The Apical Complex: a Targeted Investigation of the Molecular Functions of this Structure Essential to Apicomplexan Parasite Invasion and Replication.

顶复体是引起人类重大疾病的一大群单细胞病原体。这一群体中最臭名昭著的成员导致疟疾，这是世界上许多发展中区域的一种毁灭性疾病，每年造成5亿多例病例和60万人死亡。其他顶复合体物种引起广泛的人类疾病：隐孢子虫病，致命婴儿腹泻的主要原因；还有弓形虫病，感染了大约30%的人。此外，一些顶复体感染家畜，对人类粮食生产造成重大损失。所有顶复合体都是通过在人类（或动物）宿主的细胞内生长和分裂而致病的。它们通过非破坏性地在宿主细胞壁上形成一个临时孔进入宿主细胞，通过这个孔它们滑进去，然后重新密封。通过保持宿主细胞的存活，它为寄生虫提供了持续的食物和营养来源。只有当寄生虫分裂到原来数量的许多倍时，它们才会破裂并杀死人类细胞，然后主动寻找并侵入新的宿主细胞。病原体在入侵宿主细胞时使用的关键结构是一种称为顶端复合体的结构，这是所有顶端复合体病原体的共同特征。根尖复合体可以在显微镜下观察到，它是细胞尖端的一个内部增强点，充当细胞喷嘴或注射器。它的顶端有一个小开口，通过这个开口，它首先将粘性分子释放到病原体表面，帮助病原体附着在宿主细胞上。随后，它利用这个开口将入侵因子直接注入宿主体内，从而形成入侵孔，进入宿主体内。然后，进一步的病原体分子从顶端复合体中释放出来，使其能够以宿主为食。因此，顶端复合体是宿主细胞入侵这些协调事件的核心，因此是疾病形成的基本结构。尽管顶复合体的重要性，这种结构仍然知之甚少。已知的分子成分很少，这限制了对其结构、组装以及如何提供其一般功能的理解。本研究将使用多种方法来鉴定和编目根尖复合体的分子成分。它将采用顶复弓形虫作为最完善的顶复弓形虫实验系统。将生成顶端复合体的详细结构模型，并使用单个结构组件的遗传标记，它们的组装和行为将在活细胞中进行表征，包括在入侵事件期间。单个组成部分的功能，以及顶端复合体作为一个整体的功能，将在遗传水平上通过选择性地每次去除一个组成部分来解剖。这将提供一个机制的理解如何顶复合体实现宿主细胞渗透和利用的致命任务。对顶复合体组织和功能的综合理解将为顶复合体生物如何取得病原体这样的成功提供更清晰的见解。此外，了解它们的发病机制为战略性地设计疾病治疗策略提供了最好的机会。

Apicomplexans are a large group of single-celled pathogens that cause significant disease in humans. The most notorious member of this group causes malaria, a devastating disease in many developing regions of the world and responsible for over 500 million cases, and 0.6 million deaths per year. Other apicomplexan species cause widespread human diseases: cryptosporidiosis, a leading cause of fatal infant diarrhoea; and toxoplasmosis, which infects approximately 30% of all humans. Further, several apicomplexans infected domesticated animals causing significant loss to human food production.All apicomplexans cause disease by growing and dividing within the cells of their human (or animal) hosts. They enter their host's cells by non-destructively forming a temporary pore in the host cell wall, through which they slide in and then reseal. By keeping the host cell alive it provides a constant source of food and nutrients to the parasite. Only once the parasites have divided to many times the original number do they burst open and kill the human cell, and then actively seek out and invade new host cells.The key structure used by the pathogen during invasion of the host's cells is a structure called the apical complex, and this is a shared feature of all apicomplexan pathogens. The apical complex can be observed using microscopes as an internally reinforced point at the tip of the cell that acts as a cellular nozzle or syringe. At its apex is a small opening, through which it first releases sticky molecules onto the pathogens surface that help it adhere to its host's cells. Subsequently, it uses this opening to inject invasion factors directly into its host that create the invasion pore through which it enters the host. Further pathogen molecules are then released from the apical complex that enable it to feed on its host. Thus, the apical complex is at the heart of these coordinated events of host cell invasion, and is therefore an essential structure for disease formation.Despite the importance of the apical complex, this structure remains poorly understood. Few of the molecular components are known, and this limits understanding of its architecture, assembled, and how it provides the general functions that it does. This study will use multiple approaches to identify and catalogue the molecular components of the apical complex. It will employ the apicomplexan Toxoplasma as the best developed experimental system for apicomplexans. A detailed model of the architecture of the apical complex will be generated, and using genetic tagging of individual structural components, their assembly and behaviour will be characterised in live cells, including during the invasion events. The function of the individual components, and of the apical complex as a whole, will then be dissected by selectively removing one component at a time at a genetic level. This will provide a mechanistic understanding of how the apical complex achieves the deadly tasks of host cell penetration and exploitation.An integrated understanding of the apical complex organisation and function will provide clearer insights into how apicomplexan organisms have achieved such success as pathogens. Moreover, understanding their mechanisms of pathogenesis provides the best opportunity for strategically designing disease treatment strategies.