Common inheritance of chromosome Ia associated with clonal expansion of Toxoplasma gondii
Common inheritance of chromosome Ia associated with clonal expansion of Toxoplasma gondii
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DOI：
10.1101/gr.5318106
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发表时间：
2006-09-01
期刊：
影响因子：
7
通讯作者：
Ajioka, James W.
中科院分区：
文献类型：
--
作者：
Khan, Asis;Bohme, Ulrike;Ajioka, James W.
弓形虫是一种全球分布的原生动物寄生虫，几乎可以感染所有温血动物和人类。尽管在生命周期中存在有性阶段，但弓形虫的种群结构不同寻常，由北美和欧洲占主导地位的三个克隆谱系(类型I、II和III型)主导。这些血统是由10000年前类似的共同祖先建立的。克隆血统最近的起源和广泛分布归因于一种新的传播方式--中间宿主之间的无性传播--绕过了有性周期。无性传播似乎是多基因的，尽管调节这一特征的特定基因尚不清楚，但据预测，克隆谱系的所有成员都应该拥有相同的等位基因。遗传图谱研究表明，与基因组的其余部分相比，染色体Ia是异常单态的。为了进一步研究这一点，我们对I型毒株RH和II型毒株ME49的Ia和Ib染色体进行了测序。对两条染色体序列的比较基因组分析表明，染色体Ia在每个谱系中都遗传了相同的副本，而染色体Ib与基因组的其余部分保持了相同的株间多态频率。来自三个克隆谱系的另外七个代表菌株的染色体Ia序列采样支持单态遗传，这在基因组中是独一无二的。综上所述，我们的观察表明，染色体Ia上的特定等位基因组合与弓形虫克隆谱系的最近起源和广泛成功有关。
Toxoplasma gondii is a globally distributed protozoan parasite that can infect virtually all warm- blooded animals and humans. Despite the existence of a sexual phase in the life cycle, T. gondii has an unusual population structure dominated by three clonal lineages that predominate in North America and Europe, ( Types I, II, and III). These lineages were founded by common ancestors similar to 10,000 yr ago. The recent origin and widespread distribution of the clonal lineages is attributed to the circumvention of the sexual cycle by a new mode of transmission-asexual transmission between intermediate hosts. Asexual transmission appears to be multigenic and although the specific genes mediating this trait are unknown, it is predicted that all members of the clonal lineages should share the same alleles. Genetic mapping studies suggested that chromosome Ia was unusually monomorphic compared with the rest of the genome. To investigate this further, we sequenced chromosome Ia and chromosome Ib in the Type I strain, RH, and the Type II strain, ME49. Comparative genome analyses of the two chromosomal sequences revealed that the same copy of chromosome Ia was inherited in each lineage, whereas chromosome Ib maintained the same high frequency of between-strain polymorphism as the rest of the genome. Sampling of chromosome Ia sequence in seven additional representative strains from the three clonal lineages supports a monomorphic inheritance, which is unique within the genome. Taken together, our observations implicate a specific combination of alleles on chromosome Ia in the recent origin and widespread success of the clonal lineages of T. gondii.