Genetics & Population Structure of Plasmodium falciparum

描述（由申请人提供）：目前全球最致命的人类疟疾寄生虫，恶性疟原虫，被认为在过去几千年的某个时候经历了一个瓶颈。尽管最近有一个共同的起源，恶性疟原虫种群的特点是高度的蛋白质多态性，特别是在某些免疫显性表面蛋白中。这种广泛的遗传变异提供了巨大的适应潜力，使寄生虫逃避宿主的免疫反应。本提案的主要目的不仅是确定恶性疟原虫种群中抗原多样性的程度，而且还要确定这种变异产生和维持的主要机制。我们将研究来自非洲几个地方的恶性疟原虫自然分离株的遗传多态性。从这些分离株中，我们将量化几个分子标记之间的多态性，这些标记分散在三个完全测序的染色体（chr2， chr3和chr10）上。待检测的遗传位点为三个编码的表面蛋白基因——环孢子子蛋白（Csp，位于Chr2上）和merozoite表面蛋白-2 （Msp-2，位于Chr3上），以及25kd恶性疟原虫性期抗原（pfs25，位于Chr10上）。这些基因座中的每一个在其表达上都具有生命周期阶段特异性，并且是目前正在开发的一种或多种疫苗的靶标。除了这些蛋白质编码基因外，我们还将对排列在相同三条染色体上的几个高度多态性的微卫星位点进行分型。得到的每个分离物的多位点基因型将直接用于检测；(1)恶性疟原虫天然分离株基因组的减数分裂重组水平；(2)关键蛋白编码基因的多样化选择程度；(3)链滑脱（有丝分裂）突变在维持免疫原性、核苷酸重复位点（Csp和Msp-2）变异中的作用。这项工作将增加我们对这种寄生虫基因组进化的理解，并为评估干预疾病传播的适当策略提供有价值的信息。

DESCRIPTION (provided by applicant): The current global population of the most deadly human malaria parasite, P. falciparum, is thought to have undergone a bottleneck sometime within the past several thousand years. Despite a recent common origin, P. falciparum populations are characterized by a high degree of protein polymorphism, particularly among certain immunodominant surface proteins. This extensive genetic variation provides the great adaptive potential by which the parasite evades the host immune response. The major objective of this proposal is to determine not only the degree of antigenic diversity in P. falciparum populations, but also to determine the principle mechanisms by which this variation is generated and maintained. We will examine the genetic polymorphism among natural isolates of P. falciparum from several endemic African sites. From these isolates, we will quantify the polymorphism among several molecular markers, which are dispersed on three completely sequenced chromosomes (chr2, chr3, and chr10). The genetic loci to be examined are three encoded surface protein genes--circumsporozoite protein (Csp, on Chr2) and merozoite surface protein-2 (Msp-2, on Chr3), and the 25kd P. falciparum sexual-stage antigen (pfs25, on Chr10). Each of these loci is life cycle-stage-specific in its expression and is the target of one or more vaccines currently in development. In addition to these protein-encoding genes, we will type several highly polymorphic microsatellite loci arrayed on the same three chromosomes. The resulting multi-locus genotype of each isolate will be used to test directly; (1) the level of meiotic recombination among genomes of natural P. falciparum isolates, (2) the extent of diversifying selection among the crucial protein-encoding genes, (3) the role of slipped-strand (mitotic) mutation in maintaining variability in immunogenic, nucleotide-repeat loci (Csp and Msp-2). This work will increase our understanding of the genomic evolution of this parasite will yield valuable information for evaluating appropriate strategies for intervening in disease transmission.