家犬驯化中与攻击性行为相关的人工选择研究

Artificial Selection plays a key role in intentional breeding for humans favor specific traits in domestication of animals and plants. Dogs are one of the first domestic animals, usually considered as "the best friends of human beings". They share the main and common feature with all domestic animals, which is their ability to have direct contact with man and not to be afraid, compared to their wild ancient, feral wolves. It proposed hypothesis that 5-hydroxy-tryptophan (5-HT) system is essential for brain mechanisms converting wild aggressive animal into tame counterparts. Although there are a large amount of studies of aggressive behavior in dogs, most of which are behavioral and genetic researches, only a few works focus on artificial selection of genes regulated aggressive behavior in dogs. Our previous research on whole genome resequencing of dogs revealed some of neural and behavior-regulated genes showed significantely signal of artificial selection. From the case, this proposal will identify genes of 5-HT system referred to artificial selection during dog domestication by population genetic analysis, using wolves, indigenous dogs, and modern breeding dogs with diverse aggressive behavior. Powers and patterns of artificial selection on these genes in two stages of domestication will be further investigated. This proposal will promote revealing genetic mechanism underlying domestication history of aggressive behavior and understanding domestication in gene level in dogs. It will be helpful for molecular assisted selective breeding of dogs, as well as for revealing genetic mechanism of behavioral and neurogenic disease of human beings applying dogs as animal model.

人工选择在动植物驯化中对人类偏好性状的积累起了至关重要的作用。家犬作为最早被驯化的家养动物之一，与其野生祖先灰狼相比，攻击性显著减弱、不畏惧甚至亲近人类。对家犬的攻击性行为已有长期研究，但主要集中在行为学和分子机制研究上，对人工选择所涉及基因的受选择机制研究则很少。申请人参加的一项家犬全基因组重测序研究发现神经系统和行为控制基因表现出较强的人工选择信号。以此为切入点，本项目使用群体遗传学的分析方法，以灰狼、土狗和不同攻击性强度的现代品种犬作为研究对象，鉴定对攻击性行为调控起关键作用的5-羟色胺系统中受到人工选择影响的基因，并研究其在家犬驯化和品系化两个时期中受到人工选择的机制、强度及其异同。本项目有望促进对驯化过程在基因水平上留下的人工选择印记的理解，为今后的家犬分子辅助人工选育提供遗传理论基础，并有助于我们将家犬作为模式动物研究人类的行为和神经性疾病的分子基础提供线索。

本项目计划对灰狼到家犬驯化过程中攻击性减弱这一行为相关的遗传背景进行研究。在行为学测试中发现，攻击行为是一个复杂的表型性状，它不仅受遗传因素的影响同时也很大程度上受到后天环境因子的影响，而且还受测试者主观判断，及犬只本身状态及对测试者感受的影响。期间，我们发现家犬尤其是警用犬有转圈行为，其中极度重复转圈行为被归为强迫症的一种表现。因此我们对原计划进行了必要的调整，转变为对转圈行为的分子机制进行研究。我们首先对112只马里努阿犬和昆明犬进行了转圈行为的行为学测试并进行了严格的打分，挑选出40只极端个体，进行全基因组重测序，通过计算Tajima’D值和Fst值，筛选出369，612和775个候选基因，均富集在神经系统、能量代谢等GO聚类中，均包含谷氨酸能突触这一通路中的基因，这说明谷氨酸能神经系统可能与家犬转圈行为、尤其是极端重复转圈行为相关。同时，我们也发现CDH2基因内的一段区域在马里努阿犬中有连续高的杂合度。高杂合度往往与平衡选择相关，这与马里努阿犬中表现出的平衡性表型相符。在之前的一些家犬强迫症的研究中发现神经钙黏蛋白(Cadherin 2，CDH2)基因与强迫症相关。因此我们选取53 只马里努阿犬和23只中国土狗作为研究群体，对CDH2基因内部及上下游9个片段测序，通过LD分析、Tajima’D值分析、群体历史模拟分析、杂合度分析和中介网络图分析，均验证CDH2基因中的一个片段在马里努阿犬中受到平衡选择的作用。我们对参考序列及衍生序列的转录因子结合位点进行了预测，发现其中多态性位点G63913941A可能是影响CDH2基因功能的关键位点，通过增加C/EBPβ的结合位点来增加CDH2基因的表达，从而影响马里努阿犬的转圈行为和工作表现的平衡。