Genotypic plasticity and parasex in Candida albicans

描述（由申请人提供）：该项目的目标是解决真菌白色念珠菌的准性周期如何影响细胞适应性和发病机制。这项工作是一个长期目标的一部分，以了解在C。白色念珠菌在哺乳动物宿主中的定殖和疾病。C.白色念珠菌是口咽念珠菌病（OPC）的主要原因，即使在抗逆转录病毒治疗的时代，OPC仍是一种继续折磨HIV感染患者的病症。C.白色念珠菌也是危及生命的全身感染的普遍原因，特别是在医院和免疫功能低下的人群中。C.的一个定义性特征。白色念珠菌的生物学特征是其能够定殖并感染整个人体的许多部位。这种非凡的能力依赖于促进表型可塑性的遗传和表观遗传机制。菌株在不同的细胞状态之间进行转换，这些转换对C。白色念珠菌的生活方式既是一种寄生菌，也是一种机会致病菌。形态和表型的变化影响毒力，组织特异性，与免疫细胞的相互作用，并进入准性周期。因此，必须了解促进表型变异的机制，以及这种变异对宿主感染的后果。 这个提议的一个主要目标是确定准性周期产生新的C。具有促进致病潜力的白念珠菌菌株。准性周期包括表型转换到交配能力状态，细胞融合产生四倍体细胞，以及协调染色体丢失形成重组二倍体或非整倍体菌株。令人兴奋的初步实验表明，准性生殖可以产生具有更高毒力和对环境压力更强抵抗力的菌株。现在将对parasex后代进行系统分析，以确定具有抗应激表型的菌株，包括抗真菌药物的抗性，以及表现出毒力增加的菌株。这些分离株的基因分型将确定这些适应性事件背后的染色体变化。特别是，预计特定非整倍体染色体的存在将与特定的C。白色念珠菌表型第二个目标是确定促进准有性生殖的体内生态位。我们的研究表明，胃肠道的特定区域可能优先支持表型转换和无性生殖。这种可能性将直接测试这里概述的实验，包括在体内的准性周期的每个步骤的量化。总之，完成拟议的实验，因此将确定在体内发生的准有性生殖，以及该计划的后果，用于产生具有增加的致病性的重组菌株。

DESCRIPTION (provided by applicant): The goal of this project is to address how the parasexual cycle of the fungus Candida albicans influences cell fitness and pathogenesis. This work is part of a long-range goal to understand the role of parasexuality in C. albicans colonization and disease in the mammalian host. C. albicans is the primary cause of oropharyngeal candidiasis (OPC), a condition that continues to afflict HIV-infected patients even in the era of antiretroviral therapy. C. albicans is also a prevalent cause of life-threatening systemic infections, particularly in nosocomial and immunocompromised populations. A defining feature of C. albicans biology is its ability to colonize and infect many sites throughout the human body. This remarkable ability is dependent on genetic and epigenetic mechanisms that act to promote phenotypic plasticity. Strains undergo switching between alternative cell states, and these transitions are essential to C. albicans's lifestyle both as a commensal and as an opportunistic pathogen. Morphologic and phenotypic changes influence virulence, tissue specificity, interactions with immune cells, and entry into the parasexual cycle. It is therefore essential to understand the mechanisms promoting phenotypic variation, and the consequences of such variation for infection of the host. A major goal of this proposal is to define the abilit of the parasexual cycle to generate novel C. albicans strains with the potential to promote pathogenesis. The parasexual cycle involves phenotypic switching to a mating-competent state, cell fusion to generate tetraploid cells, and concerted chromosome loss to form recombinant diploid or aneuploid strains. Exciting preliminary experiments establish that parasexuality can generate strains with increased virulence as well as increased resistance to environmental stress. A systematic analysis of parasex progeny will now be performed to identify isolates with stress-resistant phenotypes including resistance to antifungal drugs, as well as isolates that exhibit increased virulence. Genotyping of these isolates will determine the chromosomal changes that underlie these adaptive events. In particular, it is expected that the presence of specific aneuploid chromosomes will be associated with particular C. albicans phenotypes. A second goal is to identify the in vivo niche(s) that promote parasexual reproduction. Our studies indicate that particular regions of the gastrointestinal tract may preferentially support phenotypi switching and parasexual reproduction. This possibility will be directly tested by the experiments outlined here, including quantification of each of the steps of the parasexual cycle in vivo. Together, completion of the proposed experiments will therefore determine where parasexual reproduction occurs in vivo, and the consequences of this program for generating recombinant strains with increased pathogenicity.