Genetics of Taste Perception

Alexander A Bachmanov, Monell Chemical Senses Center, Philadelphia, Pennsylvania, USA
John D Boughter, University of Tennessee Health Science Center, Memphis, Tennessee, USA

Published online: January 2012

DOI: 10.1002/9780470015902.a0023587

There is considerable genetic variation in taste perception within and among species. Some taste perception phenotypes have simple monogenic inheritance, whereas others have complex genetic architecture. Recent advances with genomic resources have made genetics a powerful approach to identify taste-related genes. Chromosomal mapping and positional cloning studies facilitated discovery of taste receptors. The genetic mapping and candidate gene association studies show that taste perception phenotypes are influenced by allelic variation of genes involved in both peripheral and central taste processing. Sequence variation of taste receptor genes explains some species differences in taste perception and sheds light on evolution of ingestive behaviour. Genetic variation in taste perception impacts human nutrition and health and may be useful as a biomarker of predisposition to some diseases. Identification of genes responsible for within- and between-species variation in taste can provide tools to better control food choice and intake in humans and other animals.

Key Concepts:

  • Genes contribute to individual variation in perception of each of the five primary taste qualities: bitter, sweet, umami, salty and sour.
  • Genetic variation in taste perception involves polymorphisms of taste receptors, genes involved in peripheral taste transduction and central taste processing.
  • Genetic variation in taste perception impacts human nutrition and health and could be used as a biomarker of predisposition to some diseases.

Keywords: taste; gustatory; bitter; sweet; umami; salty; sour; behaviour; perception; genetics

Figure 1. Taste receptors. The T1R (a) and T2R (b) proteins have seven transmembrane domains and are G protein-coupled receptors, whereas ENaC (c) is an ion channel. (a) The T1R proteins consist of ~850 amino acids and have a large extracellular N-terminus composed of a Venus Flytrap module and a cysteine-rich domain connected to the heptahelical domain. In humans and most mammalian species, this family includes three proteins: T1R1, T1R2 and T1R3. Their corresponding gene symbols are TAS1R1, TAS1R2 and TAS1R3 (in humans), and Tas1r1, Tas1r2 and Tas1r3 (in other species). Numbers of the T1R genes in different vertebrate species range from complete absence in the frog to five in some fishes (Boughter and Bachmanov, 2008). A T1R2+3 heterodimer functions as a sweet taste receptor. A T1R1+3 heterodimer functions as an umami taste receptor in humans, and is more broadly tuned l-amino acid taste receptor in rodents. (b) The T2R proteins consist of ~300–330 amino acids and have a short extracellular N-terminus. Their corresponding gene symbols are TAS2R (in humans), and Tas2r (in other species). Number of the Tas2r genes in vertebrate species with sequenced genomes varies widely (Boughter and Bachmanov, 2008). Many species in addition to functional Tas2r genes have pseudogenes. For example humans, according to different sources, have 25–38 intact genes and 5–16 pseudogenes. Over half of human T2Rs have been de-orphanised, mainly through the use of heterologous cell assays, and in all cases ligands were bitter-tasting compounds. Several T2Rs are broadly tuned to detect stimuli of different chemical classes, whereas others appear more specific, activated by one or a couple of agonists. Multiple T2Rs are co-expressed in the same taste receptor cell. As a result, a single T2R-expressing cell can respond to different bitter taste compounds. (c) The epithelial sodium channel, ENaC, is a member of the degenerin/ENaC superfamily of ion channels. The ENaC channel is a heteromer consisting of several different subunits: , , and/or . Each ENaC subunit has two transmembrane domains and is encoded by a separate gene. In humans, there are four ENaC channel subunits, , , and (encoded by the nonvoltage-gated sodium channel 1 genes SCNN1A, SCNN1B, SCNN1G and SCNN1D, respectively). Mice and rats lack ENaC subunit and therefore have only three ENaC subunits encoded by the Scnn1a, Scnn1b and Scnn1g genes. ENaC is involved in transepithelial ion transport in many tissues (kidney, lung, etc.). Because in some species sodium taste responses are suppressed by amiloride, a diuretic that inhibits the ENaC channel, ENaC was proposed as a candidate salty taste receptor. Recent work with mice genetically engineered to lack ENaC in taste cells (Bosak et al., 2010; Chandrashekar et al., 2010) has confirmed the importance of this channel in mediating sodium taste in mice.
Figure 2. Variation in sweet-liking in humans. Individual hedonic ratings of sucrose. ‘Likers’ report an increase in pleasantness with increasing sucrose concentration, ‘dislikers’ report a decrease in pleasantness at higher concentrations, and ‘neutrals’ have a minimal affective response to all concentrations. A schematic diagram drawn from data presented in Looy and Weingarten (1991); reproduced by permission of the Oxford University Press.
Figure 3. Positional cloning of the Sac (saccharin preference) locus. (a) Linkage map of mouse distal chromosome 4 based on data from the F2 intercross between C57BL/6ByJ and 129P3/J inbred strains. The X-axis shows distances between markers in recombination units (cM). The Y-axis shows the logarithm of the odds ratio (LOD) scores for sucrose and saccharin consumption. The LOD score peaks (indicated by black triangles) and confidence intervals (solid horizontal line for sucrose, and dotted horizontal line for saccharin) define the ~5 cM genomic region of the Sac locus. (b) Linkage map of the Sac-containing region defined based on the size of the donor fragment in the 129.B6-Sac congenic strain (black box). Distances between markers were estimated based on the B6×129 F2 intercross (see panel a). The Sac locus was mapped to a 0.7 cM interval corresponding to the congenic donor fragment. (c) A contig of bacterial artificial chromosome (BAC) clones and physical map of the Sac region. BAC clones are represented by horizontal lines. Dots indicate marker content of the BAC clones. Physical mapping determined that the 0.7-cM congenic donor fragment has the physical size of 194 kb. A BAC clone encompassing the donor fragment was sequenced, and the DNA sequence was analysed for gene content (d). (d) Genes within the Sac-containing interval. Filled areas indicate 12 predicted genes. Arrows indicate the predicted direction of transcription. The Tas1r3 gene encoding a G protein-coupled receptor was the most likely candidate for the Sac locus. Reproduced in a modified form from (Bachmanov et al., 2001b) by permission of the Oxford University Press.
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 Further Reading
    book Bachmanov AA (2008) "Genetic architecture of sweet taste". In: Weerasinghe DK and DuBois GE (eds) Sweetness and Sweeteners: Biology, Chemistry and Psychophysics. ACS symposium series, 979. Oxford University Press.
    Bachmanov AA (2010) Umami: fifth taste? Flavor enhancer? Perfumer and Flavorist 35(4): 52–57.
    Bachmanov AA and Beauchamp GK (2007) Taste receptor genes. Annual Review of Nutrition 27: 389–414.
    Bachmanov AA, Kiefer SW, Molina JC et al. (2003) Chemosensory factors influencing alcohol perception, preferences and consumption. Alcoholism: Clinical and Experimental Research 27(2): 220–231.
    book Basbaum AI, Kaneko A, Shepherd GM and Westheimer G (eds) (2008) The Senses: A Comprehensive Reference, vol. 4 (Firestein S and Beauchamp GK (eds)), Olfaction and Taste. San Diego: Elsevier/Academic Press.
    Behrens M and Meyerhof W (2009) Mammalian bitter taste perception. Results & Problems in Cell Differentiation 47: 203–220.
    Boughter JD and Bachmanov AA (2007) Behavioral genetics and taste. BMC Neuroscience 8(suppl. 3): S3.
    Boughter JD Jr and Gilbertson TA (1999) From channels to behavior: an integrative model of NaCl taste. Neuron 22(2): 213–215.
    book Naim M, Nir S, Spielman AI et al. (2002) "Hypothesis of receptor-dependent and receptor-independent mechanisms for bitter and sweet taste transduction: implications for slow taste onset and lingering aftertaste". In: Given P and Parades D (eds) Chemistry of Taste: Mechanisms, Behaviors, and Mimics. ACS Symposium Series; 825. Washington, DC: American Chemical Society.
    book Wysocki CJ and Kare MR (eds) (1991) Genetics of Perception and Communication. New York: Marcel Dekker.

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Article Title: Genetics of Taste Perception
 
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Bachmanov, Alexander A, and Boughter, John D(Jan 2012) Genetics of Taste Perception. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023587]