Investigating Conservation of the Cell-Cycle-Regulated Transcriptional Program in the Fungal Pathogen, Cryptococcus neoformans

Abstract

The pathogenic yeast Cryptococcus neoformans causes fungal meningitis in immune-compromised patients. Cell proliferation in the budding yeast form is required for C. neoformans to infect human hosts, and virulence factors such as capsule formation and melanin production are affected by cell-cycle perturbation. Thus, understanding cell-cycle regulation is critical for a full understanding of virulence factors for disease. Our group and others have demonstrated that a large fraction of genes in Saccharomyces cerevisiae is expressed periodically during the cell cycle, and that proper regulation of this transcriptional program is important for proper cell division. Despite the evolutionary divergence of the two budding yeasts, we found that a similar percentage of all genes (~20%) is periodically expressed during the cell cycle in both yeasts. However, the temporal ordering of periodic expression has diverged for some orthologous cell-cycle genes, especially those related to bud emergence and bud growth. Genes regulating DNA replication and mitosis exhibited a conserved ordering in both yeasts, suggesting that essential cell-cycle processes are conserved in periodicity and in timing of expression (i.e. duplication before division). In S. cerevisiae cells, we have proposed that an interconnected network of periodic transcription factors (TFs) controls the bulk of the cell-cycle transcriptional program. We found that temporal ordering of orthologous network TFs was not always maintained; however, the TF network topology at cell-cycle commitment appears to be conserved in C. neoformans. During the C. neoformans cell cycle, DNA replication genes, mitosis genes, and 40 genes involved in virulence are periodically expressed. Future work toward understanding the gene regulatory network that controls cell-cycle genes is critical for developing novel antifungals to inhibit pathogen proliferation.

Metabolic signatures of regulation by phosphorylation and acetylation

“…To check if this pattern of regulation is observed in other conditions, using CAROM, we analyzed data from nitrogen starvation response and the cell cycle in yeast, where both phospho-proteomics and transcriptomics data are available [35–38]. A similar trend of regulation was observed in these conditions with phosphorylation regulating isozymes and enzymes that can carry high fluxes (futile cycles) (Figure 2).…”

The enigmatic role of fungal annexins: the case of Cryptococcus neoformans

“…These authors also observed that conidia formation was precocious. This observation may be somehow related to the observation that in C. neoformans expression of AnxC1 peaked at the time of bud formation (41), approximately 50 min after separation of cells by centrifugal elutriation, insinuating that cryptococcal annexin, and maybe fungal annexins, are involved in membrane dynamics during cellular replication. This framework would fit within our observation that AnxC1 deletion leads to an increase in the formation of titan cells, which display very atypical size and replication patterns, requiring considerable coordination with cellular membrane dynamics.…”

A fungal arrestin protein contributes to cell cycle progression and pathogenesis

“…These data suggest that Ali1 is a regulator of cytokinesis that is particularly important in the presence of stress. Whole transcriptome analyses of synchronized C. neoformans cells have shown that Ali1 expression is cyclic, or regulated with the cell cycle, with its peak expression occuring about 15 minutes prior to bud emergence (55). As a potential regulator of cytokinesis, this expression pattern would enable the ALI1 transcript to be transcribed, and the Ali1 protein to be translated and localize to the septum and poles as cell division is occuring.…”