Abstract
Bitterness is an important taste sensation for chickens, which provides useful sensory information for acquisition and selection of diet, and warns them against ingestion of potentially harmful and noxious substances in nature. Bitter taste receptors (T2Rs) mediate the recognition of bitter compounds belonging to a family of proteins known as G-protein coupled receptors. The aim of this study was to identify and evaluate the expression of T2R7 in chicken tongue tissue and construct cT2R7-1 and cT2R7-2-expressing HEK-293T cells to access the expression of PLCβ2 and ITPR3 after exposure with different concentrations of the bitter compounds. Using real-time PCR, we show that the relative expression level of T2R7 mRNA in 5, 1, 0.1, and 10−3 mM of camphor and erythromycin solutions and 5 mM of chlorpheniramine maleate solutions was significantly higher than that in 50 mM KCL solutions. We confirmed that the bitter taste receptor T2R7 and downstream signaling effectors are sensitive to different concentrations of bitter compounds. Moreover, T2R7-1 (corresponding to the unique haplotype of the Tibetan chicken) had higher sensitivity to bitter compounds compared with that of T2R7-2 (corresponding to the unique haplotype of the Jiuyuan black-chicken). These results provide great significance of taste response on dietary intake to improve chicken feeding efficiency in poultry production and have certain reference value for future taste research in other bird species.
Highlights
Hitherto, there are five widely known basic tastes that stimulate and are perceived by taste buds—sweet, umami, sour, bitter, and salty [1, 2]
To investigate the effect of various bitter compounds in chicken, tongue tissues of chicken were stimulated with different chemical compound solutions. e relative fold changes in T2R7 mRNA expression from the RT-PCR experiments are summarized in Figure 1. e effect of different concentrations of camphor solution on the T2R7 mRNA expression was significant (P < 0.05) (Figure 1(a))
There was no significant difference detected in T2R7 mRNA expression between 10− 5 mM camphor solution and 50 mM KCL solution (P > 0.05). e effects of chlorpheniramine maleate solution with different concentrations on the expression of T2R7 mRNA are shown in Figure 1(b). e expression level of T2R7 mRNA in 5 mM chlorpheniramine maleate solution was significantly increased, compared with other lower concentrations (P < 0.05), while there were no significant differences observed between chlorpheniramine solutions (1, 0.1, 10− 3, and 10− 5 mM) and 50 mM KCL solution (P > 0.05)
Summary
There are five widely known basic tastes that stimulate and are perceived by taste buds—sweet, umami, sour, bitter, and salty [1, 2]. Identification of bitter compounds is mediated by the type 2 taste receptors (T2Rs), which belong to G-proteincoupled superfamily [6, 7]. Bitter taste receptors vary among species: a much smaller T2Rs gene repertoire exists in birds (range from 1 in the domestic pigeon to 12 in the bar-tailed trogon) in comparison to 10–69 in mammals [8, 9], and chickens (Gallus gallus domesticus) have only three functional bitter taste receptors comprising T2R1, T2R2, and T2R7 [10,11,12]. White-throated sparrows (Zonotrichia albicollis) were found to have 18 putatively functional T2Rs, indicating their sensitivity to wider range of bitter substances [13]. Bitter taste sensitivity varies within and between species.
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