Determination of morphology and virulence in Candida albicans

描述（由申请人提供）：白色念珠菌，主要的人类真菌病原体，负责各种全身和粘膜感染。艾滋病患者、器官移植受者、接受化疗的癌症患者、人工关节和假体装置受者以及其他免疫功能低下的个体特别容易感染白色念珠菌。众所周知，白色念珠菌经历了从酵母（单个圆形出芽细胞）到假菌丝和菌丝（端到端附着的细长细胞）的形态转变，这是毒力所必需的。我们的长期目标是确定白色念珠菌如何控制形态并促进对宿主环境线索的毒力。虽然假菌丝和菌丝形态之间的表型差异已经被很好地表征，但对每种形态决定生长的调控机制或每种形态在毒力中所起的特定作用知之甚少。为了解决这些问题，我们最近产生了一种白色念珠菌菌株，可以通过基因操纵在体外非丝诱导条件下在菌丝形态中完全生长。我们还发现，该菌株能够驱动增加菌丝形成和促进毒力在小鼠模型的系统性念珠菌病。我们的菌株是通过将白色念珠菌菌丝延伸和毒力的新型丝状特异性转录调节因子UME6的一个等位基因置于可调节启动子的控制下而产生的。有趣的是，虽然高水平的UME6表达驱动了完整的菌丝生长，但中等水平的UME6表达指定了大部分假菌丝种群，这表明UME6表达水平足以以剂量依赖的方式决定白色假丝酵母的形态。初步研究表明，随着UME6水平的升高，诱导的丝状特异性转录物的数量和诱导水平都有所增加。我们的假设是受宿主环境因素影响的UME6水平通过控制重叠的丝状特异性转录物的表达水平来决定白色念珠菌的形态和毒力。为了解决这一假设，我们计划实现以下三个具体目标：1)确定上游宿主环境信号和已知的白色念珠菌丝状生长调控回路如何控制UME6的表达；2)确定白色念珠菌基因在UME6剂量指定假菌丝和菌丝形态并在感染期间促进毒力时表达的转录谱；3)确定UME6水平决定白色念珠菌形态和促进毒力的特定下游机制。最终，这些研究将显著提高我们对真菌病原体如何在宿主环境中指定形态和促进毒力的理解，并将提供可能导致开发新的和更有效的抗真菌策略的信息。

DESCRIPTION (provided by applicant): Candida albicans, the major human fungal pathogen, is responsible for a wide variety of systemic and mucosal infections. AIDS patients, organ transplant recipients, cancer patients undergoing chemotherapy, recipients of artificial joints and prosthetic devices and other immunocompromised individuals are particularly susceptible to C. albicans infections. C. albicans is known to undergo a morphological transition from yeast (single, round budding cells) to pseudohyphal and hyphal filaments (elongated cells attached end-to-end) which is required for virulence. Our long-term goal is to determine how C. albicans controls morphology and promotes virulence in response to host environmental cues. Although phenotypic differences between pseudohyphal and hyphal forms have been well-characterized, very little is known about the regulatory mechanisms that determine growth in each morphology or the specific role that each morphology plays in virulence. In order to address these questions, we have recently generated a C. albicans strain that can be genetically manipulated to grow completely in the hyphal morphology under non-filament-inducing conditions in vitro. We have also found that this strain is capable of driving increased hyphal formation and promoting virulence in a mouse model of systemic candidiasis. Our strain was generated by placing one allele of a novel filament-specific transcriptional regulator of C. albicans hyphal extension and virulence, UME6, under the control of a regulatable promoter. Interestingly, while high-level UME6 expression drives complete hyphal growth, intermediate UME6 levels specify a largely pseudohyphal population, indicating that UME6 expression levels are sufficient to determine C. albicans morphology in a dosage-dependent manner. Preliminary studies show an increase in both the number of filament-specific transcripts induced as well as their level of induction as UME6 levels rise. Our hypothesis is that UME6 levels, which are affected by host environmental cues, determine C. albicans morphology and virulence by controlling the expression level of overlapping sets of filament-specific transcripts. In order to address this hypothesis we plan to carry out the following three specific aims: 1) determine how upstream host environmental signals and known C. albicans filamentous growth regulatory circuits control the expression of UME6, 2) determine the transcriptional profile of C. albicans genes expressed as UME6 dosage specifies pseudohyphal and hyphal morphologies and promotes virulence during infection, 3) identify specific downstream mechanisms that are important for the ability of UME6 levels to determine C. albicans morphology and promote virulence. Ultimately, these studies will significantly improve our understanding of how fungal pathogens specify morphology and promote virulence in the host environment and will provide information that could lead to the development of novel and more effective antifungal strategies. PUBLIC HEALTH RELEVANCE: Candida albicans is the major yeast that causes yeast infections and also kills people with weakened immune systems. This research proposal aims to gain a better understanding of how Candida albicans is able to function as such an effective pathogen. Ultimately, these studies should provide information leading to the development of more effective treatments for yeast infections.