Department of Medical Biochemistry and Microbiology, Biomedical Center (BMC), Uppsala University, Uppsala 752 37, Sweden.
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala 750 07, Sweden.
Genetics. 2021 Mar 3;217(1):1-9. doi: 10.1093/genetics/iyaa050.
Domestic chickens are less fearful, have a faster sexual development, grow bigger, and lay more eggs than their primary ancestor, the red junglefowl. Several candidate genetic variants selected during domestication have been identified, but only a few studies have directly linked them with distinct phenotypic traits. Notably, a variant of the thyroid stimulating hormone receptor (TSHR) gene has been under strong positive selection over the past millennium, but it's function and mechanisms of action are still largely unresolved. We therefore assessed the abundance of the domestic TSHR variant and possible genomic selection signatures in an extensive data set comprising multiple commercial and village chicken populations as well as wild-living extant members of the genus Gallus. Furthermore, by mean of extensive backcrossing we introgressed the wild-type TSHR variant from red junglefowl into domestic White Leghorn chickens and investigated gene expression, hormone levels, cold adaptation, and behavior in chickens possessing either the wild-type or domestic TSHR variant. While the domestic TSHR was the most common variant in all studied domestic populations and in one of two red junglefowl population, it was not detected in the other Gallus species. Functionally, the individuals with the domestic TSHR variant had a lower expression of the TSHR in the hypothalamus and marginally higher in the thyroid gland than wild-type TSHR individuals. Expression of TSHB and DIO2, two regulators of sexual maturity and reproduction in birds, was higher in the pituitary gland of the domestic-variant chickens. Furthermore, the domestic variant was associated with higher activity in the open field test. Our findings confirm that the spread of the domestic TSHR variant is limited to domesticated chickens, and to a lesser extent, their wild counterpart, the red junglefowl. Furthermore, we showed that effects of genetic variability in TSHR mirror key differences in gene expression and behavior previously described between the red junglefowl and domestic chicken.
家鸡比其主要祖先红原鸡的胆子更小、性发育更快、生长更快、产蛋更多。在驯化过程中选择了几种候选遗传变异体，但只有少数研究直接将它们与不同的表型特征联系起来。值得注意的是，甲状腺刺激素受体 (TSHR) 基因的一个变体在过去的一千年中受到强烈的正选择，但它的功能和作用机制仍在很大程度上未得到解决。因此，我们评估了在一个包含多个商业和乡村鸡种群以及现存野生鸡属成员的广泛数据集中国内 TSHR 变体的丰度和可能的基因组选择特征。此外，通过广泛的回交，我们将来自红原鸡的野生型 TSHR 变体引入了国内的白来亨鸡中，并研究了具有野生型或国内 TSHR 变体的鸡的基因表达、激素水平、对寒冷的适应能力和行为。虽然 domestic TSHR 是所有研究的国内种群中最常见的变体，并且在两个红原鸡种群中的一个中也检测到，但在其他鸡属物种中未检测到。功能上，具有 domestic TSHR 变体的个体的下丘脑 TSHR 表达低于野生型 TSHR 个体，而甲状腺中的表达略高。调节鸟类性成熟和生殖的两个基因 TSHB 和 DIO2 的表达在 domestic-variant 鸡的垂体中更高。此外， domestic 变体与开放式试验中的更高活动相关。我们的研究结果证实了 domestic TSHR 变体的传播仅限于驯化鸡，在较小程度上，它们的野生对应物，红原鸡。此外，我们表明 TSHR 遗传变异的影响反映了之前在红原鸡和家鸡之间描述的基因表达和行为的关键差异。
