Unknown,Transcriptomics,Genomics,Proteomics

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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. 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.

ORGANISM(S): Candida albicans

SUBMITTER: Kathy Barker

PROVIDER: E-GEOD-20612 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs. We queried the yeast genome for DSBs after cells were treated with 200 mM hydroxyurea during S phase. Samples were collected from 1) cells synchronized in G1 phase by alpha factor; 2) cells released from G1 into medium containing 200 mM hydroxyurea for 1 h; 3) cells recovering in fresh medium without hydroxyurea for 1 h after the 1 h exposure to HU. These samples are referred to as G1, HU 1h, and R 1h, respectively. The strains from which the samples were collected are indicated following the time point, e.g. G1_MEC1 or R 1h_mec1. The experiment with mec1 was done twice (Experiments A and B) and that with MEC1 was done once (Experiment C). In addition, a control experiment of in vitro digestion with BamHI using the G1_mec1 sample (G1_BamHI) was performed.

Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs. We queried the yeast genome for gene expression after cells were treated with 200 mM hydroxyurea during S phase. Samples were collected from 1) cells synchronized in G1 phase by alpha factor; 2) cells released from G1 into medium containing 200 mM hydroxyurea for 1 h; 3) cells recovering in fresh medium without hydroxyurea for 30 and 60 min after the 1 h exposure to HU. These samples are referred to as G1, HU 1h, R30, and R60, respectively. The strains from which the samples were collected are indicated before the time point, e.g. mec1_G1 or MEC1_R30. Stranded mRNA libraries were prepared according to manufacturer's suggestion and sequenced on Illumina MiSeq with paired-end reads of 75 bp.

Project description:Cap1p, a transcription factor of the basic region-leucine zipper family, controls the oxidative stress response in Candida albicans. It was shown that alteration of the C-terminal cysteine-rich domain (CRD) of Cap1p results in nuclear retention and constitutive transcriptional activation. To further characterize the function of Cap1p in C. albicans, we used genome-wide location profiling (ChIP-on-chip), allowing the identification of Cap1p-transcriptional targets in vivo. Location profiling using a tiled-oligonucleotide DNA microarray identified 89 targets that were bound by Cap1p-HA3 or Cap1p-CSE-HA3 (binding ratio â¥ 2-fold, P â¤ 0.01). Strikingly, Cap1p binding was not only detected at the promoter region of its target genes but also at their 3'-end and within their open-reading frame. Overrepresented functional groups of Cap1p targets (P â¤ 0.02) included notably 11 genes involved in response to oxidative stress (CAP1, GLR1, TRX1, others), 13 genes involved in response to drug (PDR16, MDR1, FLU1, others) and 3 genes involved in regulation of nitrogen utilization (orf19.2693, orf19.3121 and GST3). Bioinformatic analyses suggested that Cap1p binds to the DNA motif 5'- MTKASTMA. Transcriptome analyses showed that increased expression of most of Cap1p targets accompanies Cap1p binding at these targets, indicating that Cap1p is a transcriptional activator. We conclude that, in addition to protecting the cell against oxidative stress, Cap1p appears to have other functions including drug resistance and the regulation of nitrogen utilization. The atypical binding pattern of Cap1p suggests that this transcription factor may associate with the transcriptional or the chromatin remodeling machinery to exert its activity. We performed three gene expression profile comparisons: (1) benomyl-induced gene expression in a strain containing wildtype CAP1 (CJD21/PMK-CAP1 +/- benomyl), (2) benomyl-induced gene expression in a strain where CAP1 is disrupted (CJD21/PMK +/- benomyl), and (3) gene expression in a strain containing a hyperactive allele of CAP1 compared to a strain containing wildtype CAP1 (CJD21/PMK-CAP1-CSE vs. CJD21/PMK-CAP1). There were three biological replicates (each drug-treated and untreated strain was grown/treated in three independent experiments). Since our Affymetrix platform requires each sample is hybridized on a separate chip, there is no dye-swapping. For each benomyl-treatment experiment (comparisons 1 and 2 above), the untreated (diluent-treated) samples are the reference samples. For comparison 3, the CJD21-PMK-CAP1 sample is the reference sample.

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

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