Abstract
The sense of taste has evolved in response to diet and ecological niche. In mammalian species, sweet and amino acid perceptions are mediated by heterodimeric G protein-coupled receptors assembled by combinations of the Taste 1 Receptor (T1R) family members, T1R1, T1R2 and T1R3. The combination of T1R1-T1R3 is a broadly tuned receptor for L-amino acids (umami), while the T1R2-T1R3 heterodimer is the receptor for a range of sweet compounds of diverse structures. Functions of these receptors are often closely related to species feeding ecology. These receptors are selectively expressed in subsets of taste receptor cells and intestinal enteroendocrine cells of the gut. My talk will address two areas. 1- Is there a plasticity in T1R sensory systems across vertebrates, and 2) How early in the life of the animal are taste receptors expressed? Some obligate carnivores, such as cats, and birds such as chicken, turkey and zebra finch have lost, the T1R2 component of the sweet taste receptor and thus appetitive behaviour toward sweet compounds. However, in the nectar feeder hummingbird, the ancestral umami taste receptor T1R1-T1R3, has been repurposed allowing the hummingbird to regain sweet taste perception. Conversely, in fish the sweet taste receptor T1R2-T1R3, responds to L-amino acids rather than sweet tastants, indicating that in mammals T1R2-T1R3 was remodelled to recognise sweet compounds during the transition of vertebrates from oceans to lands. In giant panda, a member of carnivorous bear family that feeds predominantly on bamboo, the T1R1 component of the umami receptor is mutated and non-functional. In my talk I shall describe the molecular basis for these changes in taste behaviours. Furthermore, I present data showing that the T1R family members are expressed in pre-term as well as suckling and adult swine enteroendocrine cells indicating that gut-expressed taste perception is present well before weaning.