Limits...
Construction of a taste-blind medaka fish and quantitative assay of its preference-aversion behavior.

Aihara Y, Yasuoka A, Iwamoto S, Yoshida Y, Misaka T, Abe K - Genes Brain Behav. (2008)

Bottom Line: We then generated a transgenic fish expressing dominant-negative Galpha(i2) both in T1R-expressing and in T2R-expressing cells.The feeding assay revealed that the transgenic fish was unable to show a preference for AN food and an aversion to DN food.The assay system was useful for evaluating taste-blind behaviors, and the results indicate that the two taste signaling pathways conveying preferable and aversive taste information are conserved in fish as well as in mammals.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.

ABSTRACT
In vertebrates, the taste system provides information used in the regulation of food ingestion. In mammals, each cell group within the taste buds expresses either the T1R or the T2R taste receptor for preference-aversion discrimination. However, no such information is available regarding fish. We developed a novel system for quantitatively assaying taste preference-aversion in medaka fish. In this study, we prepared fluorescently labeled foods with fine cavities designed to retain tastants until they were bitten by the fish. The subjects were fed food containing a mixture of amino acids and inosine monophosphate (AN food), denatonium benzoate (DN food) or no tastant (NT food), and the amounts of ingested food were measured by fluorescence microscopy. Statistical analysis of the fluorescence intensities yielded quantitative measurements of AN food preference and DN food aversion. We then generated a transgenic fish expressing dominant-negative Galpha(i2) both in T1R-expressing and in T2R-expressing cells. The feeding assay revealed that the transgenic fish was unable to show a preference for AN food and an aversion to DN food. The assay system was useful for evaluating taste-blind behaviors, and the results indicate that the two taste signaling pathways conveying preferable and aversive taste information are conserved in fish as well as in mammals.

Show MeSH

Related in: MedlinePlus

Transgenic medaka fish with suppressed PLC-β2 activation in taste receptor cells lose their ability to discriminate between taste modalities(a) Our behavioral assay system revealed that medaka fish prefer foods containing amino acids and IMP (red stars) and that they are averse to those containing denatonium benzoate (cyan circles), which are perceived as bitter tasting by mammals. (b) The transgenic medaka fish constructed in the present study was found to be taste blind. Because the Gαi2S47C mutant (Gαi2*) expressed in the taste receptor cells inhibits the signal transduction to PLC-β2, the fish were no longer able to recognize preferable or aversive tastes.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2667311&req=5

fig06: Transgenic medaka fish with suppressed PLC-β2 activation in taste receptor cells lose their ability to discriminate between taste modalities(a) Our behavioral assay system revealed that medaka fish prefer foods containing amino acids and IMP (red stars) and that they are averse to those containing denatonium benzoate (cyan circles), which are perceived as bitter tasting by mammals. (b) The transgenic medaka fish constructed in the present study was found to be taste blind. Because the Gαi2S47C mutant (Gαi2*) expressed in the taste receptor cells inhibits the signal transduction to PLC-β2, the fish were no longer able to recognize preferable or aversive tastes.

Mentions: An amino acid–IMP mixture was used as a preferable tastant, and denatonium benzoate was used as an aversive tastant for medaka fish (Fig. 6a). These tastants also stimulate the mammalian taste system in which T1R and T2R function as taste receptors at the peripheral end of the system. T1R and T2R exhibit mutually exclusive expression patterns and different response profiles in the taste buds, and it is therefore likely that these taste receptors are responsible for discriminating between preferable and aversive tastes (Mueller et al. 2005). Despite the sharp contrast between the functions of these two receptors, they are both coexpressed with the same effector molecule, PLC-β2. It has previously been shown that mice lacking the plc-β2 gene have neither a preference for amino acids nor an aversion to denatonium benzoate (Zhang et al. 2003). This result resembles the phenotype exhibited by Gi2S47C transgenic fish in the current study (Fig. 5). We have recently shown that fish T1R is activated by all four amino acids used in this study, namely glycine, l-serine, l-proline and l-glutamate sodium salt, and that fish T2R is activated by denatonium benzoate (Oike et al. 2007). This result leads to the conclusion that the taste-blind phenotype of Gi2S47C transgenic fish results from the inhibition of both the T1R and the T2R signaling pathways (Fig. 6b). Biochemical and electrophysiological data suggested the existence of ion channels in fish taste tissue, which are directly activated by l-proline (Kumazawa et al. 1998). However, based on the phenotype of our transgenic fish created by the inhibition of the GPCR-triggered pathway in taste bud cells, it is concluded that this type of channel is less responsible for the behavioral preferences shown toward amino acids. Taken together, it is likely that teleosts and mammals share a common molecular strategy for discriminating between the two taste modalities mediated by T1R and T2R.


Construction of a taste-blind medaka fish and quantitative assay of its preference-aversion behavior.

Aihara Y, Yasuoka A, Iwamoto S, Yoshida Y, Misaka T, Abe K - Genes Brain Behav. (2008)

Transgenic medaka fish with suppressed PLC-β2 activation in taste receptor cells lose their ability to discriminate between taste modalities(a) Our behavioral assay system revealed that medaka fish prefer foods containing amino acids and IMP (red stars) and that they are averse to those containing denatonium benzoate (cyan circles), which are perceived as bitter tasting by mammals. (b) The transgenic medaka fish constructed in the present study was found to be taste blind. Because the Gαi2S47C mutant (Gαi2*) expressed in the taste receptor cells inhibits the signal transduction to PLC-β2, the fish were no longer able to recognize preferable or aversive tastes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2667311&req=5

fig06: Transgenic medaka fish with suppressed PLC-β2 activation in taste receptor cells lose their ability to discriminate between taste modalities(a) Our behavioral assay system revealed that medaka fish prefer foods containing amino acids and IMP (red stars) and that they are averse to those containing denatonium benzoate (cyan circles), which are perceived as bitter tasting by mammals. (b) The transgenic medaka fish constructed in the present study was found to be taste blind. Because the Gαi2S47C mutant (Gαi2*) expressed in the taste receptor cells inhibits the signal transduction to PLC-β2, the fish were no longer able to recognize preferable or aversive tastes.
Mentions: An amino acid–IMP mixture was used as a preferable tastant, and denatonium benzoate was used as an aversive tastant for medaka fish (Fig. 6a). These tastants also stimulate the mammalian taste system in which T1R and T2R function as taste receptors at the peripheral end of the system. T1R and T2R exhibit mutually exclusive expression patterns and different response profiles in the taste buds, and it is therefore likely that these taste receptors are responsible for discriminating between preferable and aversive tastes (Mueller et al. 2005). Despite the sharp contrast between the functions of these two receptors, they are both coexpressed with the same effector molecule, PLC-β2. It has previously been shown that mice lacking the plc-β2 gene have neither a preference for amino acids nor an aversion to denatonium benzoate (Zhang et al. 2003). This result resembles the phenotype exhibited by Gi2S47C transgenic fish in the current study (Fig. 5). We have recently shown that fish T1R is activated by all four amino acids used in this study, namely glycine, l-serine, l-proline and l-glutamate sodium salt, and that fish T2R is activated by denatonium benzoate (Oike et al. 2007). This result leads to the conclusion that the taste-blind phenotype of Gi2S47C transgenic fish results from the inhibition of both the T1R and the T2R signaling pathways (Fig. 6b). Biochemical and electrophysiological data suggested the existence of ion channels in fish taste tissue, which are directly activated by l-proline (Kumazawa et al. 1998). However, based on the phenotype of our transgenic fish created by the inhibition of the GPCR-triggered pathway in taste bud cells, it is concluded that this type of channel is less responsible for the behavioral preferences shown toward amino acids. Taken together, it is likely that teleosts and mammals share a common molecular strategy for discriminating between the two taste modalities mediated by T1R and T2R.

Bottom Line: We then generated a transgenic fish expressing dominant-negative Galpha(i2) both in T1R-expressing and in T2R-expressing cells.The feeding assay revealed that the transgenic fish was unable to show a preference for AN food and an aversion to DN food.The assay system was useful for evaluating taste-blind behaviors, and the results indicate that the two taste signaling pathways conveying preferable and aversive taste information are conserved in fish as well as in mammals.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.

ABSTRACT
In vertebrates, the taste system provides information used in the regulation of food ingestion. In mammals, each cell group within the taste buds expresses either the T1R or the T2R taste receptor for preference-aversion discrimination. However, no such information is available regarding fish. We developed a novel system for quantitatively assaying taste preference-aversion in medaka fish. In this study, we prepared fluorescently labeled foods with fine cavities designed to retain tastants until they were bitten by the fish. The subjects were fed food containing a mixture of amino acids and inosine monophosphate (AN food), denatonium benzoate (DN food) or no tastant (NT food), and the amounts of ingested food were measured by fluorescence microscopy. Statistical analysis of the fluorescence intensities yielded quantitative measurements of AN food preference and DN food aversion. We then generated a transgenic fish expressing dominant-negative Galpha(i2) both in T1R-expressing and in T2R-expressing cells. The feeding assay revealed that the transgenic fish was unable to show a preference for AN food and an aversion to DN food. The assay system was useful for evaluating taste-blind behaviors, and the results indicate that the two taste signaling pathways conveying preferable and aversive taste information are conserved in fish as well as in mammals.

Show MeSH
Related in: MedlinePlus