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

这三年的项目总结如下：疟疾寄生虫由按蚊传播。寄生卵母细胞和孢子子侵入并穿过蚊子的肠上皮细胞和唾液腺细胞，在蚊子的肠中腔内通过性融合形成，穿过肠中上皮，在肠壁上形成卵囊。经蚊虫叮咬注入宿主体内的唾液腺孢子必须穿过皮肤屏障和河窦细胞层到达并感染肝细胞。我们计划研究寄生虫入侵这些屏障细胞的分子机制。为此，我们以啮齿动物疟原虫伯氏疟原虫为模型动物，分析了卵母体和孢子子的EST（表达序列标签）。我们从EST中选取了一个标准的基因，并产生了破坏该基因的寄生虫。通过对基因被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是侵袭肠上皮细胞和唾液腺细胞的必需分子。我们还发现了两个分子，SPECT1和2，它们是侵入肝窦细胞层库普弗细胞的必要分子。我们从卵胞体和孢子体中鉴定出OSM-1，这是一种通过中肠细胞和库普弗细胞进行转运所必需的分子。我们论证了卵母细胞和孢子子细胞通过屏障细胞层、蚊子中肠细胞和正弦细胞层的共同机制。我们还首先证明了孢子子通过窦层的库普弗细胞到达肝细胞并从窦层感染。

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.