Howe D K, Summers B C, Sibley L D
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Infect Immun. 1996 Dec;64(12):5193-8. doi: 10.1128/iai.64.12.5193-5198.1996.
Toxoplasma gondii has an unusual population structure consisting of three widely distributed clonal lineages. Acute virulence in mice is strictly observed in type I strains, indicating that a genetic determinant(s) unique to this lineage controls acute pathogenesis. We have analyzed several naturally occurring recombinant strains of T. gondii that carry allele 1 at the SAG1 locus; this allele is characteristic of the type I strains and was previously found to be 100% correlated with the acute virulence phenotype. Recombinant strains G622-M and ROD both had a predominantly type III genotype, with the significant exception of allele 1 at the SAG1 locus. Although these two strains had virtually identical multilocus genotypes, they differed in their virulence in mice. Strain ROD was virulent whereas strain G622-M was nonvirulent, thus demonstrating that the presence of allele 1 at SAG1 is not alone sufficient to confer acute virulence. Several sequence polymorphisms upstream of SAG1 were found to be highly correlated with the acutely virulent lineages. Collectively, these results suggest that acute virulence is regulated by a region linked to the SAG1 locus on chromosome VIII in T. gondii.
刚地弓形虫具有一种不同寻常的种群结构，由三个广泛分布的克隆谱系组成。在小鼠中的急性毒力仅在I型菌株中严格观察到，这表明该谱系特有的一个或多个遗传决定因素控制着急性发病机制。我们分析了几种自然发生的刚地弓形虫重组菌株，这些菌株在SAG1位点携带等位基因1；该等位基因是I型菌株的特征，先前发现与急性毒力表型100%相关。重组菌株G622-M和ROD都主要具有III型基因型，但SAG1位点的等位基因1是显著例外。尽管这两个菌株实际上具有相同的多位点基因型，但它们在小鼠中的毒力不同。ROD菌株有毒力，而G622-M菌株无毒力，因此表明SAG1位点存在等位基因1并不足以单独赋予急性毒力。发现SAG1上游的几个序列多态性与急性毒力谱系高度相关。总体而言，这些结果表明急性毒力受与刚地弓形虫第八条染色体上SAG1位点相连的一个区域调控。
