Studies on the Mechanisms of Stage specific Host Infection in Malarial Parasite

这三年来执行的项目摘要如下。疟疾是由按蚊传播的。寄生虫动合子和子孢子侵入并穿过蚊的中肠上皮细胞和唾液腺细胞，在蚊的中肠腔中通过性融合形成，穿过中肠上皮细胞并在肠壁上形成卵囊。唾液腺子孢子通过蚊虫叮咬进入宿主体内，必须穿过皮肤屏障和肝窦细胞层到达肝细胞并感染肝细胞。我们计划研究寄生虫侵入这些屏障细胞的分子机制。为此，我们使用啮齿类疟原虫伯氏疟原虫作为模式动物，并分析了动合子和子孢子的EST（表达序列标签）。我们从EST中筛选基因，并产生了破坏该基因的寄生虫。通过对基因破坏的寄生虫的表型分析，研究了该基因的功能。结果表明，MAOP和MAEBL是侵袭小肠上皮细胞和唾液腺细胞的必需分子。我们还鉴定了两种分子，SPECT 1和SPECT 2，它们是侵入肝窦细胞层枯否细胞的必需分子。我们确定了OSM-1，一种从动合子和子孢子通过中肠细胞和库普弗细胞易位所必需的分子。我们证明了动合子和子孢子通过屏障细胞层、蚊子中肠细胞和窦状细胞层的共同机制。我们还首次证明了子孢子可以通过肝窦层的枯否细胞到达肝细胞，从肝窦感染。

The summary of this project performed in this three years is shown below. Malarial parasite is transmitted by Anopheline mosquito. Parasite ookinete and sporozoite invade and pass through the mosquito mig-gut epithlium cell and the salivary gland cell, and formed in the mosquito mid gut lumen by sexual fusion passes through the mid-gut epithelium and forms a oocyst on the gut wall. Salivary gland sporozoite injected into the host by mosquito bite has to pass through the skin barriers and River sinusoidal cell layer to reach and infect the hepatocyte. We planned to investigate the molecular mechanisms of the parasite invasion into those barrier cells. For this purpose, we used a rodent malarial parasite Plasmodium berghei as a model animal, and analyzed the EST (expressed sequence tags) of ookinete and sporozoite. We selected gene by a criteria from the EST and generated parasite disrupted the gene. A function of the gene was studied by the analyses of the phenotype of the gene disrupted parasite. As results, we identified MAOP and MAEBL for essential molecules for invasion to mig-gut epithelial cell and the salivary gland cell. And we also identified two molecules, SPECT1 and 2 for essential molecules to invade into the Kupffer cell in the sinusoidal cell layer of the liver. We identified OSM-1, a molecule essential for translocation through the mid-gut cell and Kupffer cell from the ookinete and sporozoite. We demonstrated the common mechanisms of the cell passage of ookinete and sporozoite through the barrier cell layer, the mosquito mid-gut cell and the sinusoidal cell layer. We also demonstrated first for the sporozoite to pass through the Kupffer cell in the sinusoidal layer to reach the hepatocyte to infect from the sinusoid.