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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

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 co-repressor, Nrm1. Using genome-wide expression analysis of cells treated with methyl methane sulfonate (MMS), hydroxyurea (HU) or camptothecin (CPT), we show that genotoxic stress during S phase specifically induces MBF-regulated genes. This occurs via direct phosphorylation of Nrm1 by Rad53, the effector checkpoint kinase, which prevents its binding to MBF target promoters. 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.

2012-02-15 | GSE33695 | GEO

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

NRS1, a nitrogen source-regulated microprotein, confers an alternative mechanism of G1/S transcriptional activation in budding yeast

Project description:Commitment to cell division at the end of G1 phase, termed Start in the budding yeast Saccharomyces cerevisiae, is strongly influenced by nutrient availability. To identify newdominant activators of Start that might operate under different nutrient conditions, we screened a genome-wide ORF overexpression library for genes that bypass a Start arrest caused by absence of the G1 cyclin Cln3 and the transcriptional activator Bck2. We recovered a hypothetical gene YLR053c, renamed NRS1 for Nitrogen-responsive Start Regulator 1, which encodes a poorly characterized 108 amino acid microprotein. Endogenous NRS1 was nuclear-localized, restricted to poor nitrogen conditions, induced upon mTORC1 inhibition, and cell cycle-regulated with a peak at Start. NRS1 interacted genetically with SWI4 and SWI6, which encode the master G1/S transcription factor complex SBF. Correspondingly, NRS1 physically interacted with Swi4 and Swi6 and was localized to G1/S promoter DNA. NRS1 exhibited inherent transactivation activity and fusion of NRS1 to the SBF inhibitor Whi5 was sufficient to suppress other Start defects. NRS1 appears to be a recently evolved microprotein that rewires the G1/S transcriptional machinery under poor nutrient conditions.

2021-08-25 | PXD018681 | Pride

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

Project description:Biosynthesis scales with cell size such that protein concentrations generally remain constant as cells grow. As an exception, synthesis of the cell-cycle inhibitor Whi5 ‘sub-scales’ with cell size so that its concentration is lower in larger cells to promote cell-cycle entry. Here, we find that a transcriptional control uncouples Whi5 synthesis from cell size and, screening for similar genes, identify histones as the major class of sub-scaling transcripts besides WHI5. Histone synthesis is thereby matched to genome content rather than cell size. Such sub-scaling proteins are challenged by asymmetric cell division because proteins are typically partitioned in proportion to new-born cell volume. To avoid this fate, Whi5 uses chromatin-binding to partition similar protein amounts to each new-born cell regardless of cell size. Finally, disrupting both Whi5 synthesis and chromatin-based partitioning compromises G1 size control. Thus, specific transcriptional and partitioning mechanisms determine protein sub-scaling to control cell size.

2021-12-01 | GSE167842 | GEO

Arp2/3 complex mutants show a pronounced lack of hyphal specific gene expression in Candida albicans

Project description:Candida albicans is a diploid fungal pathogen lacking a defined complete sexual cycle, and thus has been refractory to standard forward genetic analysis. Instead, transcription profiling and reverse genetic strategies based on Saccharomyces cerevisiae have typically been used to link genes to functions. To overcome restrictions inherent in such indirect approaches, we have investigated a forward genetic mutagenesis strategy based on the UAU1 technology. We screened 4700 random insertion mutants for defects in hyphal development, and linked two new genes (ARP2 and VPS52) to hyphal growth. Deleting ARP2 abolished hyphal formation, generated round and swollen yeast phase cells, disrupted cortical actin patches and blocked virulence in mice. The mutants also showed a global lack of induction of hyphae-specific genes upon the yeast-to-hyphae switch. Surprisingly, both arp2Î/Î and arp2Î/Îarp3Î/Î mutants were still able to endocytose FM4-64 and Lucifer Yellow, although as shown by time-lapse movies internalization of FM4-64 was somewhat delayed in mutant cells. Thus the non-essential role of the Arp2/3 complex discovered by forward genetic screening in C. albicans showed that uptake of membrane components from the plasma membrane to vacuolar structures is not dependent on this actin nucleating machinery. By forward genetic screening, we have identified genes that are essential for hyphal formation. One of the hits is the Arp2/3 complex, which is essential for hyphal formation, but not for viability in Candida albicans. To gain insights into cellular processes affected by disrupting Arp2/3 complex functions, we performed transcriptional profiling under yeast growth conditions (YPD at 30Â°C for three hours) or hyphal induction (YPD + 10% FBS at 37Â°C for three hours) and compared transcriptional consequences of deleting ARP2 to MYO5 and SLA2 microarray data sets (Oberholzer et al., 2006).

2010-10-08 | E-GEOD-19565 | biostudies-arrayexpress

Localized phosphorylation of RNA Polymerase II by G1 cyclin-Cdk promotes cell cycle entry

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.

2021-12-01 | GSE169271 | GEO

Budding yeast relies on qualitative G1 cyclin specificity to couple cell cycle progression with morphogenetic development

Project description:Two models have been put forward for cyclin-dependent kinase (Cdk) control of the cell cycle. In the qualitative model, cell cycle events are ordered by distinct substrate specificities associated with successive waves of G1, S and mitotic cyclins. Alternatively, the gradual quantitative rise of Cdk activity from G1 phase to mitosis could lead to ordered substrate phosphorylation at sequential thresholds. Here, we study the relative contributions of qualitative and quantitative Cdk control in the budding yeast S. cerevisiae. S-phase cyclins can be replaced by a single mitotic cyclin, albeit at the cost of reduced fitness. The single cyclin can in addition replace G1 cyclins to support ordered cell cycle progression, fulfilling key predictions of the quantitative model. However, single-cyclin cells fail to polarize or grow buds and thus cannot sustain proliferation. Our results suggest that budding yeast has become dependent on G1 cyclin specificity to couple cell cycle progression to essential morphogenetic events.

2021-08-23 | PXD022757 | Pride

A nitrogen source-regulated microprotein confers an alternative mechanism of G1/S transcriptional activation in budding yeast

Project description:Commitment to cell division at the end of G1 phase, termed Start in the budding yeast Saccharomyces cerevisiae, is strongly influenced by nutrient availability. To identify new dominant activators of Start that might operate under different nutrient conditions, we screened a genome-wide ORF overexpression library for genes that bypass a Start arrest caused by absence of the G1 cyclin Cln3 and the transcriptional activator Bck2. We recovered a hypothetical gene YLR053c, renamed NRS1 for Nitrogen-Responsive Start regulator 1, which encodes a poorly characterized 108 amino acid microprotein. Endogenous Nrs1 was nuclear-localized, restricted to poor nitrogen conditions, induced upon mTORC1 inhibition, and cell cycle-regulated with a peak at Start. NRS1 interacted genetically with SWI4 and SWI6, which encode subunits of the main G1/S transcription factor complex SBF. Correspondingly, Nrs1 physically interacted with Swi4 and Swi6 and was localized to G1/S promoter DNA. Nrs1 exhibited inherent transactivation activity and fusion of Nrs1 to the SBF inhibitor Whi5 was sufficient to suppress other Start defects. Nrs1 appears to be a recently evolved microprotein that rewires the G1/S transcriptional machinery under poor nutrient conditions.

2021-08-25 | GSE179366 | GEO

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