Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA.
Genome Biol Evol. 2010 Jul 12;2:358-70. doi: 10.1093/gbe/evq027.
Bitter taste perception likely evolved as a protective mechanism against the ingestion of harmful compounds in food. The evolution of the taste receptor type 2 (TAS2R) gene family, which encodes the chemoreceptors that are directly responsible for the detection of bitter compounds, has therefore been of considerable interest. Though TAS2R repertoires have been characterized for a number of species, to date the complement of TAS2Rs from just one bird, the chicken, which had a notably small number of TAS2Rs, has been established. Here, we used targeted mapping and genomic sequencing in the white-throated sparrow (Zonotrichia albicollis) and sample sequencing in other closely related birds to reconstruct the history of a TAS2R gene cluster physically linked to the break points of an evolutionary chromosomal rearrangement. In the white-throated sparrow, this TAS2R cluster encodes up to 18 functional bitter taste receptors and likely underwent a large expansion that predates and/or coincides with the radiation of the Emberizinae subfamily into the New World. In addition to signatures of gene birth-and-death evolution within this cluster, estimates of Ka/Ks for the songbird TAS2Rs were similar to those previously observed in mammals, including humans. Finally, comparison of the complete genomic sequence of the cluster from two common haplotypes in the white-throated sparrow revealed a number of nonsynonymous variants and differences in functional gene content within this species. These results suggest that interspecies and intraspecies genetic variability does exist in avian TAS2Rs and that these differences could contribute to variation in bitter taste perception in birds.
苦味感知可能是作为一种保护机制进化而来的，以防止摄入食物中的有害化合物。因此，味觉受体类型 2（TAS2R）基因家族的进化引起了相当大的兴趣，该基因家族编码直接负责检测苦味化合物的化学感受器。尽管已经对许多物种的 TAS2R 谱进行了描述，但迄今为止，只有一种鸟类，即鸡，其 TAS2R 数量明显较少，其 TAS2R 组成得到了确定。在这里，我们使用靶向映射和基因组测序在白喉雀（Zonotrichia albicollis）和其他密切相关的鸟类中的样本测序来重建与进化染色体重排断点物理相连的 TAS2R 基因簇的历史。在白喉雀中，这个 TAS2R 簇编码多达 18 个功能性苦味受体，并且可能经历了一个大规模的扩张，这个扩张发生在 Emberizinae 亚科辐射到新大陆之前和/或与之同时发生。除了这个簇内基因生死进化的特征外，鸣禽 TAS2R 的 Ka/Ks 估计值与之前在哺乳动物（包括人类）中观察到的值相似。最后，比较白喉雀两种常见单倍型的 TAS2R 簇的完整基因组序列，揭示了该物种内的许多非同义变异和功能基因含量的差异。这些结果表明，鸟类的 TAS2R 确实存在种间和种内遗传变异，这些差异可能导致鸟类苦味感知的变异。
