MECHANISM OF ANTIGENIC VARIATION IN TRYPANOSOMA BRUCEI

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 使转换为表达新外壳的锥虫能够逃脱 免疫破坏 抗原变异背后的遗传程序 涉及不同VSG基因的或多或少有序表达。 一些 VSG基因可以通过将基因重复转座到 位于染色体末端或端粒的表达位点;其他VSG基因 通常位于端粒上的蛋白质可以被激活而不会被检测到 基因附近的基因组重组。 我已经证明， 其中几个代表了位于细胞表面的不同端粒表达位点 不同的染色体（4）。 本项目的目的是调查 这些端粒表达位点的相互排斥的激活， 染色体重组参与其调节。 最近，我已经能够通过一个 新的电泳技术 这使得以前的检测 未观察到的染色体重排，取代了数百个 双胞胎。 这些可以解释转录调控的基因， 通过VSG基因启动子上的位置效应， 染色体重组 为了检验相互排斥的 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150 kb区域， 探讨重组对VSG基因的调控作用 表达：通过定位和比较VSG基因启动子， 不同的重组突变体激活了相同的位点。 我也会 研究染色体的频率和机制 重组：通过克隆突变染色体重组区 及通过确定重组的性质分析重组的性质。 供体和受体位点的核苷酸序列。 我将比较 布氏锥虫的染色体组库和染色体稳定性， 其它动质体（锥虫属，利什曼原虫属， Leptomonas和Herpetomonas）。 这将使我们对染色体的了解 稳定性和突变频率，这是重要的 因为我们理解了塑造寄生虫基因组的力量， 不断适应多变的环境。

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.