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Table 1 Taste and pheromone receptor gene (sub-)families in mice and Drosophila

From: Taste and pheromone perception in mammals and flies

 

Receptor

Number of intact genes

Conservation* within each family

Sites of expression

Known ligands (examples)

Structural notes

Mouse/ human

T1R

3 (human) 3 (mouse)

30-40%

Taste cells in the tongue; T1R1 plus T1R3 or T1R2 plus T1R3 are preferentially coexpressed, with few cells expressing all three genes

Sweet chemicals (T1R2 plus T1R3) L-amino acids, umami chemicals (T1R1 plus T1R3)

Similar to V2R (20-30% identical)

 

T2R

28 (human); approximately 40 (mouse)

25% to more than 80%

Taste cells in the tongue; most cells express many, if not all, T2R genes

Bitter compounds, such as cycloheximide (mouse T2R5), salicin (human T2R16), and PTC (human T2R38)

Similar to V1R (15-20% identical)

 

V1R

5 (human) 137 (mouse)

25% to nearly 100%

Basal layer in the vomeronasal organ; probably one V1R gene expressed per cell

2-heptanone (V1Rb1), 6-hydroxy-6-methyl-3-heptanone, n-pentylacetate, and isobutylamine

Similar to T2R (15-20% identical); important for maternal aggression

 

V2R

None in human; approximately 140 in mouse

25% to nearly 100%

Apical layer in the vomeronasal organ; probably one V2R gene expressed per cell

None identified

Similar to T1R (20-30% identical); forms a complex with MHC class Ib and β2-microglobulin; may be required for aggression between males

 

MHC 1b

None in human; 9 expressed in the mouse

40% to more than 80%

Apical layer in the vomeronasal organ; one or a few MHC 1b genes expressed per cell; coexpressed with a V2R gene

None (in the VNO)

Forms a complex with β2-microglobulin and V2Rs; may be required for aggression between males

Fly

GR

69

Approximately 15-75%

Spatially defined in one or several taste organs (labellum, labral and cibarial sense organs, legs, wings, and female genitalia)

Sugars and presumably other classes of compounds, including pheromones

Distantly related to olfactory receptor genes (Or83b); gustatory receptor probably recognize the whole spectrum of small soluble ligands; up to 20 subfamilies (with 1-8 genes each)

 

GR_S†

8

44-75%

Foreleg and labellum (Gr5a), possibly other taste sensory organs

Trehalose (Gr5a)

The knockout fly has lower sensitivity to trehalose; member of a subfamily of 7 genes

  1. *The numbers in this column refer to amino-acid sequence identity in mice and amino-acid sequence similarity in Drosophila, respectively. †Indicates proposed rather than functionally established subfamilies of gustatory receptor genes that might function as sweet (S) receptors. This information is based on the functional characterization of a single receptor in this subfamily.