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Yeast magnesium starvation, 90 minutes

ABSTRACT: To learn about the cellular processes involved in Mg2+ transport and the mechanisms allowing cells to cope with low Mg2+ availability, we performed RNA expression profiling experiments, and followed changes in gene activity upon Mg2+ depletion on a genome-wide scale. A striking portion of genes up-regulated under Mg2+ depletion is also induced by high Ca2+ and/or alkalinization. Among the genes significantly up-regulated by Mg2+ starvation, Ca2+ stress and alkalinization are ENA1 (encoding a P-type ATPase sodium pump) and PHO89 (encoding a sodium/phosphate cotransporter). We show that up-regulation of these genes is dependent on the calcineurin/Crz1p signaling pathway. Similarly to Ca2+ stress, Mg2+ starvation induces translocation of the transcription factor Crz1p from the cytoplasm into the nucleus. The up-regulation of ENA1 and PHO89 upon Mg2+ starvation depends on extracellular Ca2+. Using fluorescence resonance energy transfer microscopy we demonstrate that removal of Mg2+ results in an immediate increase in free cytoplasmic Ca2+. This effect is dependent on external Ca2+. Results presented indicate that Mg2+ depletion in yeast cells leads to enhanced cellular Ca2+ concentrations, which activate the Crz1p/calcineurin pathway. We provide evidence that calcineurin/Crz1p signaling is crucial for yeast cells to cope with Mg2+ depletion stress. Keywords: stress response (magnesium starvation)

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE6687 | GEO | 2007/03/08

SECONDARY ACCESSION(S): PRJNA99065

REPOSITORIES: GEO

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Project description:Exposure of the budding Saccharomyces cerevisiae to an alkaline environment produces a robust transcriptional response involving hundreds of genes. Part of this response is triggered by an almost immediate burst of calcium that activates the Ser/Thr protein phosphatase calcineurin. Activated calcineurin dephosphorylates the transcription factor Crz1, which moves to the nucleus and binds to calcineurin/Crz1 responsive gene promoters. In this work we present a genome-wide study of the binding of Crz1 to gene promoters in response to high pH stress. Environmental alkalinization promoted a time-dependent recruitment of Crz1 to 152 intergenic regions, the vast majority between 1 to 5 min upon stress onset. Positional evaluation of the genomic coordinates combined with existing transcriptional studies allowed identifying 139 genes likely responsive to Crz1 regulation. Gene Ontology analysis confirmed the relevant impact of calcineurin/Crz1 on a set of genes involved in glucose utilization, and uncovered novel targets, such as genes responsible for trehalose metabolism. We also identified over a dozen of genes encoding transcription factors that are likely under the control of Crz1, suggesting a possible mechanism for amplification of the signal at the transcription level. Further analysis of the binding sites allowed refining the consensus sequence for Crz1 binding to gene promoters and the effect of chromatin accessibility in the timing of Crz1 recruitment to promoters. The present work defines at the genomic-wide level the kinetics of binding of Crz1 to gene promoters in response to alkaline stress, confirms diverse previously known Crz1 targets and identifies many putative novel ones. Because the relevance of calcineurin/Crz1 in signaling diverse stress conditions, our data will contribute to understand the transcriptional response in other circumstances that also involves calcium signaling, such as exposition to sexual pheromones or saline stress. ChIP-Seq from five time points after alkalinization (t=0, 1, 2, 5 and 20 min) was collected from two independent experiments (A and B) and the ratio Tx/T0 was calculated.

Project description:Calcineurin is a highly conserved Ca2+/calmodulin-dependent serine/threonine-specific protein phosphatase that orchestrates cellular Ca2+ signaling responses. In Cryptococcus neoformans, calcineurin is activated by multiple stresses including high temperature, and is essential for stress adaptation and virulence. The transcription factor Crz1 is a major calcineurin effector in Saccharomyces cerevisiae and other fungi. Calcineurin dephosphorylates Crz1, thereby enabling Crz1 nuclear translocation and transcription of target genes. Here we show that Crz1 is dephosphorylated by calcineurin, and crz1Δ mutants display phenotypes intermediate between wild-type and calcineurin mutants. RNA-sequencing revealed 102 genes that are regulated in a calcineurin/Crz1-dependent manner at 37°C. 99 genes were down-regulated in cna1Δ and crz1Δ mutants, indicating these genes are normally activated by the calcineurin/Crz1 pathway at high temperature. About 58% of calcineurin-Crz1 target genes have unknown functions, while genes with known or predicted functions are involved in cell wall remodeling, calcium transport, and pheromone production. Surprisingly, only five genes have orthologs known to be calcineurin/Crz1-dependent in S. cerevisiae. 393 genes are independently regulated by calcineurin, and Crz1 regulates 59 genes independently of calcineurin. Taken together, these results indicate that the calcineurin/Crz1-dependent pathway controls a transcriptional circuit that has been extensively rewired in C. neoformans compared to S. cerevisiae. Given the intermediate crz1Δ mutant phenotype, and our recent evidence for a calcineurin regulatory network impacting mRNA in P-bodies and stress granules independently of Crz1, calcineurin likely acts on factors beyond Crz1 that govern mRNA expression/stability to operate a branched transcriptional/post-transcriptional stress response network necessary for fungal virulence. Taken together, our findings reveal the core calcineurin-Crz1 stress response cascade is maintained from ascomycetes to a pathogenic basidiomycete fungus, but its output has been extensively rewired to promote fungal virulence.

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Yeast magnesium starvation, 90 minutes

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