Temperature-Regulated Transcription in the Pathogenic Fungus Cryptococcus neoformans

Abstract

The basidiomycete fungus Cryptococcus neoformans is an opportunistic pathogen of worldwide importance that causes meningitis, leading to death in immunocompromised individuals. Unlike many basidiomycete fungi, C. neoformans is thermotolerant, and its ability to grow at 37°C is considered to be a virulence factor. We used serial analysis of gene expression (SAGE) to characterize the transcriptomes of C. neoformans strains that represent two varieties with different polysaccharide capsule serotypes. These include a serotype D strain of the C. neoformans variety neoformans and a serotype A strain of variety grubii. In this report, we describe the construction and characterization of SAGE libraries from each strain grown at 25°C and 37°C. The SAGE data reveal transcriptome differences between the two strains, even at this early stage of analysis, and identify sets of genes with higher transcript levels at 25°C or 37°C. Notably, growth at the lower temperature increased transcript levels for histone genes, indicating a general influence of temperature on chromatin structure. At 37°C, we noted elevated transcript levels for several genes encoding heat shock proteins and translation machinery. Some of these genes may play a role in temperature-regulated phenotypes in C. neoformans, such as the adaptation of the fungus to growth in the host and the dimorphic transition between budding and filamentous growth. Overall, this work provides the most comprehensive gene expression data available for C. neoformans; this information will be a critical resource both for gene discovery and genome annotation in this pathogen.[This paper is dedicated to the memory of Michael Smith, founding director of the Biotechnology Laboratory and the British Columbia Genome Sciences Centre. The following individuals kindly provided reagents, samples, or unpublished information as indicated in the paper:

Rewiring of Signaling Networks Modulating Thermotolerance in the Human Pathogen Cryptococcus neoformans

“…We compared our array data of the WT strain to those from other microarray analyses performed independently to identify temperature-regulated or heat-shock responsive genes in C. neoformans (Steen et al 2002;Kraus et al 2004;Chow et al 2007). Steen et al (2002) demonstrated that the tag representing cyclophilin A (CPA1 and CPA2) is expressed at higher levels at 37°than at 25°.…”

“…Steen et al (2002) demonstrated that the tag representing cyclophilin A (CPA1 and CPA2) is expressed at higher levels at 37°than at 25°. Our array data also confirmed this finding (Table S3 and Table S4).…”

“…Steen et al (2002) reported that a peroxiredoxin (TSA1) and a superoxide dismutase (SOD) are highly expressed at 37°. Similarly, Chow et al (2007) reported that the expression of the genes involved in the thioredoxin system (TRR1, thioredoxin reductase; TRX3, thioredoxin) is induced by the heat shock response.…”

Ccr4 Promotes Resolution of the Endoplasmic Reticulum Stress Response during Host Temperature Adaptation in Cryptococcus neoformans

“…Unifying characteristics of the pathogenic cryptococci include the production of a polysaccharide capsule, the ability to form melanin pigments through the activity of the multicopper oxidase laccase, and the ability to adapt to and thrive at mammalian host temperature. Adaptation of C. neoformans to the host temperature is accompanied by major changes in gene expression as measured by microarray analysis and serial analysis of gene expression (SAGE) (5,19,29). This modulation of gene expression likely requires alterations in mRNA synthesis rates through activation of transcriptional transactivators and repressors, as well as alterations in chromatin structure.…”

The relevance of heat shock regulation in fungal pathogens of humans

“…Molecular biologists regularly apply acute insults to provoke dramatic molecular responses that are easy to assay 19 Hsp90 negatively regulates hyphal development in C. albicans (ca). 24 temperature upshifts also induce HSP90 expression in C. neoformans (cn), H. capsulatum (Hc) and P. brasiliensis (Pb) [31][32][33] and promote yeast growth rather than hyphal development in these fungi. this raises the possibility that Hsp90 might also regulate morphogenesis in these pathogenic fungi (see text).…”