The FACT subunit TbSpt16 is involved in cell cycle specific control of VSG expression sites in Trypanosoma brucei
The FACT subunit TbSpt16 is involved in cell cycle specific control of VSG expression sites in Trypanosoma brucei
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DOI：
10.1111/j.1365-2958.2010.07350.x
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发表时间：
2010-10-01
影响因子：
3.6
通讯作者：
Rudenko, Gloria
中科院分区：
文献类型：
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作者：
Denninger, Viola;Fullbrook, Alexander;Rudenko, Gloria
非洲锥虫布鲁氏锥虫单等位表达1000多个变异表面糖蛋白（VSG）基因中的一个。活性VSG是从大约15个VSG端粒表达位点（ESs）中的一个转录而来。目前尚不清楚VSG的单等位基因表达是如何被控制的，以及不活跃的VSG是如何被沉默的。在这里，我们发现阻断布鲁氏体FACT亚基TbSpt16的合成会在血流和昆虫形式的布鲁氏体中触发G2/早期M期细胞周期阻滞。在这些停滞的细胞中，布鲁氏体小染色体的分离受损，暗示FACT参与着丝粒的维持。引人注目的是，TbSpt16的敲除导致布鲁氏t血液中沉默的VSG ES启动子降低20- 23倍，并且这种降低仅发生在G2/M细胞周期阶段。在昆虫形式的布氏体中，TbSpt16敲除导致16- 25倍的VSG ES下降。利用染色质免疫沉淀（ChIP）技术，发现TbSpt16在布鲁氏体血液中沉默但不活跃的VSG ESs的启动子区域特别富集。因此，染色质重塑因子FACT与维持沉默VSG ES启动子中存在的被抑制染色质有关，但也可能通过维持功能性着丝粒而对染色体分离至关重要。
P>The African trypanosome Trypanosoma brucei monoallelically expresses one of more than 1000 Variant Surface Glycoprotein (VSG) genes. The active VSG is transcribed from one of about 15 telomeric VSG expression sites (ESs). It is unclear how monoallelic expression of VSG is controlled, and how inactive VSG ESs are silenced. Here, we show that blocking synthesis of the T. brucei FACT subunit TbSpt16 triggers a G2/early M phase cell cycle arrest in both bloodstream and insect form T. brucei. Segregation of T. brucei minichromosomes in these stalled cells is impaired, implicating FACT in maintenance of centromeres. Strikingly, knock-down of TbSpt16 results in 20- to 23-fold derepression of silent VSG ES promoters in bloodstream form T. brucei, with derepression specific to the G2/M cell cycle stage. In insect form T. brucei TbSpt16 knock-down results in 16- to 25-fold VSG ES derepression. Using chromatin immunoprecipitation (ChIP), TbSpt16 was found to be particularly enriched at the promoter region of silent but not active VSG ESs in bloodstream form T. brucei. The chromatin remodeler FACT is therefore implicated in maintenance of repressed chromatin present at silent VSG ES promoters, but is also essential for chromosome segregation presumably through maintenance of functional centromeres.