MECHANISMS OF MALARIA SEXUAL STAGE GENE EXPRESSION

恶性疟原虫（P. falciparum）的生命周期以明显的形态变化为特征。这些变化与寄生虫表面独特蛋白质的阶段特异性表达有关。针对受精卵和卵母细胞主要表面蛋白Pfs25和Pfs28的抗体可阻断疟原虫在蚊子中肠的形态发育。这表明这些蛋白的表达对性征阶段的发育至关重要。这一信息已用于研制阻断传播的疫苗。然而，对这些关键蛋白的性阶段特异性表达的分子机制的定义，由于对寄生虫高度富含AT的基因间区域进行测序的技术困难以及无法对假定的基因调控元件进行功能测试，一直受到阻碍。疟疾基因组计划的成功和疟疾寄生虫转染技术的发展现在允许描述性阶段特异性基因表达的分子机制。了解恶性疟原虫性阶段基因表达的基本机制可以为阻断疾病传播提供新的策略或方法。我们利用鸡疟原虫（P. gallinaceum）有性阶段的基因转染系统作为模型系统来定义进化上密切相关的恶性疟原虫的基因调控元件。对Pfs28同源基因Pgs28的研究表明，Pgs28蛋白的表达需要一种独特的富t元素与Pgs28 3' UTR中的真核聚腺苷化共识信号相结合。富含t的3′基因侧翼元件在其他与发育相关的真核基因中的功能支持了Pfs25和Pfs28的协调表达是由3′基因侧翼调控元件介导的假设。该项目的具体目的是：1)确定富t元素调控Pgs28表达的分子机制；2)明确Pfs25和Pfs28协同表达的分子机制；3)确定3′基因侧翼元件在介导性分期特异性基因表达中的作用。

The life cycle of Plasmodium falciparum (P. falciparum) is characterized by pronounced morphologic changes. These changes are associated with the stage-specific expression of unique proteins on the parasite's surface. Antibodies to the major surface proteins of fertilized zygotes and ookinetes, Pfs25 and Pfs28 respectively, block the morphologic development of the parasite in the mosquito midgut. This indicates that the expression of these proteins is critical to the development of the sexual stages. This information has been utilized in the formulation of transmission blocking vaccines. Definition of the molecular mechanisms responsible for the sexual stage-specific expression of these critical proteins, however, has been hampered by technical difficulties in sequencing the parasite's highly AT- rich intergenic regions and the inability to functionally test putative gene regulatory elements. The success of the malaria genome project and the development of transfection techniques for the malaria parasite now permit the delineation of the molecular mechanisms of sexual stage-specific gene expression. Understanding the basic mechanisms of P. falciparum sexual stage gene expression could suggest novel strategies or methods to block disease transmission. We have utilized a gene transfection system of the sexual stages of the chicken malaria Plasmodium gallinaceum (P. gallinaceum) as a model system for defining the gene regulatory elements of the evolutionarily closely related P. falciparum parasite. Studies of the P. gallinaceum homologue of Pfs28, Pgs28, reveal that a unique T-rich element in conjunction with a eukaryotic polyadenylation consensus signal in the pgs28 3' UTR are required for Pgs28 protein expression. The function of T-rich 3' gene flanking elements in other eukaryotic genes associated with development supports the hypothesis that the coordinated expression of Pfs25 and Pfs28 is mediated by 3' gene flanking regulatory elements. The specific aims of this project are: 1) to determine the molecular mechanism by which the T-rich element regulates Pgs28 expression; 2) to define the molecular mechanisms responsible for the coordinated expression of Pfs25 and Pfs28; 3) to determine the contribution of 3' gene flanking elements in mediating sexual stage-specific gene expression.