United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1, Yanagido, Gifu 501-1193, Japan; Department of Nursing, Heisei College of Health Sciences, 180 Kurono, Gifu 501-1131, Japan.
Department of Functional Bioscience, Gifu University School of Medicine, 1-1, Yanagido, Gifu 501-1193, Japan.
Gene. 2019 May 30;699:73-79. doi: 10.1016/j.gene.2019.03.008. Epub 2019 Mar 9.
Toxoplasma gondii is an important protozoan pathogen that infects many wild and domestic animals and causes infections in immunocompromised humans. However, there has been little investigation of the molecular evolutionary trajectories of this pathogenic protozoa using comparative genomics data. Here, we employed a comparative evolutionary genomics approach to identify genes that are under site- and lineage-specific positive selection in nine strains of T. gondii, including two closely related species, Neospora caninum and Hammondia hammondi. Based on the analyses of five coccidian core genomes, 4.5% of the 5788 core genome genes showed strong signals for positive selection in the site model. In addition, the branch-site model analyses in the nine T. gondii core genomes indicated that 2 to 20 genes underwent significant positive selection along each lineage leading to T. gondii strains. Many of the protein products encoded by the positively selected genes are secretory or surface proteins that have previously been implicated in host pathogenesis. The adaptive changes in these positively selected genes might be related to dynamic interactions between the host immune systems and might play a crucial role in the infection and pathogenic processes of T. gondii.
刚地弓形虫是一种重要的原生动物病原体，感染许多野生动物和家养动物，并导致免疫功能低下的人类感染。然而，利用比较基因组学数据对这种致病原生动物的分子进化轨迹进行的研究很少。在这里，我们采用比较进化基因组学的方法，鉴定了在包括两种密切相关的物种新孢子虫和哈氏巴贝斯虫在内的 9 株刚地弓形虫中，受位点和谱系特异性正选择影响的基因。基于对 5788 个核心基因组基因的分析，在 5 个球虫核心基因组中，有 4.5%的基因在位点模型中显示出强烈的正选择信号。此外，在 9 株刚地弓形虫核心基因组中的分支位点模型分析表明，在导致刚地弓形虫株的每条谱系上，有 2 到 20 个基因经历了显著的正选择。这些受正选择基因编码的许多蛋白质产物是分泌蛋白或表面蛋白，先前曾与宿主发病机制有关。这些正选择基因的适应性变化可能与宿主免疫系统的动态相互作用有关，并可能在刚地弓形虫的感染和发病过程中发挥关键作用。
