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Pharyngeal sense organs drive robust sugar consumption in Drosophila.

LeDue EE, Chen YC, Jung AY, Dahanukar A, Gordon MD - Nat Commun (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Cell and Developmental Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.

ABSTRACT
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.

No MeSH data available.


poxn  mutants retain functional pharyngeal sense organs (a,b) Pharyngeal GRNs labeled by Gr43a-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70  mutants (b). Arrows point to GRNs in the LSO and VCSO. (c,d) Labellar GRNs labeled by Gr64e-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70  mutants (b). Arrows point to taste peg GRNs in d. (e-h) Immunofluorescence of anti-GFP (green) and nc82 (magenta) in the brains of poxnΔM22-B5/+ heterozygotes (e,g) and poxnΔM22-B5/poxn70  mutants (f,h) expressing GCaMP3 under control of Gr43a-GAL4 (e,f) or Gr64e-GAL4 (g,h). Arrows point to GRN projections originating from the various body locations. (i-j) Peak fluorescence changes of GCaMP3 in Gr43a-GAL4 pharyngeal (i) or Gr64e-GAL4 taste peg (j) axon terminals in poxnΔM22-B5/poxn70  mutants during ingestion of the indicated compounds. Values represent mean +/− s.e.m. for n = 5 flies, with data collected over at least 2 days. Asterisks indicate significant difference from sorbitol (i) or water (j) by one way ANOVA with Bonferroni correction for multiple comparisons: **p < 0.01, ***p < 0.001, ns = not significant. Scale bars are 100 μm.
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Figure 3: poxn mutants retain functional pharyngeal sense organs (a,b) Pharyngeal GRNs labeled by Gr43a-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70 mutants (b). Arrows point to GRNs in the LSO and VCSO. (c,d) Labellar GRNs labeled by Gr64e-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70 mutants (b). Arrows point to taste peg GRNs in d. (e-h) Immunofluorescence of anti-GFP (green) and nc82 (magenta) in the brains of poxnΔM22-B5/+ heterozygotes (e,g) and poxnΔM22-B5/poxn70 mutants (f,h) expressing GCaMP3 under control of Gr43a-GAL4 (e,f) or Gr64e-GAL4 (g,h). Arrows point to GRN projections originating from the various body locations. (i-j) Peak fluorescence changes of GCaMP3 in Gr43a-GAL4 pharyngeal (i) or Gr64e-GAL4 taste peg (j) axon terminals in poxnΔM22-B5/poxn70 mutants during ingestion of the indicated compounds. Values represent mean +/− s.e.m. for n = 5 flies, with data collected over at least 2 days. Asterisks indicate significant difference from sorbitol (i) or water (j) by one way ANOVA with Bonferroni correction for multiple comparisons: **p < 0.01, ***p < 0.001, ns = not significant. Scale bars are 100 μm.

Mentions: Transheterozygotes for two poxn alleles (poxn70 and poxnΔM22-B5) showed normal expression of Gr43a-GAL4 in GRNs of the LSO and VCSO (Figure 3a,b). Additionally, brains from poxn mutants had morphologically normal projections from pharyngeal GRNs, while they lacked the leg projections seen in otherwise wild-type flies (Figure 3e,f). Examining Gr64e-GAL4 expression in the poxn background confirmed these results and additionally demonstrated that labellar taste peg GRNs are also present in poxn mutants (Figure 3c,d,g,h). To ask whether the pharyngeal GRNs of poxn mutants are functional, we expressed GCaMP3 under the control of Gr43a-GAL4 in the poxn mutant background, and measured calcium responses during ingestion of sweet compounds. We observed robust activation of Gr43a+ pharyngeal GRNs upon ingestion of fructose and glycerol but not sorbitol (Figure 3i). Due to the technical difficulties in stimulating flies lacking external taste sensation to ingest sweet tastants during calcium imaging, we did not expand our analysis to a larger panel of compounds. However, it is very likely that poxn Gr43a+ pharyngeal neurons retain the same receptive fields seen in a wild-type background (Figure 2e). By contrast, Gr64e+ taste peg GRNs did not respond to any of the sweet compounds tested but were activated by carbonated water (Figure 3j), as previously reported for taste pegs in a wild-type background32. Together, these data demonstrate unequivocally that poxn mutants retain functional pharyngeal taste sensilla that are capable of responding to sweet compounds. Moreover, while functional taste peg GRNs also exist in these mutants, they do not respond to sweet compounds and thus are unlikely to affect our subsequent behavioural analyses of sweet taste preferences driven by the pharyngeal sense organs.


Pharyngeal sense organs drive robust sugar consumption in Drosophila.

LeDue EE, Chen YC, Jung AY, Dahanukar A, Gordon MD - Nat Commun (2015)

poxn  mutants retain functional pharyngeal sense organs (a,b) Pharyngeal GRNs labeled by Gr43a-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70  mutants (b). Arrows point to GRNs in the LSO and VCSO. (c,d) Labellar GRNs labeled by Gr64e-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70  mutants (b). Arrows point to taste peg GRNs in d. (e-h) Immunofluorescence of anti-GFP (green) and nc82 (magenta) in the brains of poxnΔM22-B5/+ heterozygotes (e,g) and poxnΔM22-B5/poxn70  mutants (f,h) expressing GCaMP3 under control of Gr43a-GAL4 (e,f) or Gr64e-GAL4 (g,h). Arrows point to GRN projections originating from the various body locations. (i-j) Peak fluorescence changes of GCaMP3 in Gr43a-GAL4 pharyngeal (i) or Gr64e-GAL4 taste peg (j) axon terminals in poxnΔM22-B5/poxn70  mutants during ingestion of the indicated compounds. Values represent mean +/− s.e.m. for n = 5 flies, with data collected over at least 2 days. Asterisks indicate significant difference from sorbitol (i) or water (j) by one way ANOVA with Bonferroni correction for multiple comparisons: **p < 0.01, ***p < 0.001, ns = not significant. Scale bars are 100 μm.
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Figure 3: poxn mutants retain functional pharyngeal sense organs (a,b) Pharyngeal GRNs labeled by Gr43a-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70 mutants (b). Arrows point to GRNs in the LSO and VCSO. (c,d) Labellar GRNs labeled by Gr64e-GAL4 driving UAS-TdTomato in poxnΔM22-B5/+ heterozygotes (a) and poxnΔM22-B5/poxn70 mutants (b). Arrows point to taste peg GRNs in d. (e-h) Immunofluorescence of anti-GFP (green) and nc82 (magenta) in the brains of poxnΔM22-B5/+ heterozygotes (e,g) and poxnΔM22-B5/poxn70 mutants (f,h) expressing GCaMP3 under control of Gr43a-GAL4 (e,f) or Gr64e-GAL4 (g,h). Arrows point to GRN projections originating from the various body locations. (i-j) Peak fluorescence changes of GCaMP3 in Gr43a-GAL4 pharyngeal (i) or Gr64e-GAL4 taste peg (j) axon terminals in poxnΔM22-B5/poxn70 mutants during ingestion of the indicated compounds. Values represent mean +/− s.e.m. for n = 5 flies, with data collected over at least 2 days. Asterisks indicate significant difference from sorbitol (i) or water (j) by one way ANOVA with Bonferroni correction for multiple comparisons: **p < 0.01, ***p < 0.001, ns = not significant. Scale bars are 100 μm.
Mentions: Transheterozygotes for two poxn alleles (poxn70 and poxnΔM22-B5) showed normal expression of Gr43a-GAL4 in GRNs of the LSO and VCSO (Figure 3a,b). Additionally, brains from poxn mutants had morphologically normal projections from pharyngeal GRNs, while they lacked the leg projections seen in otherwise wild-type flies (Figure 3e,f). Examining Gr64e-GAL4 expression in the poxn background confirmed these results and additionally demonstrated that labellar taste peg GRNs are also present in poxn mutants (Figure 3c,d,g,h). To ask whether the pharyngeal GRNs of poxn mutants are functional, we expressed GCaMP3 under the control of Gr43a-GAL4 in the poxn mutant background, and measured calcium responses during ingestion of sweet compounds. We observed robust activation of Gr43a+ pharyngeal GRNs upon ingestion of fructose and glycerol but not sorbitol (Figure 3i). Due to the technical difficulties in stimulating flies lacking external taste sensation to ingest sweet tastants during calcium imaging, we did not expand our analysis to a larger panel of compounds. However, it is very likely that poxn Gr43a+ pharyngeal neurons retain the same receptive fields seen in a wild-type background (Figure 2e). By contrast, Gr64e+ taste peg GRNs did not respond to any of the sweet compounds tested but were activated by carbonated water (Figure 3j), as previously reported for taste pegs in a wild-type background32. Together, these data demonstrate unequivocally that poxn mutants retain functional pharyngeal taste sensilla that are capable of responding to sweet compounds. Moreover, while functional taste peg GRNs also exist in these mutants, they do not respond to sweet compounds and thus are unlikely to affect our subsequent behavioural analyses of sweet taste preferences driven by the pharyngeal sense organs.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Cell and Developmental Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.

ABSTRACT
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.

No MeSH data available.