Bitter taste receptors confer diverse functions to neurons
- Yale University, United States
Figures
Figure 1
Sensillum types on the labellum.
Left: The four bitter-responsive types, S-a (green), S-b (blue), I-a (purple) and I-b (red), are differently distributed on the labellar surface. L sensilla (gray) show little if any response to …
Figure 2
Ectopic expression of Gr22b in I-a bitter neurons leads to novel responses to three bitter compounds.
(a) Sample electrophysiological responses from I-a sensilla of parental controls and of flies ectopically expressing UAS-Gr22b. (b) Mean responses. Asterisks indicate responses that are different …
Figure 3
Electrophysiological responses of sensilla in which seven individual Grs are expressed in I-a bitter neurons.
(a) 'N' indicates a novel response, to which there was no significant response in the wild-type control. Each experimental genotype is Gr89a-GAL4; UAS-GrX. Asterisks indicate responses that are …
Figure 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.
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 …
Figure 5
Electrophysiological responses of sensilla in which four individual Grs are expressed in S-a and I-b bitter neurons.
Each experimental genotype is Gr89a-GAL4; UAS-GrX. (a) Response profiles of both parental controls and flies expressing UAS-Gr22b in S-a bitter neurons. Asterisks indicate responses that are …
Figure 6
Electrophysiological response profiles generated by expression of Gr59c in I-b, S-a, and I-a, relative to the wild-type GAL4 parental control (p ≤ 0.001, except that p≤ 0.05 in the case of the response of I-b to THE and CAF. n ≥ 8).
The experimental genotype was Gr89a-GAL4; UAS-Gr59c.
Figure 7 with 2 supplements
Electrophysiological response profiles of w− Canton-S (wCS) control I-a sensilla, ΔGr59c mutant I-a sensilla, wCS control I-b sensilla, and ΔGr59c I-a sensilla that had been rescued with a UAS-Gr59c construct driven by Gr66a-GAL4.
Rescued ΔGr59c flies were tested with a reduced panel of 16 compounds; the other genotypes were tested with the full panel of 21 compounds.
Figure 7—figure supplement 1
The ΔGr59c mutation was generated through FLP-FRT-mediated recombination between piggybac transposon lines f03881 and f04393 (Parks et al., 2004).
A ~17kb region of the genome was deleted; it encompassed Gr59c, as well as several other genes. This deletion was backcrossed to a wCS control background for 7 generations.
Figure 7—figure supplement 2
Electrophysiological response profiles of wCS control S-a sensilla and ΔGr59c S-a sensilla.
Response to DEN is reduced in ΔGr59c mutant S-a sensilla (p ≤ 0.0001, n ≥ 12).
Figure 8
Fluorescent confocal microscopy of whole-mount labella reveals that the ΔGr59c mutation does not cause loss of Gr59c-GAL4 expression in I-a sensilla (top two panels).
The ΔGr59c mutation does not cause gain of Gr28b.a-, Gr28a-, or Gr22b-GAL4 expression in I-a sensilla (bottom six panels). (n ≥ 5 flies per genotype). White arrowheads indicate the positions of …
Figure 9
UAS-Gr59c expression in adult flies is sufficient to restore wild-type responses to ΔGr59c mutant I-a sensilla.
All genotypes have identical 2nd chromosomes: ΔGr59c, Gr89a-GAL4. Flies were subjected to the four indicated temperature regimes. (a) GAL80ts parental control flies without UAS-Gr59c display mutant, …
Figure 10
Electrophysiological responses in sensilla ectopically expressing four individual Grs, in ΔGr59c I-a bitter neurons.
Novel responses are indicated by 'N'. The experimental genotypes are: ΔGr59c, Gr89a-GAL4; UAS-GrX, except that in the case of Gr22b, the experimental genotype is ΔGr59c; UAS-Gr22b/Gr66a-GAL4. …
Figure 11 with 1 supplement
Gr ectopic expression produces receptor-specific and neuron-specific effects on the response profiles.
Effects are delineated for each tastant in Figure 11—figure supplement 1.
Figure 11—figure supplement 1
Summary of effects of UAS-Gr expression on responses to tastants in different sensillum types, based on comparison with tested control lines.
'+' indicates an increase in the level of an endogenous response. '*' indicates a novel response not observed in parental control lines examined. '-' indicates suppression of an endogenous response.
Figure 12
Findings and models.
Four findings of this study are indicated, along with one possible model to explain each. i) Expression of a Gr, indicated by the blue sphere, decreases the response to a tastant, represented by the …
Tables
Table 1
Panel of 21 bitter taste compounds tested in electrophysiological recordings. a '−' indicates that insecticidal activity has not been described.
| Tastant | Abbreviation | Concentration | Chemical class | Source | Insecticidal activitya |
|---|---|---|---|---|---|
| Aristolochic acid | ARI | 1 mM | phenanthrene | Aristolochia family of plants | − |
| Azadirachtin | AZA | 1 mM | terpenoid | Neem tree | + |
| Berberine chloride | BER | 1 mM | alkaloid | Golden seal, bayberry, Oregon grape and goldthread | − |
| Caffeine | CAF | 1 mM | alkaloid | Coffee, chocolate, tea, kola nut | − |
| Coumarin | COU | 10 mM | benzopyrone | Tonka bean, honey clover | + |
| Cucurbitacin I hydrate | CUC | 1 mM | glycoside | Pumpkins, gourds, cucumbers | + |
| N,N-Diethyl-m-toluamide | DEET | 10 mM | N,N-dialkylamide | synthetic | + |
| Denatonium benzoate | DEN | 10 mM | quaternary ammonium cation | synthetic | − |
| Escin | ESC | 1 mM | terpenoid | Horse chestnut tree | − |
| Gossypol | GOS | 1 mM | terpenoid | Cotton | + |
| (-)-lobeline HCl | LOB | 1 mM | alkaloid | Indian tobacco, Cardinal flower | + |
| Myricetin | MYR | 1 mM | flavonoid | Berries, wine | − |
| Quinine | QUI | 1mM | alkaloid | Cinchona tree bark | − |
| Rotenone | ROT | 1 mM | ketone | Jicama | + |
| Saponin | SAP | 1% | terpenoid | Soapbark tree | + |
| D-(+)-sucrose octaacetate | SOA | 1 mM | acetylated sucrose derivative | synthetic | + |
| Sparteine sulfate salt | SPS | 10 mM | alkaloid | Scotch broom | + |
| Strychnine nitrate salt | STR | 10 mM | alkaloid | Strychnos seeds | + |
| Theobromine | THE | 1 mM | alkaloid | Cacao, tea, kola nut, chocolate | − |
| Theophylline | TPH | 10 mM | alkaloid | Tea leaves | + |
| Umbelliferone | UMB | 1 mM | phenylpropanoid | Carrot, coriander | − |
Table 2
Endogenous expression patterns of Grs selected for analysis, as determined primarily by Gr-GAL4 analysis.
| Gene | Labellum | Legs | Pharynx | Larva | Antenna |
|---|---|---|---|---|---|
| Gr2a | − | − | + | + | − |
| Gr10a | − | − | − | + | + |
| Gr22b | + (I-b, S-a) | + | + | + | − |
| Gr28a | + (I-b, S-a, S-b) | + | + | + | − |
| Gr28b.a | + (I-b, S-a, S-b) | + | + | + | − |
| Gr36a | + (S-b) | + | − | − | − |
| Gr58c | − | + | − | − | − |
| Gr59c | + (I-a, S-a) | − | − | + | − |
Additional files
-
Supplementary file 1
(A) Responses of I-a sensilla recorded from flies of the indicated genotypes. (a) Mean spikes/s. (b) S.E.M. (c) n, where n represents the number of traces analyzed. (B) Responses of I-b sensilla recorded from flies of the indicated genotypes. (a) Mean spikes/s. (b) S.E.M. (c) n, where n represents the number of traces analyzed. (C) Responses of S-a sensilla recorded from flies of the indicated genotypes. (a) Mean spikes/s. (b) S.E.M. (c) n, where n represents the number of traces analyzed. (D) Responses of ΔGr59c I-a sensilla recorded from flies of the indicated genotypes. (a) Mean spikes/s. (b) S.E.M. (c) n, where n represents the number of traces analyzed.
- https://doi.org/10.7554/eLife.11181.020
