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Bedford, Elise

University of British Columbia

The pathogenesis of Cryptococcus neoformans is largely attributed to the polysaccharide capsule and its impact on survival of the fungus in the harsh conditions of the host. These conditions include a robust immune response and starvation due to the variability of available nutrients present in different tissues. The ability of the pathogen to survive in nutrient deprived conditions has yet to be extensively studied, but one hypothesis posits that extended survival involves the degradation (alteration) of capsule and cell wall components to provide sources of carbon. In this study, alterations in capsule and cell wall were measured in response to starvation through a variety of assays to determine the validity of the hypothesis. These assays demonstrated that starvation influences the overall structure of the capsule with regard to porosity and density without a change in capsule diameter, and also alters the cell wall. Based on these findings, a collection of capsule and cell wall relevant mutants was examined to determine which cellular components were involved in the starvation response. The starvation response was additionally examined using a RNA-seq and proteomics approaches. These transcriptional data identified enzymes with potential relevance to the starvation response and polysaccharide changes, including enzymes for β-glucan hydrolysis, and also identified components of the Ras signaling pathway that maintains the homeostasis of the cell wall. The mutant screen and RNA-seq data suggested interactions between the cell wall and capsule involving 𝛼-glucans and β-glucans are crucial for the density and porosity changes observed during starvation. Key mutants supporting this conclusion include cps1Δ, kre64Δ and chsΔ1-8 encoding hyaluronic acid synthase, β-glucan specific glycosidase, and chitin synthases, respectively. Finally, the RNA-seq analysis identified transcripts for carbohydrate active enzymes in the top regulated genes in the starvation condition, and these enzymes are key targets for further investigation of their contribution to capsule and cell wall alterations during starvation.

Text

2024-12-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89857

Microbiology and Immunology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/