The Xenopus tropicalis response to infection by Batrachochytrium dendrobatidis

冷血脊椎动物（外温动物）对传染病的个体水平反应是一个被忽视的研究领域。然而，最近出现的外温动物疾病的实际和潜在的经济成本是巨大的。壶菌真菌病原体，Batrachochytrium dendrobatim，最近在1997年被描述为圈养两栖动物的病原体，壶菌病目前正在全球范围内破坏商业两栖动物农场，研究菌落和自然种群。目前关于这种真菌感染的知识显然是不够的;我们理解的主要差距是两栖动物如何应对这种壶菌以及这种壶菌如何导致宿主死亡。我们缺乏这方面的信息，由于缺乏一个可靠的两栖动物模型系统，可用于确定生物学机制的基础上的主机-病原体相互作用。我们的项目将通过调查使用非洲爪蟾热带爪蟾作为模型系统来研究壶菌病的可行性来纠正这种不平衡。X. topicalis，不同于其姊妹类群X. laevis对壶菌病高度敏感。完整注释的X. tropicalis的研究现已完成，这有助于分析两栖动物对感染的反应，如通过关键感染相关基因的变化来衡量。我们最初的实验将集中在表征X。热带病-在（i）不同剂量的病原体和（ii）不同温度下对感染的反应。使用共聚焦显微镜，我们将可视化的爪蟾病原体的相互作用，通过对与体液和细胞介导的爪蟾免疫反应的武器相关的关键抗原染色。随后，我们将分析未感染、非致死性感染和致死性感染动物之间的基因表达变化。我们将通过设计稳健的定量PCR检测来实现这一点，该检测在感染的时间过程中监测参与（i）Th 1（细胞介导的）、（ii）Th 2（基于抗体的）和（iii）先天免疫应答的基因类别的基因表达。我们将把我们的分析集中在已知在其他脊椎动物物种中控制感染方面很重要的基因上，并且我们已经从X。tropicalis基因组的比较基因组学技术。这些分析将首次揭示两栖动物对感染的适应性和先天反应的类型和程度。理解这些过程将使我们能够进一步发展X。tropicalis作为一个模式物种，在其中我们可以研究宿主病原体生物学在一个易于处理的系统，具有发达的免疫学和遗传学工具箱。这将使我们能够将我们的研究应用于针对B的疫苗开发。这是一个紧迫的目标，因为这种疾病的全球经济成本。最后，确定与两栖动物感染性疾病相关的宿主反应类型，对于了解其他迄今被忽视的冷血物种的宿主反应具有广泛的相关性。

The individual-level response of cold-blooded vertebrates (ectotherms) to infectious disease is a neglected area of research. However, the realized and potential economic costs of recently emerged diseases of ectotherms are substantial. The chytrid fungal pathogen, Batrachochytrium dendrobatidis, was recently described in 1997 as a pathogen of captive amphibians, and chytridiomycosis is presently devastating commercial amphibian farms, research colonies and natural populations on a global basis. The current state of knowledge regarding this fungal infection is manifestly inadequate; major gaps in our understanding are how amphibians respond to this chytrid and how this chytrid causes the death of its host. We lack this information due to the absence of a reliable amphibian model system that can be used to identify the biological mechanisms underpinning the host-pathogen interaction. Our project will rectify this imbalance by investigating the feasibility of using the African clawed frog Xenopus tropicalis as a model system to research chytridiomycosis. X. topicalis, unlike its sister taxa X. laevis, is highly susceptible to chytridiomycosis. The fully annotated genome sequence for X. tropicalis is now complete which facilitates the analysis of amphibian responses to infection as measured by changes in key infection-related genes. Our initial experiments will focus on characterising the X. tropicalis-response to infection under (i) different dosages of the pathogen and (ii) different temperatures. Using confocal microscopy, we will visualise the Xenopus-pathogen interaction by staining against key antigens that are associated with the humoral and cell-mediated arms of the Xenopus immune-response. Subsequently, we will then analyse the changes in gene-expression between uninfected, non-lethally infected and lethally infected animals. We will do this by designing robust quantitative PCR assays that monitor gene-expression over the time-course of an infection for classes of genes that are involved in (i) the Th1 (cell-mediated), (ii) the Th2 (antibody-based) and (iii) innate immune response. We will focus our analyses on genes that are known to be important in controlling infection in other vertebrate species, and that we have data-mined from the X. tropicalis genome by our use of comparative-genomic techniques. These analyses will reveal, for the first time, the type and magnitude of the amphibian adaptive and innate response(s) to infection. Understanding these processes will allow us to further develop X. tropicalis as a model species within which we can investigate host-pathogen biology within a tractable system that has well-developed immunological and genetic-toolboxes. This will allow us to apply our research to vaccine development against B. dendrobatidis, an urgent goal given the global economic cost of this disease. Finally, determining the type of host response that is associated with infectious disease in amphibians will have a broad relevance for understanding host responses in other, thus far neglected, cold-blooded species.