The zinc cluster transcription factor Ahr1p directs Mcm1p regulation of Candida albicans adhesion
ABSTRACT: Biofilm development by Candida albicans requires cell adhesion for the initial establishment of the biofilm and the continued stability after hyphal development occurs; however, the regulation of the process has not been fully established. Using chromatin immunoprecipitation coupled to microarray analysis (ChIP-chip) we have characterized a regulon containing the Mcm1p factor that is required for the initial surface adhesion during biofilm formation. In the yeast Saccharomyces cerevisiae several Mcm1p regulons have been characterized in which regulatory specificity is achieved through co-factors binding a sequence adjacent to the Mcm1p-binding site. This new Mcm1p regulon in C. albicans also requires a co-factor, which we identify as the transcription factor Ahr1p. However, in contrast to the other yeast regulons, Ahr1p alone binds the target promoters, which include several key adhesion genes, and recruits Mcm1p to these sites. Through transcription profiling and qPCR analysis, we demonstrate that this Ahr1p-Mcm1p complex directly activates these adhesion genes. When the regulon was disrupted by deleting AHR1, the strain displayed reduced adherence to a polystyrene surface. We also demonstrate a role for the regulon in hyphal growth and in virulence. Our work thus establishes a new mechanism of Mcm1p-directed regulation distinct from those observed for other Mcm1p co-regulators. We performed genome wide occupancy experiments (YPD, 30oC) with Ahr1p and Mcm1p to determine their binding sites. To confirm an interaction between the two factors we also performed genome wide occupancy with Mcm1p in an ahr1 deletion strain. To complement with genome wide occupancy experiments, we performed a transcription profile with an ahr1 deletion strain under yeast conditions (YPD, 30oC).
Project description:Biofilm development by Candida albicans requires cell adhesion for the initial establishment of the biofilm and the continued stability after hyphal development occurs; however, the regulation of the process has not been fully established. Using chromatin immunoprecipitation coupled to microarray analysis (ChIP-chip) we have characterized a regulon containing the Mcm1p factor that is required for the initial surface adhesion during biofilm formation. In the yeast Saccharomyces cerevisiae several Mcm1p regulons have been characterized in which regulatory specificity is achieved through co-factors binding a sequence adjacent to the Mcm1p-binding site. This new Mcm1p regulon in C. albicans also requires a co-factor, which we identify as the transcription factor Ahr1p. However, in contrast to the other yeast regulons, Ahr1p alone binds the target promoters, which include several key adhesion genes, and recruits Mcm1p to these sites. Through transcription profiling and qPCR analysis, we demonstrate that this Ahr1p-Mcm1p complex directly activates these adhesion genes. When the regulon was disrupted by deleting AHR1, the strain displayed reduced adherence to a polystyrene surface. We also demonstrate a role for the regulon in hyphal growth and in virulence. Our work thus establishes a new mechanism of Mcm1p-directed regulation distinct from those observed for other Mcm1p co-regulators. Overall design: We performed genome wide occupancy experiments (YPD, 30oC) with Ahr1p and Mcm1p to determine their binding sites. To confirm an interaction between the two factors we also performed genome wide occupancy with Mcm1p in an ahr1 deletion strain. To complement with genome wide occupancy experiments, we performed a transcription profile with an ahr1 deletion strain under yeast conditions (YPD, 30oC).
Project description:Compared to other model organisms and despite the clinical relevance of the pathogenic yeast Candida albicans, no comprehensive analysis has been done to provide experimental support of its in silico-based genome annotation. Here we have undertaken a genome-wide experimental annotation to accurately uncover the transcriptional landscape of the pathogenic yeast C. albicans using strand-specific high-density tiling arrays. RNAs were purified from cells growing under conditions relevant to C. albicans pathogenicity, including biofilm, lab-grown yeast and serum-induced hyphae as well as cells isolated from the mouse caecum. This work provides a genome-wide experimental validation for a large number of predicted ORFs for which transcription had not been detected by other approaches. Additionally, we identified more than 2000 novel transcriptional segments, including new ORFs and exons, non-coding RNAs (ncRNA) as well as convincing cases of antisense gene transcription. We also characterized the 5’- and 3’-untranslated regions (UTR) of expressed ORFs, and established that genes with long 5’UTRs are significantly enriched in regulatory functions controlling filamentous growth. Furthermore, we found that genomic regions adjacent to telomeres harbor a cluster of expressed ncRNAs. To validate and confirm new ncRNA candidates, we adapted an iterative strategy combining both genome-wide occupancy of the different subunits of RNA polymerases I, II and III, and expression data. This comprehensive approach allowed the identification of different families of ncRNA. In summary, we provide a comprehensive expression atlas that covers relevant C. albicans pathogenic developmental stages in addition to a discovery of new ORF and non-coding genetic elements. We have undertaken a genome-wide experimental annotation to accurately uncover the transcriptional landscape of the pathogenic yeast C. albicans using strand-specific high-density tiling arrays. RNAs were purified from cells growing under conditions relevant to Candida albicans pathogenicity, including biofilm, lab-grown yeast and serum-induced hyphae as well as cells isolated from the mouse caecum. We also adapted a strategy in which genome-wide occupancy of different subunits of RNA polymerases (RNAP) I, II and III, is combined with expression data to annotate ncRNAs resulting from real transcriptional events. For this purpose we have performed ChIP-chip of subunits that represent the three RNAP machines in C. albicans cells growing in rich media (YPD) at 30°C. In this study, we performed peak detection only for RNA Polymerase III (Rpc82p). All detected peaks and their genomic features are included as a supplementary file on the Sample record (GSM561024).
Project description:We have focused our investigation on the characterization of the role of the fungal specific SWI/SNF subunit, Snf6. Our data show that, although the C. albicans subunit has only limited sequence similarity to other fungal orthologs, Snf6 was copurified with SWI/SNF complex subunits including the catalytic ATPase subunit, Snf2. We show that Snf6 plays a critical role in biological processes that are essential for fungal pathogenesis including carbon metabolic flexibility, stress response and morphogenesis. The Snf6 regulon was determined by combining both genome-wide location (ChIP-chip) and transcriptional profiling (microarrays) to identify targets of the SWI/SNF complex under both yeast- and hyphal-promoting conditions. Overall design: We performed genome wide occupancy experiments (YPD, 30oC and YPD, 37oC ) with Snf6p to determine their binding sites. To complement with genome wide occupancy experiments, we performed a transcription profile with an snf6 Grace strain under yeast and hyphae conditions (YPD+/- tet, 30oC and YPD+10%serum +/- tet , 37oC ).
Project description:Deleting components of the Arp2/3 complex in Candida albicans resulted in a global lack of hyphal specific gene induction. This observation suggests that the failure in hyphal growth of Arp2/3 complex mutants could be a result of failure to activate hyphal specific genes. If the hyphal defect was primarily due to failure to activate gene expression, de-repressing hyphal-specific gene expression by deleting the NRG1 repressor could potentially suppress the defect, as deletion of NRG1 leads to constitutive filamentous growth even in the absence of any hyphal induction signals (Garcia-Sanchez et al., 2005, Kadosh & Johnson, 2005). We therefore created an nrg1Δ/Δarp2Δ/Δ mutant. When grown under non-inducing conditions, nrg1Δ/Δarp2Δ/Δ cells showed the arp2Δ/Δ mutant morphology of round and swollen cells. When induced for hyphal growth, nrg1Δ/Δarp2Δ/Δ cells also exhibited the arp2Δ/Δ cell morphology and did not form hyphae even after extended overnight incubation times. To determine if the hyphal-specific genes are de-repressed in the nrg1Δ/Δarp2Δ/Δ mutant, we performed transcript profiling. We compared the nrg1Δ/Δarp2Δ/Δ mutant grown under hyphal conditions to the arp2Δ/Δ mutant grown under the same conditions (10% serum, 37C, three hours), and found that a significant number of hyphal-specific genes that are normally induced when WT cells are undergoing the yeast to hyphae switch (WT-HY) showed greater expression in the nrg1Δ/Δarp2Δ/Δ mutant compared to arp2Δ/Δ cells (p-value 4.9x10-9). When we examined the set of NRG1-dependent hyphal-specific genes previously identified (Kadosh & Johnson, 2005), we found that seven of 28 genes (HYR1, SAP5, SAP4, KIP4, ORF19.6079, ALS3 and UME6) showed significantly increased expression (≥ 2 fold) in nrg1Δ/Δarp2Δ/Δ cells compared to arp2Δ/Δ cells, while a further four genes (IHD1, CBP1, ORF19.6705 and ALS10) showed moderately increased expression between 1.5 and 2-fold. Thus, while deleting a transcriptional repressor of the filamentation program leads to de-repression of many hyphal genes, the entire regulated gene set is not de-repressed; this presumably reflects the complex interplay that different transcriptional (co-) repressors exert on the yeast-to-hyphae transition (Garcia-Sanchez et al., 2005, Kadosh & Johnson, 2005). We further found that despite the increased induction of some hyphal genes in the nrg1Δ/Δarp2Δ/Δ mutant, a few of those genes are not as highly induced as in WT cells. One gene that was induced in both the ‘nrg1Δ/Δarp2Δ/Δ vs arp2Δ/Δ’ and the ‘nrg1Δ/Δarp2Δ/Δ vs WT’-comparisons is UME6, a recently identified key regulator of the hyphal program (Banerjee et al., 2008, Zeidler et al., 2009). Interestingly, although constitutive over-expression of UME6 in WT cells resulted in constitutive filamentous growth even in the absence of hyphae signals (Carlisle et al., 2009), the increased expression level of UME6 in the nrg1Δ/Δarp2Δ/Δ mutant is not sufficient to restore filamentation in the absence of a functional Arp2/3 complex. Thus despite partial de-repression of the hyphal program, hyphae do not form, making it likely other roles of the Arp2/3 complex, such as its function in actin patch formation and actin branching, are required for hyphal development.
Project description:The capacity to sense and transduce temperature signals pervades all aspects of biology, and temperature exerts powerful control over the development and virulence of diverse pathogens. In the leading fungal pathogen of humans, Candida albicans, temperature has a profound impact on morphogenesis, a key virulence trait. Many cues that induce the transition from yeast to filamentous growth are contingent on a minimum temperature of 37ºC, while further elevatation to 39ºC serves as an independent inducing cue. The molecular chaperone Hsp90 is a key regulator of C. albicans temperature-dependent morphogenesis, as induction of filamentous growth requires relief from Hsp90-mediated repression of the morphogenetic program. Compromise of Hsp90 function genetically, pharmacologically, or by elevated temperature induces filamentation in a manner that depends on protein kinase A (PKA) signaling, but is independent of the terminal transcription factor, Efg1. Here, we determine that despite morphological and regulatory differences, inhibition of Hsp90 induces a transcriptional profile similar to that induced by other filamentation cues, and does so in a manner that is independent of Efg1. Further, we identify Hms1 as a transcriptional regulator required for morphogenesis induced by elevated temperature or compromise of Hsp90 function. Hms1 functions downstream of the cyclin Pcl, and the cyclin-dependent kinase Pho85, both of which are required for temperature-dependent filamentation. Upon Hsp90 inhibition, Hms1 binds to DNA elements involved in filamentous growth, including UME6 and RBT5, and regulates their expression, providing a mechanism through which Pho85, Pcl1, and Hms1 govern morphogenesis. Consistent with the importance of morphogenetic flexibility with virulence, deletion of C. albicans HMS1 attenuates virulence in a metazoan model of infection. Thus, we establish a new mechanism through which Hsp90 orchestrates C. albicans morphogenesis, and define novel regulatory circuitry governing a temperature-dependent developmental program, with broad implications for temperature sensing and virulence of microbial pathogens. Genome-wide occupancy experiments (Chip-CHIP) of FLAG-tagged Hms1p from cells grown in the presence or absence of geldanamycin (GldA). Co-precipitating genomic DNA was labelled and hybridized to whole-genome tiling arrays.
Project description:This SuperSeries is composed of the following subset Series: GSE19565: Arp2/3 complex mutants show a pronounced lack of hyphal specific gene expression in Candida albicans GSE19582: Partial de-repression of the hyphal program does not restore hyphae formation in absence of a functional Arp2/3 complex Refer to individual Series
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 arp2Δ/Δ and arp2Δ/Δarp3Δ/Δ 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 30°C for three hours) or hyphal induction (YPD + 10% FBS at 37°C for three hours) and compared transcriptional consequences of deleting ARP2 to MYO5 and SLA2 microarray data sets (Oberholzer et al., 2006).
Project description:Candida albicans is an opportunistic fungal pathogen capable of causing superficial and systemic infections in humans. The ability of C. albicans to switch between various morphological forms depending on its host environment is thought to contribute to its virulence. Filamentous growth states are associated with tissue invasion, biofilm formation, evasion of innate host defences and mating. Although the mechanisms of activation of filamentous growth pathways are well understood, less is known about which factors control the negative regulation of filamentation. In this study, we have identified a previously uncharacterized Orf that shares sequence similarity with Saccharomyces cerevisiae Dig1p and Dig2p. Deletion of the gene encoding this Orf triggers invasive growth in C. albicans and so we have retained the yeast designation of Dig1 (for Down-regulation of Invasive Growth). Mutants lacking CaDIG1 form cultures of hyperpolarized cells, form robust biofilms, are highly invasive in vitro but not in vivo and are constitutively activated for the pheromone response. Deletion of key transcription factors that act downstream of Dig1p provide evidence to suggest that CaDig1 regulates filamentation and mating through multiple signalling pathways. Transcriptional analysis of the C. albicans dig1Δ/dig1Δ homozygous mutant versus the wild type (SN148) in the MTLa/alpha background. Four biological replicates of the mutant and the wild type were included in the analysis. Samples were grown at 30 °C in YPD medium plus uridine
Project description:The cyclic AMP-protein kinase A pathway has a central role in the biology of Candida albicans, a prominent fungal pathogen of humans. The two catalytic subunits for cyclic AMP-dependent protein kinase, Tpk1 (orf19.4892) and Tpk2 (orf19.2277), have divergent roles, and most studies indicate a more pronounced role for Tpk2. Here we dissect two Tpk1-responsive properties: adherence and cell wall integrity. Homozygous tpk1/tpk1 mutants are hyperadherent, and a Tpk1 defect enables biofilm formation in the absence of Bcr1, a central transcriptional regulator of biofilm adhesins. Microarray analysis revealed an enrichment for cell wall and surface functions among Tpk1-repressed genes, and overexpression of individual target genes indicates that cell surface proteins Als1, Als2, Als4, Csh1, and Csp37 contribute to Tpk1-regulated adherence. Tpk1 is also required for cell wall integrity, but has no role in the cell wall integrity gene expression response. Interestingly, increased expression of the adhesin gene ALS2 conferred a cell wall defect, as manifested in hypersensitivity to the cell wall inhibitor caspofungin and a shallow cell wall structure. Our findings indicate that Tpk1 has a central role in C. albicans cell wall properties that is exerted through repression of select cell surface protein genes. Two-color microarrays using a closed-loop experimental design to determine the effects of a ∆tpk1 deletion in the absence or presence of the antifungal Caspofungin (CF)
Project description:The polymorphic yeast Candida albicans exists in blastospore and filamentous forms. The switch from one morphological state to the other coincides with the expression of virulence factors, which makes the yeast-to-hypha transition an attractive target for the development of new antifungal agents. Because an untapped therapeutic potential resides in small molecules that hinder C. albicans filamentation, we characterized the inhibitory effect of conjugated linoleic acid (CLA) on hyphal growth and addressed its mechanism of action. CLA inhibited hyphal growth in a dose-dependent fashion, in both liquid- and solid-inducing media. The fatty acid blocked germ tube formation and impeded hyphal elongation. Global transcriptional profiling revealed that CLA downregulated the expression of hypha-specific genes and abrogated the induction of several morphogenesis regulators, including RAS1, TEC1 and UME6. CLA’s repressive effect on TEC1 expression was Ras1-dependent, but Efg1-independent. CLA treatment resulted in the delocalization of Ras1 and its degradation, resulting in the downregulation of the Ras1-cAMP-PKA signaling pathway. This study provides the biological and molecular explanations that underlie CLA’s ability to inhibit hyphal growth in C. albicans. Two-color experimental design that consistently used growth in Spider Media at 30℃ as the control. We tested the effect of high temperature as well as the effect of adding 100 mµ CLA at either low or high temperature. RNA from each replicate came from independent cultures.