Abstract
Although previous studies have indicated importance of taste receptors in food habits formation in mammals, little is known about those in fish. Grass carp is an excellent model for studying vegetarian adaptation, as it shows food habit transition from carnivore to herbivore. In the present study, pseudogenization or frameshift mutations of the umami receptors that hypothesized related to dietary switch in vertebrates, were not found in grass carp, suggesting other mechanisms for vegetarian adaptation in grass carp. T1R1 and T1R3 strongly responded to L-Arg and L-Lys, differing from those of zebrafish and medaka, contributing to high species specificity in amino acid preferences and diet selection of grass carp. After food habit transition of grass carp, DNA methylation levels were higher in CPG1 and CPG3 islands of upstream control region of T1R1 gene. Luciferase activity assay of upstream regulatory region of T1R1 (−2500-0 bp) without CPG1 or CPG3 indicated that CPG1 and CPG3 might be involved in transcriptional regulation of T1R1 gene. Subsequently, high DNA methylation decreased expression of T1R1 in intestinal tract. It could be a new mechanism to explain, at least partially, the vegetarian adaptation of grass carp by regulation of expression of umami receptor via epigenetic modification.
Highlights
Taste receptors belong to G-protein coupled receptors, which were firstly cloned and characterized in topographically distinct subpopulations of taste receptor cells and taste buds[1]
No pseudogenization or frameshift mutations of T1R1 and T1R3 genes were found in the herbivore grass carp
T1R1 and T1R3 of grass carp were most evolutionarily related to zebrafish, as they belong to Cyprinidae, rather than a product of independent evolution with its herbivorous food habit
Summary
Taste receptors belong to G-protein coupled receptors, which were firstly cloned and characterized in topographically distinct subpopulations of taste receptor cells and taste buds[1] They were identified in non-gustatory tissue including the gut, pancreas, and even the brain, suggesting their functional roles in other tissue[2]. Little information is known about the function and evolution of umami taste receptor gene nor the relationship with food habits[13]. We investigated the DNA methylation profiles and mRNA expression of T1R1 and T1R3 genes in grass carp before and after the transition from carnivore to herbivore. These results might provide new insight into the function and evolution of umami taste receptors during food habit formation in fish
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