Oliveira R P, Melo A I, Macedo A M, Chiari E, Pena S D
Departamento de Ciências Biológicas, Universidade Federal de Ouro Preto, Brazil.
Mem Inst Oswaldo Cruz. 1999;94 Suppl 1:65-70. doi: 10.1590/s0074-02761999000700006.
Recently we cloned and sequenced the first eight Trypanosoma cruzi polymorphic microsatellite loci and studied 31 clones and strains to obtain valuable information about the population structure of the parasite. We have now studied 23 further strains, increasing from 11 to 31 the number of strains obtained from patients with chronic Chagas disease. This expanded set of 54 strains and clones analyzed with the eight microsatellites markers confirmed the previously observed diploidy, clonal population organization and very high polymorphism of T. cruzi. Moreover, this new study disclosed two new features of the population genetic structure of T. cruzi. The first was the discovery that, similarly to what we had previously shown for strains isolated from insect vectors, mammals and humans with acute disease, isolates from patients in the chronic phase of Chagas disease could also be multiclonal, albeit at a reduced proportion. Second, when we used parsimony to display the genetic relationship among the clonal lineages in an unrooted Wagner network we observed, like before, a good correlation of the tree topography with the classification in three clusters on the basis of single locus analysis of the ribosomal RNA genes. However, a significant new finding was that now the strains belonging to cluster 2 split in two distant sub-clusters. This observation suggests that the evolutionary history of T. cruzi may be more complex than we previously thought.
最近，我们克隆并测序了克氏锥虫的前8个多态性微卫星基因座，并研究了31个克隆和菌株，以获取有关该寄生虫种群结构的有价值信息。我们现在又研究了23个菌株，使从慢性恰加斯病患者中获得的菌株数量从11个增加到31个。用这8个微卫星标记对这54个菌株和克隆进行的分析证实了先前观察到的克氏锥虫的二倍体、克隆种群组织和非常高的多态性。此外，这项新研究揭示了克氏锥虫种群遗传结构的两个新特征。第一个是发现，与我们之前对从昆虫媒介、患有急性疾病的哺乳动物和人类中分离出的菌株所显示的情况类似，从恰加斯病慢性期患者中分离出的菌株也可能是多克隆的，尽管比例有所降低。其次，当我们用简约法在无根瓦格纳网络中展示克隆谱系之间的遗传关系时，我们像以前一样观察到，树形拓扑与基于核糖体RNA基因单基因座分析的三个簇的分类之间有很好的相关性。然而，一个重要的新发现是，现在属于第2簇中的菌株分裂成了两个相距甚远的亚簇。这一观察结果表明，克氏锥虫进化史可能比我们之前认为的更为复杂。
