Genetics & Population Structure of Plasmodium falciparum

描述(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瓶颈。尽管最近有共同的起源，但恶性疟原虫种群的特征是高度的蛋白质多态性，特别是在某些免疫优势表面蛋白之间。这种广泛的遗传变异为寄生虫逃避宿主免疫反应提供了巨大的适应潜力。这项建议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，而且还确定产生和维持这种变异的主要机制。我们将检查来自非洲几个流行地点的恶性疟原虫自然分离株的遗传多态。从这些分离株中，我们将量化分布在三条完全测序的染色体(chr2、chr3和chr10)上的几个分子标记之间的多态性。要检测的遗传位点是三个编码的表面蛋白基因--环子孢子蛋白(csp，位于chr2上)和裂殖子表面蛋白-2(msp-2，位于chr3上)，以及25kd恶性疟原虫有性阶段抗原(Pfs25，位于chr10上)。每个基因座的表达都是生命周期阶段特有的，是目前正在研发的一种或多种疫苗的靶标。除了这些编码蛋白质的基因外，我们还将对排列在相同三条染色体上的几个高度多态的微卫星座位进行分型。由此产生的每个分离株的多位点型将被用于直接测试：(1)恶性疟原虫天然分离株基因组间减数分裂重组的水平，(2)关键蛋白编码基因之间多样化选择的程度，(3)滑链(有丝分裂)突变在维持免疫原性核苷酸重复座位(CSP和MSP-2)变异性中的作用。这项工作将增加我们对这种寄生虫基因组进化的了解，将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.