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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Article
  • Peer Reviewed
UC Riverside Previously Published Works (2017)
The Drosophila pharyngeal taste organs are poorly characterized despite their location at important sites for monitoring food quality. Functional analysis of pharyngeal neurons has been hindered by the paucity of molecular tools to manipulate them, as well as their relative inaccessibility for neurophysiological investigations. Here, we generate receptor-to-neuron maps of all three pharyngeal taste organs by performing a comprehensive chemoreceptor-GAL4/LexA expression analysis. The organization of pharyngeal neurons reveals similarities and distinctions in receptor repertoires and neuronal groupings compared to external taste neurons. We validate the mapping results by pinpointing a single pharyngeal neuron required for feeding avoidance of L-canavanine. Inducible activation of pharyngeal taste neurons reveals functional differences between external and internal taste neurons and functional subdivision within pharyngeal sweet neurons. Our results provide roadmaps of pharyngeal taste organs in an insect model system for probing the role of these understudied neurons in controlling feeding behaviors.
    Cover page: Molecular and Cellular Organization of Taste Neurons in Adult Drosophila Pharynx
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2020)
    The insect gustatory system senses taste information from environmental food substrates and processes it to control feeding behaviors. Drosophila melanogaster has been a powerful genetic model for investigating how various chemical cues are detected at the molecular and cellular levels. In addition to an understanding of how tastants belonging to five historically described taste modalities (sweet, bitter, acid, salt, and amino acid) are sensed, recent findings have identified taste neurons and receptors that recognize tastants of non-canonical modalities, including fatty acids, carbonated water, polyamines, H2O2, bacterial lipopolysaccharide (LPS), ammonia, and calcium. Analyses of response profiles of taste neurons expressing different suites of chemosensory receptors have allowed exploration of taste coding mechanisms in primary sensory neurons. In this review, we present the current knowledge of the molecular and cellular basis of taste detection of various categories of tastants. We also summarize evidence for organotopic and multimodal functions of the taste system. Functional characterization of peripheral taste neurons in different organs has greatly increased our understanding of how insect behavior is regulated by the gustatory system, which may inform development of novel insect pest control strategies.
      Cover page: Recent advances in the genetic basis of taste detection in Drosophila
      • Thesis
      • Peer Reviewed
      UC Riverside Electronic Theses and Dissertations (2019)

      Feeding behaviors, guided by the taste system, serve universal and essential functions in animals. The availability of molecular genetic tools and assays to measure behavioral outcomes at high resolution in real time have made the fly, Drosophila melanogaster, an invaluable model to identify molecular components and dissect circuit logic of how the quality and quantity of ingested food is controlled. However, most investigations of taste responses have focused on neurons residing in external taste hairs in the labellum, legs, and wing margins. There remains a complex repertoire of pharyngeal taste neurons lying in an anatomical position to control food intake, which has been largely overlooked. This comparatively limited knowledge of the molecular or functional nature of internal taste neurons in the pharynx represents a critical missing link between taste sensory input and feeding behavior output. Notably, taste-guided feeding behaviors of insect disease vectors and pests impose a substantial economic and health burden in the world. An understanding of taste circuits that regulate feeding may lead to the development of behavior-modifying strategies for insect control. In this dissertation, I present a receptor-to-neuron map for all pharyngeal organs, comprising in a genetic toolkit that allows manipulation of specific cell types in the pharynx, and genetic dissection experiments to assess the roles of selected classes of pharyngeal taste neurons in food selection and intake. The results uncover mechanisms of combinatorial taste coding in pharyngeal taste neurons that mediate feeding avoidance of aversive compounds such as bitter compounds, acids, and high salts. I then report the development of a taste-blind system to examine function of individual classes of pharyngeal taste neurons in controlling food intake of appetitive tastants, such as sugars and amino acids. Finally, I describe efforts to identify potential higher-order brain neurons that control feeding behaviors, and discovery of a subset of brain neurons that might receive pharyngeal input and mediate regurgitation behavior. Taking advantage of tools established by this study for probing pharyngeal function, future investigations can accomplish a systems-level analysis of pharyngeal taste neurons and circuits, and explore functional intersections between taste input and neuroendocrine function in the brain towards guiding feeding behaviors.

        Cover page: Pharyngeal Taste in Drosophila – From Periphery to BrainCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Riverside Undergraduate Research Journal, Volume 12, Issue 1 (2018)
        Taste is essential for humans and animals alike to evaluate food quality and make important decisionsabout food choice and intake. How complex brains process sensory information to produce behavioris an essential question in the field of sensory neurobiology. Currently, little is known about tastecircuits in the brain as compared to other sensory systems. Here, we used the common vinegar fly,Drosophila melanogaster, to explore the potential role of brain neurons labeled by a transgenic line(VT041723-GAL4) in producing “proboscis holding” behavior (extrusion of the mouthpart withoutwithdrawal). By utilizing the GAL4/UAS binary expression system, we expressed a heat-activatedcation channel (UAS-dTrpA1) in these brain neurons and artificially activated them by elevationof temperature, subsequently examining behavior in the heat-activated proboscis extension reflex(PER) assay. We found that activation of these neurons induced proboscis holding. Interestingly, theproboscis holding phenotype was sexually dimorphic. Male flies rarely showed proboscis holdingand those that did had shorter proboscis holding durations. On the other hand, both mated and virginfemales showed significantly more proboscis holding and had longer proboscis holding durationsthan male flies. Overall, we identified a subset of brain neurons labeled by the VT041723-GAL4 linethat controls a sexually dimorphic feeding response (proboscis holding) upon activation.
          Cover page: A Subset of Brain Neurons Controls a Sexually Dimorphic Proboscis Holding Behavior in Adult Drosophilia MelanogasterCreative Commons 'BY-NC' version 4.0 license
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2019)
          Taste drives appropriate food preference and intake. In Drosophila, taste neurons are housed in both external and internal organs, but the latter have been relatively underexplored. Here, we report that Poxn mutants with a minimal taste system of pharyngeal neurons can avoid many aversive tastants, including bitter compounds, acid, and salt, suggesting that pharyngeal taste is sufficient for rejecting intake of aversive compounds. Optogenetic activation of selected pharyngeal bitter neurons during feeding events elicits changes in feeding parameters that can suppress intake. Functional dissection experiments indicate that multiple classes of pharyngeal neurons are involved in achieving behavioral avoidance, by virtue of being inhibited or activated by aversive tastants. Tracing second-order pharyngeal circuits reveals two main relay centers for processing pharyngeal taste inputs. Together, our results suggest that the pharynx can control the ingestion of harmful compounds by integrating taste input from different classes of pharyngeal neurons.
            Cover page: Combinatorial Pharyngeal Taste Coding for Feeding Avoidance in Adult Drosophila
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2015)
            The fly pharyngeal sense organs lie at the transition between external and internal nutrient-sensing mechanisms. Here we investigate the function of pharyngeal sweet gustatory receptor neurons, demonstrating that they express a subset of the nine previously identified sweet receptors and respond to stimulation with a panel of sweet compounds. We show that pox-neuro (poxn) mutants lacking taste function in the legs and labial palps have intact pharyngeal sweet taste, which is both necessary and sufficient to drive preferred consumption of sweet compounds by prolonging ingestion. Moreover, flies putatively lacking all sweet taste show little preference for nutritive or non-nutritive sugars in a short-term feeding assay. Together, our data demonstrate that pharyngeal sense organs play an important role in directing sustained consumption of sweet compounds, and suggest that post-ingestive sugar sensing does not effectively drive food choice in a simple short-term feeding paradigm.
              Cover page: Pharyngeal sense organs drive robust sugar consumption in Drosophila
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2021)
              Insect gustatory systems comprise multiple taste organs for detecting chemicals that signal palatable or noxious quality. Although much is known about how taste neurons sense various chemicals, many questions remain about how individual taste neurons in each taste organ control feeding. Here, we use the Drosophila pharynx as a model to investigate how taste information is encoded at the cellular level to regulate consumption of sugars and amino acids. We first generate taste-blind animals and establish a critical role for pharyngeal input in food selection. We then investigate feeding behavior of both male and female flies in which only selected classes of pharyngeal neurons are restored via binary choice feeding preference assays as well as Fly Liquid-Food Interaction Counter (FLIC) assays. We find instances of integration as well as redundancy in how pharyngeal neurons control behavioral responses to sugars and amino acids. Additionally, we find that pharyngeal neurons drive sugar feeding preference based on sweet taste but not on nutritional value. Finally, we demonstrate functional specialization of pharyngeal and external neurons using optogenetic activation. Overall, our genetic taste neuron protection system in a taste-blind background provides a powerful approach to elucidate principles of pharyngeal taste coding and demonstrates functional overlap and subdivision among taste neurons.SIGNIFICANCE STATEMENTDietary intake of nutritious chemicals such as sugars and amino acids is essential for an animal's survival. In insects, distinct classes of taste neurons control acceptance or rejection of food sources. Here we develop a genetic system to investigate how individual taste neurons in the Drosophila pharynx encode specific tastants, focusing on sugars and amino acids. By examining flies in which only a single class of taste neurons is active, we find evidence for functional overlap as well as redundancy in responses to sugars and amino acids. We also uncover functional subdivision between pharyngeal and external neurons in driving feeding responses. Overall, we find that different pharyngeal neurons act together to control intake of the two categories of appetitive tastants.
                Cover page: Control of sugar and amino acid feeding via pharyngeal taste neurons.
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