DNA methylation as a potential epigenetic driver of morphological development in Candida albicans
by Pia Simone Sternisek
Date of Examination:2021-12-08
Date of issue:2022-01-04
Advisor:Dr. Oliver Bader
Referee:Prof. Dr. Uwe Groß
Referee:Prof. Dr. Gerhard Braus
Persistent Address:
http://dx.doi.org/10.53846/goediss-9029
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Abstract
English
Candida albicans is a commensal yeast in the mammalian gut, but also has retained its virulence potential while co-evolving in mammalian species. As a perfectly adapted opportunist colonizing mucosal surfaces, it is also the most frequently observed human fungal pathogen. Additionally to superficial infections of skin, nails, and mucosal surfaces, it can also invade and disseminate via the bloodstream into the organs, causing life-threatening infections. Changing its morphology in response to environmental cues is a crucial characteristic and central part of its virulence. Previous studies indicated the presence of varying levels of the epigenetic modification 5-methylcytosine in the DNA of C. albicans. The apparent differential distribution of 5mC between yeast- and hyphae-form states brings up the question of its potential involvement in gene regulation. Here, we looked at DNA methylation in different genomic features in C. albicans using WGBS at single-base resolution. Our results confirmed a very low global methylation content of ~0.08 – 0.11% distributed over the whole genome, in CG as well as CHG and CHH contexts. We observed characteristic patterns of methylation: in protein coding sequences methylation levels were higher in the 5’ and 3’ adjacent regions and dropped in between. Regions encoding lncRNA or transposable elements showed higher levels of methylation. This shows that DNA methylation is not random in C. albicans, but occurs in meaningful patterns, indicating a different function of DNA methylation in different genomic features. Treatment of C. albicans with the demethylating agent 5-Azacytidine resulted in the de-repression of hyphae related genes already in the yeast stage. 5-Azacytidine also induced hyphae formation in previously morphologically attenuated clinical isolates, together indicating an involvement of DNA methylation in mechanisms of hyphae repression. Screening C. albicans clinical isolates from different clinical specimen types on hyphae inducing medium suggested a correlation between sample origin (primary sterile vs. coinhabitated body sites) and morphological attenuation. Partial conversion of attenuated to non-attenuated strains by 5-Aza treatment increased tissue invasion. Likewise, attenuation of SC5314 after gut passage could be partially restored again by 5-Aza treatment. Taken together our results strongly suggest a direct connection of DNA methylation and the repression of morphological development of C. albicans, which might be the key to its high adaptation potential to host environments.
Keywords: Candida albicans; 5-methylcytosine; DNA methylation patterns; morphogenesis; hyphal formation; 5-Azacytidine; gene expression; WGBS