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Environmental induction of white-opaque switching in Candida albicans.

ABSTRACT: Candida albicans strains that are homozygous at the mating type locus (MTLa or MTLalpha) can spontaneously switch at a low frequency from the normal yeast cell morphology (white) to an elongated cell type (opaque), which is the mating-competent form of the fungus. The ability to switch reversibly between these two cell types also contributes to the pathogenicity of C. albicans, as white and opaque cells are differently adapted to specific host niches. We found that in strain WO-1, a strain in which genomic alterations have occurred, but not in other tested strains, switching from the white to the opaque phase can also be induced by environmental conditions. Transient incubation of white cells under anaerobic conditions programmed the cells to switch en masse to the opaque phase. The anaerobic induction of white-opaque switching was controlled by the transcription factor CZF1, which in heterozygous MTLa/alpha cells regulates filamentous growth under embedded, hypoxic conditions. Intriguingly, passage of white cells of strain WO-1 through the mouse intestine, a host niche in which the cells are likely to be exposed to anaerobic conditions, resulted in a strongly increased frequency of switching to the opaque phase. These results demonstrate that white-opaque switching is not only a spontaneous process but, in combination with genomic alterations, can also be induced by environmental signals, suggesting that switching and mating of C. albicans may occur with high efficiency in appropriate niches within its human host.

SUBMITTER: Ramirez-Zavala B

PROVIDER: S-EPMC2405950 | biostudies-literature |

REPOSITORIES: biostudies-literature

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TOS9 regulates white-opaque switching in Candida albicans.

Project description:In Candida albicans, the a1-alpha2 complex represses white-opaque switching, as well as mating. Based upon the assumption that the a1-alpha2 corepressor complex binds to the gene that regulates white-opaque switching, a chromatinimmunoprecipitation-microarray analysis strategy was used to identify 52 genes that bound to the complex. One of these genes, TOS9, exhibited an expression pattern consistent with a "master switch gene." TOS9 was only expressed in opaque cells, and its gene product, Tos9p, localized to the nucleus. Deletion of the gene blocked cells in the white phase, misexpression in the white phase caused stable mass conversion of cells to the opaque state, and misexpression blocked temperature-induced mass conversion from the opaque state to the white state. A model was developed for the regulation of spontaneous switching between the opaque state and the white state that includes stochastic changes of Tos9p levels above and below a threshold that induce changes in the chromatin state of an as-yet-unidentified switching locus. TOS9 has also been referred to as EAP2 and WOR1.

| S-EPMC1595353 | biostudies-literature

CO(2) regulates white-to-opaque switching in Candida albicans.

Project description:To mate, Candida albicans must undergo homozygosis at the mating type-like locus MTL[1, 2], then switch from the white to opaque phenotype [3, 4]. Paradoxically, when opaque cells are transferred in vitro to 37 degrees C, the temperature of their animal host, they switch en masse to white [5-7], suggesting that their major niche might not be conducive to mating. It has been suggested that pheromones secreted by opaque cells of opposite mating type [8] or the hypoxic condition of host niches [9, 10] stabilize opaque cells. There is, however, an additional possibility, namely that CO(2), which achieves levels in the host 100 times higher than in air [11-13], stabilizes the opaque phenotype. CO(2) has been demonstrated to regulate the bud-hypha transition in C. albicans[14, 15], expression of virulence genes in bacteria [16], and mating events in Cryptococcus neoformans[14, 17]. We tested the possibility that CO(2) stabilizes the opaque phenotype, and found that physiological levels of CO(2) induce white-to-opaque switching and stabilize the opaque phenotype at 37 degrees C. It exerts this control equally under anaerobic and aerobic conditions. These results suggest that the high levels of CO(2) in the host induce and stabilize the opaque phenotype, thus facilitating mating.

| S-EPMC2667266 | biostudies-literature

Interlocking transcriptional feedback loops control white-opaque switching in Candida albicans.

Project description:The human pathogen Candida albicans can assume either of two distinct cell types, designated "white" and "opaque." Each cell type is maintained for many generations; switching between them is rare and stochastic, and occurs without any known changes in the nucleotide sequence of the genome. The two cell types differ dramatically in cell shape, colony appearance, mating competence, and virulence properties. In this work, we investigate the transcriptional circuitry that specifies the two cell types and controls the switching between them. First, we identify two new transcriptional regulators of white-opaque switching, Czf1 and white-opaque regulator 2 (Wor2). Analysis of a large set of double mutants and ectopic expression strains revealed genetic relationships between CZF1, WOR2, and two previously identified regulators of white-opaque switching, WOR1 and EFG1. Using chromatin immunoprecipitation, we show that Wor1 binds the intergenic regions upstream of the genes encoding three additional transcriptional regulators of white-opaque switching (CZF1, EFG1, and WOR2), and also occupies the promoters of numerous white- and opaque-enriched genes. Based on these interactions, we have placed these four genes in a circuit controlling white-opaque switching whose topology is a network of positive feedback loops, with the master regulator gene WOR1 occupying a central position. Our observations indicate that a key role of the interlocking feedback loop network is to stably maintain each epigenetic state through many cell divisions.

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pH Regulates White-Opaque Switching and Sexual Mating in Candida albicans.

Project description:As a successful commensal and pathogen of humans, Candida albicans encounters a wide range of environmental conditions. Among them, ambient pH, which changes frequently and affects many biological processes in this species, is an important factor, and the ability to adapt to pH changes is tightly linked with pathogenesis and morphogenesis. In this study, we report that pH has a profound effect on white-opaque switching and sexual mating in C. albicans. Acidic pH promotes white-to-opaque switching under certain culture conditions but represses sexual mating. The Rim101-mediated pH-sensing pathway is involved in the control of pH-regulated white-opaque switching and the mating response. Phr2 and Rim101 could play a major role in acidic pH-induced opaque cell formation. Despite the fact that the cyclic AMP (cAMP) signaling pathway does not play a major role in pH-regulated white-opaque switching and mating, white and opaque cells of the cyr1/cyr1 mutant, which is defective in the production of cAMP, showed distinct growth defects under acidic and alkaline conditions. We further discovered that acidic pH conditions repressed sexual mating due to the failure of activation of the Ste2-mediated α-pheromone response pathway in opaque A: cells. The effects of pH changes on phenotypic switching and sexual mating could involve a balance of host adaptation and sexual reproduction in C. albicans.

| S-EPMC4621312 | biostudies-literature

TOS9 Regulates White-Opaque Switching in Candida albicans

Project description:In Candida albicans, the a1-alpha2 complex represses white-opaque switching as well as mating. A ChIP-chip strategy was, therefore, used to screen for genes with a1-alpha2 binding sites and expression patterns consistent with a master switch gene (MSG). Of 51 genes identified with an a1-alpha2 binding site, one gene, TOS9, also referred to as EAP2, exhibited an expression pattern consistent with a MSG. TOS9 is expressed in opaque, not white a/a and alpha/alpha cells and Tos9p localizes to the opaque cell nucleus. Deletion of TOS9 blocks cells in the white phase, and misexpression in the white phase of the parent tos9+/tos9+ strain results in mass conversion to opaque. Expression of TOS9 under control of a MET promoter rescues the TOS9 null mutant tos9-/tos9- phenotype. Temperature-induced mass conversion of opaque to white in the parent strain results in the immediate cessation of TOS9 transcription, and loss of Tos9p prior to the point of commitment to white (the switch event), which occurs at the time of the second cell doubling. Misexpression of TOS9, as well as inhibition of the second round of DNA replication inhibits the temperature-induced switch from opaque to white. Based on these observations, a model is developed for the regulation and role of TOS9 in switching. Keywords: ChIP chip

2006-09-19 | GSE5493 | GEO

Structure of the transcriptional network controlling white-opaque switching in Candida albicans.

Project description:The human fungal pathogen Candida albicans can switch between two phenotypic cell types, termed 'white' and 'opaque'. Both cell types are heritable for many generations, and the switch between the two types occurs epigenetically, that is, without a change in the primary DNA sequence of the genome. Previous work identified six key transcriptional regulators important for white-opaque switching: Wor1, Wor2, Wor3, Czf1, Efg1, and Ahr1. In this work, we describe the structure of the transcriptional network that specifies the white and opaque cell types and governs the ability to switch between them. In particular, we use a combination of genome-wide chromatin immunoprecipitation, gene expression profiling, and microfluidics-based DNA binding experiments to determine the direct and indirect regulatory interactions that form the switch network. The six regulators are arranged together in a complex, interlocking network with many seemingly redundant and overlapping connections. We propose that the structure (or topology) of this network is responsible for the epigenetic maintenance of the white and opaque states, the switching between them, and the specialized properties of each state.

| S-EPMC3888361 | biostudies-literature

The Glyoxylate Cycle Is Involved in White-Opaque Switching in Candida albicans.

Project description:Candida albicans is a commensal yeast that inhabits the gastrointestinal tract of humans. The master regulator of the white-opaque transition WOR1 has been implicated in the adaptation to this commensal status. A proteomic analysis of cells overexpressing this transcription factor (WOR1OE) suggested an altered metabolism of carbon sources and a phenotypic analysis confirmed this alteration. The WOR1OE cells are deficient in using trehalose and xylose and are unable to use 2C sources, which is consistent with a reduction in the amount of Icl1, the isocitrate lyase enzyme. The icl1Δ/Δ mutants overexpressing WOR1 are deficient in the production of phloxine B positive cells, a main characteristic of opaque cells, a phenotype also observed in mating type hemizygous mtla1Δ icl1Δ/Δ cells, suggesting the involvement of Icl1 in the adaptation to the commensal state. In fact, icl1Δ/Δ cells have reduced fitness in mouse gastrointestinal tract as compared with essentially isogenic heterozygous ICL1/icl1Δ, but overproduction of WOR1 in an icl1Δ/Δ mutant does not restore fitness. These results implicate the glyoxylate shunt in the adaptation to commensalism of C. albicans by mechanisms that are partially independent of WOR1.

| S-EPMC8304919 | biostudies-literature

Sac7 and Rho1 regulate the white-to-opaque switching in Candida albicans.

Project description:Candida albicans cells homozygous at the mating-type locus stochastically undergo the white-to-opaque switching to become mating-competent. This switching is regulated by a core circuit of transcription factors organized through interlocking feedback loops around the master regulator Wor1. Although a range of distinct environmental cues is known to induce the switching, the pathways linking the external stimuli to the central control mechanism remains largely unknown. By screening a C. albicans haploid gene-deletion library, we found that SAC7 encoding a GTPase-activating protein of Rho1 is required for the white-to-opaque switching. We demonstrate that Sac7 physically associates with Rho1-GTP and the constitutively active Rho1G18V mutant impairs the white-to-opaque switching while the inactive Rho1D124A mutant promotes it. Overexpressing WOR1 in both sac7Δ/Δ and rho1 G18V cells suppresses the switching defect, indicating that the Sac7/Rho1 module acts upstream of Wor1. Furthermore, we provide evidence that Sac7/Rho1 functions in a pathway independent of the Ras/cAMP pathway which has previously been positioned upstream of Wor1. Taken together, we have discovered new regulators and a signaling pathway that regulate the white-to-opaque switching in the most prevalent human fungal pathogen C. albicans.

| S-EPMC5772354 | biostudies-literature

Coordinate regulation of two opaque-phase-specific genes during white-opaque switching in Candida albicans.

Project description:Cells of Candida albicans WO-1 switch spontaneously and frequently between a white and an opaque CFU. Recently, an opaque-phase-specific cDNA, PEP1, was cloned and was demonstrated to code for a pepsinogen. By using a differential hybridization screen, a second opaque-phase-specific cDNA, Op4, has been isolated and its corresponding gene has been cloned. Op4 is coordinately regulated with PEP1 but resides on a different chromosome. During temperature-induced mass conversion from opaque to white, transcription of PEP1 and Op4 is immediately inhibited by the increase in temperature, but transcription of both genes can be rapidly reestablished by a downshift in temperature prior to phenotypic commitment. However, the capacity to rapidly induce both PEP1 and Op4 is lost coincidentally with the second semisynchronous round of cell division and phenotypic commitment during mass conversion. Op4 shows no significant base or amino acid sequence homology with a known gene or protein, respectively. However, the deduced Op4 protein exhibits several interesting characteristics, including a hydrophobic amino terminus with 26 amino acids, a pI of 10.73 for the last 100 amino acids, two serine repeats adjacent to alanine repeats, and the potential for alpha-helical conformation within the alanine-rich sequences. No genomic reorganization was evident in the proximity of Op4 during transcriptional activation and deactivation accompanying the white-opaque transition.

| S-EPMC280771 | biostudies-other

Candida albicans White-Opaque Switching Influences Virulence but Not Mating during Oropharyngeal Candidiasis.

Project description:The capacity of Candida albicans to switch reversibly between the white phenotype and the opaque phenotype is required for the fungus to mate. It also influences virulence during hematogenously disseminated candidiasis. We investigated the roles of the mating type loci (MTL) and white-opaque switching in the capacity of C. albicans to mate in the oropharynx and cause oropharyngeal candidiasis (OPC). When immunosuppressed mice were orally infected with mating-competent opaque a/a and ?/? cells either alone or mixed with white cells, no detectable mating occurred, indicating that the mating frequency was less than 1.6 × 10-6 Opaque cells were also highly attenuated in virulence; they either were cleared from the oropharynx or switched to the white phenotype during OPC. Although there were strain-to-strain differences in the virulence of white cells, they were consistently more virulent than opaque cells. In vitro studies indicated that relative to white cells, opaque cells had decreased capacity to invade and damage oral epithelial cells. The reduced invasion of at least one opaque strain was due to reduced surface expression of the Als3 invasin and inability to activate the epidermal growth factor receptor, which is required to stimulate the epithelial cell endocytic machinery. These results suggest that mating is a rare event during OPC because opaque cells have reduced capacity to invade and damage the epithelial cells of the oral mucosa.

| S-EPMC5964503 | biostudies-literature

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