The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Richard J. Bennett - One of the best experts on this subject based on the ideXlab platform.
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Parasexuality and Ploidy Change in Candida tropicalis
2016Co-Authors: Riyad N.h. Seervai, Stephen K. Jones, Matthew P. Hirakawa, Allison M. Porman, Richard J. BennettAbstract:Candida species exhibit a variety of ploidy states andmodes of sexual reproduction. Most species possess the requisite genes for sexual reproduction, recombination, andmeiosis, yet only a few have been reported to undergo a complete sexual Cycle includ-ing mating and sporulation. Candida albicans, the most studied Candida species and a prevalent human fungal pathogen, com-pletes its sexual Cycle via a Parasexual process of concerted chromosome loss rather than a conventional meiosis. In this study, we examine ploidy changes in Candida tropicalis, a closely related species to C. albicans that was recently revealed to undergo sexual mating. C. tropicalis diploid cells mate to form tetraploid cells, and we show that these can be induced to undergo chro-mosome loss to regenerate diploid forms by growth on sorbose medium. The diploid products are themselves mating competent, thereby establishing a Parasexual Cycle in this species for the first time. Extended incubation (>120 generations) of C. tropicalis tetraploid cells under rich culture conditions also resulted in instability of the tetraploid form and a gradual reduction in ploidy back to the diploid state. The fitness levels of C. tropicalis diploid and tetraploid cells were compared, and diploid cells exhibited increased fitness relative to tetraploid cells in vitro, despite diploid and tetraploid cells having similar doubling times. Collec-tively, these experiments demonstrate distinct pathways by which a Parasexual Cycle can occur in C. tropicalis and indicate that nonmeiotic mechanisms drive ploidy changes in this prevalent human pathogen. Many yeast species can reproduce by both sexual and asexualmechanisms. Asexual reproduction is generally utilized when conditions are favorable for growth, while sexual reproduc
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The Parasexual lifestyle of Candida albicans.
Current opinion in microbiology, 2015Co-Authors: Richard J. BennettAbstract:Candida albicans is both a prevalent human commensal and the most commonly encountered human fungal pathogen. This lifestyle is dependent on the ability of the fungus to undergo rapid genetic and epigenetic changes, often in response to specific environmental cues. A Parasexual Cycle in C. albicans has been defined that includes several unique properties when compared to the related model yeast, Saccharomyces cerevisiae. Novel features include strict regulation of mating via a phenotypic switch, enhanced conjugation within a sexual biofilm, and a program of concerted chromosome loss in place of a conventional meiosis. It is expected that several of these adaptations co-evolved with the ability of C. albicans to colonize the mammalian host.
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Parasexuality and Ploidy Change in Candida tropicalis
Eukaryotic cell, 2013Co-Authors: Riyad N.h. Seervai, Stephen K. Jones, Matthew P. Hirakawa, Allison M. Porman, Richard J. BennettAbstract:ABSTRACT Candida species exhibit a variety of ploidy states and modes of sexual reproduction. Most species possess the requisite genes for sexual reproduction, recombination, and meiosis, yet only a few have been reported to undergo a complete sexual Cycle including mating and sporulation. Candida albicans, the most studied Candida species and a prevalent human fungal pathogen, completes its sexual Cycle via a Parasexual process of concerted chromosome loss rather than a conventional meiosis. In this study, we examine ploidy changes in Candida tropicalis, a closely related species to C. albicans that was recently revealed to undergo sexual mating. C. tropicalis diploid cells mate to form tetraploid cells, and we show that these can be induced to undergo chromosome loss to regenerate diploid forms by growth on sorbose medium. The diploid products are themselves mating competent, thereby establishing a Parasexual Cycle in this species for the first time. Extended incubation (>120 generations) of C. tropicalis tetraploid cells under rich culture conditions also resulted in instability of the tetraploid form and a gradual reduction in ploidy back to the diploid state. The fitness levels of C. tropicalis diploid and tetraploid cells were compared, and diploid cells exhibited increased fitness relative to tetraploid cells in vitro , despite diploid and tetraploid cells having similar doubling times. Collectively, these experiments demonstrate distinct pathways by which a Parasexual Cycle can occur in C. tropicalis and indicate that nonmeiotic mechanisms drive ploidy changes in this prevalent human pathogen.
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The Parasexual Cycle in Candida albicans Provides an Alternative Pathway to Meiosis for the Formation of Recombinant Strains
2013Co-Authors: Anja Forche, Dana Schaefer, Judith Berman, Kevin Alby, Er D. Johnson, Richard J. BennettAbstract:Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and a strains. The product of mating is a tetraploid a/a cell that must undergo a reductional division to return to the diploid state. Despite the presence of several ‘‘meiosis-specific’ ’ genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans Parasexual Cycle. We show that the Parasexual Cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the Parasexual Cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans Parasexual Cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative Parasexual life Cycle of C. albicans. We discuss, in light of the long association of C. albicans wit
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The Parasexual Cycle in Candida albicans provides an alternative pathway to meiosis for the formation of recombinant strains
PLoS Biology, 2008Co-Authors: Anja Forche, Dana Schaefer, Judith Berman, Kevin Alby, Alexander D Johnson, Richard J. BennettAbstract:Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and alpha strains. The product of mating is a tetraploid a/alpha cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans Parasexual Cycle. We show that the Parasexual Cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the Parasexual Cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans Parasexual Cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative Parasexual life Cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a Parasexual Cycle over a conventional sexual Cycle.
Judith Berman - One of the best experts on this subject based on the ideXlab platform.
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Does stress induce (para)sex? Implications for Candida albicans evolution. Trends Genet 28
2015Co-Authors: Judith Berman, Lilach HadanyAbstract:Theory predicts that stress is a key factor in explaining the evolutionary role of sex in facultatively sexual organisms, including microorganisms. Organisms capable of reproducing both sexually and asexually are expected to mate more frequently when stressed, and such stress-induced mating is predicted to facilitate adaptation. Here, we propose that stress has an analogous effect on the Parasexual Cycle in Candida albicans, which involves alternation of generations between diploid and tetraploid cells. The Parasexual Cycle can generate high levels of diversity, including aneuploidy, yet it apparently occurs only rarely in nature. We review the evidence that stress facilitates four major steps in the Parasexual Cycle, and suggest that parasex ensues much more frequently under stress conditions. This may explain both the evolutionary significance of parasex and its apparent rarity. The Parasexual Cycle in Candida albicans C. albicans, the most prevalent fungal pathogen of humans, is constantly challenged by interactions with the immune system as well as by the need to survive in a broad range of ecological niches within its human host. When exposed to severe stress, such as a
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Parasexual Ploidy Reduction Drives Population Heterogeneity Through Random and Transient Aneuploidy in Candida albicans
Genetics, 2015Co-Authors: Meleah A. Hickman, Carsten Paulson, Aimée M. Dudley, Judith BermanAbstract:The opportunistic pathogen Candida albicans has a large repertoire of mechanisms to generate genetic and phenotypic diversity despite the lack of meiosis in its life Cycle. Its Parasexual Cycle enables shifts in ploidy, which in turn facilitate recombination, aneuploidy, and homozygosis of whole chromosomes to fuel rapid adaptation. Here we show that the tetraploid state potentiates ploidy variation and drives population heterogeneity. In tetraploids, the rate of losing a single heterozygous marker [loss of heterozygosity (LOH)] is elevated ∼30-fold higher than the rate in diploid cells. Furthermore, isolates recovered after selection for LOH of one, two, or three markers were highly aneuploid, with a broad range of karyotypes including strains with a combination of di-, tri-, and tetrasomic chromosomes. We followed the ploidy trajectories for these tetraploid- and aneuploid-derived isolates, using a combination of flow cytometry and double-digestion restriction-site-associated DNA analyzed with next-generation sequencing. Isolates derived from either tetraploid or aneuploid isolates predominately resolved to a stable euploid state. The majority of isolates reduced to the conventional diploid state; however, stable triploid and tetraploid states were observed in ∼30% of the isolates. Notably, aneuploid isolates were more transient than tetraploid isolates, resolving to a euploid state within a few passages. Furthermore, the likelihood that a particular isolate will resolve to the same ploidy state in replicate evolution experiments is only ∼50%, supporting the idea that the chromosome loss process of the Parasexual Cycle is random and does not follow trajectories involving specific combinations of chromosomes. Together, our results indicate that tetraploid progenitors can produce populations of progeny cells with a high degree of genomic diversity, from altered ploidy to homozygosis, providing an excellent source of genetic variation upon which selection can act.
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The Parasexual Cycle in Candida albicans Provides an Alternative Pathway to Meiosis for the Formation of Recombinant Strains
2013Co-Authors: Anja Forche, Dana Schaefer, Judith Berman, Kevin Alby, Er D. Johnson, Richard J. BennettAbstract:Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and a strains. The product of mating is a tetraploid a/a cell that must undergo a reductional division to return to the diploid state. Despite the presence of several ‘‘meiosis-specific’ ’ genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans Parasexual Cycle. We show that the Parasexual Cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the Parasexual Cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans Parasexual Cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative Parasexual life Cycle of C. albicans. We discuss, in light of the long association of C. albicans wit
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Does stress induce (para)sex? Implications for Candida albicans evolution
Trends in genetics : TIG, 2012Co-Authors: Judith Berman, Lilach HadanyAbstract:Theory predicts that stress is a key factor in explaining the evolutionary role of sex in facultatively sexual organisms, including microorganisms. Organisms capable of reproducing both sexually and asexually are expected to mate more frequently when stressed, and such stress-induced mating is predicted to facilitate adaptation. Here, we propose that stress has an analogous effect on the Parasexual Cycle in Candida albicans, which involves alternation of generations between diploid and tetraploid cells. The Parasexual Cycle can generate high levels of diversity, including aneuploidy, yet it apparently occurs only rarely in nature. We review the evidence that stress facilitates four major steps in the Parasexual Cycle and suggest that parasex occurs much more frequently under stress conditions. This may explain both the evolutionary significance of parasex and its apparent rarity.
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The Parasexual Cycle in Candida albicans provides an alternative pathway to meiosis for the formation of recombinant strains
PLoS Biology, 2008Co-Authors: Anja Forche, Dana Schaefer, Judith Berman, Kevin Alby, Alexander D Johnson, Richard J. BennettAbstract:Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and alpha strains. The product of mating is a tetraploid a/alpha cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans Parasexual Cycle. We show that the Parasexual Cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the Parasexual Cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans Parasexual Cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative Parasexual life Cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a Parasexual Cycle over a conventional sexual Cycle.
Lilach Hadany - One of the best experts on this subject based on the ideXlab platform.
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Does stress induce (para)sex? Implications for Candida albicans evolution. Trends Genet 28
2015Co-Authors: Judith Berman, Lilach HadanyAbstract:Theory predicts that stress is a key factor in explaining the evolutionary role of sex in facultatively sexual organisms, including microorganisms. Organisms capable of reproducing both sexually and asexually are expected to mate more frequently when stressed, and such stress-induced mating is predicted to facilitate adaptation. Here, we propose that stress has an analogous effect on the Parasexual Cycle in Candida albicans, which involves alternation of generations between diploid and tetraploid cells. The Parasexual Cycle can generate high levels of diversity, including aneuploidy, yet it apparently occurs only rarely in nature. We review the evidence that stress facilitates four major steps in the Parasexual Cycle, and suggest that parasex ensues much more frequently under stress conditions. This may explain both the evolutionary significance of parasex and its apparent rarity. The Parasexual Cycle in Candida albicans C. albicans, the most prevalent fungal pathogen of humans, is constantly challenged by interactions with the immune system as well as by the need to survive in a broad range of ecological niches within its human host. When exposed to severe stress, such as a
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Does stress induce (para)sex? Implications for Candida albicans evolution
Trends in genetics : TIG, 2012Co-Authors: Judith Berman, Lilach HadanyAbstract:Theory predicts that stress is a key factor in explaining the evolutionary role of sex in facultatively sexual organisms, including microorganisms. Organisms capable of reproducing both sexually and asexually are expected to mate more frequently when stressed, and such stress-induced mating is predicted to facilitate adaptation. Here, we propose that stress has an analogous effect on the Parasexual Cycle in Candida albicans, which involves alternation of generations between diploid and tetraploid cells. The Parasexual Cycle can generate high levels of diversity, including aneuploidy, yet it apparently occurs only rarely in nature. We review the evidence that stress facilitates four major steps in the Parasexual Cycle and suggest that parasex occurs much more frequently under stress conditions. This may explain both the evolutionary significance of parasex and its apparent rarity.
Michel Fèvre - One of the best experts on this subject based on the ideXlab platform.
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Randomly amplified polymorphic DNAs assess recombination following an induced Parasexual Cycle in Penicillium roqueforti
Current genetics, 1993Co-Authors: Nathalie Durand, Pascale Reymond, Michel FèvreAbstract:Random amplified polymorphic DNAs (RAPDs) were used as a genetic marker system to characterize recombinant strains following the Parasexual Cycle of Penicillium roqueforti. After protoplast fusion and haploidization of diploid hybrids, segregants characterized by a reassortment of the parental genetic markers displayed specific RAPD fingerprints. The appearance or the loss of RAPD fragments demonstrate that these markers provide an efficient method to analyze recombination and to characterize somatic hybrids.
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Transmission and modification of transformation markers during an induced Parasexual Cycle in Penicillium roqueforti
Current Genetics, 1992Co-Authors: Nathalie Durand, Pascale Reymond, Michel FèvreAbstract:Protoplasts of two wild-type strains of Penicillium roqueforti were transformed to hygromycin B and phleomycin resistance using resistance genes. DNAs were stably integrated into the fungal chromosomes. Protoplasts from transformed strains have been fused to produce diploid hybrids. After induced haploidization, segregants characterized by a reassortment of the parental genetic markers were isolated indicating that recombination had occurred during the Parasexual Cycle. Southern blot hydridization experiments revealed that transmission of the transformed phenotype was accompanied by extensive rearrangement and/or deletions dependent on the number of integrated plasmid copies. Methylation of cytosine residues of integrated DNA was also detected. These observations suggest that foreign DNA sequences transmitted during the Parasexual Cycle undergo modifications similar to the rearrangement of transformed characters induced premeiotically (RIP) through sexual crosses.
Jan Schmid - One of the best experts on this subject based on the ideXlab platform.
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Last hope for the doomed? Thoughts on the importance of a Parasexual Cycle for the yeast Candida albicans
Current genetics, 2015Co-Authors: Jan Schmid, Ningxin Zhang, P. T. Magee, Barbara R. Holland, Richard D. Cannon, B. B. MageeAbstract:The yeast Candida albicans, a commensal colonizer and occasional pathogen of humans, has a rudimentary mating ability. However, mating is a cumbersome process that has never been observed outside the laboratory, and the population structure of the species is predominantly clonal. Here we discuss recent findings that indicate that mating ability is under selection in C. albicans, i.e. that it is a biologically relevant process. C. albicans strains can only mate after they have sustained genetic damage. We propose that the rescue of such damaged strains by mating may be the primary reason why mating ability is under selection.
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Selective advantages of a Parasexual Cycle for the yeast Candida albicans
Genetics, 2015Co-Authors: Ningxin Zhang, B. B. Magee, P. T. Magee, Barbara R. Holland, Ely Rodrigues, Ann R. Holmes, Richard D. Cannon, Jan SchmidAbstract:The yeast Candida albicans can mate. However, in the natural environment mating may generate progeny (fusants) fitter than clonal lineages too rarely to render mating biologically significant: C. albicans has never been observed to mate in its natural environment, the human host, and the population structure of the species is largely clonal. It seems incapable of meiosis, and most isolates are diploid and carry both mating-type-like (MTL) locus alleles, preventing mating. Only chromosome loss or localized loss of heterozygosity can generate mating-competent cells, and recombination of parental alleles is limited. To determine if mating is a biologically significant process, we investigated if mating is under selection. The ratio of nonsynonymous to synonymous mutations in mating genes and the frequency of mutations abolishing mating indicated that mating is under selection. The MTL locus is located on chromosome 5, and when we induced chromosome 5 loss in 10 clinical isolates, most of the resulting MTL-homozygotes could mate with each other, producing fusants. In laboratory culture, a novel environment favoring novel genotypes, some fusants grew faster than their parents, in which loss of heterozygosity had reduced growth rates, and also faster than their MTL-heterozygous ancestors—albeit often only after serial propagation. In a small number of experiments in which co-inoculation of an oral colonization model with MTL-homozygotes yielded small numbers of fusants, their numbers declined over time relative to those of the parents. Overall, our results indicate that mating generates genotypes superior to existing MTL-heterozygotes often enough to be under selection.
