Biology of the Apicomplexan Plastid

描述(申请人提供)：Apicomplexa门包含一大群原生动物寄生虫，这些寄生虫导致许多重要的人类和牲畜疾病。其中几种生物(弓形虫、隐孢子虫和环孢子虫)也被列为潜在的生物防御关注的B型病原体。在这些疾病的抗微生物药物治疗方面仍然存在重大挑战。残存叶绿体--质外体的发现，现在提供了几种寄生虫特定的途径，可以作为特定的药物靶标来帮助克服其中的一些挑战。基因组、遗传学和药理学数据表明，顶体在疟原虫和弓形虫的发育和致病过程中是必不可少的，证实了它是一个靶标，并证明了细胞器对生物体生物学的重要性。这项提议的重点是解开寄生虫用来忠实复制和分离这个重要细胞器及其基因组的机制。 植物和藻类中的叶绿体分裂机制在很大程度上依赖于蓝藻起源的基因，其中细菌微管蛋白同源物FtsZ是最突出的。我们的基因组分析还没有发现这些基因在Apicomplexa中有任何明确的同源基因。在没有保守机制的情况下，质外体是如何分裂的？基于我们的细胞生物学研究，我们假设，与植物形成鲜明对比的是，无顶复合体是通过一种真正的真核机制--与有丝分裂纺锤体的中心体结合--来分离的。这一提议开发了一些机制模型来解释质体如何忠实地分离成子细胞，如何在寄生细胞周期内发生分裂和计时，以及细胞器基因组的复制和维持如何与这一过程联系在一起。为了验证这些假设，我们组装了一套高度兼容的细胞生物学、比较基因组学和遗传学实验。基因组和基因筛查将允许我们进一步完善我们的假设，并将帮助我们在现有基因和蛋白质之外增加额外的分子参与者。

DESCRIPTION (provided by applicant): The phylum Apicomplexa contains a large group of protozoan parasites responsible for numerous important human and livestock diseases. Several of these organisms (Toxoplasma, Cryptosporidium & Cyclospora) are also listed as type B pathogens of potential biodefense concern. Significant challenges remain in the antimicrobial drug treatment for these diseases. The discovery of a remnant chloroplast, the apicoplast, now presents several parasite specific pathways that can be exploited as specific drug targets to help overcome some of these challenges. Genomie, genetic and pharmacological data show that the apicoplast is essential for development and pathogenesis for Plasmodium and Toxoplasma validating it as a target and demonstrating the importance of the organelle for the biology of the organism. This proposal is focused on unraveling the mechanisms used by the parasite to faithfully replicate and segregate this important organelle and its genome. The chloroplast division machinery in plants and algae depends overwhelmingly on genes of cyanobacterial origin, with the bacterial tubulin homolog ftsZ being the most prominent. Our genomic analysis has not identified any clear homologs of these genes in Apicomplexa. How is the apicoplast divided in the absence of the conserved machinery? Based on our cell biological studies we hypothesize that in sharp contrast to plants the plastid in Apicomplexa is segregated using a genuinely eukaryotic mechanism - association with the centrosomes of the mitotic spindle. This proposal develops a number of mechanistic models to explain how the plastid is faithfully segregated into daughter cells, how fission occurs and is timed within the parasite cell cycle, and how the replication and maintenance of the organellar genome is tied into this process. To test these hypotheses we have assembled a set of highly compatible cell biological, comparative genomic and genetic experiments. Genomic and genetic screens will permit us to further refine our hypotheses, and will help us to populate them with additional molecular players beyond the genes and proteins already in hand.