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。 受精卵和动合子的主要表面蛋白的抗体，Pfs 25和Pfs 28，分别阻止蚊子中肠的寄生虫的形态发育。 这表明这些蛋白质的表达对性阶段的发育至关重要。 这一信息已被用于传播阻断疫苗的配制。 然而，负责这些关键蛋白质的性阶段特异性表达的分子机制的定义受到了寄生虫高度AT丰富的基因间区域测序的技术困难和无法功能测试推定的基因调控元件的阻碍。 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绘性阶段特异性基因表达的分子机制。了解恶性疟原虫性期基因表达的基本机制，可以提出阻断疾病传播的新策略或方法。我们已经利用鸡疟原虫（P. gallinaceum）的性阶段的基因转染系统作为定义进化上密切相关的恶性疟原虫寄生虫的基因调控元件的模型系统。 对Pfs 28的鸡疫霉同源物Pgs 28的研究揭示，Pgs 28蛋白表达需要与pgs 28 3' UTR中的真核多腺苷酸化共有信号结合的独特的富含T的元件。 其他与发育相关的真核基因中富含T的3'基因侧翼元件的功能支持了Pfs 25和Pfs 28的协调表达是由3'基因侧翼调控元件介导的假设。本项目的具体目标是：1）确定富T元件调控Pgs 28表达的分子机制; 2）确定Pfs 25和Pfs 28协调表达的分子机制; 3）确定3'基因侧翼元件在介导性阶段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.