Var gene regulation and antigenic variation in malaria

疟疾中的 Var 基因调控和抗原变异

• 批准号: 7234045
• 负责人: Kirk W Deitsch
• 金额: $ 35.84万
• 依托单位: WEILL MEDICAL COLL OF CORNELL UNIV
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7234045
• 关键词: Anemia; Antibodies; Antibody Formation; Antigenic Variation; Automobile Driving; Biological Assay; Blood Cells; Cell Cycle; Cell Nucleus; Cells; Cerebral Malaria; Chromatin; Chromatin Structure; Complex; DNA; Digestion; Disease; Elements; Episome; Epitopes; Erythrocytes; Experimental Designs; Family; Fluorescent in Situ Hybridization; Gene Expression; Gene Expression Regulation; Gene Family; Gene Silencing; Genes; Genetic Transcription; Genome; Germ Lines; Histone Acetylation; Histones; Homologous Protein; Human; Hypersensitivity; Immune; Individual; Infection; Introns; Invaded; Malaria; Mediating; Modification; Molecular; Morbidity - disease rate; Nature; Nucleic Acid Regulatory Sequences; Organism; Parasitemia; Parasites; Phenotype; Plasmids; Plasmodium falciparum; Population; Principal Investigator; Process; Property; Proteins; Regulation; Regulatory Element; Reporter Genes; Reproduction; Role; Site-Directed Mutagenesis; Syndrome; System; Testing; Time; Transcriptional Silencer Elements; Transfection; Variant; chromatin immunoprecipitation; deletion analysis; inhibitor/antagonist; member; mortality; promoter; research study; restriction enzyme; tool

DESCRIPTION (provided by the applicant): Malaria remains one of the leading causes of morbidity and mortality in the developing world. The disease is caused by protozoan parasites that invade and ultimately destroy circulating red blood cells of their host, leading to severe anemia and the frequently lethal syndrome of cerebral malaria. These parasites have evolved a complex mechanism of immune evasion whereby, over the course of an infection, small sub-populations of parasites arise that have an altered antigenic phenotype, thus avoiding the antibody response of the host. This process of antigenic variation and is responsible for the persistent nature of the disease as well as the waves of parasitemia frequently observed in individuals infected by P. falciparum. The variation in antigenic phenotype is the result of switches in expression between individual members of the multicopy var gene family. This family consists of approximately 40-50 genes that encode the predominant antigenic determinant, a protein called PIEMPI. Only a single var gene is expressed at a time by any given parasite, thus determining the antigenic type of the infected cell. Changes in var gene expression and the resulting antigenic variation appear to be controlled at the level of transcription. The objective of this proposal is to determine the molecular mechanisms that maintain all but a single var gene in a transcriptionally silent state. The hypothesis to be tested is that var promoters are silenced through the assembly of a condensed, heterochromatic state and that chromatin modification and remodeling regulates expression of var genes and antigenic variation in Plasmodium falciparum. The experimental design exploits the recent discovery that elements upstream of var promoters act in a cooperative fashion with a conserved intron found in all var genes to silence transcription of all but a single gene. This transcriptionally silent state can be assembled on transfected episomes containing a reporter gene flanked by a var promoter and intron. Using this episomal system, the chromatin structure and subnuclear localization of silent and active var promoters will be determined. In addition, the specific DNA elements necessary for var gene silencing and activation will be identified, and the sequence requirements for DNA elements to functions as silencers or activators elucidated.

描述（由申请人提供）：疟疾仍然是发展中国家发病率和死亡率的主要原因之一。这种疾病是由原生动物寄生虫引起的，寄生虫侵入并最终破坏宿主的循环红细胞，导致严重的贫血和经常致命的脑型疟疾综合征。这些寄生虫已经进化出一种复杂的免疫逃避机制，由此，在感染过程中，产生具有改变的抗原表型的寄生虫的小亚群，从而避免宿主的抗体应答。这种抗原变异的过程是恶性疟原虫感染者中经常观察到的疾病持续性和寄生虫血症波的原因。抗原表型的变化是多拷贝var基因家族的个体成员之间表达转换的结果。这个家族由大约40-50个编码主要抗原决定簇的基因组成，这种蛋白质称为PIEMPI。任何给定的寄生虫一次只表达一个var基因，从而决定了受感染细胞的抗原类型。var基因表达的变化和由此产生的抗原变异似乎在转录水平上受到控制。这个建议的目的是确定维持所有，但一个单一的var基因在转录沉默状态的分子机制。要测试的假设是，通过组装的压缩，异染色质状态的var启动子沉默，染色质修饰和重塑调节恶性疟原虫的var基因和抗原变异的表达。实验设计利用了最近的发现，即var启动子上游的元件与所有var基因中发现的保守内含子以合作方式起作用，以沉默除单个基因之外的所有基因的转录。这种转录沉默状态可以组装在转染的附加体上，所述附加体含有侧翼为var启动子和内含子的报告基因。使用这种附加型系统，将确定沉默和活性var启动子的染色质结构和亚核定位。此外，将确定var基因沉默和激活所需的特定DNA元件，并阐明DNA元件作为沉默剂或激活剂的序列要求。