101
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Miranda I, Rocha R, Santos MC, Mateus DD, Moura GR, Carreto L, Santos MAS. A genetic code alteration is a phenotype diversity generator in the human pathogen Candida albicans. PLoS One 2007; 2:e996. [PMID: 17912373 PMCID: PMC1991585 DOI: 10.1371/journal.pone.0000996] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2007] [Accepted: 09/18/2007] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The discovery of genetic code alterations and expansions in both prokaryotes and eukaryotes abolished the hypothesis of a frozen and universal genetic code and exposed unanticipated flexibility in codon and amino acid assignments. It is now clear that codon identity alterations involve sense and non-sense codons and can occur in organisms with complex genomes and proteomes. However, the biological functions, the molecular mechanisms of evolution and the diversity of genetic code alterations remain largely unknown. In various species of the genus Candida, the leucine CUG codon is decoded as serine by a unique serine tRNA that contains a leucine 5'-CAG-3'anticodon (tRNA(CAG)(Ser)). We are using this codon identity redefinition as a model system to elucidate the evolution of genetic code alterations. METHODOLOGY/PRINCIPAL FINDINGS We have reconstructed the early stages of the Candida genetic code alteration by engineering tRNAs that partially reverted the identity of serine CUG codons back to their standard leucine meaning. Such genetic code manipulation had profound cellular consequences as it exposed important morphological variation, altered gene expression, re-arranged the karyotype, increased cell-cell adhesion and secretion of hydrolytic enzymes. CONCLUSION/SIGNIFICANCE Our study provides the first experimental evidence for an important role of genetic code alterations as generators of phenotypic diversity of high selective potential and supports the hypothesis that they speed up evolution of new phenotypes.
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Affiliation(s)
- Isabel Miranda
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Rita Rocha
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Maria C. Santos
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Denisa D. Mateus
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Gabriela R. Moura
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Laura Carreto
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
| | - Manuel A. S. Santos
- Department of Biology, Centro de Estudos do Ambiente e do Mar (CESAM), University of Aveiro, Aveiro, Portugal
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102
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Vinces MD, Kumamoto CA. The morphogenetic regulator Czf1p is a DNA-binding protein that regulates white–opaque switching in Candida albicans. Microbiology (Reading) 2007; 153:2877-2884. [PMID: 17768232 DOI: 10.1099/mic.0.2007/005983-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Czf1p has been demonstrated to regulate the switch between the yeast-cell morphology and filamentous morphologies of the human fungal pathogen Candida albicans. The predicted amino acid sequence of Czf1p contains a zinc-cluster motif similar to the DNA-binding domains of proteins such as Saccharomyces cerevisiae Gal4p, suggesting that Czf1p is a DNA-binding protein. Czf1p also demonstrates genetic interaction and a two-hybrid interaction with a second regulator of C. albicans cellular morphology, Efg1p. During growth in contact with an agar matrix, Efg1p has a negative effect on filamentation and Czf1p antagonizes this effect. In addition to regulating cellular morphology, Efg1p plays a role in regulating the cell-type switch between the commonly observed white phase of C. albicans and the opaque, mating-competent phase. While overexpression of EFG1 stimulates the switch from opaque to white, the results reported here demonstrate that overexpression of CZF1 promotes the reverse switch, from white to opaque. We also demonstrate that Czf1p binds CZF1 promoter DNA in vitro. Therefore, for the regulation of both contact-dependent filamentation and white-opaque switching, Czf1p and Efg1p have opposing functions.
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Affiliation(s)
- Marcelo D Vinces
- Department of Molecular Biology and Microbiology, Tufts University, 136 Harrison Ave., Boston, MA 02111, USA
| | - Carol A Kumamoto
- Department of Molecular Biology and Microbiology, Tufts University, 136 Harrison Ave., Boston, MA 02111, USA
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103
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Wu W, Lockhart SR, Pujol C, Srikantha T, Soll DR. Heterozygosity of genes on the sex chromosome regulates Candida albicans virulence. Mol Microbiol 2007; 64:1587-604. [PMID: 17555440 DOI: 10.1111/j.1365-2958.2007.05759.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
In the mouse model for systemic infection, natural a/alpha strains of C. albicans are more virulent and more competitive than their spontaneous MTL-homozygous offspring, which arise primarily by loss of one chromosome 5 homologue followed by duplication of the retained homologue (uniparental disomy). Deletion of either the a or alpha copy of the MTL locus of natural a/alpha strains results in a small decrease in virulence, and a small decrease in competitiveness. Loss of the heterozygosity of non-MTL genes along chromosome 5, however, results in larger decreases in virulence and competitiveness. Natural MTL-homozygous strains are on average less virulent than natural MTL-heterozygous strains and arise by multiple mitotic cross-overs along chromosome 5 outside of the MTL region. These results are consistent with the hypothesis that a competitive advantage of natural a/alpha strains over MTL-homozygous offspring maintains the mating system of C. albicans.
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Affiliation(s)
- Wei Wu
- Department of Biological Sciences, The University of Iowa, Iowa City, IA 52252, USA
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104
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Coste A, Selmecki A, Forche A, Diogo D, Bougnoux ME, d'Enfert C, Berman J, Sanglard D. Genotypic evolution of azole resistance mechanisms in sequential Candida albicans isolates. EUKARYOTIC CELL 2007; 6:1889-904. [PMID: 17693596 PMCID: PMC2043391 DOI: 10.1128/ec.00151-07] [Citation(s) in RCA: 226] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
TAC1 (for transcriptional activator of CDR genes) is critical for the upregulation of the ABC transporters CDR1 and CDR2, which mediate azole resistance in Candida albicans. While a wild-type TAC1 allele drives high expression of CDR1/2 in response to inducers, we showed previously that TAC1 can be hyperactive by a gain-of-function (GOF) point mutation responsible for constitutive high expression of CDR1/2. High azole resistance levels are achieved when C. albicans carries hyperactive alleles only as a consequence of loss of heterozygosity (LOH) at the TAC1 locus on chromosome 5 (Chr 5), which is linked to the mating-type-like (MTL) locus. Both are located on the Chr 5 left arm along with ERG11 (target of azoles). In this work, five groups of related isolates containing azole-susceptible and -resistant strains were analyzed for the TAC1 and ERG11 alleles and for Chr 5 alterations. While recovered ERG11 alleles contained known mutations, 17 new TAC1 alleles were isolated, including 7 hyperactive alleles with five separate new GOF mutations. Single-nucleotide-polymorphism analysis of Chr 5 revealed that azole-resistant strains acquired TAC1 hyperactive alleles and, in most cases, ERG11 mutant alleles by LOH events not systematically including the MTL locus. TAC1 LOH resulted from mitotic recombination of the left arm of Chr 5, gene conversion within the TAC1 locus, or the loss and reduplication of the entire Chr 5. In one case, two independent TAC1 hyperactive alleles were acquired. Comparative genome hybridization and karyotype analysis revealed the presence of isochromosome 5L [i(5L)] in two azole-resistant strains. i(5L) leads to increased copy numbers of azole resistance genes present on the left arm of Chr 5, among them TAC1 and ERG11. Our work shows that azole resistance was due not only to the presence of specific mutations in azole resistance genes (at least ERG11 and TAC1) but also to their increase in copy number by LOH and to the addition of extra Chr 5 copies. With the combination of these different modifications, sophisticated genotypes were obtained. The development of azole resistance in C. albicans is therefore a powerful instrument for generating genetic diversity.
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Affiliation(s)
- Alix Coste
- Institute of Microbiology, University of Lausanne and University Hospital Center, Rue du Bugnon 48, CH-1011, Lausanne, Switzerland
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105
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Schaefer D, Côte P, Whiteway M, Bennett RJ. Barrier activity in Candida albicans mediates pheromone degradation and promotes mating. EUKARYOTIC CELL 2007; 6:907-18. [PMID: 17416895 PMCID: PMC1951518 DOI: 10.1128/ec.00090-07] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mating in Candida albicans and Saccharomyces cerevisiae is regulated by the secretion of peptide pheromones that initiate the mating process. An important regulator of pheromone activity in S. cerevisiae is barrier activity, involving an extracellular aspartyl protease encoded by the BAR1 gene that degrades the alpha pheromone. We have characterized an equivalent barrier activity in C. albicans and demonstrate that the loss of C. albicans BAR1 activity results in opaque a cells exhibiting hypersensitivity to alpha pheromone. Hypersensitivity to pheromone is clearly seen in halo assays; in response to alpha pheromone, a lawn of C. albicans Deltabar1 mutant cells produces a marked zone in which cell growth is inhibited, whereas wild-type strains fail to show halo formation. C. albicans mutants lacking BAR1 also exhibit a striking mating defect in a cells, but not in alpha cells, due to overstimulation of the response to alpha pheromone. The block to mating occurs prior to cell fusion, as very few mating zygotes were observed in mixes of Deltabar1 a and alpha cells. Finally, in a barrier assay using a highly pheromone-sensitive strain, we were able to demonstrate that barrier activity in C. albicans is dependent on Bar1p. These studies reveal that a barrier activity to alpha pheromone exists in C. albicans and that the activity is analogous to that caused by Bar1p in S. cerevisiae.
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Affiliation(s)
- Dana Schaefer
- MMI Department, Brown University, 171 Meeting Street, Providence, RI 02912, USA
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106
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Edwards-Ingram L, Gitsham P, Burton N, Warhurst G, Clarke I, Hoyle D, Oliver SG, Stateva L. Genotypic and physiological characterization of Saccharomyces boulardii, the probiotic strain of Saccharomyces cerevisiae. Appl Environ Microbiol 2007; 73:2458-67. [PMID: 17293506 PMCID: PMC1855594 DOI: 10.1128/aem.02201-06] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Saccharomyces boulardii, a yeast that was isolated from fruit in Indochina, has been used as a remedy for diarrhea since 1950 and is now a commercially available treatment throughout Europe, Africa, and South America. Though initially classified as a separate species of Saccharomyces, recent publications have shown that the genome of S. boulardii is so similar to Saccharomyces cerevisiae that the two should be classified as conspecific. This raises the question of the distinguishing molecular and phenotypic characteristics present in S. boulardii that make it perform more effectively as a probiotic organism compared to other strains of S. cerevisiae. This investigation reports some of these distinguishing characteristics including enhanced ability for pseudohyphal switching upon nitrogen limitation and increased resistance to acidic pH. However, these differences did not correlate with increased adherence to epithelial cells or transit through mouse gut. Pertinent characteristics of the S. boulardii genome such as trisomy of chromosome IX, altered copy number of a number of individual genes, and sporulation deficiency have been revealed by comparative genome hybridization using oligonucleotide-based microarrays coupled with a rigorous statistical analysis. The contributions of the different genomic and phenotypic features of S. boulardii to its probiotic nature are discussed.
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Affiliation(s)
- Laura Edwards-Ingram
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Oxford Road, Manchester, UK
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107
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Bennett RJ, Johnson AD. The role of nutrient regulation and the Gpa2 protein in the mating pheromone response of C. albicans. Mol Microbiol 2007; 62:100-19. [PMID: 16987174 DOI: 10.1111/j.1365-2958.2006.05367.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Although traditionally classified as asexual, the human fungal pathogen Candida albicans can undergo highly efficient mating. A key component of this mating is the response to pheromone, which is mediated by a conserved kinase cascade that transduces the signal from the pheromone receptor to a transcriptional response in the nucleus. In this paper we show (i) that the detailed response of C. albicans to the alpha pheromone differs among clinical isolates, (ii) that the response depends critically on nutritional conditions, (iii) that the entire response is mediated by the Ste2 receptor, and (iv) that, in terms of genes induced, the response to alpha pheromone in C. albicans shows only marginal overlap with the response in Saccharomyces cerevisiae. We further investigated the nutritional control of pheromone induction and identify the GPA2 gene as a critical component. We found that Deltagpa2/Deltagpa2 mutants are hypersensitive to pheromone and, unlike wild-type strains, show efficient cell cycle arrest (including the formation of characteristic halos on solid medium) in response to mating pheromone. These results indicate that C. albicans, like several other fungal species but unlike S. cerevisiae, integrates signals from a nutrient-sensing pathway with those of the pheromone response MAP kinase pathway to generate the final transcriptional response.
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Affiliation(s)
- Richard J Bennett
- Department of Microbiology and Immunology, University of California San Francisco, San Francisco, CA 94143, USA
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108
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Andaluz E, Gómez-Raja J, Hermosa B, Ciudad T, Rustchenko E, Calderone R, Larriba G. Loss and fragmentation of chromosome 5 are major events linked to the adaptation of rad52-DeltaDelta strains of Candida albicans to sorbose. Fungal Genet Biol 2007; 44:789-98. [PMID: 17300968 PMCID: PMC2000335 DOI: 10.1016/j.fgb.2007.01.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2006] [Revised: 12/30/2006] [Accepted: 01/05/2007] [Indexed: 12/27/2022]
Abstract
Candida albicans can adapt and grow on sorbose plates by losing one copy of Chr5. Since rad52 mutants of Saccharomyces cerevisiae lose chromosomes at a high rate, we have investigated the ability of C. albicans rad52 to adapt to sorbose. Carad52-DeltaDelta mutants generate Sou(+) strains earlier than wild-type but the final yield is lower, probably because they die at a higher rate in sorbose. As other strains of C. albicans, CAF2 and rad52-DeltaDelta derivatives generate Sou(+) strains by a loss of one copy of Chr5 about 75% of the time. In addition, rad52 strains were able to produce Sou(+) strains by a fragmentation/deletion event in one copy of Chr5, consisting of loss of a region adjacent to the right telomere. Finally, both CAF2 and rad52-DeltaDelta produced Sou(+) strains with two apparent full copies of Chr5, suggesting that additional genomic changes may also regulate adaptation to sorbose.
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Affiliation(s)
- Encarnación Andaluz
- Departamento de Microbiología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
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109
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Lephart PR, Magee PT. Effect of the major repeat sequence on mitotic recombination in Candida albicans. Genetics 2006; 174:1737-44. [PMID: 17028326 PMCID: PMC1698643 DOI: 10.1534/genetics.106.063271] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The major repeat sequence (MRS) is known to play a role in karyotypic variation in Candida albicans. The MRS affects karyotypic variation by expanding and contracting internal repeats, by altering the frequency of chromosome loss, and by serving as a hotspot for chromosome translocation. We proposed that the effects of the MRS on translocation could be better understood by examination of the effect of the MRS on a similar event, mitotic recombination between two chromosome homologs. We examined the frequency of mitotic recombination across an MRS of average size (approximately 50 kb) as well as the rate of recombination in a 325-kb stretch of DNA adjacent to the MRS. Our results indicate that mitotic recombination frequencies across the MRS were not enhanced compared to the frequencies measured across the 325-kb region adjacent to the MRS. Mitotic recombination events were found to occur throughout the 325-kb region analyzed as well as within the MRS itself. This analysis of mitotic recombination frequencies across a large portion of chromosome 5 is the first large-scale analysis of mitotic recombination done in C. albicans and indicates that mitotic recombination frequencies are similar to the rates found in Saccharomyces cerevisiae.
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Affiliation(s)
- Paul R Lephart
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota 01702, USA
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110
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Abstract
Resistance to the limited number of available antifungal drugs is a serious problem in the treatment of Candida albicans. We found that aneuploidy in general and a specific segmental aneuploidy, consisting of an isochromosome composed of the two left arms of chromosome 5, were associated with azole resistance. The isochromosome forms around a single centromere flanked by an inverted repeat and was found as an independent chromosome or fused at the telomere to a full-length homolog of chromosome 5. Increases and decreases in drug resistance were strongly associated with gain and loss of this isochromosome, which bears genes expressing the enzyme in the ergosterol pathway targeted by azole drugs, efflux pumps, and a transcription factor that positively regulates a subset of efflux pump genes.
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Affiliation(s)
- Anna Selmecki
- Department of Genetics, Cell Biology, and Development
| | - Anja Forche
- Department of Genetics, Cell Biology, and Development
| | - Judith Berman
- Department of Genetics, Cell Biology, and Development
- Department of Microbiology, University of Minnesota, 6-160
Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455, USA
- *To whom correspondence should be addressed. E-mail:
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111
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Abstract
The release of the diploid genomic sequence of Candida albicans and its recent community-based annotation have permitted a number of studies which have significantly advanced our understanding of the biology of this important human pathogen. These advances range from analysis of genomic changes to differential gene expression under a variety of conditions. A few general conclusions can be drawn from the data presently in hand; one can expect more and more new insights as the number and kind of experiments grows.
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Affiliation(s)
- Beatrice B Magee
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 321 Church St. SE, Minneapolis, MN 55455, USA.
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112
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Andaluz E, Ciudad T, Gómez-Raja J, Calderone R, Larriba G. Rad52 depletion in Candida albicans triggers both the DNA-damage checkpoint and filamentation accompanied by but independent of expression of hypha-specific genes. Mol Microbiol 2006; 59:1452-72. [PMID: 16468988 DOI: 10.1111/j.1365-2958.2005.05038.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have analysed the effect of RAD52 deletion in several aspects of the cell biology of Candida albicans. Cultures of rad52Delta strains exhibited slow growth and contained abundant cells with a filamentous morphology. Filamentation with polarization of actin patches was accompanied by the induction of the hypha-specific genes (HSG) ECE1, HWP1 and HGC1. However, filament formation occurred in the absence of the transcription factors Efg1 and Cph1, even though disruption of EFG1 prevented expression of HSG. Therefore, expression of HSG genes accompanies but is dispensable for rad52Delta filamentation. However, deletion of adenylate cyclase severely impaired filamentation, this effect being largely reverted by the addition of exogenous cAMP. Filaments resembled elongated pseudohyphae, but some of them looked like true hyphae. Following depletion of Rad52, many cells arrested at the G2/M phase of the cell cycle with a single nucleus suggesting the early induction of the DNA-damage checkpoint. Filaments formed later, preferentially from G2/M cells. The filamentation process was accompanied by the uncoupling of several landmark events of the cell cycle and was partially dependent on the action of the cell cycle modulator Swe1. Hyphae were still induced by serum, but a large number of rad52 cells myceliated in G2/M.
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Affiliation(s)
- Encarnación Andaluz
- Departamento de Microbiología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
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113
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Chauhan N, Ciudad T, Rodríguez-Alejandre A, Larriba G, Calderone R, Andaluz E. Virulence and karyotype analyses of rad52 mutants of Candida albicans: regeneration of a truncated chromosome of a reintegrant strain (rad52/RAD52) in the host. Infect Immun 2006; 73:8069-78. [PMID: 16299301 PMCID: PMC1307084 DOI: 10.1128/iai.73.12.8069-8078.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The virulence of Candida albicans mutants lacking one or both copies of RAD52, a gene involved in homologous recombination (HR), was evaluated in a murine model of hematogenously disseminated candidiasis. In this study, the virulence of the rad52Delta mutant was dependent upon the inoculum concentration. Mice survived at a cell inoculum of 1 x 10(6), but there was a decrease in survival time at dosages of 1.5 x 10(6) and especially at 3 x 10(6) cells per animal. The heterozygote RAD52/rad52 behaved like wild type, whereas a reintegrant strain was intermediate in its ability to cause death compared to these strains and to the avirulent rad52/rad52 null at inocula of 1 x 10(6) and 1.5 x 10(6) cells. A double mutant, lig4/lig4/rad52/rad52, was avirulent at all inocula used. PCR analysis of the RAD52 and/or LIG4 loci showed that all strains recovered from animals matched the genotype of the inoculated strains. Analysis of the electrophoretical karyotypes indicated that the inoculated, reintegrant strain carried a large deletion in one copy of chromosome 6 (the shortest homologue, or Chr6b). Interestingly, truncated Chr6b was regenerated in all the strains recovered from moribund animals using the homologue as a template. Further, regeneration of Chr6b was paralleled by an increase in virulence that was still lower than that of wild type, likely because of the persistent loss of heterozygosity in the regenerated region. Overall, our results indicate that systemic candidiasis can develop in the absence of HR, but simultaneous elimination of both recombination pathways, HR and nonhomologous end-joining, suppresses virulence even at very high inocula.
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Affiliation(s)
- Neeraj Chauhan
- Georgetown University Medical Center, Department of Microbiology & Immunology, Washington, DC, USA
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114
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Abstract
Candida albicans is a normal part of the human microflora, but it is also an opportunistic fungal pathogen that causes both mucosal infections and life-threatening systemic infections. Until recently, C. albicans was thought to be asexual, existing only as an obligate diploid. However, a mating locus was identified that was homologous to those in sexually reproducing fungi, and mating of C. albicans strains was subsequently demonstrated in the laboratory. In this review, we compare and contrast the mating process in C. albicans with that of other fungi, particularly Saccharomyces cerevisiae, whose mating has been most intensively studied. Several features of the mating pathway appear unique to C. albicans, including aspects of gene regulation and cell biology, as well as the involvement of "white-opaque" switching, an alteration between two quasi-stable inheritable states. These specializations of the mating process may have evolved to promote the survival of C. albicans in the hostile environment of a mammalian host.
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Affiliation(s)
- R J Bennett
- Department of Microbiology and Immunology, University of California, San Francisco, California 94143, USA.
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115
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Chibana H, Mikami Y. [Structural and functional analyses of MRS (major repeated sequnece) in Candida albicans. Application for genotyping and the eternal way to the complete genome sequence]. NIHON ISHINKIN GAKKAI ZASSHI = JAPANESE JOURNAL OF MEDICAL MYCOLOGY 2006; 47:129-34. [PMID: 16940945 DOI: 10.3314/jjmm.47.129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
There are several different types of repeated sequences in the genome of Candida albicans, including the MRS (Major repeated sequence). In 2004, the whole genome sequence of C. albicans was published. Assembly of the sequences to chromosomal length contigs was not achieved, mainly due to interruption of the sequences by MRS. However, MRS including Ca3, 27A and RPS have been playing important roles in a number of epidemiological studies and basic biological investigations into C. albicans chromosome loss events and associated phenotypic changes. Here we summarize structural analyses from subrepeat sequences to the chromosome level, and functional analyses of MRS.
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Affiliation(s)
- Hiroji Chibana
- Research Center for Pathogenic Fungi and Microbial Toxicoses, Chiba University, Japan.
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116
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Ibrahim AS, Magee BB, Sheppard DC, Yang M, Kauffman S, Becker J, Edwards JE, Magee PT. Effects of ploidy and mating type on virulence of Candida albicans. Infect Immun 2005; 73:7366-74. [PMID: 16239535 PMCID: PMC1273887 DOI: 10.1128/iai.73.11.7366-7374.2005] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Candida albicans is the most common fungal pathogen of humans. The recent discovery of sexuality in this organism has led to the demonstration of a mating type locus which is usually heterozygous, although some isolates are homozygous. Tetraploids can be formed between homozygotes of the opposite mating type. However, the role of the mating process and tetraploid formation in virulence has not been investigated. We describe here experiments using a murine model of disseminated candidiasis which demonstrate that in three strains, including CAI-4, the most commonly used strain background, tetraploids are less virulent than diploids and can undergo changes in ploidy during infection. In contrast to reports with other strains, we find that MTL homozygotes are almost as virulent as the heterozygotes. These results show that the level of ploidy in Candida albicans can affect virulence, but the mating type configuration does not necessarily do so.
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Affiliation(s)
- Ashraf S Ibrahim
- Department of Genetics, Cell Biology, and Development, 320 Church St. SE, Minneapolis, MN 55455, USA
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117
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Lephart PR, Chibana H, Magee PT. Effect of the major repeat sequence on chromosome loss in Candida albicans. EUKARYOTIC CELL 2005; 4:733-41. [PMID: 15821133 PMCID: PMC1087809 DOI: 10.1128/ec.4.4.733-741.2005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The major repeat sequence (MRS) is found at least once on all but one chromosome in Candida albicans, but as yet it has no known relation to the phenotype. The MRS affects karyotypic variation by serving as a hot spot for chromosome translocation and by expanding and contracting internal repeats, thereby changing chromosome length. Thus, MRSs on different chromosomes and those on chromosome homologues can differ in size. We proposed that the MRS's unique repeat structure and, more specifically, the size of the MRS could also affect karyotypic variation by altering the frequency of mitotic nondisjunction. Subsequent analysis shows that both natural and artificially induced differences in the size of the chromosome 5 MRS can affect chromosome segregation. Strains with chromosome 5 homologues that differ in the size of the naturally occurring MRSs show a preferential loss of the homologue with the larger MRS on sorbose, indicating that a larger MRS leads to a higher risk of mitotic nondisjunction for that homologue. While deletion of an MRS has no deleterious effect on the deletion chromosome under normal growth conditions and leads to no obvious phenotype, strains that have the MRS deleted from one chromosome 5 homologue preferentially lose the homologue with the MRS remaining. This effect on chromosome segregation is the first demonstration of a phenotype associated with the MRS.
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Affiliation(s)
- Paul R Lephart
- Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455, USA
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118
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Kabir MA, Ahmad A, Greenberg JR, Wang YK, Rustchenko E. Loss and gain of chromosome 5 controls growth of Candida albicans on sorbose due to dispersed redundant negative regulators. Proc Natl Acad Sci U S A 2005; 102:12147-52. [PMID: 16099828 PMCID: PMC1189348 DOI: 10.1073/pnas.0505625102] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Indexed: 12/19/2022] Open
Abstract
A reversible decrease or increase of Candida albicans chromosome copy number was found to be a prevalent means of survival of this opportunistic pathogen, under conditions that kill cells or inhibit their propagation. The utilization of a secondary carbon source, l-sorbose, by reversible loss of chromosome 5, serves as a model system. We have determined that an approximately 209-kbp portion of the right arm of chromosome 5 contains at least five spatially separated, functionally redundant regions that control utilization of l-sorbose. The regions bear no structural similarity among themselves, and four of them contain sequences that bear no similarity with any known sequence. We identified a regulatory gene in region A that encodes a helix-loop-helix protein. Most important, the multiple redundant regulators scattered along chromosome 5 explain, in a simple, elegant way, why the loss of the entire homologue is usually required for growth on sorbose. Thus, an entire chromosome acts as a single regulatory unit, a feature not previously considered. Our finding appears to be a paradigm for the control of other phenotypes in C. albicans that also depend on chromosome loss, thus implying that C. albicans genes are not distributed randomly among different chromosomes.
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Affiliation(s)
- M Anaul Kabir
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, NY 14642, USA
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119
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Nassonova E, Cornillot E, Méténier G, Agafonova N, Kudryavtsev B, Skarlato S, Vivarès CP. Chromosomal composition of the genome in the monomorphic diplokaryotic microsporidium Paranosema grylli: analysis by two-dimensional pulsed-field gel electrophoresis. Folia Parasitol (Praha) 2005; 52:145-57. [PMID: 16004374 DOI: 10.14411/fp.2005.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The molecular karyotype of Paranosema grylli Sokolova, Seleznev, Dolgikh et Issi, 1994, a monomorphic diplokaryotic microsporidium, comprises numerous bright and faint bands of nonstoichiometric staining intensity. Restriction analysis of chromosomal DNAs by "karyotype and restriction display" 2-D PFGE has demonstrated that the complexity of molecular karyotype of P. grylli is related to the pronounced length polymorphism of-homologous chromosomes. The background of this phenomenon is discussed in the context of ploidy state, reproductive strategy and population structure in this microsporidium. We propose that the remarkable size variation between homologous chromosomes in P. grylli may be a consequence of ectopic recombination at the chromosome extremities.
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Affiliation(s)
- Elena Nassonova
- Institute of Cytology, Russian Academy of Sciences, Tikhoretsky Ave. 4, 194064 St. Petersburg, Russia.
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120
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Bennett RJ, Miller MG, Chua PR, Maxon ME, Johnson AD. Nuclear fusion occurs during mating in Candida albicans and is dependent on the KAR3 gene. Mol Microbiol 2005; 55:1046-59. [PMID: 15686553 DOI: 10.1111/j.1365-2958.2005.04466.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
It is now well established that mating can occur between diploid a and alpha cells of Candida albicans. There is, however, controversy over when, and with what efficiency, nuclear fusion follows cell fusion to create stable tetraploid a/alpha cells. In this study, we have analysed the mating process between C. albicans strains using both cytological and genetic approaches. Using strains derived from SC5314, we used a number of techniques, including time-lapse microscopy, to demonstrate that efficient nuclear fusion occurs in the zygote before formation of the first daughter cell. Consistent with these observations, zygotes micromanipulated from mating mixes gave rise to mononuclear tetraploid cells, even when no selection for successful mating was applied to them. Mating between different clinical isolates of C. albicans revealed that while all isolates could undergo nuclear fusion, the efficiency of nuclear fusion varied in different crosses. We also show that nuclear fusion in C. albicans requires the Kar3 microtubule motor protein. Deletion of the CaKAR3 gene from both mating partners had little or no effect on zygote formation but reduced the formation of stable tetraploids more than 600-fold, as determined by quantitative mating assays. These findings demonstrate that nuclear fusion is an active process that can occur in C. albicans at high frequency to produce stable, mononucleate mating products.
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Affiliation(s)
- Richard J Bennett
- Department of Microbiology and Immunology, UCSF, San Francisco, CA 94143, USA
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121
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Janiak AM, Sargsyan H, Russo J, Naider F, Hauser M, Becker JM. Functional expression of the Candida albicans alpha-factor receptor in Saccharomyces cerevisiae. Fungal Genet Biol 2005; 42:328-38. [PMID: 15749052 DOI: 10.1016/j.fgb.2005.01.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2004] [Revised: 01/05/2005] [Accepted: 01/05/2005] [Indexed: 10/25/2022]
Abstract
Candida albicans genes involved in mating have been identified previously by homology to Saccharomyces cerevisiae mating pathway components. The C. albicans genome encodes CaSte2p, a homolog of the S. cerevisiae alpha-mating pheromone receptor Ste2p, and two potential pheromones, alpha-F13 (GFRLTNFGYFEPG) and alpha-F14 (GFRLTNFGYFEPGK). The response of several C. albicans strains to the synthesized peptides was determined. The alpha-F13 was degraded by a C. albicans MTLa strain but not by S. cerevisiae MATa cells. The CaSTE2 gene was cloned and expressed in a ste2-deleted strain of S. cerevisiae. Growth arrest and beta-galactosidase activity induced from a FUS1-lacZ reporter construct increased in a dose-dependent manner upon exposure of transgenic S. cerevisiae to alpha-F13. Mating between the strain expressing CaSTE2 and an opposite mating type was mediated by alpha-F13 and not by the S. cerevisiae alpha-factor. The results indicated that CaSte2p effectively coupled to the S. cerevisiae signal transduction pathway. Functional expression of CaSte2p in S. cerevisiae provides a well-defined system for studying the biochemistry and molecular biology of the C. albicans pheromone and its receptor.
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Affiliation(s)
- Agnieszka M Janiak
- Department of Microbiology, University of Tennessee, Knoxville, TN 37996, USA
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122
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Costa JM, Eloy O, Botterel F, Janbon G, Bretagne S. Use of microsatellite markers and gene dosage to quantify gene copy numbers in Candida albicans. J Clin Microbiol 2005; 43:1387-9. [PMID: 15750114 PMCID: PMC1081221 DOI: 10.1128/jcm.43.3.1387-1389.2005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
With microsatellite marker typing, the number of alleles must be known for calculation of allelic frequencies in the diploid Candida albicans for a given locus. We describe a gene dosage with a double real-time PCR. Such a dosage should also be useful in exploring the loss of heterozygosity in C. albicans.
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Affiliation(s)
- J-M Costa
- Laboratoire de Parasitologie-Mycologie, Hôpital H. Mondor, 51 avenue du Maréchal DeLattre de Tassigny, 94010 Créteil, France
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123
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Selmecki A, Bergmann S, Berman J. Comparative genome hybridization reveals widespread aneuploidy in Candida albicans laboratory strains. Mol Microbiol 2005; 55:1553-65. [PMID: 15720560 DOI: 10.1111/j.1365-2958.2005.04492.x] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Clinical strains of Candida albicans are highly tolerant of aneuploidies and other genome rearrangements. We have used comparative genome hybridization (CGH), in an array format, to analyse the copy number of over 6000 open reading frames (ORFs) in the genomic DNA of C. albicans laboratory strains carrying one (CAI-4) to three (BWP17) auxotrophies. We find that during disruption of the HIS1 locus all genes telomeric to HIS1 were deleted and telomeric repeats were added to a 9 nt sequence within the transforming DNA. This deletion occurred in approximately 10% of transformants analysed and was stably maintained through two additional rounds of transformation and counterselection of the transformation marker. In one example, the deletion was repaired, apparently via break-induced replication. Furthermore, all CAI-4 strains tested were trisomic for chromosome 2 although this trisomy appears to be unstable, as it is not detected in strains subsequently derived from CAI-4. Our data indicate CGH arrays can be used to detect monosomies and trisomies, to predict the sites of chromosome breaks, and to identify chromosomal aberrations that have not been detected with other approaches in C. albicans strains. Furthermore, they highlight the high level of genome instability in C. albicans laboratory strains exposed to the stress of transformation and counterselection on 5-fluoro-orotic acid.
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Affiliation(s)
- Anna Selmecki
- Department of Genetics, Cell Biology and Development, University of Minnesota, MN, USA
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124
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Wu W, Pujol C, Lockhart SR, Soll DR. Chromosome loss followed by duplication is the major mechanism of spontaneous mating-type locus homozygosis in Candida albicans. Genetics 2005; 169:1311-27. [PMID: 15654090 PMCID: PMC1449533 DOI: 10.1534/genetics.104.033167] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Candida albicans, which is diploid, possesses a single mating-type (MTL) locus on chromosome 5, which is normally heterozygous (a/alpha). To mate, C. albicans must undergo MTL homozygosis to a/a or alpha/alpha. Three possible mechanisms may be used in this process, mitotic recombination, gene conversion, or loss of one chromosome 5 homolog, followed by duplication of the retained homolog. To distinguish among these mechanisms, 16 spontaneous a/a and alpha/alpha derivatives were cloned from four natural a/alpha strains, P37037, P37039, P75063, and P34048, grown on nutrient agar. Eighteen polymorphic (heterozygous) markers were identified on chromosome 5, 6 to the left and 12 to the right of the MTL locus. These markers were then analyzed in MTL-homozygous derivatives of the four natural a/alpha strains to distinguish among the three mechanisms of homozygosis. An analysis of polymorphisms on chromosomes 1, 2, and R excluded meiosis as a mechanism of MTL homozygosis. The results demonstrate that while mitotic recombination was the mechanism for homozygosis in one offspring, loss of one chromosome 5 homolog followed by duplication of the retained homolog was the mechanism in the remaining 15 offspring, indicating that the latter mechanism is the most common in the spontaneous generation of MTL homozygotes in natural strains of C. albicans in culture.
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Affiliation(s)
- Wei Wu
- Department of Biological Sciences, University of Iowa, Iowa City, 52242, USA
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125
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Greenberg JR, Price NP, Oliver RP, Sherman F, Rustchenko E. Candida albicans SOU1 encodes a sorbose reductase required forL-sorbose utilization. Yeast 2005; 22:957-69. [PMID: 16134116 DOI: 10.1002/yea.1282] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous work in our laboratory showed that L-sorbose utilization in Candida albicans is subject to a novel form of regulation which involves a reversible increase or decrease in the copy number of chromosome 5. Furthermore, the structural gene SOU1 is required for L-sorbose utilization and encodes a member of the short chain dehydrogenase family. However, the precise function of SOU1 was not known and neither was the pathway for L-sorbose utilization. We have now expressed SOU1 at a high level from a replicative plasmid having a constitutive ADH1 promoter and purified a version of Sou1p tagged with the FLAG epitope at the N-terminus. Sou1FLAGNp has a sorbose reductase activity which utilizes NADPH as a co-factor and converts L-sorbose to D-sorbitol. It can also less efficiently utilize fructose as a substrate with NADPH as a co-factor, converting fructose to mannitol. In agreement with prediction, the purified enzyme has a subunit molecular weight of 31 kDa and a pI of about 4.8. It probably consists of four identical subunits and has a pH optimum of 6.2. The L-sorbose utilization pathway in C. albicans probably converts L-sorbose to fructose-6-phosphate via D-sorbitol as an intermediate. The first step is catalysed by Sou1p. We also found that C. albicans extracts have a D-sorbitol-6-phosphate dehydrogenase activity, not encoded by SOU1, which utilizes NADP as a co-factor. This activity has not been described previously in yeasts and may be involved in the conversion of phosphorylated D-sorbitol to fructose-6-phosphate or glucose-6-phosphate.
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Affiliation(s)
- Jay R Greenberg
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Box 712, Rochester, NY 14642, USA.
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126
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Kabir MA, Rustchenko E. Determination of gaps by contig alignment with telomere-mediated chromosomal fragmentation in Candida albicans. Gene 2005; 345:279-87. [PMID: 15716104 DOI: 10.1016/j.gene.2004.11.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2004] [Revised: 10/29/2004] [Accepted: 11/24/2004] [Indexed: 10/26/2022]
Abstract
We have adopted a method of telomere-mediated chromosome fragmentation in order to demonstrate the alignment of contigs and determination of gaps. We established the order and orientation of four contigs of Candida albicans chromosome 5 and determined the sizes of three gaps between these contigs. We confirmed this proposed alignment of contigs, as well as gap sizes, by sequencing one gap and analyzing three mega deletions of approximately 41 kbp, 58 kbp, and 77 kbp, which covered two other gaps. These gaps could be also conveniently sequenced, which is an important step in establishing a complete sequence. The combined length of contigs and gaps covered approximately 422 kbp, which is one third of chromosome 5. Telomere-mediated chromosome fragmentation, used here for the first time to align the contigs of C. albicans and determine the gaps, proved to be a reliable method. The method could be helpful in sequencing projects of other diploid organisms, in particular those in which centromeres have not been identified. In addition, our approach can be used to assign any contig to a chromosome, or to induce the loss of a specific chromosome.
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Affiliation(s)
- M Anaul Kabir
- Department of Biochemistry and Biophysics, Box 712, University of Rochester Medical School, Rochester, NY 14642, USA
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127
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Wellington M, Rustchenko E. 5-Fluoro-orotic acid induces chromosome alterations inCandida albicans. Yeast 2005; 22:57-70. [PMID: 15635674 DOI: 10.1002/yea.1191] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Treatment of a prototrophic laboratory strain of Candida albicans with 5-fluoro-orotic acid (5-FOA) produced two major types of mutants with chromosomal alterations, 5-FOA-resistant (FoaR) and those remaining sensitive (FoaS). Both major types remained Ura+. FoaR mutants, produced after a long exposure, contained either a duplication of chromosome 4b or an inner enlargement of chromosome 5b. The average mutant frequency was approximately 1.0 x 10(-5). The reverse mutation of FoaR to FoaS also caused the loss of either the extra chromosome 4b or the enlarged chromosome 5b, revealing a causal relationship between the resistance and the specific chromosome constitution. The cells remained sensitive after a relatively short 24 h exposure to 5-FOA medium, but the treatment induced non-specific changes in lengths of various chromosomes. Furthermore, FoaR type mutants acquired a notable chromosomal and phenotypic instability. Our results indicate the necessity of electrokaryotyping of strains that have been exposed to 5-FOA, especially with studies of gene function and with DNA microarray assays.
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Affiliation(s)
- Melanie Wellington
- Department of Pediatrics, University of Rochester Medical Center, Rochester, NY 14642, USA
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128
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Panwar SL, Legrand M, Dignard D, Whiteway M, Magee PT. MFalpha1, the gene encoding the alpha mating pheromone of Candida albicans. EUKARYOTIC CELL 2004; 2:1350-60. [PMID: 14665468 PMCID: PMC326654 DOI: 10.1128/ec.2.6.1350-1360.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans, the single most frequently isolated human fungal pathogen, was thought to be asexual until the recent discovery of the mating-type-like locus (MTL). Homozygous MTL strains were constructed and shown to mate. Furthermore, it has been demonstrated that opaque-phase cells are more efficient in mating than white-phase cells. The similarity of the genes involved in the mating pathway in Saccharomyces cerevisiae and C. albicans includes at least one gene (KEX2) that is involved in the processing of the alpha mating pheromone in the two yeasts. Taking into account this similarity, we searched the C. albicans genome for sequences that would encode the alpha pheromone gene. Here we report the isolation and characterization of the gene MFalpha1, which codes for the precursor of the alpha mating pheromone in C. albicans. Two active alpha-peptides, 13 and 14 amino acids long, would be generated after the precursor molecule is processed in C. albicans. To examine the role of this gene in mating, we constructed an mfalpha1 null mutant of C. albicans. The mfalpha1 null mutant fails to mate as MTLalpha, while MTLa mfalpha1 cells are still mating competent. Experiments performed with the synthetic alpha-peptides show that they are capable of inducing growth arrest, as demonstrated by halo tests, and also induce shmooing in MTLa cells of C. albicans. These peptides are also able to complement the mating defect of an MTLalpha kex2 mutant strain when added exogenously, thereby confirming their roles as alpha mating pheromones.
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Affiliation(s)
- Sneh L Panwar
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota 55455, USA
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129
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Affiliation(s)
- Vincent M Bruno
- Integrated Program in Cellular, Molecular and Biophysical Studies, Columbia University, 701 West 168th Street, Room HHSC908, New York, NY 10032, USA
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130
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Tavanti A, Gow NAR, Maiden MCJ, Odds FC, Shaw DJ. Genetic evidence for recombination in Candida albicans based on haplotype analysis. Fungal Genet Biol 2004; 41:553-62. [PMID: 15050544 DOI: 10.1016/j.fgb.2003.12.008] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Accepted: 12/24/2003] [Indexed: 10/26/2022]
Abstract
The possibility of sexual reproduction in the human pathogenic fungus Candida albicans is a question of great interest in medical mycology. Not only is it a fundamental biological issue, but it is also a potential mechanism for contributing to the phenotypic plasticity (and hence the virulence) of the organism. Molecular genotyping methods such as multi-locus sequence typing (MLST) are generating data that can shed light on this question. In the present study we have used MLST information to generate haplotypes that identify many different homologues of a chromosome within a collection of strains. Particular combinations of these haplotypes provide evidence for chromosomal segregation and intra-chromosome recombination. All of our observations of haplotype diversity could also be explained by other mechanisms, such as gene conversion or mitotic recombination, and the resolution of these issues will require a denser map of accurately localised markers. A common event observed in strain evolution is loss of heterozygosity at a particular marker. Our results contribute to the emerging picture of C. albicans as an organism whose primary means of reproduction is clonal, but with a small but important contribution from sexual reproduction, occurring in nature but not under commonly used laboratory conditions.
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Affiliation(s)
- Arianna Tavanti
- Department of Molecular and Cell Biology, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, UK
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131
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Ciudad T, Andaluz E, Steinberg-Neifach O, Lue NF, Gow NAR, Calderone RA, Larriba G. Homologous recombination in Candida albicans: role of CaRad52p in DNA repair, integration of linear DNA fragments and telomere length. Mol Microbiol 2004; 53:1177-94. [PMID: 15306020 DOI: 10.1111/j.1365-2958.2004.04197.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chromosomal rearrangements are common in both clinical isolates and spontaneous mutants of Candida albicans. It appears that many of these rearrangements are caused by translocations around the major sequence repeat (MSR) that is present in all chromosomes except chromosome 3, suggesting that homologous recombination (HR) may play an important role in the survival of this organism. In order to gain information on these processes, we have cloned the homologue of RAD52, which in Saccharomyces cerevisiae is the only gene required for all HR events. CaRAD52 complemented poorly a rad52 mutant of S. cerevisiae. Two null Carad52Delta/Carad52Delta mutants were constructed by sequential deletion of both alleles and two reconstituted strains were obtained by reintegration of the gene. Characterization of these mutants indicated that HR plays an essential role in the repair of DNA lesions caused by both UV light and the radiomimetic compound methyl-methane-sulphonate (MMS), whereas the non-homologous end-joining pathway (NHEJ) is used only in the absence of Rad52p or after extensive DNA damage. Repair by HR is more efficient in exponentially growing than in stationary cells, probably because a larger number of cells are in late S or G2 phases of the cell cycle (and therefore, can use a sister chromatid as a substrate for recombinational repair), whereas stationary phase cells are mainly in G0 or G1, and only can be repaired using the chromosomal homologue. In addition, CaRad52p is absolutely required for the integration of linear DNA with long flanking homologous sequences. Finally, the absence of CaRad52p results in the lengthening of telomeres, even in the presence of an active telomerase, an observation not described in any other organism. This raises the possibility that both telomerase and homologous recombination may function simultaneously at C. albicans telomeres.
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Affiliation(s)
- Toni Ciudad
- Departamento de Microbiología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
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132
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Chen X, Magee BB, Dawson D, Magee PT, Kumamoto CA. Chromosome 1 trisomy compromises the virulence of Candida albicans. Mol Microbiol 2004; 51:551-65. [PMID: 14756793 DOI: 10.1046/j.1365-2958.2003.03852.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Although increases in chromosome copy number typically have devastating developmental consequences in mammals, fungal cells such as Saccharomyces cerevisiae seem to tolerate trisomies without obvious impairment of growth. Here, we demonstrate that two commonly used laboratory strains of the yeast Candida albicans, CAI-4 and SGY-243, can carry three copies of chromosome 1. Although the trisomic strains grow well in the laboratory, Ura+ derivatives of CAI-4, carrying three copies of chromosome 1, are avirulent in the intravenously inoculated mouse model, unlike closely related strains carrying two copies of chromosome 1. Furthermore, changes in chromosome copy number occur during growth in an animal host and during growth in the presence of growth-inhibiting drugs. These results suggest that chromosome copy number variation provides a mechanism for genetic variation in this asexual organism.
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Affiliation(s)
- Xi Chen
- Department of Molecular Biology and Microbiology and Genetics Program, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111, USA
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133
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Abstract
Candida albicans has maintained an elaborate--but largely hidden--mating apparatus, which shares some features with the closely related 'model' yeast Saccharomyces cerevisiae, but which also has some important differences. The differences are particularly noteworthy, as they could indicate the strategies that allow C. albicans to survive and mate in the hostile environment of a mammalian host. Indeed, some features of C. albicans mating seem to be intimately connected to its host.
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Affiliation(s)
- Alexander Johnson
- Department of Microbiology and Immunology, University of California, San Francisco, Mission Bay Genentech Hall, 600 16th Street, San Francisco, California 94143-2200, USA.
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134
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Soll DR. Mating-type locus homozygosis, phenotypic switching and mating: a unique sequence of dependencies in Candida albicans. Bioessays 2004; 26:10-20. [PMID: 14696036 DOI: 10.1002/bies.10379] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A small proportion of clinical strains of Candida albicans undergo white-opaque switching. Until recently it was not clear why, since most strains carry the genes differentially expressed in the unique opaque phase. The answer to this enigma lies in the mating process. The majority of C. albicans strains are heterozygous for the mating type locus MTL (a/alpha) and cannot undergo white-opaque switching. However, when these cells undergo homozygosis at the mating type locus (i.e., become a/a or alpha/alpha), they can switch, and they must switch in order to mate. Even though the newly identified stages of mating mimic those of Saccharomyces cerevisiae, the process differs in its dependency on switching, and the effects switching has on gene regulation. This unique feature of C. albicans mating appears to be intimately intertwined with its pathogenesis. The unique, newly discovered dependencies of switching on homozygosis at the MTL locus and of mating on switching are, therefore, reviewed within the context of pathogenesis.
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Affiliation(s)
- David R Soll
- Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA.
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135
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Biswas K, Rieger KJ, Morschhäuser J. Functional characterization of CaCBF1, the Candida albicans homolog of centromere binding factor 1. Gene 2004; 323:43-55. [PMID: 14659878 DOI: 10.1016/j.gene.2003.09.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The centromere binding factor 1 (Cbf1) is necessary for proper chromosome segregation and transcriptional activation of methionine biosynthesis genes in the yeast Saccharomyces cerevisiae and is essential for viability in the related yeasts Kluyveromyces lactis and Candida glabrata. To study the function of Cbf1p in Candida albicans, the major human fungal pathogen, we constructed strains in which both alleles of the CaCBF1 gene were deleted. The Deltacbf1 mutants exhibited a slow growth phenotype and were temperature-sensitive at 42 degrees C. In addition, the mutants were auxotrophic for sulfur amino acids and could grow on minimal medium only when it was supplemented with either methionine or cysteine, suggesting that CaCBF1 is necessary for the expression of genes involved in assimilation of inorganic sulfate. Deletion of CaCBF1 also resulted in morphological abnormalities, many cells being unusually large. All mutant phenotypes were complemented by reintroduction of a functional CaCBF1 copy. The Deltacbf1 mutants neither showed enhanced sensitivity to the microtubule destabilizing agent thiabendazole nor did they exhibit an increased frequency of chromosome loss. These results suggest that Cbf1p is not necessary for efficient chromosome segregation in C. albicans.
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Affiliation(s)
- Kajal Biswas
- Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070, Würzburg, Germany
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136
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Bennett RJ, Uhl MA, Miller MG, Johnson AD. Identification and characterization of a Candida albicans mating pheromone. Mol Cell Biol 2003; 23:8189-201. [PMID: 14585977 PMCID: PMC262406 DOI: 10.1128/mcb.23.22.8189-8201.2003] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Candida albicans, the most prevalent fungal pathogen of humans, has recently been shown to undergo mating. Here we describe a mating pheromone produced by C. albicans alpha cells and show that the gene which encodes it (MFalpha) is required for alpha cells, but not a cells, to mate. We also identify the receptor for this mating pheromone as the product of the STE2 gene and show that this gene is required for the mating of a cells, but not alpha cells. Cells of the a mating type respond to the alpha mating pheromone by producing long polarized projections, similar to those observed in bona fide mating mixtures of C. albicans a and alpha cells. During this process, transcription of approximately 62 genes is induced. Although some of these genes correspond to those induced in Saccharomyces cerevisiae by S. cerevisiae alpha-factor, most are specific to the C. albicans pheromone response. The most surprising class encode cell surface and secreted proteins previously implicated in virulence of C. albicans in a mouse model of disseminated candidiasis. This observation suggests that aspects of cell-cell communication in mating may have been evolutionarily adopted for host-pathogen interactions in C. albicans.
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Affiliation(s)
- Richard J Bennett
- Department of Microbiology and Immunology, University of California-San Francisco, 600 16th Street, Suite N372, San Francisco, CA 94143, USA
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137
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Soll DR, Lockhart SR, Zhao R. Relationship between switching and mating in Candida albicans. EUKARYOTIC CELL 2003; 2:390-7. [PMID: 12796284 PMCID: PMC161441 DOI: 10.1128/ec.2.3.390-397.2003] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- David R Soll
- Department of Biological Sciences, The University of Iowa, Iowa City, Iowa 52242, USA.
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138
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Bennett RJ, Johnson AD. Completion of a parasexual cycle in Candida albicans by induced chromosome loss in tetraploid strains. EMBO J 2003; 22:2505-15. [PMID: 12743044 PMCID: PMC155993 DOI: 10.1093/emboj/cdg235] [Citation(s) in RCA: 276] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The human pathogenic fungus Candida albicans has traditionally been classified as a diploid, asexual organism. However, mating-competent forms of the organism were recently described that produced tetraploid mating products. In principle, the C.albicans life cycle could be completed via a sexual process, via a parasexual mechanism, or by both mechanisms. Here we describe conditions in which growth of a tetraploid strain of C.albicans on Saccharomyces cerevisiae 'pre-sporulation' medium induced efficient, random chromosome loss in the tetraploid. The products of chromosome loss were often strains that were diploid, or very close to diploid, in DNA content. If they inherited the appropriate MTL (mating-type like) loci, these diploid products were themselves mating competent. Thus, an efficient parasexual cycle can be performed in C.albicans, one that leads to the reassortment of genetic material in this organism. We show that this parasexual cycle-consisting of mating followed by chromosome loss-can be used in the laboratory for simple genetic manipulations in C.albicans.
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Affiliation(s)
- Richard J Bennett
- Department of Microbiology, University of California, San Francisco 94143, USA
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139
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Magee BB, Legrand M, Alarco AM, Raymond M, Magee PT. Many of the genes required for mating in Saccharomyces cerevisiae are also required for mating in Candida albicans. Mol Microbiol 2002; 46:1345-51. [PMID: 12453220 DOI: 10.1046/j.1365-2958.2002.03263.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans is the single, most frequently isolated human fungal pathogen. As with most fungal pathogens, the factors which contribute to pathogenesis in C. albicans are not known, despite more than a decade of molecular genetic analysis. Candida albicans was thought to be asexual until the discovery of the MTL loci homologous to the mating type (MAT) loci in Saccharomyces cerevisiae led to the demonstration that mating is possible. Using Candida albicans mutants in genes likely to be involved in mating, we analysed the process to determine its similarity to mating in Saccharomyces cerevisiae. We examined disruptions of three of the genes in the MAPK pathway which is involved in filamentous growth in both S. cerevisiae and C. albicans and is known to control pheromone response in the former fungus. Disruptions in HST7 and CPH1 blocked mating in both MTLa and MTL(alpha) strains, whereas disruptions in STE20 had no effect. A disruption in KEX2, a gene involved in processing the S. cerevisiae pheromone Mf(alpha), prevented mating in MTL(alpha) but not MTLa cells, whereas a disruption in HST6, the orthologue of the STE6 gene which encodes an ABC transporter responsible for secretion of the Mfa pheromone, prevented mating in MTLa but not in MTL(alpha) cells. Disruption of two cell wall genes, ALS1 and INT1, had no effect on mating, even though ALS1 was identified by similarity to the S. cerevisiae sexual agglutinin, SAG1. The results reveal that these two diverged yeasts show a surprising similarity in their mating processes.
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Affiliation(s)
- B B Magee
- Department of Genetics, Cell Biology, and Development, University of Minnesota, St. Paul, MN 55108, USA
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140
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Chen J, Chen J, Lane S, Liu H. A conserved mitogen-activated protein kinase pathway is required for mating in Candida albicans. Mol Microbiol 2002; 46:1335-44. [PMID: 12453219 DOI: 10.1046/j.1365-2958.2002.03249.x] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans had been thought to lack a mating process until the recent discovery of a mating type-like locus and mating between MTLa and MTL(alpha) strains. To elucidate the molecular mechanisms that regulate mating in C. albicans, we examined the function of Cph1 and its upstream mitogen-activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone-responsive MAP kinase pathway in Saccharomyces cerevisiae. We found that overexpressing CPH1 in MTLa, but not in MTLa/alpha strains, induced the transcription of orthologues of S. cerevisiae pheromone-induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae. The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTL(alpha), but not in MTLa/alpha cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans. We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient-sensing pathways in mating in addition to the MAP kinase pathway.
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Affiliation(s)
- Jiangye Chen
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, SIBS, CAS, 320 Yue-yang Road, Shanghai 200031, China
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141
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Berman J, Sudbery PE. Candida Albicans: a molecular revolution built on lessons from budding yeast. Nat Rev Genet 2002; 3:918-30. [PMID: 12459722 DOI: 10.1038/nrg948] [Citation(s) in RCA: 382] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Candida albicans is an opportunistic fungal pathogen that is found in the normal gastrointestinal flora of most healthy humans. However, in immunocompromised patients, blood-stream infections often cause death, despite the use of anti-fungal therapies. The recent completion of the C. albicans genome sequence, the availability of whole-genome microarrays and the development of tools for rapid molecular-genetic manipulations of the C. albicans genome are generating an explosion of information about the intriguing biology of this pathogen and about its mechanisms of virulence. They also reveal the extent of similarities and differences between C. albicans and its benign relative, Saccharomyces cerevisiae.
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Affiliation(s)
- Judith Berman
- Department of Genetics, Cell Biology and Development, 6-160 Jackson Hall, 321 Church Street SE, Minneapolis, Minnesota 55455, USA.
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142
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Trail F, Xu H. Purification and characterization of mannitol dehydrogenase and identification of the corresponding cDNA from the head blight fungus, Gibberella zeae (Fusarium graminearum). PHYTOCHEMISTRY 2002; 61:791-796. [PMID: 12453571 DOI: 10.1016/s0031-9422(02)00430-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The mannitol-2-dehydrogenase (MtDH) from Gibberella zeae was purified and the corresponding cDNA identified. Purification of MtDH was accomplished using a combination of ammonium sulfate fractionation, anion exchange and dye-ligand chromatography. Final purification was achieved following electroelution from a native gel. Molecular mass determination based on SDS-PAGE indicated that the denatured protein was 29 kDa. Native protein mass was determined to be 110 kDa using gel permeation chromatography, indicating a tetrameric form. The pH optima for mannitol oxidation and fructose reductase activities were 9.0, and 7.0, respectively. Activity with sorbitol as the substrate was 21% of activity with mannitol. Kinetic parameters were determined by direct-linear plots of enzyme activity vs. substrate concentrations. Fructose concentrations above 600 mM and NADPH concentrations above 0.3 mM caused substrate inhibition. Comparisons of predicted amino acid sequences of several fungal MtDHs indicated high conservation within the phyla. A possible role for MtDH in generation of turgor pressure for forcible ascospore discharge is discussed.
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Affiliation(s)
- Frances Trail
- Department of Plant Biology, Michigan State University, East Lansing, MI 48824-1312, USA.
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143
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Heymann P, Gerads M, Schaller M, Dromer F, Winkelmann G, Ernst JF. The siderophore iron transporter of Candida albicans (Sit1p/Arn1p) mediates uptake of ferrichrome-type siderophores and is required for epithelial invasion. Infect Immun 2002; 70:5246-55. [PMID: 12183576 PMCID: PMC128288 DOI: 10.1128/iai.70.9.5246-5255.2002] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human fungal pathogen Candida albicans contains a close homologue of yeast siderophore transporters, designated Sit1p/Arn1p. We have characterized the function of SIT1 in C. albicans by constructing sit1 deletion strains and testing their virulence and ability to utilize a range of siderophores and other iron complexes. sit1 mutant strains are defective in the uptake of ferrichrome-type siderophores including ferricrocin, ferrichrysin, ferrirubin, coprogen, and triacetylfusarinine C. A mutation of FTR1 did not impair the use of these siderophores but did affect the uptake of ferrioxamines E and B, as well as of ferric citrate, indicating that their utilization was independent of Sit1p. Hemin was a source of iron for both sit1 and ftr1 mutants, suggesting a pathway of hemin uptake distinct from that of siderophores and iron salts. Heterologous expression of SIT1 in the yeast Saccharomyces cerevisiae confirmed the function of Sit1p as a transporter for ferrichrome-type siderophores. The sit1 mutant was defective in infection of a reconstituted human epithelium as a model for human oral mucosa, while the SIT1 strain was invasive. In contrast, both sit1 and SIT1 strains were equally virulent in the mouse model of systemic infection. These results suggest that siderophore uptake by Sit1p/Arn1p is required in a specific process of C. albicans infection, namely epithelial invasion and penetration, while in the blood or within organs other sources of iron, including heme, may be used.
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Affiliation(s)
- Petra Heymann
- Institut für Mikrobiologie, Heinrich-Heine-Universität Düsseldorf, Germany
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144
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Miller MG, Johnson AD. White-opaque switching in Candida albicans is controlled by mating-type locus homeodomain proteins and allows efficient mating. Cell 2002; 110:293-302. [PMID: 12176317 DOI: 10.1016/s0092-8674(02)00837-1] [Citation(s) in RCA: 404] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Discovered over a decade ago, white-opaque switching in the human fungal pathogen Candida albicans is an alternation between two quasistable, heritable transcriptional states. Here, we show that white-opaque switching and sexual mating are both controlled by mating type locus homeodomain proteins and that opaque cells mate approximately 10(6) times more efficiently than do white cells. These results show that opaque cells are a mating-competent form of C. albicans and that this pathogen undergoes a white-to-opaque switch as a critical step in the mating process. As white cells are generally more robust in a mammalian host than are opaque cells, this strategy allows the organism to survive the rigors of life within a mammalian host, yet generate mating-competent cells.
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Affiliation(s)
- Mathew G Miller
- Department of Microbiology and Immunology, University of California, San Francisco 94143, USA
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145
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Andaluz E, Ciudad T, Larriba G. An evaluation of the role ofLIG4in genomic instability and adaptive mutagenesis inCandida albicans. FEMS Yeast Res 2002. [DOI: 10.1111/j.1567-1364.2002.tb00103.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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146
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Bai C, Ramanan N, Wang YM, Wang Y. Spindle assembly checkpoint component CaMad2p is indispensable for Candida albicans survival and virulence in mice. Mol Microbiol 2002; 45:31-44. [PMID: 12100546 DOI: 10.1046/j.1365-2958.2002.02995.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Here, we report an indispensable role for spindle assembly checkpoint (SAC) component CaMad2p in the survival and virulence of Candida albicans in mice. We hypothesized that cell cycle checkpoint functions, especially those monitoring the integrity of DNA and chromosome segregation, might be required for the pathogen to repair damage caused by host defence. To test this idea, we created SAC-defective mutants by deleting the CaMAD2 gene that encodes a key component of the SAC pathway. The CaMAD2 mutant appears normal in morphology, growth rate and growth mode switch in unperturbed conditions. However, it quickly loses viability when treated with nocodazole, which causes disassembly of mitotic spindles. The mutant also exhibits increased frequency of chromosome loss. The virulence of the mutant is greatly reduced in mice, presumably because of the inability of the mutant cells to stop the cell cycle when the host defence damages cellular components important for chromosome segregation. Supporting this hypothesis, unlike the wild-type cells that can proliferate within and eventually grow out of macrophages, most of the CaMAD2 null mutant cells are unable to survive. This study suggests that SAC is required for survival of C. albicans in the host and could thus be targeted for anti-C. albicans therapies.
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Affiliation(s)
- Chen Bai
- Microbial Collection and Screening Laboratory, Institute of Molecular and Cell Biology, Singapore
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147
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Rustad TR, Stevens DA, Pfaller MA, White TC. Homozygosity at the Candida albicans MTL locus associated with azole resistance. MICROBIOLOGY (READING, ENGLAND) 2002; 148:1061-1072. [PMID: 11932451 DOI: 10.1099/00221287-148-4-1061] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Antifungal drug resistance in the pathogenic fungus Candida albicans is a serious threat to the growing population of immunocompromised patients. This study describes a significant correlation between loss of heterozygosity at the C. albicans mating-type-like (MTL) locus and resistance to azole antifungals. A pool of 96 clinical isolates consisting of 50 azole-resistant or susceptible dose-dependent isolates and 46 azole-susceptible isolates was screened by PCR for the presence of MTLa1 and MTLalpha1. These genes were used as markers for the MTLa and MTLalpha loci. Both loci were present in 84 of the isolates. Six isolates failed to amplify MTLa1 and six failed to amplify MTLalpha1. Further PCR analysis demonstrated that loss of the MTLa1 and MTLalpha1 genes corresponded to loss of all of the loci-specific genes, resulting in homozygosity at the MTL locus. Southern analysis and single nucleotide polymorphism (SNP) analysis were used to determine that this loss of heterogeneity was due to replacement of one of the MTL loci with a duplicate of the other locus resulting in two homozygous copies of the MTL locus. Of the 12 homozygous isolates, one isolate was sensitive to azole drugs. Statistical analysis of the data demonstrates a strong correlation between homozygosity at the MTL locus and azole resistance (P<0 small middle dot003). In a set of serial isolates, an increase in azole resistance correlated with the loss of heterozygosity at the MTL locus, lending further strength to the correlation. Gene disruptions of the MTL loci were found to have no effect on azole susceptibility.
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Affiliation(s)
- Tige R Rustad
- Seattle Biomedical Research Institute, 4 Nickerson St Suite 200, Seattle, WA 98109-1651, USA2
- Department of Pathobiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195, USA1
| | - David A Stevens
- Department of Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University, Stanford, CA 52242, USA4
- Department of Medicine, Santa Clara Valley Medical Center and California Institute for Medical Research, San Jose, CA 95128, USA3
| | - Michael A Pfaller
- Department of Pathology, University of Iowa, Iowa City, IA 52242, USA5
| | - Theodore C White
- Seattle Biomedical Research Institute, 4 Nickerson St Suite 200, Seattle, WA 98109-1651, USA2
- Department of Pathobiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195, USA1
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148
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Iwaguchi SI, Sato M, Magee BB, Magee PT, Makimura K, Suzuki T. Extensive chromosome translocation in a clinical isolate showing the distinctive carbohydrate assimilation profile from a candidiasis patient. Yeast 2001; 18:1035-46. [PMID: 11481674 DOI: 10.1002/yea.748] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Variation of the electrophoretic karyotype is common among clinical strains of Candida albicans and chromosome translocation is considered one of the causes of karyotypic variation. Such chromosome translocations may be a mechanism to confer phenotypic diversity on the imperfect fungus C. albicans. A clinical strain, TCH23, from a vaginal candidiasis patient shows distinct carbohydrate assimilation profile, serotype B, no chlamydospore formation and an atypical karyotype (Asakura et al., 1991). To examine the taxonomic relationship among C. albicans, Candida dubliniensis and this strain, we sequenced the internal transcribed spacer 1 (ITS1) of nuclear ribosomal DNA. The ITS1 sequence of TCH23 was identical with that of C. albicans but not of C. dubliniensis. Thus, strain TCH23 was classified as a variant of C. albicans with an atypical phenotype. The chromosomal DNAs of this strain were resolved into 13 bands on pulse-field gel electrophoresis (PFGE). Using DNA probes located at or near both ends of each chromosome of C. albicans, we investigated the chromosome organization of this strain. Referring to the SfiI map of C. albicans 1006 (Chu et al., 1993), we found that seven chromosomal DNA bands in strain TCH23 were reciprocal chromosome translocations. One homologue from chromosomes 1, 2 and 6 and both homologues from chromosomes 4 and 7 participated in these events. One translocation product was composed of three SfiI fragments, one each from chromosomes 2, 4 and 7. We deduced the breakpoints of chromosome translocation from the physical map of this strain; between 1J and 1J1, between 2A and 2U, both ends of 4F2, between 6C and 6O and both ends of 7F.
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Affiliation(s)
- S I Iwaguchi
- Department of Biological Science, Nara Women's University, Nara 630-8506, Japan.
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149
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Abstract
Although plasmids containing rRNA genes (rDNA) are commonly found in fungi, they have not been reported in Candida. We discovered that the yeast opportunistic pathogen Candida albicans contains two types of rDNA plasmids which differ in their structure and number of rDNA repeats. A large circular plasmid of unknown size consists of multiple rDNA repeats, each of which includes an associated autonomously replicating sequence (ARS). In contrast, a linear plasmid, which is represented by a series of molecules with a spread of sizes ranging from 50-150 kbp, carries a limited number of rDNA units and associated ARSs, as well as telomeres. The number of linear plasmids per cell is growth cycle-dependent, accumulating in abundance in actively growing cells. We suggest that the total copy number of rDNA is better controlled when a portion of copies are on a linear extrachromosomal plasmid, thus allowing a rapid shift in the number of corresponding genes and, as a result, better adaptation to the environment. This is the first report of a linear rDNA plasmid in yeast, as well as of the coexistence of circular and linear plasmids. In addition, this is a first report of naturally occurring plasmids in C. albicans.
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MESH Headings
- Blotting, Southern
- Candida albicans/chemistry
- Candida albicans/genetics
- Candida albicans/growth & development
- Chromosomes, Fungal/chemistry
- Chromosomes, Fungal/genetics
- DNA Probes/chemistry
- DNA, Circular/genetics
- DNA, Fungal/chemistry
- DNA, Fungal/genetics
- DNA, Fungal/isolation & purification
- DNA, Ribosomal/chemistry
- DNA, Ribosomal/genetics
- DNA, Ribosomal/isolation & purification
- Electrophoresis, Gel, Pulsed-Field
- Plasmids/chemistry
- Plasmids/genetics
- Plasmids/isolation & purification
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Affiliation(s)
- D Huber
- Department of Biochemistry and Biophysics, University of Rochester Medical School, Rochester, NY 14642, USA
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150
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Andaluz E, Calderone R, Reyes G, Larriba G. Phenotypic analysis and virulence of Candida albicans LIG4 mutants. Infect Immun 2001; 69:137-47. [PMID: 11119499 PMCID: PMC97865 DOI: 10.1128/iai.69.01.137-147.2001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In previous studies, we reported the isolation and preliminary characterization of a DNA ligase-encoding gene of Candida albicans. This gene (LIG4) is the structural and functional homologue of both yeast and human ligase IV, which is involved in nonhomologous end joining (NHEJ) of DNA double-strand breaks. In the present study, we have shown that there are no other LIG4 homologues in C. albicans. In order to study the function of LIG4 in morphogenesis and virulence, we constructed gene deletions. LIG4 transcript levels were reduced in the heterozygote and were completely absent in null strains. Concomitantly, the heterozygote showed a pronounced defect in myceliation, which was slightly greater in the null strain. This was true with several solid and liquid media, such as Spider medium, medium 199, and 2% glucose-1% yeast extract-2% Bacto Peptone, at several pHs. Reintroduction of the wild-type allele into the null mutant partially restored the ability of cells to form hyphae. In agreement with the positive role of LIG4 in morphogenesis, we detected a significant rise in mRNA levels during the morphological transition. LIG4 is not essential for DNA replication or for the repair of DNA damage induced by ionizing radiation or UV light, indicating that these lesions are repaired primarily by homologous recombination. However, our data show that the NHEJ apparatus of C. albicans may control morphogenesis in this diploid organism. In addition, deletion of one or both copies of LIG4 resulted in attenuation of virulence in a murine model of candidiasis.
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Affiliation(s)
- E Andaluz
- Departamento de Microbiología, Universidad de Extremadura, 06071 Badajoz, Spain
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