Gene Circuits that Control Morphology in Histoplasma

描述（由申请人提供）：本研究的长期目标是确定温度等环境信号如何调节真菌病原体荚膜组织浆的形态和毒力。荚膜菌在土壤中以丝状生长；一旦被吸入哺乳动物宿主体内，这些细胞就会将其生长程序转换为寄生酵母形式，从而破坏先天免疫系统，引发疾病。在进化相关的系统性二态真菌病原体中也观察到类似的从土壤到宿主形式的转换，其中包括荚膜孢子虫和选择性病原体，如球虫。对于所有这些病原体，温度是调节这种形态发生开关的关键信号，这被认为是荚膜芽孢杆菌毒力的必要条件。通过阐明荚膜孢子虫细胞如何感知和响应宿主温度，我们将确定促进形态变化和毒力性状表达的关键分子标志。这些研究将揭示诸如信号转导和基因调控等基本过程，并揭示温度依赖性途径在真菌发病机制中的作用。在上一个资助期内，我们确定了酵母生长对宿主温度响应所需的第一个转录调节因子。这些被命名为Ryp1， Ryp2和Ryp3的因子与其他真菌中的关键发育调节因子同源，并且代表了荚膜荚膜菌中温度依赖性调节回路的关键元件。有趣的是，其他真菌中同源调节因子的精确生化功能尚不清楚，因此为我们在荚膜荚膜菌中的功能表征增加了额外的意义。我们最近发现Ryp蛋白与形态和毒力基因的上游区域相关，表明它们直接调节形态和毒力程序的基本组成部分。此外，这些数据提供了第一个分子证据，表明形态和毒力因子的转录调控是耦合的。在这个提案中，我们的具体目标是研究和确定(1)温度激活Ryp蛋白的分子机制；(2) Ryp蛋白调控基因表达的机制；(3)位于这些因子下游的依赖于yl的调控回路的元件及其对形态和毒力的影响。综上所述，所得数据将极大地增强我们对荚膜荚膜孢子对宿主温度的分子反应途径的理解。此外，我们将获得关于个体形态和毒力因素的宝贵知识，这些都是荚膜孢子虫在宿主中发病所必需的。

DESCRIPTION (provided by applicant): The long-term goal of this research is to determine how environmental signals such as temperature regulate morphology and virulence in the fungal pathogen Histoplasma capsulatum. H. capsulatum grows in a filamentous form in the soil; once inhaled into a mammalian host, these cells switch their growth program to a parasitic yeast form that subverts the innate immune system to cause disease. A similar switch from soil to host form is observed for the evolutionarily related systemic dimorphic fungal pathogens, which include H. capsulatum as well as select agent pathogens such as Coccidioides species. For all of these pathogens, temperature is a key signal that regulates this morphogenetic switch, which is thought to be essential for H. capsulatum virulence. By elucidating how H. capsulatum cells sense and respond to host temperature, we will define critical molecular landmarks that promote changes in morphology as well as the expression of virulence traits. These studies will shed light on fundamental processes such as signal transduction and gene regulation, as well as uncover the role of temperature-dependent pathways in fungal pathogenesis. Over the last funding period, we identified the first transcriptional regulators required for growth in the yeast form in response to host temperature. These factors, named Ryp1, Ryp2, and Ryp3, are homologous to key developmental regulators in other fungi, and represent critical elements of the temperature-dependent regulatory circuit in H. capsulatum. Interestingly, the precise biochemical function of the orthologous regulators in other fungi is unclear, thus adding additional significance to our functional characterization in H. capsulatum. We have recently shown that the Ryp proteins associate with the upstream regions of both morphology and virulence genes, suggesting that they directly regulate essential components of the morphology and virulence programs. Furthermore, these data provide the first molecular evidence that the transcriptional regulation of morphology and virulence factors is coupled. In this proposal, our specific aims are to investigate and identify (1) the molecular mechanism of activation of the Ryp proteins by temperature; (2) the mechanisms by which the Ryp proteins regulate gene expression; and (3) the elements of the Ryp-dependent regulatory circuit that lie downstream of these factors and their effect on morphology and virulence. Taken together, the resultant data will greatly enhance our understanding of the molecular response pathway of H. capsulatum to host temperature. Additionally, we will gain valuable knowledge about individual morphology and virulence factors that are required for H. capsulatum pathogenesis in the host. PUBLIC HEALTH RELEVANCE: Histoplasma capsulatum is a primary pathogen that infects approximately 500,000 individuals per year in the U.S. and is a significant source of morbidity and mortality in immunocompromised patients. Since very little is understood about how this fungus causes disease, the identification of fungal factors that influence pathogenesis and manipulate the host immune response will significantly advance the field and allow for the development of new therapeutics.