DNA repair and recombination within the var gene family of P. falciparum

描述（由申请人提供）：疟疾由疟原虫属的原生动物寄生虫引起。 恶性疟原虫是毒性最强的物种，是造成大多数发病率和死亡率的原因，包括每年约80万例死亡，主要发生在幼儿中。寄生虫能够在宿主免疫系统的攻击下存活的关键是它修复DNA损伤的能力。DNA双链断裂（DSB）如果不修复是致命的，疟疾寄生虫似乎缺少大多数真核生物修复这种断裂的两个主要途径之一。此外，剩余的通路需要与断裂位点同源的第二个DNA拷贝作为修复的模板。考虑到疟疾寄生虫在其生命周期的大部分时间里都是单倍体，因此大部分基因组都是以单拷贝的形式维持的，它们如何修复DSB仍然是一个谜。该提案的长期目标是了解寄生虫如何保持其基因组的完整性，并确定DNA修复途径如何有助于编码其主要表面抗原的基因的多样化。为了解决这些问题，一种可调节的位点特异性核酸内切酶系统已被改造用于培养的寄生虫。该系统能够在基因组的靶位点内诱导单个DSB，然后快速有效地分离修复产物。在该项目的第一个人工智能中，该系统将用于表征寄生虫修复DSB的基本机制，包括该过程如何容易出错，是否需要模板以及错配修复途径在DSB修复中的作用。在第二个目标中，该系统将被应用于研究var基因家族的多样性。var基因编码PfEMP 1，主要的疟疾毒力因子。这个庞大的多拷贝基因家族经历了快速和持续的多样化，使寄生虫能够通过抗原变异避开免疫系统。多样化背后的机制尚不清楚，但这一过程似乎涉及片段的频繁“洗牌”，这是DSB修复产物基因转换事件的标志。位点特异性核酸内切酶系统将用于确定DSB修复如何有助于var基因多样化。 公共卫生相关性：疟疾寄生虫利用其基本的DNA修复途径，既能在人类免疫反应引起的DNA损伤中存活，又能在编码受感染红细胞表面上表达的蛋白质的基因内产生多样性。研究寄生虫如何能够避免免疫或确定寄生虫修复DNA损伤能力的潜在弱点，将有助于开发新的疾病干预策略。

DESCRIPTION (provided by applicant): Malaria is caused by protozoan parasites of the genus Plasmodium. P. falciparum is the most virulent species and is responsible for the majority of both morbidity and mortality, including approximately 800,000 deaths per year that occur mainly among young children. Key to the parasite's ability to survive attack by the host's immune system is its ability to repair DNA damage. DNA double strand breaks (DSBs) are lethal if not repaired, and malaria parasites appear to be missing one of the two primary pathways used by most eukaryotes to repair such breaks. In addition, the remaining pathway requires a second DNA copy homologous to the site of the break to serve as a template for repair. Considering that malaria parasites are haploid for most of their lifecycle and therefore the majority of the genome is maintained as a single copy, how they repair DSBs remains a mystery. The long-term objectives of this proposal are to understand how parasites maintain the integrity of their genomes, and to determine how DNA repair pathways contribute to diversification of the genes encoding their primary surface antigens. To address these objectives, a regulatable, site-specific endonuclease system has been adapted for use in cultured parasites. This system enables the induction of a single DSB within a targeted site of the genome followed by the rapid and efficient isolation of the products of repair. In the first ai of the project, this system will be used to characterize the basic mechanisms employed by parasites to repair DSBs, including how error prone the process is, whether a template is required, and the role of the mismatch repair pathway in DSB repair. In the second aim, the system will be applied to investigating diversification of the var gene family. var genes encode PfEMP1, the primary malaria virulence factor. This large, multi-copy gene family undergoes rapid and continuous diversification that enables the parasite to avoid the immune system through antigenic variation. The mechanisms underlying diversification are unknown, but the process appears to involve frequent "shuffling" of segments, a hallmark of gene conversion events that are a product of DSB repair. The site-specific endonuclease system will be used to determine how DSB repair contributes to var gene diversification. PUBLIC HEALTH RELEVANCE: Malaria parasites utilize their basic DNA repair pathways both to survive DNA damage resulting from the human immune response and to generate diversity within the genes encoding proteins expressed on the surface of infected red blood cells. Investigations into how the parasite is able to avoid immunity or identify potential weaknesses in the parasite's ability to repair DNA damage will contribute to the development of novel disease intervention strategies.