Silencing subtelomeric VSGs by Trypanosoma brucei RAP1 at the insect stage involves chromatin structure changes
Silencing subtelomeric VSGs by Trypanosoma brucei RAP1 at the insect stage involves chromatin structure changes
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DOI：
10.1093/nar/gkt562
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发表时间：
2013-09-01
影响因子：
14.9
通讯作者：
Li, Bibo
中科院分区：
文献类型：
--
作者：
Pandya, Unnati M.;Sandhu, Ranjodh;Li, Bibo
布氏锥虫会引起人类非洲锥虫病，并定期转换其主要表面抗原变异表面糖蛋白（VSG）以逃避哺乳动物宿主在血流形式（BF）阶段的免疫反应。 BF表达位点（BES）连接的VSG的单等位基因表达和BF细胞中元环VSG（mVSG）的沉默对于抗原变异至关重要，而原环形式（PF）细胞中BES连接和mVSG的沉默对于其昆虫载体中肠中的细胞存活很重要。我们之前已经表明，BF 细胞中 BES 连接的 VSG 的沉默取决于 TbRAP1。我们现在证明 TbRAP1 在 BF 和 PF 阶段都会沉默 BES 相关的和 mVSG。 TbRAP1 介导的 BES 相关 VSG 沉默的强度在 PF 细胞中比在 BF 细胞中更强。此外，甲醛辅助调节元件分离分析和 MNase 消化表明，PF 细胞中 TbRAP1 的消耗导致染色质结构变化，这种变化在亚端粒 VSG 位点明显强于染色体内部位点。相反，在 BF 细胞中去除 TbRAP1 后，没有检测到显着的染色质结构变化。我们的观察表明，TbRAP1 有助于确定昆虫阶段的染色质结构，这可能有助于其对 VSG 产生强大的沉默作用。
Trypanosoma brucei causes human African trypanosomiasis and regularly switches its major surface antigen variant surface glycoprotein (VSG) to evade mammalian host immune responses at the bloodstream form (BF) stage. Monoallelic expression of BF Expression Site (BES)-linked VSGs and silencing of metacyclic VSGs (mVSGs) in BF cells are essential for antigenic variation, whereas silencing of both BES-linked and mVSGs in the procyclic form (PF) cells is important for cell survival in the midgut of its insect vector. We have previously shown that silencing BES-linked VSGs in BF cells depends on TbRAP1. We now show that TbRAP1 silences both BES-linked and mVSGs at both BF and PF stages. The strength of TbRAP1-mediated BES-linked VSG silencing is stronger in the PF cells than that in BF cells. In addition, Formaldehyde-Assisted Isolation of Regulatory Elements analysis and MNase digestion demonstrated that depletion of TbRAP1 in PF cells led to a chromatin structure change, which is significantly stronger at the subtelomeric VSG loci than at chromosome internal loci. On the contrary, no significant chromatin structure changes were detected on depletion of TbRAP1 in BF cells. Our observations indicate that TbRAP1 helps to determine the chromatin structure at the insect stage, which likely contributes to its strong silencing effect on VSGs.