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A temperature-responsive network links cell shape and virulence traits in a primary fungal pathogen -- RNAi mutants (1)

ABSTRACT: The ability to grow at host temperature is a critical trait for most pathogenic microbes of humans. Thermally dimorphic fungal pathogens, including Histoplasma capsulatum, are a class of soil fungi that undergo a dramatic change in cell shape and virulence gene expression in response to host temperature. Here we elucidate a complex temperature-responsive network in H. capsulatum, which switches from an environmental filamentous form to a pathogenic yeast form. We dissect the circuit driven by three regulators that control yeast-phase growth, and demonstrate that these factors, including two deeply conserved Velvet family proteins of unknown function, associate with DNA. We identify and characterize a fourth regulator of this pathway, and define cis-acting motifs that recruit these transcription factors to a tightly interwoven network of temperature-responsive target genes. Our results provide the first comprehensive analysis of the complex transcriptional network that links temperature to morphology and virulence in thermally dimorphic fungi. This submission gives the expression profiling results.

ORGANISM(S): Histoplasma capsulatum

PROVIDER: GSE46938 | GEO | 2013/06/14

SECONDARY ACCESSION(S): PRJNA208220

REPOSITORIES: GEO

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Project description:Thermally dimorphic human fungal pathogens undergo a reversible program of cellular differentiation in response to their environment that is essential for infectivity and pathogenicity. In the soil, these organisms grow as highly polarized, multicellular hyphal filaments that produce infectious particles. When inhaled by a mammalian host, these cells switch to a unicellular yeast form that causes disease even in healthy hosts. Temperature is considered to be the primary environmental cue that promotes reversible cellular differentiation; however, a shift to a lower temperature in vitro induces filamentous growth in an inefficient and asynchronous manner. In a search for other signals that regulate morphogenesis, we considered the monosaccharide N-acetylglucosamine (GlcNAc), which is a major component of microbial cell walls and is ubiquitous in the environment. GlcNAc was a potent and specific inducer of the yeast-to-filament transition in two thermally dimorphic fungi, Histoplasma capsulatum and Blastomyces dermatitidis. Micromolar concentrations of GlcNAc induced a robust morphological transition of H. capsulatum after temperature shift, indicating that fungal cells sense GlcNAc to promote filamentation. The synchronous morphologic transition stimulated by low temperature and GlcNAc allowed us to examine the temporal regulation of the transcriptome during morphogenesis to reveal candidate genes involved in establishing the filamentous growth program. Through this analysis, we identified two genes encoding GlcNAc transporters, NGT1 and NGT2, that were necessary for H. capsulatum cells to robustly filament in response to GlcNAc. Unexpectedly, NGT1 and NGT2 were important for efficient H. capsulatum yeast-to-filament conversion in standard glucose medium, suggesting that Ngt1 and Ngt2 monitor endogenous levels of GlcNAc to control multicellular filamentous growth in response to temperature. Overall, our work indicates that GlcNAc functions as a highly conserved cue of morphogenesis in fungi, which further enhances the significance of this ubiquitous sugar in cellular signaling in eukaryotes.

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A temperature-responsive network links cell shape and virulence traits in a primary fungal pathogen -- RNAi mutants (1)

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