Study on genetic factors controlling liver copper concentration in sheep

众所周知，绵羊从肝脏排出过量铜的能力受损，因此比其他农场动物更容易受到铜中毒的影响。另一方面，铜缺乏症也是绵羊养殖中一个众所周知的问题。因此，在绵羊日粮中添加足够的铜的余地很小。有趣的是，不同品种的羊对铜缺乏和铜中毒的敏感性不同。此外，肝铜浓度似乎具有高度的遗传性，而且在绵羊品种之间和品种内部都是可变的。因此，本研究的目的是确定显著控制绵羊肝脏铜浓度的分子遗传因素。在该项目的第一部分中，将测量已收集的美利诺羊屠宰羔羊的肝脏样本中的铜浓度。应用SNP芯片，将对其中96个样本的DNA进行基因分型，以确定绵羊基因组中分布的约60万个遗传变异。由此产生的表型和基因分型数据将用于全基因组关联研究（GWAS）。随后，筛选与肝铜浓度相关的基因组区域，寻找可直接控制肝铜浓度的遗传变异。这一步将采用合适的下一代测序方法。最后，这些遗传变异中最有希望的将在另外五个羊品种中收集和表型样品中测试它们对肝脏铜浓度的影响，这些羊品种在绵羊生产中很重要，并且/或者已知它们对铜中毒或缺乏的易感性不同。本项目的研究结果将进一步加深对肝脏铜代谢遗传调控的认识，并有助于为治疗和预防绵羊铜中毒和缺乏症提供新的思路。

Sheep are known to be impaired regarding their ability to excrete excess copper (Cu) from the liver and therefore to be more susceptible to Cu intoxication than other farm animals. On the other hand, Cu deficiency is also a known problem in sheep husbandry. In consequence, there is little scope for adequate Cu supplementation in the sheep diet. Interestingly, the susceptibility for Cu deficiency as well as for Cu intoxication varies between sheep breeds. Moreover, liver copper concentration seems to be highly heritable and variable between and within sheep breeds. Hence, it is the aim of this study to identify the molecular genetic factors which significantly control the liver copper concentration in sheep. In the first part of this project, Cu concentration will be measured in already collected liver samples from performance tested slaughter lambs of the Merinoland sheep breed. Applying an SNP chip, DNA from 96 of these samples will be genotyped for about 600,000 genetic variants distributed in the sheep genome. Resulting phenotyping and genotyping data will be used for a genome wide association study (GWAS). Subsequently, genome regions which showed to be associated with liver Cu concentration will be screened for genetic variants which could directly control liver copper concentration. For this step, an appropriate next generation sequencing method will be employed. Finally, the most promising among those genetic variants will be tested for their effect on liver copper concentration in additionally collected and phenotyped samples from five more sheep breeds, which are of importance in sheep production and/or known to differ in their susceptibility to Cu intoxication or deficiency. The results of this project will enhance the knowledge on the genetic control of liver Cu metabolism and can help to develop new concepts for therapy and prevention of Cu intoxication and deficiency in sheep.