MOLECULAR AND CELLULAR MECHANISMS OF INSECT GUSTATION

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0221412
• Project Start Date: Jul 1, 2010
• Project End Date: Jun 30, 2015
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF CALIFORNIA, RIVERSIDE
(N/A)
RIVERSIDE,CA 92521

Performing Department
Entomology, Riverside

Non Technical Summary
Our proposal seeks to understand how insects detect and discriminate amongst a wide variety of chemicals in the environment and how sensory information is used to make appropriate behavioral decisions, such as ingestion of a high calorie food source or avoidance of a poisonous substance. We propose a multidisciplinary approach using molecular genetic and genomics approaches combined with electrophysiological and behavioral analysis to dissect the function of the receptors and cells that detect taste chemicals using the fruit fly, Drosophila melanogaster. We will focus on identification and functional characterization of taste receptors that are involved in detection of various appetitive stimuli and investigate their roles in feeding behavior. We will then characterize the function of similar receptors in other insect species that have relevance for agriculture or human disease. We will include insects such as the pea aphid, Asian citrus psyllid and the red flour beetle, which are responsible for damage to crops or stored products, and three species of mosquitoes, which are responsible for transmitting disease such as West Nile fever, dengue fever and malaria. Specifically, we propose to examine the function of sugar receptors in insects and identify compounds that enhance or inhibit their activity. We will test whether the presence of these compounds alters feeding behavior. Our research may offer insight into new mechanisms for control of pests or insect disease vectors, which rely on chemical cues to find and identify their hosts. We also propose to develop a novel strategy for introducing deleterious genes in natural populations of insects. Such a strategy may allow the introduction of genes that affect the insect's reproductive potential, or viability, or ability to transmit disease and could be used as part of an integrated pest management program.

Animal Health Component

40%

Research Effort Categories

Basic

60%

Applied

40%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
721	3110	1040	70%
721	3110	1080	30%

Knowledge Area
721 - Insects and Other Pests Affecting Humans;

Subject Of Investigation
3110 - Insects;

Field Of Science
1040 - Molecular biology; 1080 - Genetics;

Keywords

insect

chemosensory

receptors

taste

gr genes

physiology

behavior

phagostimulants

anti-feedants

genetic drive

medea

nanos

hunchback

Goals / Objectives
We propose to investigate the molecular and cellular mechanisms that underlie feeding behavior in insects, and to indentify compounds that potentiate or inhibit taste receptor activity as a means to develop novel tools to control insect pests or to reduce insect-host contact. We also propose to develop a novel strategy for gene drive in insects that may be used for driving deleterious genes in pest/vector insect populations. A. To identify the functional roles of a sub-family of candidate insect "sugar" taste receptors and investigate their roles in feeding behavior in Drosophila, and to investigate the function of orthologous receptors in other insects by functional heterologous expression in a Drosophila "empty" taste neuron system. B. To characterize the molecular mechanisms of taste receptor signaling using a pharmacological approach, to identify compounds that potentiate or inhibit the activities of taste receptors and to determine the effects of these compounds on taste behavior using the two-choice feeding preference assay. C. To develop a novel strategy for gene drive in insects based on the principles that underlie the selfish propagation of the naturally occurring Medea element in Tribolium castaneum, which will employ the regulatory interactions of nanos and hunchback, two genes that play a role in early embryonic development in insects.

Project Methods
Objective 1: We will test electrophysiological responses of sugar neurons Drosophila mutants that lack one or more members of the highly conserved "sugar" receptor sub-family of taste receptors using the tip recording method, which is well established in the laboratory. We will test the mutants with an initial group of ~100-150 compounds comprising a large and diverse panel of sugars, sugar derivatives, L-amino acid derivatives, D-amino acids, vitamins, fatty acids and saponins. We may also test a few complex natural stimuli such as fruit extracts, fermenting fruit extracts, yeast extract, soluble fly extracts, and bacterial metabolites. We will use established taste behavior assays to test each of these mutants: Proboscis extension response (PER), 2-choice feeding preference test, and capillary feeding assay. Proboscis extension is considered to be a qualitative sign of acceptance behavior, the 2-choice test allows evaluation of relative feeding preference between two different stimuli, and the capillary feeding assay facilitates measurement of temporal aspects of feeding behavior. We will use these assays to characterize the response of the mutants to the varying concentrations of ligands identified by electrophysiology. The use of multiple concentrations will allow us to quantitate differences in the strengths of behavioral responses to each compound. Objective 2: To determine which signaling pathways are involved in generating sugar responses in taste neurons we will use a pharmacological approach. We will test pharmacological agents that modulate known signaling pathways in mixtures with sucrose using the tip recording technique. We will test no more than one agent on a single sensillum. We will measure the effect on firing rates as well as on adaptation. We will perform an electrophysiological screen to identify chemicals that potentiate or inhibit the activity of sugar neurons. We will test a large panel of compounds with sucrose in order to identify compounds that potentiate or inhibit sugar responses. We will perform 2-choice feeding preference tests to determine if and how the presence of each of the identified modulators affects feeding behavior of adult Drosophila. Objective 3: We propose to engineer a Medea element that encodes a Nos maternal toxin as well as a hb zygotic antidote. We plan to use nos(ΔTCE) as the maternal toxin, which will be maternally transcribed and result in uniform accumulation of Nos protein throughout the embryo. For the zygotic antidote, we propose to use a hb zygotic promoter, which drives in the anterior half of the embryo, to express hb(ΔNRE) that is insensitive to the wild-type Nos toxin. We plan to measure the fitness costs associated with the nos-hb Medea element by monitoring the hatching rates and survival to adulthood of embryos from females carrying zero, one or two copies of the Medea element. We also plan to determine the frequency of the Medea element over 20 generations when introduced at an initial frequency of 25 percent.

Progress 07/01/10 to 06/30/15

Outputs
(N/A)

Impacts
An understanding of the genes and neurons that regulate insect feeding behavior may offer novel tools with which to control insects. Identification of taste receptor agonists and antagonists will provide insight into the functional properties of insect taste receptor proteins, which are novel proteins with no homology to other known protein families. The technique that we have developed to investigate this problem will be applicable to the study of taste receptors in other insects, which may facilitate the identification of specis-specific phagostimulants and anti-feedants.

Publications

• No publications reported this period

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: Under this reporting period, my lab focused on three main research areas related to understanding insect feeding behavior in insects. First, we identified novel functions for Drosophila taste receptors that belong to a highly conserved clade of insect chemosensory receptors. Second, we have established an in vivo heterologous expression system for functional studies of insect taste receptors. Using this system we found that not only are Drosophila sweet receptors selectively activated by subsets of sugars but they are also directly inhibited by one ore more plant alkaloids. Third, we have characterized contact chemosensory and feeding behaviors to novel categories of taste compounds. Finally, we have initiated studies to investigate the molecular and cellular mechanisms of feeding behavior regulation by changes in internal physiological state. PARTICIPANTS: Sandhya Charlu (Graduate Student) Erica Freeman (Graduate Student) Anindya Ganguly (Graduate Student) Sarah Siemens (Graduate Student) Zev Wisotsky (Graduate Student) Adriana Medina (Lab Assistant/Junior Specialist) Jonathan Clark (Undergraduate Student) Kimberly Lung (Undergraduate Student) TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Our studies on insect feeding behavior will provide fundamental insight into regulation of a behavior that is the most proximal cause of crop damage and pathogen transmission to plants and animals. The study of taste receptor properties provides us with a powerful platform for identifying receptor-specific compounds for insect pests, which can then be tested as chemical agents to disrupt contact chemosensory behaviors such as feeding and egg-laying. We expect that an understanding of fundamental pathways that modulate the activity of conserved taste receptors in insects will provide novel targets for disrupting insect feeding behavior.

Publications

• Wisotsky, Z., Medina, A., Freeman, E. and Dahanukar, A. 2011 Evolutionary differences in food preference rely on Gr64e, a receptor for glycerol. Nat Neurosci 14:1534-1541.
• Kwon, J.Y., Dahanukar, A., Weiss, L.A. and Carlson, J.R. 2011 Molecular and cellular organization of the taste system in the Drosophila larva. J Neurosci 31:15300-15309.
• Weiss, L.A., Dahanukar, A., Kwon, J.Y., Banerjee, D. and Carlson, J.R. 2011 The molecular and cellular basis of bitter taste in Drosophila. Neuron 69:258-272.
• Dahanukar, A. and Ray, A. 2011 Courtship, aggression and avoidance: Pheromone, receptors and neurons for social behaviors in Drosophila. Fly 5:1.

Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: Under this reporting period, my lab focused on three main research areas related to understanding feeding behavior in insects. We identified novel functions for Drosophila taste receptors that belong to a highly conserved clade of insect chemosensory receptors and established insect adult and larval feeding behavior assays to measure effects of naturally-occurring plant compounds. We initiated efforts towards using Drosophila to test insect taste receptors and identify receptor-specific inhibitors that disrupt feeding behavior. We are also characterizing physiological mechanisms that modulate the activity of insect taste receptors and alter feeding behavior. PARTICIPANTS: Sandhya Charlu (Graduate Student), Erica Freeman (Graduate Student), Zev Wisotsky (Graduate Student), Adriana Medina (Lab Assistant), Kyle Risser (Lab Assistant), Jonathan Clark (Undergraduate Student), Kimberly Lung (Undergraduate Student). TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The study of taste receptor properties provides us with a powerful platform for identifying receptor-specific compounds for insect pests, which can then be tested for their ability to disrupt contact chemosensory behaviors such as feeding and egg-laying. We expect that an understanding of fundamental pathways that modulate the activity of conserved taste receptors in insects will provide novel targets for disrupting insect feeding behavior.

Publications

• Weiss, L.A., Dahanukar, A., Kwon, J.Y., Banerjee, D. and Carlson, J.R. 2011. The molecular and cellular basis of bitter taste in Drosophila. Neuron 69:258-272.
• Dahanukar, A. and Ray, A. 2011. Courtship, aggression and avoidance: Pheromones, receptors and neurons for social behaviors in Drosophila. Fly 5:1.
• Benton, R. and Dahanukar, A. 2010. Chemosensory coding in single sensilla. In Drosophila neurobiology methods: A companion to the Cold Spring Harbor Neurobiology of Drosophila course, Scott Waddell, Bing Zhang and Marc Freeman (ed.), CSHL Press. pp.247-276.