Weir William, Ben-Miled Leila, Karagenç Tülin, Katzer Frank, Darghouth Mohamed, Shiels Brian, Tait Andrew
Parasitology Group, Division of Infection and Immunity, Institute of Comparative Medicine, Glasgow University Veterinary School, Bearsden Road, Glasgow G61 1QH, UK.
Mol Biochem Parasitol. 2007 Aug;154(2):170-80. doi: 10.1016/j.molbiopara.2007.04.015. Epub 2007 Apr 27.
Tropical theileriosis, caused by the tick-transmitted protozoan Theileria annulata, is a major disease of cattle in many regions of the developing world. Development and deployment of current and novel control strategies should take into account the potential diversity of parasite populations and therefore it is important that the nature and basis for this genetic variation is investigated and quantified. The recently completed genome sequence of T. annulata provided an opportunity to develop a panel of genetic markers for population studies. Bioinformatic screening of the genome sequence identified micro- and mini-satellite loci, which were PCR amplified from a series of diverse parasite stocks in order to characterise their polymorphism and determine their species-specificity. A panel of 10 polymorphic markers was then selected for population genetic studies and used to genotype both cloned and uncloned isolates maintained as cell lines of T. annulata isolated from different countries. Uncloned isolates comprised a multiplicity of genotypes, while cloned isolates showed evidence of a single haploid genome. Population genetic analysis revealed a high level of genotypic diversity both between and within countries, as measured by the number of distinct multilocus genotypes. Based on measures of genetic differentiation (F(ST) and Nei's genetic distance), the parasite populations are geographically sub-structured and these measurements positively correlate with geographical distance. To investigate whether genetic exchange occurs at random and the populations are panmictic, the level of linkage disequilibrium was measured using the index of association across all loci. Linkage disequilibrium was observed when isolates from all countries were treated as a single population but when the isolates from Tunisia were analysed separately, linkage equilibrium was observed.
热带泰勒虫病由蜱传播的原生动物环形泰勒虫引起，是发展中世界许多地区牛的主要疾病。当前和新型控制策略的开发与应用应考虑寄生虫种群的潜在多样性，因此，研究和量化这种遗传变异的性质及基础非常重要。最近完成的环形泰勒虫基因组序列为开展种群研究开发一组遗传标记提供了契机。对基因组序列进行生物信息学筛选，确定了微卫星和小卫星位点，从一系列不同的寄生虫株系中进行PCR扩增，以表征其多态性并确定其物种特异性。然后选择一组10个多态性标记用于种群遗传学研究，并用于对来自不同国家的作为环形泰勒虫细胞系保存的克隆和未克隆分离株进行基因分型。未克隆分离株包含多种基因型，而克隆分离株显示出单倍体基因组的证据。种群遗传分析表明，无论是在国家之间还是国家内部，通过不同多位点基因型的数量衡量，基因型多样性水平都很高。基于遗传分化指标（F(ST)和内氏遗传距离），寄生虫种群在地理上存在亚结构，并且这些测量值与地理距离呈正相关。为了研究基因交换是否随机发生以及种群是否随机交配，使用所有位点的关联指数测量连锁不平衡水平。当将来自所有国家的分离株视为一个单一群体时，观察到连锁不平衡，但当单独分析来自突尼斯的分离株时，观察到连锁平衡。
