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Functions of the Mediator subunit Med31 in Candida albicans support a role in shaping species-specific gene expression.

ABSTRACT: Mediator is an essential, evolutionarily conserved co-regulator of RNA polymerase II. Studies in model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe showed remarkably conserved roles for Mediator despite high species divergence, and thus whether Mediator contributed to establishment of species-specific gene expression programs within related fungal species remains an open question. Here we show that in the fungal pathogen Candida albicans, the Mediator middle domain subunit Med31 has a conserved role with non-pathogenic model yeasts in regulation of Ace2-dependent cytokinesis genes and stress responses, but also additional roles in the transcription of genes associated with virulence traits: genes related to filamentous growth and gene families expanded in pathogenic vs non-pathogenic yeasts, such as the ALS adhesins and the FGR6 family of filamentous growth regulators. Consistently, Med31 is required for two key virulence attributes of C. albicans: filamentous growth and biofilm formation. Unlike our data in C. albicans, no role for Med31 in adhesin expression has been reported in model yeasts. To show biological relevance for the control over adhesin gene expression, we demonstrate that ALS1 is a relevant Med31 target for development of biofilms. Collectively, our data supports a role for Med31 in shaping species-specific gene expression in related fungal species.

ORGANISM(S): Candida albicans

PROVIDER: GSE31632 | GEO | 2012/02/20

SECONDARY ACCESSION(S): PRJNA145555

REPOSITORIES: GEO

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Functions of the Mediator subunit Med31 in Candida albicans support a role in shaping species-specific gene expression.

Project description:Mediator is an essential, evolutionarily conserved co-regulator of RNA polymerase II. Studies in model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe showed remarkably conserved roles for Mediator despite high species divergence, and thus whether Mediator contributed to establishment of species-specific gene expression programs within related fungal species remains an open question. Here we show that in the fungal pathogen Candida albicans, the Mediator middle domain subunit Med31 has a conserved role with non-pathogenic model yeasts in regulation of Ace2-dependent cytokinesis genes and stress responses, but also additional roles in the transcription of genes associated with virulence traits: genes related to filamentous growth and gene families expanded in pathogenic vs non-pathogenic yeasts, such as the ALS adhesins and the FGR6 family of filamentous growth regulators. Consistently, Med31 is required for two key virulence attributes of C. albicans: filamentous growth and biofilm formation. Unlike our data in C. albicans, no role for Med31 in adhesin expression has been reported in model yeasts. To show biological relevance for the control over adhesin gene expression, we demonstrate that ALS1 is a relevant Med31 target for development of biofilms. Collectively, our data supports a role for Med31 in shaping species-specific gene expression in related fungal species. Two-color experimental design comparing cells with a ?med31 mutation with a control strain in which the MED31 gene was reintroduced. RNA from each replicate came from independent cultures.

2012-02-20 | E-GEOD-31632 | biostudies-arrayexpress

The protein kinase Tor1 regulates adhesin expression in Candida albicans

Project description:Eukaryotic cell growth is coordinated in response to nutrient availability, growth factors, and environmental stimuli, enabling cell–cell interactions that promote survival. The rapamycin-sensitive Tor1 protein kinase, which is conserved from yeasts to humans, participates in a signaling pathway central to cellular nutrient responses. To gain insight into Tor-mediated processes in human fungal pathogens, we have characterized Tor signaling in Candida albicans. Global transcriptional profiling revealed evolutionarily conserved roles for Tor1 in regulating the expression of genes involved in nitrogen starvation responses and ribosome biogenesis. Interestingly, we found that in C. albicans Tor1 plays a novel role in regulating the expression of several cell wall and hyphal specific genes, including adhesins and their transcriptional repressors Nrg1 and Tup1. In accord with this transcriptional profile, rapamycin induced extensive cellular aggregation in an adhesin-dependent fashion. Moreover, adhesin gene induction and cellular aggregation of rapamycin-treated cells were strongly dependent on the transactivators Bcr1 and Efg1. These findings support models in which Tor1 negatively controls cellular adhesion by governing the activities of Bcr1 and Efg1. Taken together, these results provide evidence that Tor1-mediated cellular adhesion might be broadly conserved among eukaryotic organisms.

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Project description:The yeast-filament transition is essential for the virulence of a variety of fungi that are pathogenic to humans. N-acetylglucosamine (GlcNAc), a ubiquitous molecule in both the environment and host, is one of the most potent inducers of filamentation in Candida albicans and thermally dimorphic fungi such as Histoplasma capsulatum and Blastomyces dermatitidis. However, GlcNAc suppresses rather than promotes filamentation in Candida tropicalis, a fungal species that is closely related to C. albicans. Furthermore, we discover that glucose induces filamentous growth in C. tropicalis. Mutation and overexpression assays demonstrate that the conserved cAMP signaling pathway plays a central role in the regulation of filamentation in C. tropicalis. Activation of this pathway promotes filamentation in C. tropicalis, while inactivation of this pathway results in a serious growth defect in filamentation. By screening an overexpression library of 154 transcription factors, we have identified approximately 40 regulators of filamentous growth in C. tropicalis. Although most of the regulators (e.g., Tec1, Gat2, Nrg1, Sfl1, Sfl2, and Ash1) demonstrate a conserved role in the regulation of filamentation, similar to their homologs in C. albicans or S. cerevisiae, some of them are specific to C. tropicalis. For example, Czf1 and Efh1 repress filamentation, while Wor1, Zcf3, and Hcm1 promote filamentation in C. tropicalis. Bcr1, Aaf1, and Csr1 play a specific role in the process of GlcNAc-regulated filamentation. Our findings indicate that multiple interconnected signaling pathways are involved in the regulation of filamentation in C. tropicalis. These mechanisms have conserved and divergent features among different Candida species. Total RNA profiles of cells grown in Lee's glucose or Lee's GlcNAc medium.

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Project description:Aberrant CD4+ T cell reactivity against intestinal microbes is considered to drive mucosal inflammation in inflammatory bowel diseases. The disease-relevant microbial species and the corresponding microbe-specific pathogenic T cell phenotypes remain unknown. Here, we identify common gut commensal and food-derived yeasts, as direct activators of aberrant CD4+ T cell reactions in patients with Crohn´s disease (CD). Yeast-responsive CD4+ T cells in CD display a cytotoxic Th1 phenotype and selective clonal expansion of cells highly cross-reactive to several commensal, as well as food-derived, fungal species. This indicates cross-reactive T cell selection by repeated encounter with conserved fungal antigens in the context of chronic intestinal disease. Our results highlight a role of fungi in driving immunopathology in patients with CD and suggest that both, gut-resident fungal commensals, and daily dietary intake of yeasts, may contribute to chronic activation of pathogenic CD4+ T cell responses involved in disease pathophysiology.

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Genome-wide location of Candida albicans transcription factor Skn7p

Project description:Skn7 is a conserved fungal heat shock factor-type transcriptional regulator. It participates in maintaining cell wall integrity and regulates the osmotic/oxidative stress response (OSR) in S. cerevisiae, where it is part of a two-component signal transduction system. Here, we comprehensively address the function of Skn7 in the human fungal pathogen Candida albicans. We provide evidence reinforcing functional divergence, with loss of the cell wall/osmotic stress-protective roles and acquisition of the ability to regulate morphogenesis on solid medium. Mapping of the Skn7 transcriptional circuitry, through combination of genome-wide expression and location technologies, pointed to a dual regulatory role encompassing OSR and filamentous growth. Genetic interaction analyses revealed close functional interactions between Skn7 and master regulators of morphogenesis, including Efg1, Cph1 and Ume6. Intracellular biochemical assays revealed that Skn7 is crucial for limiting the accumulation of reactive oxygen species (ROS) during filamentous growth on solid medium. Interestingly, functional domain mapping using site-directed mutagenesis allowed decoupling of Skn7 function in morphogenesis from protection against intracellular ROS. Our work identifies Skn7 as an integral part of the transcriptional circuitry controlling C. albicans filamentous growth and illuminates how C. albicans relies on an evolutionarily-conserved regulator to protect itself from intracellular ROS during morphological development.

2017-06-30 | GSE85276 | GEO

Genome-wide expression profiling of Candida albicans transcription factor Skn7p

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Regulation of filamentation in the human fungal pathogen Candida tropicalis

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High throughput RNA sequencing of C. albicans colonizing the murine GI tract reveals a role for a secreted effecter in commensalism

Project description:Candida albicans is a human gut commensal and an opportunistic pathogen. The ability to transition from yeasts to invasive hyphae is a central virulence attribute, but it is unclear how these two cell types function during commensal growth. Using FISH to visualize C. albicans in a murine gut colonization model, we observed the co-occurrence of yeasts and hyphae throughout the gastrointestinal tract. Forward genetic analysis revealed that major transcriptional activators of yeast-to-hypha morphogenesis have unexpected activity as potent inhibitors of commensalism. In vivo FISH, transcriptomic, and genetic analyses indicate that the morphogenesis program inhibits commensal fitness, not through control of cell shape as expected from in vitro studies, but by activating expression of a hypha-specific pro-inflammatory secreted protease and a hyphal cell surface adhesin. These results reveal a tradeoff between fungal programs supporting commensalism and virulence within the commensal niche in which selection against hypha-specific markers limits the disease-causing potential of this ubiquitous commensal-pathogen.

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Screens of C. albicans deletion collections in the murine reveals role for filamentation transcription factors

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Small RNAs in budding yeast

Project description:RNAi, a gene-silencing pathway triggered by double-stranded RNA, is conserved in diverse eukaryotic species but has been lost in the model budding yeast, Saccharomyces cerevisiae. We report that RNAi is present in other budding-yeast species, including Saccharomyces castellii and Candida albicans. These species use noncanonical Dicer proteins to generate siRNAs, which mostly correspond to transposable elements and YM-BM-4 subtelomeric repeats. In S. castellii, RNAi mutants are viable but have excess YM-BM-4 mRNA levels. In S. cerevisiae, introducing Dicer and Argonaute of S. castellii restores RNAi, and the reconstituted pathway silences endogenous retrotransposons. These results identify a novel class of Dicer proteins, bring the tool of RNAi to the study of budding yeasts, and bring the tools of budding yeast to the study of RNAi. Employ high-throughput sequencing of endogenous small RNAs from the budding yeasts Saccharomyces castellii, Kluyveromyces polysporus, Candida albicans, Saccharomyces cerevisiae, and Saccharomyces bayanus.

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