Hyphal Growth and Virulence in Candida albicans
Fungi grow either as unicellular yeasts or form elongated tubes known as hyphae that, by branching, can form large mycelia. Yeast-like growth, as seen, e.g. in the unicellular brewer’s and baker’s yeast Saccharomyces cerevisiae, includes an active step of cell separation after mitosis. Such a cytokinesis requires a partial degradation of the cell wall and the chitin-rich septum at the mother daughter cell junction to allow separation of both cells. In contrast, hyphae consist of multiple concatenated cells which are compartmentalized by septation but which are not fragmented. Dimorphic fungi, such as the human pathogen Candida albicans can switch growth modes between yeast and hyphal stages. This versatility allows conquering different environmental or host niches and in C. albicans contributes to the successful colonization and infection of its host. The pathogenicity of C. albicans is brought about in concert with other virulence factors such as the production of secreted aspartic proteases and lipases or the phase-specific expression of genes, as well as the reduced ability of the host to fight off infections due to a compromised immune system. In this chapter we discuss differences on the molecular level between yeast and hyphal growth by comparison of C. albicans with S. cerevisiae. From there we review the signals that induce filamentation in C. albicans, the signal transduction cascades used to process these signals, and the output in terms of changes at the transcriptional level that induce phase-specific gene expression.
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