylated strand. Crossing treated males to mismatch-repair-deficient females had no apparent effect on mutation rate.     

Chemical sensing of DNT by engineered olfactory yeast strain

With the increasing threat of environmental toxicants including biological and chemical warfare agents, fabricating innovative biomimetic systems to detect these harmful agents is critically important. With the broad objective of developing such a biosensor, here we report the construction of a Saccharomyces cerevisiae strain containing the primary components of the mammalian olfactory signaling pathway. In this engineered yeast strain, WIF-1alpha, olfactory receptor signaling is coupled to green fluorescent protein expression. Using this 'olfactory yeast', we screened for olfactory receptors that could report the presence of the odorant 2,4-dinitrotoluene, an explosive residue mimic. With this approach, we have identified the novel rat olfactory receptor Olfr226, which is closely related to the mouse olfactory receptors Olfr2 and MOR226-1, as a 2,4-dinitrotoluene-responsive receptor.     

Chemical modification of cell death in the Bar eye of Drosophila

Summary Cell death during the development of the mutant Bar of Drosophila melanogaster has been further investigated. The temporal and spatial distribution of degenerating cells was determined by light microscopy of serial sections of Bar eye discs. It appears that the presumptive eye cells die during the initial stage of differentiation; i.e., during their organization into groups of cells corresponding to the future ommatidia.The effects of acetamide and cytosine treatment on the development of the Bar eye disc were also examined. Both of these compounds, when fed to larvae, greatly increase facet number in the adult fly. Acetamide increases facet number by inhibiting Bar specific cell death, while cytosine delays degeneration to a later stage in development when ommatidial organization is almost complete.     

Gustatory receptor 22e is essential for sensing chloroquine and strychnine in Drosophila melanogaster

Chloroquine, an amino quinolone derivative commonly used as an anti-malarial drug, is known to impart an unpleasant taste. Little research has been done to study chloroquine taste in insects, therefore, we examined both the deterrant properties and mechanisms underlying chloroquine perception in fruit flies. We identified the antifeedant effect of chloroquine by screening 21 gustatory receptor (Grs) mutants through behavioral feeding assays and electrophysiology experiments. We discovered that two molecular sensors, GR22e and GR33a, act as chloroquine receptors, and found that chloroquine-mediated activation of GRNs occurs through S-type sensilla. At the same time, we successfully recapitulated the chloroquine receptor by expressing GR22e in ectopic gustatory receptor neurons. We also found that GR22e forms a part of the strychnine receptor. We suggest that the Drosophila strychnine receptor might have a very complex structure since five different GRs are required for strychnine-induced action potentials.     

Modeling metabolic homeostasis and nutrient sensing in Drosophila: implications for aging and metabolic diseases

Over the past decade, numerous reports have underscored the similarities between the metabolism of Drosophila and vertebrates, with the identification of evolutionarily conserved enzymes and analogous organs that regulate carbohydrate and lipid metabolism. It is now well established that the major metabolic, energy-sensing and endocrine signaling networks of vertebrate systems are also conserved in flies. Accordingly, studies in Drosophila are beginning to unravel how perturbed energy balance impinges on lifespan and on the ensuing diseases when energy homeostasis goes awry. Here, we highlight several emerging concepts that are at the nexus between obesity, nutrient sensing, metabolic homeostasis and aging. Specifically, we summarize the endocrine mechanisms that regulate carbohydrate and lipid metabolism, and provide an overview of the neuropeptides that regulate feeding behavior. We further describe the various efforts at modeling the effects of high-fat or -sugar diets in Drosophila and the signaling mechanisms involved in integrating organ function. Finally, we draw attention to some of the cardinal discoveries made with these disease models and how these could spur new research questions in vertebrate systems.KEY WORDS: Metabolic homeostasis, Nutrient sensing, Drosophila     

Chemical cues from competitors change the oviposition preference of Drosophila suzukii

Although Drosophila suzukii Matsumura (Diptera: Drosophilidae) infests fresh and ripening fruits, it is attracted to fermented fruits as well. Because fermented fruits attract other flies too, if D. suzukii utilizes fermented fruits as oviposition substrates, competition can be more intense on them. To avoid such competition, D. suzukii may change oviposition preference when particular species of competitor flies are present, but the effect of odor cues associated with competitors on the oviposition preference of D. suzukii is still unknown. To examine such an effect, we investigated the oviposition preference of D. suzukii in the presence of four competitor fly species – Drosophila melanogaster Meigen, Drosophila lutescens Malloch, Drosophila rufa Kikkawa & Peng, and Drosophila auraria Peng – and D. suzukii itself. We prepared artificial substrates with yeast treatment (Y⁺: yeast supplementation, Y⁻: control) and competitor fly treatment (F⁺: pre-inoculated with competitor fly odor, F⁻: control), and performed two-choice experiments using the substrates with various Y and F treatments. Our results showed that D. suzukii oviposited more eggs on Y⁺ substrates than on Y⁻ substrates when no competitor flies were present and the presence of competitor flies influenced D. suzukii’s oviposition preference for yeast-supplemented substrates and its effect changed depending on the competitor fly species. If the presence of competitors around fallen fruits on the ground suppresses D. suzukii’s oviposition on the fallen fruits and facilitates the oviposition on non-fermenting substrates in nature, it may drive D. suzukii to use ripening fruits on the tree. Such selective pressure may facilitate the evolution of morphological traits such as a serrated ovipositor in D. suzukii.     

Dual detection of fungal infections in Drosophila via recognition of glucans and sensing of virulence factors

The Drosophila immune system discriminates between various types of infections and activates appropriate signal transduction pathways to combat the invading microorganisms. The Toll pathway is required for the host response against fungal and most Gram-positive bacterial infections. The sensing of Gram-positive bacteria is mediated by the pattern recognition receptors PGRP-SA and GNBP1 that cooperate to detect the presence of infections in the host. Here, we report that GNBP3 is a pattern recognition receptor that is required for the detection of fungal cell wall components. Strikingly, we find that there is a second, parallel pathway acting jointly with GNBP3. The Drosophila Persephone protease activates the Toll pathway when proteolytically matured by the secreted fungal virulence factor PR1. Thus, the detection of fungal infections in Drosophila relies both on the recognition of invariant microbial patterns and on monitoring the effects of virulence factors on the host.