var gene regulation and antigenic variation in malaria

描述（由申请人提供）：恶性疟原虫是导致最严重形式的人类疟疾的病原体，这种疾病每年导致100多万人死亡，其中大多数是非洲的幼儿。这些原生动物寄生虫侵入并最终破坏其宿主的循环红细胞（RBC），导致严重贫血和脑型疟疾和妊娠相关疟疾的经常致命的综合征。在感染过程中，出现抗原表型改变的寄生虫小亚群，从而避免宿主的抗体应答。这一过程被称为抗原变异，并负责疾病的持续性以及在恶性疟原虫感染中经常观察到的寄生虫血症波。恶性疟原虫感染的红细胞的抗原变异是由多拷贝var基因家族的个体成员之间的表达转换引起的。每个var基因编码不同形式的蛋白质，称为PfEMP 1。这种蛋白质被放置在感染的RBC的表面上，并介导与感染个体的血管壁的内皮表面上发现的特异性受体的粘附。这种粘附是恶性疟原虫感染的许多疾病表现的原因，包括脑型疟疾和妊娠相关疟疾。任何给定的寄生虫在同一时间只表达一个var基因，因此决定了感染细胞的抗原表型以及它们的粘附特性。因此，var基因的表达是疟疾感染的抗原变异和毒力的核心。本项目旨在了解疟原虫var基因表达和抗原变异的分子调控机制。先前的工作已经证明，var基因的互斥表达涉及每个var基因处的染色质结构的特定修饰，然而这些修饰如何协调以导致在60个家族中的一次仅单个基因的表达仍然未知。该项目的具体目标是：1）鉴定和表征调节var基因染色质组装的染色质边界/绝缘子元件，2）确定非编码RNA在将染色质组装靶向var基因位点中的作用，3）研究妊娠相关疟疾中涉及的特定var基因的翻译调节机制。实验设计依赖于使用报告基因和药物选择标记来快速确定这些调控元件在控制var基因表达中的作用来创建转基因寄生虫系。长期目标是开发破坏抗原变异过程的方法，从而缩短感染的时间并降低其严重程度。公共卫生相关性：疟疾仍然是当今世界最重要的传染病杀手之一，每年造成100多万人死亡，主要是撒哈拉以南非洲的幼儿。该项目的重点是疟疾寄生虫避免人体免疫反应和导致严重疾病的能力。更好地了解这些过程将导致新的、新颖的治疗形式，这将有助于减轻疟疾给发展中国家造成的巨大公共卫生负担。

DESCRIPTION (provided by applicant): Plasmodium falciparum is the causative agent responsible for the most severe form of human malaria, a disease that kills more than a million people a year, mostly young children in Africa. These protozoan parasites invade and ultimately destroy circulating red blood cells (RBCs) of their host, leading to severe anemia and the frequently lethal syndromes of cerebral malaria and pregnancy associated malaria. 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 is referred to as antigenic variation and is responsible for the persistent nature of the disease as well as the waves of parasitemia frequently observed in P. falciparum infections. Antigenic variation of P. falciparum infected RBCs results from switches in expression between individual members of the multi-copy var gene family. Each var gene encodes a different form of a protein called PfEMP1. This protein is placed on the surface of the infected RBCs and mediates adhesion to specific receptors found on the endothelial surfaces of the blood vessel walls of the infected individual. This adhesion is responsible for many of the disease manifestations of infection with P. falciparum, including both cerebral malaria and pregnancy associated malaria. Only a single var gene is expressed at a time by any given parasite, thus determining both the antigenic phenotype of the infected cells as well as their adhesive properties. Therefore var gene expression is the heart of both antigenic variation and virulence of malaria infections. This project is designed to understand the molecular mechanisms the regulate var gene expression and antigenic variation by malaria parasites. Previous work has demonstrated that mutually exclusive expression of var genes involves specific modifications to the chromatin structure at each var gene, however how these modifications are coordinated to result in expression of only a single gene at a time out of a family of 60 remains unknown. The specific aims of the project are 1) to identify and characterize chromatin boundary/insulator elements that regulate chromatin assembly at var genes, 2) to determine the role of noncoding RNAs in targeting chromatin assembly to var gene loci, and 3) to investigate the mechanism of translational regulation of a specific var gene implicated in pregnancy associated malaria. The experimental design relies on creating transgenic parasite lines using reporter genes and drug selectable markers to rapidly determine the role of these regulatory elements in controlling var gene expression. The long-term goals are to develop methods to disrupt the process of antigenic variation and thereby shorten the length of an infection and reduce its severity. PUBLIC HEALTH RELEVANCE: Malaria remains one of the most important infectious disease killers in the world today, causing more than a million deaths annually, primarily of young children in sub-Saharan Africa. This project focuses on the ability of malaria parasites to avoid the human immune response and to cause severe disease. A better understanding of these processes will lead to new, novel forms of treatment that will help to relieve the enormous public health burden that malaria inflicts on the developing world.