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Role of a Candida albicans Whi5/Nrm1 homolog in cell cycle and hyphal-specific gene expression

ABSTRACT: Candida albicans is an opportunistic pathogenic fungus that is able to assume several morphologies, including yeast and hyphal growth forms. The hyphal morphology can be induced by various environmental stimuli and is accompanied by expression of a large set of hyphal-specific genes (HSGs). Cell cycle and morphogenetic programs are interconnected: notably, inhibition of cell cycle progression often causes a switch to filamentous growth. Here we identify and characterize CaNrm1, a C. albicans homolog of the S. cerevisiae Whi5 and Nrm1 transcription inhibitors that, analogous to mammalian Rb, regulate the cell cycle transcription program in the G1 phase and at the G1/S transition. CaNRM1 is able to complement the phenotypes of both whi5 and nrm1 mutants in S. cerevisiae. Deletion of CaNRM1 causes a reduction in cell size and results in increased resistance to hydroxyurea (HU), an inhibitor of DNA replication; analysis of the expression of ribonucleotide reductase, the target of HU, suggests that its transcriptional induction in response to HU is mainly dependent upon CaNrm1. Genetic epistasis analysis suggests that CaNrm1 interacts with the SBF and MBF transcription factors in S. cerevisiae and with the MBF functional homolog in C. albicans. At the transcription level, deletion of CaNRM1 causes an induction of many G1 and G1/S-specific genes. Induction of the HSGs is dampened under certain conditions in the Canrm1-/- mutant, suggesting that the cell cycle transcription program influences the morphogenetic transcription program of C. albicans.

ORGANISM(S): Candida albicans

PROVIDER: GSE20612 | GEO | 2012/01/01

SECONDARY ACCESSION(S): PRJNA124791

REPOSITORIES: GEO

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Role of a Candida albicans Whi5/Nrm1 homolog in cell cycle and hyphal-specific gene expression

Project description:Candida albicans is an opportunistic pathogenic fungus that is able to assume several morphologies, including yeast and hyphal growth forms. The hyphal morphology can be induced by various environmental stimuli and is accompanied by expression of a large set of hyphal-specific genes (HSGs). Cell cycle and morphogenetic programs are interconnected: notably, inhibition of cell cycle progression often causes a switch to filamentous growth. Here we identify and characterize CaNrm1, a C. albicans homolog of the S. cerevisiae Whi5 and Nrm1 transcription inhibitors that, analogous to mammalian Rb, regulate the cell cycle transcription program in the G1 phase and at the G1/S transition. CaNRM1 is able to complement the phenotypes of both whi5 and nrm1 mutants in S. cerevisiae. Deletion of CaNRM1 causes a reduction in cell size and results in increased resistance to hydroxyurea (HU), an inhibitor of DNA replication; analysis of the expression of ribonucleotide reductase, the target of HU, suggests that its transcriptional induction in response to HU is mainly dependent upon CaNrm1. Genetic epistasis analysis suggests that CaNrm1 interacts with the SBF and MBF transcription factors in S. cerevisiae and with the MBF functional homolog in C. albicans. At the transcription level, deletion of CaNRM1 causes an induction of many G1 and G1/S-specific genes. Induction of the HSGs is dampened under certain conditions in the Canrm1-/- mutant, suggesting that the cell cycle transcription program influences the morphogenetic transcription program of C. albicans. One aspect of the characterization of the C. albicans Whi5/Nrm1 gene was to examine how this molecule influences global gene expression. To that end, we isolated total RNA from log-phase nrm1-/nrm1- (as well as parent/background strain) cells in two independent replicate experiments. These samples were processed, labeled, and subsequently used for hybridization of custom C. albicans Affymetrix arrays.

2012-01-01 | E-GEOD-20612 | biostudies-arrayexpress

DNA replication stress differentially regulates G1/S genes via Rad53-dependent inactivation of Nrm1

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Differential regulation of SBF and MBF target genes by genotoxic stress occurs via Rad53-dependent inactivation of the MBF correpressor Nrm1

Project description:MBF and SBF transcription factors regulate a large family of coordinately expressed G1/S genes required for early cell cycle functions including DNA replication and repair. SBF is inactivated upon S phase entry by Clb/CDK whereas MBF targets are repressed by the corepressor, Nrm1. Using genome-wide expression analysis, we show that genotoxic stress during S phase specifically induces MBF-regulated genes via direct phosphorylation of Nrm1 by Rad53, the effector checkpoint kinase, and prevents its binding to MBF target promoters. Interestingly, some previously defined targets of SBF, including Swe1, are activated by replication stress. Swe1 undergoes a transcription factor exchange leading to its repression by Nrm1/MBF, which renders it sensitive to derepression by the S phase checkpoint. We conclude that MBF-regulated genes are distinguished from SBF-regulated genes by their sensitivity to activation by the S phase checkpoint, thereby, providing an effective mechanism for enhancing DNA replication and repair and promoting genome stability. Modified Loop Time-series design, time points at 0, 30, 45, 60 and 75 minutes. Conditions are untreated (UT), methyl methane sulfonate (MMS-0.033%), camptothecin (CPT-50uM), and hydroxyurea (HU-0.2M)

2012-02-15 | E-GEOD-33695 | biostudies-arrayexpress

Candida albicans

Project description:Role of a Candida albicans Whi5/Nrm1 homolog in cell cycle and hyphal-specific gene expression

| PRJNA124791 | ENA

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Transcriptional and chromatin-based partitioning mechanisms uncouple protein scaling from cell size

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Project description:The cell cycle is thought to be initiated by cyclin-dependent kinases (Cdk) inactivating transcriptional inhibitors of cell cycle gene-expression. In budding yeast, the G1 cyclin Cln3-Cdk1 complex is thought to directly phosphorylate Whi5, thereby releasing the transcription factor SBF and committing cells to division. Here, we report that Cln3-Cdk1 does not phosphorylate Whi5, but instead phosphorylates the RNA Polymerase II subunit Rpb1’s C-terminal domain (CTD) on S5 of its heptapeptide repeats. Cln3-Cdk1 binds SBF-regulated promoters(8) and Cln3’s function can be performed by the canonical S5 kinase Ccl1-Kin28 when synthetically recruited to SBF. Thus, Cln3-Cdk1 triggers cell division by phosphorylating Rpb1 at SBF-regulated promoters to promote transcription. Our findings blur the distinction between cell cycle and transcriptional Cdks to highlight the ancient relationship between these processes.

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