Transcriptional control of telomeric expression sites and antigenic variation

端粒表达位点和抗原变异的转录控制

• 批准号: RGPIN-2019-04658
• 负责人: Cestari, Igor
• 金额: $ 2.99万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=715094
• 关键词: Transcriptional; control; telomeric; expression; sites

Allelic exclusion of variant surface glycoprotein (VSG) genes is essential for the protozoa parasite Trypanosoma brucei spp. to evade the host immune response by antigenic variation. T. brucei expresses only one of its ~2,000 VSG genes at a time, which is exclusively transcribed at one of the 20 telomeric expression sites (ESs), and it periodically switches VSG gene expression to evade host antibody recognition. This VSG allelic exclusion mechanism ensures the expression of only one VSG protein on T. brucei surface, and the antigenic variation occurs by transcriptional switching between telomeric ESs or by VSG gene recombination. The molecular mechanisms that control VSG allelic exclusion and the periodic switching in VSG gene expression are poorly understood. My long-term goal is to understand the molecular basis underlying the control of antigenic variation with a focus on epigenetic and signalling mechanisms that control allelic exclusion, telomere silencing, and switching of VSG genes. We previously found that the control of VSG allelic exclusion and switching involves a multiprotein complex and is regulated by a phosphoinositol system. This protein complex associates with telomeric ES chromatin and includes proteins that function in DNA binding, RNA processing, the nuclear lamina, and protein kinases and phosphatases. We will study the protein composition of this telomere regulatory complex and its functional role in VSG allelic exclusion. We will focus on the epigenetic role of phosphoinositides in the silencing activity of this protein complex, and the protein complex function in ES chromatin organization and VSG transcription. Specifically, we will (aim 1) use chemical cross-linking and mass spectrometry to map the telomere regulatory protein complex composition and determine how this composition changes during silencing and transcription of VSG genes. Moreover (aim 2), using CRISPR-Cas9 mutagenesis and biochemical assays we will determine how the phosphoinositol regulatory system controls the silencing of VSG genes. Finally (aim 3), we will determine how this protein complex affects the telomeric ES chromatin structural organization, and how the ES chromatin changes during silencing and transcription of VSG genes. These studies will advance our understanding of the fundamental molecular processes that control allelic exclusion and antigenic variation in T. brucei and other organisms, e.g., Plasmodium spp., Giardia sp. It might also advance our knowledge of allelic exclusion of genes in other systems such as olfactory neuron receptors in mammals. My research program will also benefit economic and social sectors through the training of students in interdisciplinary, technological and innovative research.

变异表面糖蛋白（VSG）基因的等位基因排除是原生寄生虫布鲁氏锥虫通过抗原变异逃避宿主免疫应答的必要条件。布氏体一次只表达其约2,000个VSG基因中的一个，该基因在20个端粒表达位点（ESs）中的一个进行特异性转录，并周期性地转换VSG基因表达以逃避宿主抗体识别。这种VSG等位基因排斥机制保证了布鲁氏体表面只表达一种VSG蛋白，其抗原变异是通过端粒间的转录转换或VSG基因重组发生的。调控VSG等位基因排斥和VSG基因表达周期转换的分子机制尚不清楚。我的长期目标是了解控制抗原变异的分子基础，重点研究控制等位基因排斥、端粒沉默和VSG基因开关的表观遗传和信号机制。