Genome-wide mapping and identification of genes controlling resistance to Marek's Disease virus infection in commercial layer chickens

马立克氏病（MD）是由一种高度传染性病毒（MDV）引起的，它持续威胁着我们的全球家禽业和粮食安全，估计每年损失10 - 20亿英镑。这些损失与该病的成本有关，原因是死亡率上升、疫苗接种费用上升和产蛋量减少。因此，这种疾病对我们的经济和国际竞争能力产生了影响，并对动物健康和福利以及我们的全球粮食安全产生了额外的关注。尽管该病已通过疫苗接种控制了40多年，但来自研究人员的越来越多的证据表明，疫苗的大量使用正在促使该病毒具有越来越强的杀死家禽的能力，每年都在继续出现更具攻击性的该病毒株。目前正在寻求控制这一疾病的另一种方法，即培育对MDV具有更强抵抗力的鸟类。这种差异在近80年前首次被报道。随后，与主要组织相容性复合体（MHC）相关的基因（MHC在免疫系统中起重要作用）被证明有助于抵抗MDV。尽管如此，其他基因也对MDV抗性有很强的影响。这一点最有效地确定于使用具有相同MHC但在对MDV的易感性方面仍然表现出差异的鸡的近交系的研究。已经确定了许多控制MDV抗性的染色体区域（数量性状位点，或QTL），但很少有基因被证实控制宿主对这种疾病的反应，这是大多数复杂性状的典型特征。已鉴定的包括生长激素（GH1）、细胞因子SCYC1和淋巴细胞表面标记物LY6E。确定与MDV抗性（或易感性）相关的基因并确定它们的作用对于理解这种疾病以及为什么它似乎变得更致命至关重要。这些知识很重要；提供控制和减少这种对家禽业的威胁的手段。这一建议非常及时，因为我们现在拥有许多新的研究工具，可以使我们能够识别参与抵抗MD感染的基因。这些包括QTL数据，MDV挑战设施的访问，鸡系的基因组序列，基于父母对MDV抗性不同的大型QTL高分辨率定位群体（现在是第6代），以及一个600K snp（单核苷酸多态性-遗传标记）面板，可以一起用于精确定位马立克病QTL的高分辨率定位到包含约25个基因的基因组区域。结合高通量测序和生物信息学方法，我们不仅可以预测MD耐药的候选基因，还可以预测这些基因内可能的致病突变。我们还将所有的MDV蛋白克隆到合适的载体中，用于“酵母-2-杂交”实验，用于病毒和宿主蛋白之间的直接蛋白/蛋白结合。通过这种方式，我们将能够识别直接与病毒蛋白结合的基因，然后继续测试这些基因内的突变是否会改变任何结合相互作用。在这一提议中，我们的目标是确定在商品蛋鸡中发挥MD抗性作用的染色体区域，鉴定候选基因内的遗传变异，探索宿主和病毒蛋白之间的直接蛋白质结合相互作用，并检查这些基因遗传变异的功能后果。该项目的结果将是鉴定和鉴定商业蛋鸡品系中有价值的遗传标记，用于家禽业的选择性育种计划，这将产生巨大的经济和健康效益。目前，随着世界人口的增长和对粮食安全的担忧加剧，家禽业面临新的压力。

Marek's Disease (MD) is caused by a highly contagious virus (MDV), which is a continuing threat to our global poultry industry and food security with estimated losses of £1-2 billion per year. These losses are associated with the cost of the disease, due to increased mortality, escalating vaccination costs and reduced egg production. It is therefore a disease that has an impact on our economy and ability to compete internationally, with additional concerns for animal health and welfare, and our global food security. Although it has been controlled by vaccination for over 40 years, there is growing evidence from researchers that intensive use of vaccines is driving the virus to have an increasing ability to kill poultry, with more aggressive strains of the disease continuing to emerge each year.An alternative means to control this disease is being sought through breeding birds with enhanced resistance to MDV. Such differences were first reported nearly 80 years ago. Subsequently, genes associated with the major histocompatibility complex (MHC), which plays an important role in the immune system, were shown to contribute towards resistance to MDV. Despite this, other genes also have a strong influence on MDV resistance. This has been determined most effectively from studies using inbred strains of chickens that have identical MHC but still show differences in their susceptibility towards MDV.Many chromosomal regions that control MDV resistance have been defined (quantitative trait loci, or QTL) but very few genes have been verified as controlling the host response towards this disease, which is typical for most complex traits. Those which have been identified include growth hormone (GH1), the cytokine SCYC1 and the cell surface marker on lymphocytes LY6E. Identifying genes involved in resistance (or susceptibility) to MDV and resolving their role is crucial to understanding this disease and why it appears to becoming more fatal. This knowledge is important; providing the means to control and reduce this threat to the poultry industry.This proposal is extremely timely in that we now have at our disposal many new research tools which may enable us to identify genes involved in resistance to MD infection. These include QTL data, access to MDV challenge facilities, genomic sequences of chicken lines, a large QTL high resolution mapping population (now in its 6th generation) based on parents differing in their resistance to MDV and a panel of 600K SNPs (single nucleotide polymorphisms - genetic markers) which can be used together to fine map Marek's Disease QTL to high resolution to genomic regions containing around 25 genes. This, in conjunction with high throughput sequencing and bioinformatics approaches, will allow us to not only predict candidate genes for MD resistance but also possible causative mutations within these genes.We also have available to us all the MDV proteins cloned into suitable vectors for testing in 'yeast-2-hybrid' experiments for direct protein/protein binding between viral and host proteins. In this way we will be able to identify genes which bind directly with viral proteins and then go on to test whether mutations within these genes alter any binding interactions.In this proposal we aim to determine the chromosomal regions that play a role in MD resistance in commercial egg-layers, identify genetic variation within candidate genes, explore direct protein binding interactions between host and viral proteins, and examine the functional consequences of genetic variation in these genes.The outcome of this project will be the identification and characterization of valuable genetic markers in commercial egg-layer lines for use in selective breeding programs within the poultry industry, which would result in large economic and health benefits. This comes at a time when there are renewed pressures on the poultry industry as the world population expands and concerns over food security increase.