An RNA Transport System in Candida albicans Regulates Hyphal Morphology and Invasive Growth

Fred Hutchinson Cancer Research Center, United States of America
PLoS Genetics (Impact Factor: 7.53). 09/2009; 5(9):e1000664. DOI: 10.1371/journal.pgen.1000664
Source: PubMed


Author Summary
Generation of cellular polarity – asymmetry in shape, protein distribution, and/or sub-cellular function – is an essential feature of most eukaryotic cells and underlies such diverse processes as differentiation, mating, nutrient acquisition, and growth. Localization of specific mRNAs is one mechanism through which cells achieve polarity. We describe an RNA transport system in Candida albicans, a fungal pathogen of humans, that grows in both single cell (budding yeast) and filamentous (hyphal and pseudohyphal) forms. Hyphae are chains of elongated cells that remain attached after cell division and exhibit highly polarized growth at their tips. We show that the C. albicans She3-dependent RNA transport system binds to 40 mRNAs and transports these mRNAs to yeast buds and to the tips of hyphae. Both the transport system itself and many of the genes encoded by transported mRNAs are required for normal growth and function of hyphae. Although the basic transport mechanism appears conserved with that of the model yeast, Saccharomyces cerevisiae, the cargo mRNAs are largely distinct. The apparently rapid evolution of the transported mRNAs probably reflects distinct selective pressures acting on the two organisms.

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    • "On SLAD agar the hsp21Δ/Δ mutant formed aberrant colonies which completely lacked the peripheral filaments observed for the wild type. When grown on Spider agar the wild type typically forms colonies with a central wrinkled area consisting of yeast, hyphae and pseudohyphae and a peripheral area consisting mainly of agar-invading filaments [77]. In contrast, the hsp21Δ/Δ mutant developed wrinkled colonies that completely lacked peripheral hyphae. "
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    ABSTRACT: Small heat shock proteins (sHsps) have multiple cellular functions. However, the biological function of sHsps in pathogenic microorganisms is largely unknown. In the present study we identified and characterized the novel sHsp Hsp21 of the human fungal pathogen Candida albicans. Using a reverse genetics approach we demonstrate the importance of Hsp21 for resistance of C. albicans to specific stresses, including thermal and oxidative stress. Furthermore, a hsp21Δ/Δ mutant was defective in invasive growth and formed significantly shorter filaments compared to the wild type under various filament-inducing conditions. Although adhesion to and invasion into human-derived endothelial and oral epithelial cells was unaltered, the hsp21Δ/Δ mutant exhibited a strongly reduced capacity to damage both cell lines. Furthermore, Hsp21 was required for resisting killing by human neutrophils. Measurements of intracellular levels of stress protective molecules demonstrated that Hsp21 is involved in both glycerol and glycogen regulation and plays a major role in trehalose homeostasis in response to elevated temperatures. Mutants defective in trehalose and, to a lesser extent, glycerol synthesis phenocopied HSP21 deletion in terms of increased susceptibility to environmental stress, strongly impaired capacity to damage epithelial cells and increased sensitivity to the killing activities of human primary neutrophils. Via systematic analysis of the three main C. albicans stress-responsive kinases (Mkc1, Cek1, Hog1) under a range of stressors, we demonstrate Hsp21-dependent phosphorylation of Cek1 in response to elevated temperatures. Finally, the hsp21Δ/Δ mutant displayed strongly attenuated virulence in two in vivo infection models. Taken together, Hsp21 mediates adaptation to specific stresses via fine-tuning homeostasis of compatible solutes and activation of the Cek1 pathway, and is crucial for multiple stages of C. albicans pathogenicity. Hsp21 therefore represents the first reported example of a small heat shock protein functioning as a virulence factor in a eukaryotic pathogen.
    PLoS ONE 06/2012; 7(6):e38584. DOI:10.1371/journal.pone.0038584 · 3.23 Impact Factor
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    • "In distant fungal species such as Candida albicans, a She3p homolog but not a She2p homolog is present in the genome [72]. As in S.cerevisiae, ASH1 mRNA in C. albicans is transported in a She3p-dependent manner [72]. "
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    ABSTRACT: mRNA localization and localized translation is a common mechanism by which cellular asymmetry is achieved. In higher eukaryotes the mRNA transport machinery is required for such diverse processes as stem cell division and neuronal plasticity. Because mRNA localization in metazoans is highly complex, studies at the molecular level have proven to be cumbersome. However, active mRNA transport has also been reported in fungi including Saccharomyces cerevisiae, Ustilago maydis and Candida albicans, in which these events are less difficult to study. Amongst them, budding yeast S. cerevisiae has yielded mechanistic insights that exceed our understanding of other mRNA localization events to date. In contrast to most reviews, we refrain here from summarizing mRNA localization events from different organisms. Instead we give an in-depth account of ASH1 mRNA localization in budding yeast. This approach is particularly suited to providing a more holistic view of the interconnection between the individual steps of mRNA localization, from transcriptional events to cytoplasmic mRNA transport and localized translation. Because of our advanced mechanistic understanding of mRNA localization in yeast, the present review may also be informative for scientists working, for example, on mRNA localization in embryogenesis or in neurons.
    Cellular and Molecular Life Sciences CMLS 12/2011; 69(11):1843-53. DOI:10.1007/s00018-011-0902-4 · 5.81 Impact Factor
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    • "A high rate of RNA decay of transcripts involved in regulatory systems has been reported in S. cerevisiae as well [34]. Intriguingly, of the 38 RNAs identified recently as She3-transported in C. albicans during hyphal growth [35], 9 were found to exhibit long 5' UTRs (P = 4.3e-04). This leads us to speculate that long 5' UTRs are probably required for RNA transport to cellular locations where hyphal buds are produced. "
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    ABSTRACT: Compared to other model organisms and despite the clinical relevance of the pathogenic yeast Candida albicans, no comprehensive analysis has been done to provide experimental support of its in silico-based genome annotation. We have undertaken a genome-wide experimental annotation to accurately uncover the transcriptional landscape of the pathogenic yeast C. albicans using strand-specific high-density tiling arrays. RNAs were purified from cells growing under conditions relevant to C. albicans pathogenicity, including biofilm, lab-grown yeast and serum-induced hyphae, as well as cells isolated from the mouse caecum. This work provides a genome-wide experimental validation for a large number of predicted ORFs for which transcription had not been detected by other approaches. Additionally, we identified more than 2,000 novel transcriptional segments, including new ORFs and exons, non-coding RNAs (ncRNAs) as well as convincing cases of antisense gene transcription. We also characterized the 5' and 3' UTRs of expressed ORFs, and established that genes with long 5' UTRs are significantly enriched in regulatory functions controlling filamentous growth. Furthermore, we found that genomic regions adjacent to telomeres harbor a cluster of expressed ncRNAs. To validate and confirm new ncRNA candidates, we adapted an iterative strategy combining both genome-wide occupancy of the different subunits of RNA polymerases I, II and III and expression data. This comprehensive approach allowed the identification of different families of ncRNAs. In summary, we provide a comprehensive expression atlas that covers relevant C. albicans pathogenic developmental stages in addition to the discovery of new ORF and non-coding genetic elements.
    Genome biology 07/2010; 11(7):R71. DOI:10.1186/gb-2010-11-7-r71 · 10.81 Impact Factor
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