MECHANISM OF ANTIGENIC VARIATION IN TRYPANOSOMA BRUCEI

布氏锥虫抗原变异机制

• 批准号: 3132136
• 负责人: L H T VAN DER PLOEG
• 金额: $ 15.55万
• 依托单位: COLUMBIA UNIV NEW YORK MORNINGSIDE
• 依托单位国家: 美国
• 财政年份: 1985
• 资助国家: 美国
• 起止时间: 1985-07-01 至 1988-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/3132136
• 关键词: Trypanosoma; chromosome translocation; gene expression; genetic manipulation; genetic recombination; genetic transcription; genome; membrane activity; microorganism genetics; microorganism immunology; mutant; nucleic acid sequence; protozoal antigen; trypanosomiasis

Antigenic variation of trypanosomes is brought about by the periodic expression of genes that code for the Variant Cell Surface Glycoprotein (VSG) coat. The expression of immunologically distinct surface coats enables trypanosomes that switched to the expression of new coat to escape immune destruction. The genetic program underlying antigenic variation involves the more or less ordered expression of different VSG genes. Some VSG genes can be activated by a duplicative transposition of the gene to an expression site located at a chromosome end or telomere; other VSG genes that are always located at telomeres can be activated without detectable genomic recombinations in the vicinity of the gene. I have shown that several of these represent different telomeric expression sites situated on different chromosomes (4). It is the aim of this project to investigate the mutually exclusive activation of these telomeric expression sites and the involvement of chromosomal recombinations in their regulation. Recently I have been able to size separate trypanosomal chromosomes by a new electrophoretic technique. This allowed the detection of previously unobserved chromosome rearrangements, displacing hundreds of kilobasepairs. These could explain transcriptional regulation of the expression sites by a position effect on the VSG gene promoter due to the chromosomal recombinations. In order to examine the mutually exclusive regulation of the expression sites I will isolate recombination mutants, clone an area of 150 kb comprising the expression site of VSG gene 1.8 and investigate the regulatory effect of the recombinations on VSG gene expression: by localisation and comparison of the VSG gene promoter in different recombination mutants that activated the same site. I will also examine the frequency and mechanism underlying the chromosome recombinations: by cloning of the mutant chromosome recombination regions and analysis of the nature of the recombinations by determination of the nucleotide sequences at donor and acceptor sites. I will compare the chromosome repertoire and chromosomal stability in T.brucei, with that of other Kinetoplastida (species of the genera Trypanosoma, Leishmania, Leptomonas, and Herpetomonas). This will give insight in the chromosome stability and mutation frequency in these protozoa which is of importance for our understanding of the forces molding the parasites genome in its continuous adaptation to a highly variable environment.

锥虫的抗原变异是由周期性的 编码变异细胞表面糖蛋白的基因的表达 （VSG）外套。 免疫学上不同的表面涂层的表达 使转换为新外壳表达的锥虫能够逃脱 免疫破坏。 抗原变异背后的遗传程序 涉及不同 VSG 基因或多或少有序的表达。 一些 VSG 基因可以通过基因重复转座来激活 表达位点位于染色体末端或端粒；其他 VSG 基因 始终位于端粒的细胞可以在无法检测到的情况下被激活 基因组重组发生在基因附近。 我已经证明了 其中几个代表位于不同端粒表达位点 不同的染色体（4）。 该项目的目的是调查 这些端粒表达位点的相互排斥的激活和 染色体重组参与其调节。 最近我已经能够通过一个方法来确定单独的锥虫染色体的大小 新的电泳技术。 这允许检测先前的 未观察到的染色体重排，取代了数百条染色体 千碱基对。 这些可以解释转录调控 表达位点受 VSG 基因启动子位置效应的影响 染色体重组。 为了检验互斥的 表达位点的调节我将分离重组突变体， 克隆包含VSG基因1.8的表达位点的150kb区域，并且 研究重组对VSG基因的调控作用 表达：通过VSG基因启动子的定位和比较 激活同一位点的不同重组突变体。 我也会 检查染色体的频率和机制 重组：通过克隆突变染色体重组区域 并通过测定来分析重组的性质 供体和受体位点的核苷酸序列。 我将比较 T.brucei 的染色体库和染色体稳定性，与 其他动质体（锥虫属、利什曼原虫属、 细单胞菌和疱疹单胞菌）。 这将深入了解染色体 这些原生动物的稳定性和突变频率非常重要 为了我们了解塑造寄生虫基因组的力量 不断适应高度变化的环境。