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Bitter taste receptors confer diverse functions to neurons.

Delventhal R, Carlson JR - Elife (2016)

Bottom Line: Expression of individual Grs conferred strikingly different effects in different neurons.The results support a model in which bitter Grs interact, exhibiting competition, inhibition, or activation.The results have broad implications for the problem of how taste systems evolve to detect new environmental dangers.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, United States.

ABSTRACT
Bitter compounds elicit an aversive response. In Drosophila, bitter-sensitive taste neurons coexpress many members of the Gr family of taste receptors. However, the molecular logic of bitter signaling is unknown. We used an in vivo expression approach to analyze the logic of bitter taste signaling. Ectopic or overexpression of bitter Grs increased endogenous responses or conferred novel responses. Surprisingly, expression of Grs also suppressed many endogenous bitter responses. Conversely, deletion of an endogenous Gr led to novel responses. Expression of individual Grs conferred strikingly different effects in different neurons. The results support a model in which bitter Grs interact, exhibiting competition, inhibition, or activation. The results have broad implications for the problem of how taste systems evolve to detect new environmental dangers.

No MeSH data available.


Related in: MedlinePlus

Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.Tastant order and x-axis scales differ between panels a and c for clarity of presentation. The experimental genotypes were Gr89a-GAL4; UAS-GrX. (a) In I-b sensilla, Gr28b.a conferred an increased response to ARI (p ≤ 0.0001, n ≥ 10) and BER (p ≤ 0.01, n ≥ 10) relative to the GAL4 parental control line. Gr28a conferred response to SAP (p ≤ 0.001, n ≥ 13) and TPH (p ≤ 0.05, n ≥ 13) relative to the GAL4 parental control line. Gr36a conferred no increased responses (n ≥ 6). (b) A dose-response analysis using both parental controls revealed increases in ARI response in I-b sensilla (* indicates p ≤ 0.05, n ≥ 22). Concentrations are graphed on a logarithmic scale. (c) In S-a sensilla, Gr28a conferred decreased responses (ARI: p ≤ 0.0001, UMB: p ≤ 0.001, DEN and BER: p ≤ 0.02. n ≥ 11), while Gr28b.a and Gr36a did not (n ≥ 6).DOI:http://dx.doi.org/10.7554/eLife.11181.008
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fig4: Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.Tastant order and x-axis scales differ between panels a and c for clarity of presentation. The experimental genotypes were Gr89a-GAL4; UAS-GrX. (a) In I-b sensilla, Gr28b.a conferred an increased response to ARI (p ≤ 0.0001, n ≥ 10) and BER (p ≤ 0.01, n ≥ 10) relative to the GAL4 parental control line. Gr28a conferred response to SAP (p ≤ 0.001, n ≥ 13) and TPH (p ≤ 0.05, n ≥ 13) relative to the GAL4 parental control line. Gr36a conferred no increased responses (n ≥ 6). (b) A dose-response analysis using both parental controls revealed increases in ARI response in I-b sensilla (* indicates p ≤ 0.05, n ≥ 22). Concentrations are graphed on a logarithmic scale. (c) In S-a sensilla, Gr28a conferred decreased responses (ARI: p ≤ 0.0001, UMB: p ≤ 0.001, DEN and BER: p ≤ 0.02. n ≥ 11), while Gr28b.a and Gr36a did not (n ≥ 6).DOI:http://dx.doi.org/10.7554/eLife.11181.008

Mentions: Expression of Gr28b.a in I-b sensilla, where it is expressed endogenously, conferred an increased response to aristolochic acid (ARI), as well as to berberine (BER) (Figure 4a). The increase to ARI was confirmed in an independent dose-response analysis: responses in I-b sensilla of the Gr89a-GAL4; UAS-Gr28b.a line were greater than in either parental control at the two higher concentrations tested (Figure 4b; higher concentrations were not tested due to limited solubility). At the highest concentration, the response of Gr89a-GAL4; UAS-Gr28b.a approached 25 spikes/s.10.7554/eLife.11181.008Figure 4.Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.


Bitter taste receptors confer diverse functions to neurons.

Delventhal R, Carlson JR - Elife (2016)

Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.Tastant order and x-axis scales differ between panels a and c for clarity of presentation. The experimental genotypes were Gr89a-GAL4; UAS-GrX. (a) In I-b sensilla, Gr28b.a conferred an increased response to ARI (p ≤ 0.0001, n ≥ 10) and BER (p ≤ 0.01, n ≥ 10) relative to the GAL4 parental control line. Gr28a conferred response to SAP (p ≤ 0.001, n ≥ 13) and TPH (p ≤ 0.05, n ≥ 13) relative to the GAL4 parental control line. Gr36a conferred no increased responses (n ≥ 6). (b) A dose-response analysis using both parental controls revealed increases in ARI response in I-b sensilla (* indicates p ≤ 0.05, n ≥ 22). Concentrations are graphed on a logarithmic scale. (c) In S-a sensilla, Gr28a conferred decreased responses (ARI: p ≤ 0.0001, UMB: p ≤ 0.001, DEN and BER: p ≤ 0.02. n ≥ 11), while Gr28b.a and Gr36a did not (n ≥ 6).DOI:http://dx.doi.org/10.7554/eLife.11181.008
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fig4: Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.Tastant order and x-axis scales differ between panels a and c for clarity of presentation. The experimental genotypes were Gr89a-GAL4; UAS-GrX. (a) In I-b sensilla, Gr28b.a conferred an increased response to ARI (p ≤ 0.0001, n ≥ 10) and BER (p ≤ 0.01, n ≥ 10) relative to the GAL4 parental control line. Gr28a conferred response to SAP (p ≤ 0.001, n ≥ 13) and TPH (p ≤ 0.05, n ≥ 13) relative to the GAL4 parental control line. Gr36a conferred no increased responses (n ≥ 6). (b) A dose-response analysis using both parental controls revealed increases in ARI response in I-b sensilla (* indicates p ≤ 0.05, n ≥ 22). Concentrations are graphed on a logarithmic scale. (c) In S-a sensilla, Gr28a conferred decreased responses (ARI: p ≤ 0.0001, UMB: p ≤ 0.001, DEN and BER: p ≤ 0.02. n ≥ 11), while Gr28b.a and Gr36a did not (n ≥ 6).DOI:http://dx.doi.org/10.7554/eLife.11181.008
Mentions: Expression of Gr28b.a in I-b sensilla, where it is expressed endogenously, conferred an increased response to aristolochic acid (ARI), as well as to berberine (BER) (Figure 4a). The increase to ARI was confirmed in an independent dose-response analysis: responses in I-b sensilla of the Gr89a-GAL4; UAS-Gr28b.a line were greater than in either parental control at the two higher concentrations tested (Figure 4b; higher concentrations were not tested due to limited solubility). At the highest concentration, the response of Gr89a-GAL4; UAS-Gr28b.a approached 25 spikes/s.10.7554/eLife.11181.008Figure 4.Electrophysiological responses of sensilla in which three individual Grs (Gr28b.a, Gr28a, Gr36a) are expressed in I-b (a) and S-a (c) bitter neurons.

Bottom Line: Expression of individual Grs conferred strikingly different effects in different neurons.The results support a model in which bitter Grs interact, exhibiting competition, inhibition, or activation.The results have broad implications for the problem of how taste systems evolve to detect new environmental dangers.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, United States.

ABSTRACT
Bitter compounds elicit an aversive response. In Drosophila, bitter-sensitive taste neurons coexpress many members of the Gr family of taste receptors. However, the molecular logic of bitter signaling is unknown. We used an in vivo expression approach to analyze the logic of bitter taste signaling. Ectopic or overexpression of bitter Grs increased endogenous responses or conferred novel responses. Surprisingly, expression of Grs also suppressed many endogenous bitter responses. Conversely, deletion of an endogenous Gr led to novel responses. Expression of individual Grs conferred strikingly different effects in different neurons. The results support a model in which bitter Grs interact, exhibiting competition, inhibition, or activation. The results have broad implications for the problem of how taste systems evolve to detect new environmental dangers.

No MeSH data available.


Related in: MedlinePlus