Department of Biology, Boston College, Chestnut Hill, MA 02467, USA.
Mol Microbiol. 2012 May;84(3):566-77. doi: 10.1111/j.1365-2958.2012.08044.x. Epub 2012 Apr 9.
Toxoplasma gondii is an obligate intracellular protozoan parasite whose rapid lytic replication cycles define its pathogenicity. We identified a temperature-sensitive growth mutant, FV-P6, which irreversibly arrests before the middle of the G1 stage of the tachyzoite cell cycle. This arrest is caused by a point mutation in a gene conserved across eukaryotes, Cactin, whose product localizes to the nucleus. To elucidate the role of TgCactin we performed genome-wide expression profiling. Besides the expected G1 expression profile, many genes associated with the extracellular state as well as with the bradyzoite cyst stage were identified. Consistent with these profiles were the expression of AP2 transcription factors typically associated with extracellular and bradyzoite stage parasites. This suggests a role for TgCactin in control of gene expression. As TgCactin does not contain any functionally defined domains we reasoned TgCactin exerts its function through interactions with other proteins. In support of this model we demonstrated that TgCactin is present in a protein complex and can oligomerize. Taken together, these results suggest that TgCactin acts as a pivotal protein potentially regulating gene expression at several transition points in parasite development.
刚地弓形虫是一种专性细胞内原生动物寄生虫，其快速裂解复制周期定义了其致病性。我们鉴定了一个温度敏感生长突变体 FV-P6，它在速殖子细胞周期的 G1 期中期之前不可逆地停滞。这种停滞是由一个在真核生物中保守的基因 Cactin 中的点突变引起的，其产物定位于细胞核。为了阐明 TgCactin 的作用，我们进行了全基因组表达谱分析。除了预期的 G1 表达谱外，还鉴定了许多与细胞外状态以及缓殖子囊阶段相关的基因。与这些图谱一致的是与细胞外和缓殖子阶段寄生虫相关的 AP2 转录因子的表达。这表明 TgCactin 在控制基因表达中起作用。由于 TgCactin 不包含任何具有功能定义的结构域，我们推断 TgCactin 通过与其他蛋白质的相互作用发挥其功能。为了支持这个模型，我们证明了 TgCactin 存在于一个蛋白质复合物中并且可以寡聚化。总之，这些结果表明 TgCactin 作为一种关键蛋白，可能在寄生虫发育的几个转换点调节基因表达。
