Functional dissection of Condensin and Cohesin in atypical mitosis and meiosis in Plasmodium

疟原虫是疟疾的病原体，每年造成大约584 000人死亡，其中大多数是5岁以下儿童。这种寄生虫对现有药物的抵抗力日益增强，以及缺乏有效的疫苗，是消除这一负担的主要障碍。因此，迫切需要开发创新的治疗方法。疟原虫具有复杂的生命周期，宿主环境多样，细胞形状、大小和运动变化，细胞增殖模式不典型。当疟疾寄生虫侵入宿主红细胞时，这种疾病的症状就会显现出来，其中寄生虫会多次分裂和繁殖（内膜有丝分裂），最终导致宿主细胞的破坏。一些寄生细胞可能停止分裂，成为前体细胞（雄性和雌性配子体）。当雌性蚊子叮咬感染者时，它们会在血液中摄入寄生虫，这就会触发蚊子肠道内的前体性细胞。雄性配子体经过快速细胞分裂（内复制）产生八个雄性配子，然后使雌性配子受精，寄生虫的生命周期在蚊子的肠道中继续进行。经过进一步的发育和繁殖，寄生虫进入蚊子的唾液腺，并在蚊子进食时再次传递给新的人类宿主。疟原虫细胞在宿主红细胞中的分裂过程和蚊子载体的性发育过程非常不同，但两者都是寄生虫生长和传播所必需的。如果这些阶段中的任何一个被阻断，那么扩散和传播都将受到限制。因此，了解寄生虫如何在这些阶段繁殖和分裂是至关重要的，这样我们就可以设计出通过开发适当的药物来干扰它们的方法。在寄生虫中控制这些类型的非典型细胞分裂的分子知之甚少。本课题拟研究两种重要的蛋白复合物：凝缩蛋白和黏结蛋白的作用。虽然已知这些复合物在许多模型系统中参与细胞分裂，但尚不清楚它们在疟疾寄生虫细胞分裂和增殖过程中如何发挥作用。我们可以从使用在模型系统中收集的知识开始，并将其应用于疟疾寄生虫。例如，我们最近在疟原虫中发现了一种这样的蛋白（CDC20），并表明它在调节雄性配子形成中起关键作用。初步工作表明我们的方法是可行的，我们已经获得了在红细胞、雄性生殖细胞和减数分裂细胞（卵母细胞）内繁殖的寄生虫中存在凝缩蛋白和粘聚蛋白的证据。在分析疟疾基因方面的最新进展使我们能够研究这些分子的功能。例如，通过去除基因，我们可以看到当蛋白质不再产生时会发生什么，如果用荧光标记实验性地标记它们，我们可以在显微镜下看到它们在寄生虫中的位置。我们还将研究这些分子在染色体分离和细胞质分裂等各种过程中如何与其他蛋白质相互作用。我们还可以纯化这些蛋白质复合物，并使用基于质谱的方法研究它们的相互作用。因此，我们现在可以探索这些复合物是如何控制疟疾细胞分裂的，我们可以研究这些分子是如何调节细胞分裂的不同阶段的。我们的研究可能会确定宿主红细胞中寄生虫细胞分裂和蚊子载体中细胞分裂的重要分子靶点。因此，我们可以确定药物或疫苗的潜在目标，这些药物或疫苗将来可以用来阻止寄生虫在血液中的复制和通过蚊子从一个人传播到另一个人。

Plasmodium is the causative agent of malaria and is responsible for about 584,000 human deaths annually, mostly children under the age of 5. The increasing resistance of the parasite to existing drugs and the lack of an efficient vaccine represent the main obstacles to combat this burden. Therefore, there is an urgent need for the development of innovative therapeutics. Plasmodium has a complex life cycle with diverse host environments, changes in cell shape, size and motility and an atypical mode of cell proliferation. The symptoms of the disease are manifest when malaria parasites invade host red blood cells, wherein the parasite divides and multiplies many times (endomitosis), eventually leading to destruction of the host cell. Some of the parasite cells may cease to divide and they become precursor sex cells (male and female gametocytes). When a female mosquito bites an infected person they ingest parasites along with the blood and this acts as a trigger to activate the precursor sex cells within the mosquito gut. The male gametocytes undergo rapid cell division (endoreduplication) to produce eight male gametes, which then fertilise the female gametes and the parasite life cycle continues in the mosquito gut. After further development and multiplication the parasite moves to the mosquito's salivary glands and is passed again to a new human host when the mosquito feeds.The process of Plasmodium cell division in host red blood cells, and during sexual development in the mosquito vector is very different, but both are essential for parasite growth and transmission. If any of these stages are blocked then both proliferation and transmission are curtailed. Therefore, it is critically important to understand how the parasite multiplies and divides at these stages so that we can devise ways to interfere with them by developing appropriate drugs. The molecules that control these types of atypical cell division in the parasite are very poorly understood. The project proposed here is to study the role of two important protein complexes: condensin and cohesin. Although these complexes are known to be involved in cell division in many model systems, there is no knowledge of how they function during malaria parasite cell division and proliferation. We can start by using the knowledge gathered in model systems and applying this to the malaria parasite. For example, we have recently identified one such protein (CDC20) in the malaria parasite and showed that it has a key role in regulating male gamete formation. In preliminary work showing that our approach is feasible, we have obtained evidence for the presence of condensin and cohesin in the parasite multiplying within the red blood cell, in the male sex cell and in the meiotic cell (an ookinete). Recent advances in analysing genes in malaria allow us to study the function of these molecules. For example, by taking away the gene, we can see what happens when the proteins are no longer made, and if they are tagged experimentally with a fluorescent marker we can see under the microscope where they are located in the parasite. We will also study how these molecules interact with other proteins during various processes such as chromosome segregation and cytokinesis, to name two. We can also purify these protein complexes and study their interactions using mass spectroscopy-based approaches. Therefore, we are now in a position where we can explore how cell division in malaria is controlled by these complexes and we can study how these molecules regulate different stages of cell division.Our study may identify molecular targets important in parasite cell division in host red blood cells and in the cells dividing within the mosquito vector. As a result, we may identify potential targets for drugs or vaccines that could in the future be used to block parasite replication in the blood and transmission from one individual to another through the mosquito.