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1.  Nutrient sensors 
Current biology : CB  2013;23(9):R369-R373.
PMCID: PMC4332773  PMID: 23660359
2.  Diverse roles for the Drosophila fructose sensor Gr43a 
Fly  2013;8(1):19-25.
The detection of nutrients, both in food and within the body, is crucial for the regulation of feeding behavior, growth, and metabolism. While the molecular basis for sensing food chemicals by the taste system has been firmly linked to specific taste receptors, relatively little is known about the molecular nature of the sensors that monitor nutrients internally. Recent reports of taste receptors expressed in other organ systems, foremost in the gastrointestinal tract of mammals and insects, has led to the proposition that some taste receptors may also be used as sensors of internal nutrients. Indeed, we provided direct evidence that the Drosophila gustatory receptor 43a (Gr43a) plays a critical role in sensing internal fructose levels in the fly brain. In addition to the brain and the taste system, Gr43a is also expressed in neurons of the proventricular ganglion and the uterus. Here, we discuss the multiple potential roles of Gr43a in the fly. We also provide evidence that its activation in the brain is likely mediated by the neuropeptide Corazonin. Finally, we posit that Gr43a may represent only a precedent for other taste receptors that sense internal nutrients, not only in flies but, quite possibly, in other animals, including mammals.
PMCID: PMC3974889  PMID: 24406333
brain; corazonin; fructose; nutrient sensor; proventriculus; receptor; taste; uterus; valence
3.  A fructose receptor functions as a nutrient sensor in the Drosophila brain 
Cell  2012;151(5):1113-1125.
Internal nutrient sensors play important roles in feeding behavior, yet their molecular structure and mechanism of action are poorly understood. Using Ca2+ imaging and behavioral assays, we show that the Gustatory Receptor 43a functions as a narrowly tuned fructose receptor in taste neurons. Remarkably, GR43a also functions as a fructose receptor in the brain. Interestingly, hemolymph fructose levels are tightly linked to feeding status: after nutritious carbohydrate consumption, fructose levels rise several fold and reach a concentration sufficient to activate GR43a in the brain. By using different feeding paradigms and artificial activation of Gr43a-expressing brain neurons, we show that GR43a is both necessary and sufficient to sense hemolymph fructose and promote feeding in hungry flies, but suppress feeding in satiated flies. Thus, our studies indicate that the Gr43a-expressing brain neurons function as a nutrient sensor for hemolymph fructose and assign opposing valence to feeding experiences in a satiation-dependent manner.
PMCID: PMC3509419  PMID: 23178127
4.  Identification of a Drosophila Glucose Receptor Using Ca2+ Imaging of Single Chemosensory Neurons 
PLoS ONE  2013;8(2):e56304.
Evaluation of food compounds by chemosensory cells is essential for animals to make appropriate feeding decisions. In the fruit fly Drosophila melanogaster, structurally diverse chemicals are detected by multimeric receptors composed of members of a large family of Gustatory receptor (Gr) proteins. Putative sugar and bitter receptors are expressed in distinct subsets of Gustatory Receptor Neurons (GRN) of taste sensilla, thereby assigning distinct taste qualities to sugars and bitter tasting compounds, respectively. Here we report a Ca2+ imaging method that allows association of ligand-mediated responses to a single GRN. We find that different sweet neurons exhibit distinct response profiles when stimulated with various sugars, and likewise, different bitter neurons exhibit distinct response profiles when stimulated with a set of bitter chemicals. These observations suggest that individual neurons within a taste modality are represented by distinct repertoires of sweet and bitter taste receptors, respectively. Furthermore, we employed this novel method to identify glucose as the primary ligand for the sugar receptor Gr61a, which is not only expressed in sweet sensing neurons of classical chemosensory sensilla, but also in two supersensitive neurons of atypical taste sensilla. Thus, single cell Ca2+ imaging can be employed as a powerful tool to identify ligands for orphan Gr proteins.
PMCID: PMC3571953  PMID: 23418550
5.  Hierarchical chemosensory regulation of male-male social interactions in Drosophila 
Nature neuroscience  2011;14(6):757-762.
Pheromones regulate male social behaviors in Drosophila, but the identities and behavioral role(s) of these chemosensory signals, and how they interact, are incompletely understood. Here we show that (Z)-7-tricosene (7-T), a male-enriched cuticular hydrocarbon (CH) previously shown to inhibit male-male courtship, is also essential for normal levels of aggression. The opposite influences of 7-T on aggression and courtship are independent, but both require the gustatory receptor Gr32a. Surprisingly, sensitivity to 7-T is required for the aggression-promoting effect of 11-cis-vaccenyl acetate (cVA), an olfactory pheromone, but 7-T sensitivity is independent of cVA. 7-T and cVA therefore regulate aggression in a hierarchical manner. Furthermore, the increased courtship caused by depletion of male CHs is suppressed by a mutation in the olfactory receptor Or47b. Thus, male social behaviors are controlled by gustatory pheromones that promote and suppress aggression and courtship, respectively, and whose influences are dominant to olfactory pheromones that enhance these behaviors.
PMCID: PMC3102769  PMID: 21516101
6.  Recognition of RNA Editing Sites Is Directed by Unique Proteins in Chloroplasts: Biochemical Identification of cis-Acting Elements and trans-Acting Factors Involved in RNA Editing in Tobacco and Pea Chloroplasts 
Molecular and Cellular Biology  2002;22(19):6726-6734.
RNA editing in higher-plant chloroplasts involves C-to-U conversions at specific sites. Although in vivo analyses have been performed, little is known about the biochemical aspects of chloroplast editing reactions. Here we improved our original in vitro system and devised a procedure for preparing active chloroplast extracts not only from tobacco plants but also from pea plants. Using our tobacco in vitro system, cis-acting elements were defined for psbE and petB mRNAs. Distinct proteins were found to bind specifically to each cis-element, a 56-kDa protein to the psbE site and a 70-kDa species to the petB site. Pea chloroplasts lack the corresponding editing site in psbE since T is already present in the DNA. Parallel in vitro analyses with tobacco and pea extracts revealed that the pea plant has no editing activity for psbE mRNAs and lacks the 56-kDa protein, whereas petB mRNAs are edited and the 70-kDa protein is also present. Therefore, coevolution of an editing site and its cognate trans-factor was demonstrated biochemically in psbE mRNA editing between tobacco and pea plants.
PMCID: PMC134032  PMID: 12215530

Results 1-6 (6)