Elfwing Magnus, Fallahshahroudi Amir, Lindgren Isa, Jensen Per, Altimiras Jordi
AVIAN Behavioural Genomics and Physiology Group, Division of Biology, IFM Biology, Linköping University, Linköping, Sweden.
PLoS One. 2014 Aug 11;9(8):e103218. doi: 10.1371/journal.pone.0103218. eCollection 2014.
Analysis of selective sweeps to pinpoint causative genomic regions involved in chicken domestication has revealed a strong selective sweep on chromosome 4 in layer chickens. The autoregulatory α-adrenergic receptor 2C (ADRA2C) gene is the closest to the selective sweep and was proposed as an important gene in the domestication of layer chickens. The ADRA2C promoter region was also hypermethylated in comparison to the non-selected ancestor of all domesticated chicken breeds, the Red Junglefowl, further supporting its relevance. In mice the receptor is involved in the fight-or-flight response as it modulates epinephrine release from the adrenals. To investigate the involvement of ADRA2C in chicken domestication, we measured gene expression in the adrenals and radiolabeled receptor ligand in three brain regions comparing the domestic White Leghorn strain with the wild ancestor Red Junglefowl. In adrenals ADRA2C was twofold greater expressed than the related receptor gene ADRA2A, indicating that ADRA2C is the predominant modulator of epinephrine release but no strain differences were measured. In hypothalamus and amygdala, regions associated with the stress response, and in striatum, receptor binding pIC50 values ranged between 8.1-8.4, and the level was not influenced by the genotyped allele. Because chicken strains differ in morphology, physiology and behavior, differences attributed to a single gene may be lost in the noise caused by the heterogeneous genetic background. Therefore an F10 advanced intercross strain between White Leghorn and Red Junglefowl was used to investigate effects of ADRA2C alleles on fear related behaviors and fecundity. We did not find compelling genotype effects in open field, tonic immobility, aerial predator, associative learning or fecundity. Therefore we conclude that ADRA2C is probably not involved in the domestication of the stress response in chicken, and the strong selective sweep is probably caused by selection of some unknown genetic element in the vicinity of the gene.
对选择性清除进行分析以确定参与家鸡驯化的致病基因组区域，结果显示蛋鸡的4号染色体上存在强烈的选择性清除。自调节α-肾上腺素能受体2C（ADRA2C）基因最接近该选择性清除区域，并被认为是蛋鸡驯化中的一个重要基因。与所有驯化鸡品种的非选择祖先原鸡相比，ADRA2C启动子区域也存在高甲基化，进一步证明了其相关性。在小鼠中，该受体参与应激反应，因为它调节肾上腺中肾上腺素的释放。为了研究ADRA2C在家鸡驯化中的作用，我们比较了家鸡白来航品系和野生祖先原鸡，测量了肾上腺中的基因表达以及三个脑区中放射性标记的受体配体。在肾上腺中，ADRA2C的表达量比相关受体基因ADRA2A高两倍，表明ADRA2C是肾上腺素释放的主要调节因子，但未检测到品系差异。在与应激反应相关的下丘脑和杏仁核以及纹状体中，受体结合pIC50值在8.1 - 8.4之间，且该水平不受基因分型等位基因的影响。由于鸡品系在形态、生理和行为上存在差异，单个基因导致的差异可能会在异质遗传背景引起的噪声中丢失。因此，我们使用白来航鸡和原鸡之间的F10高级杂交品系来研究ADRA2C等位基因对恐惧相关行为和繁殖力的影响。我们在旷场试验、强直性静止、空中捕食者、联想学习或繁殖力方面未发现令人信服的基因型效应。因此我们得出结论，ADRA2C可能不参与家鸡应激反应的驯化，强烈的选择性清除可能是由该基因附近一些未知遗传元件的选择引起的。
