Natural Variation in the Fitness Consequences of Gene Amplification in Wild Saccharomyces cerevisiae Isolates [Bar-seq]
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ABSTRACT: Genetic variation that underlies phenotypic differences provides the material on which evolutionary selection acts. Gene duplication/amplification is one type of genetic variation that can allow an organism to rapidly respond to environmental changes by increasing gene dosage. While the potential benefits afforded by gene amplification during evolution are well known, there is also a significant fitness cost to increasing gene dosage including resource shortages and burdening cellular systems. Although the evolutionary importance of gene duplication has long been appreciated, little is known about natural variation in the tolerance of duplication of specific genes. To investigate this question, we expressed the same high-copy gene overexpression (OE) library in a laboratory strain and 14 different wild S. cerevisiae isolates, together representing 4 lineages and several admixed strains, to explore the natural variation in tolerance to gene OE. Our results distinguish universal effects common to many studied strains versus strain-specific effects including broad-scale and gene-specific differences in the consequences of OE. These results raise important implications for the accessibility of evolutionary trajectories afforded by gene OE, depending on genetic background.
Project description:Free-living cells live in fluctuating environments and must be able to respond rapidly in order to survive. Genetic background can influence how an individual responds to a changing environment, including stressful changes. Changes in gene copy number can influence stress tolerance and responses, presumably due to corresponding changes in gene expression. However, we recently showed that strains vary in their ability to tolerate gene copy number differences; how this influences variation in stress tolerance is relatively unknown. Here we measured the tolerance to gene overexpression (OE) in four different Saccharomyces cerevisiae strains, including wild isolates, when strains were grown under osmotic and ionic stress induced by sodium chloride (NaCl). OE genes that were deleterious to most strains under NaCl stress were enriched for translation processes, similar to the enrichments of deleterious genes in rich, non-stress medium. We found that the West African NCYC3290 strain and the North American YPS128 strain are more sensitive to NaCl stress than other strains. These strains showed the greatest number of sensitivities to gene OE compared to other strains. Although most genes were deleterious in these strains, subsets of genes are highly beneficial when OE during NaCl stress. Many of these highly beneficial genes are functionally related and point to underlying differences in strain physiology. This work illustrates how tolerance to gene overexpression is influenced by genotype-environment interactions.
Project description:Heteroresistance in bacteria describes a subpopulational phenomenon of transient antibiotic resistance variation among cells of a generally susceptible population. Here, we investigated the molecular mechanisms and phenotypic characteristics underlying heteroresistance to ceftazidime (CAZ) in a clinical Enterobacter cloacae complex strain (ECC). We identified a plasmid-borne gene duplication-amplification (GDA) event of a region harboring an ampC gene encoding a β-lactamase blaDHA-1 as the key determinant of heteroresistance. Individual colonies exhibited variations in the copy number of the genes resulting in resistance level variation which correlated with growth onset (lag times) and growth rates in the presence of CAZ, analysed in linear models. GDA copy number heterogeneity occurred within single resistant colonies, demonstrating heterogeneity of GDA on the single-cell level. The interdependence between GDA, lag time and antibiotic treatment and the strong plasticity underlying heteroresistance underlines the high risk for misdetection of antimicrobial heteroresistance and subsequent treatment failure.
Project description:We show that aneuploidy is common in wild isolates of yeast, which are inherently tolerant to chromosome amplification and down-regulate expression at 40% of amplified genes. To dissect the mechanism of this dosage response, we generated isogenic strain panels in which diploid cells carried either two, three, or four copies of the affected chromosomes. Using a mixture of linear regression (MLR) model to classify genes, we find that expression is actively down regulated in proportion to increased gene copy at up to 30% of genes. Genes subject to dosage control are under higher expression constraint – but show elevated rates of gene amplification – in wild populations, suggesting that dosage compensation buffers copy number variation (CNV) at toxic genes
Project description:Mantle cell lymphoma (MCL) is a lymphoma characterized by aberrant activation of CCND1/cyclin D1 followed by sequential genetic abnormalities. Genomic abnormalities in MCL have been extensively examined by classical cytogenetics and microarray-based comparative genomic hybridization techniques, pointing out a number of alterations in genomic regions that correlate with the neoplastic phenotype and survival. Recently, single nucleotide polymorphism genomic microarrays (SNP-chip) have been developed and used for analysis of cancer genomics. This technique allows detection of genomic changes with higher resolution, including loss of heterozygosity without changes of gene dosage, so-called acquired uniparental disomy (aUPD). As a result of the analysis, known alterations were confirmed by SNP arrays, including deletion of INK4A/ARF, duplication/amplification of MYC, deletion of ATM, and deletion of TP53. We also identified a duplication/amplification that occurred at 13q involving oncogenic microRNA, miR17-92. We found other genomic abnormalities, including duplication/amplification of cyclin D1, del(1p), del(6q), dup(3q) and dup(18q). Our SNP-chip analysis detected these abnormalities at high resolution, allowing us to narrow the size of the commonly deleted regions, including 1p and 6q. Our SNP-chip analysis detected a number of aUPD sites, including whole chromosome 9 aUPD and 9p aUPD. We also found an MCL case with 19p, leading to homozygous deletion of TNFSF genes. keyword: SNP-chip; Kawmata_MCL
Project description:Copy-number variants (CNVs) are large-scale amplifications or deletions of DNA that can drive rapid adaptive evolution and result in large-scale changes in gene expression. Whereas alterations in the copy number of one or more genes within a CNV can confer a selective advantage, other genes within a CNV can decrease fitness when their dosage is changed. Dosage compensation - in which the gene expression output from multiple gene copies is less than expected - is one means by which an organism can mitigate the fitness costs of deleterious gene amplification. Previous research has shown evidence for dosage compensation at both the transcriptional level and at the level of protein expression; however, the extent of compensation differs substantially between genes, strains, and studies. Here, we investigated sources of dosage compensation at multiple levels of gene expression regulation by defining the transcriptome, translatome and proteome of experimentally evolved yeast (Saccharomyces cerevisiae) strains containing adaptive CNVs.
Project description:Intratumor heterogeneity and phenotypic plasticity drive tumour progression and therapy resistance. Oncogene dosage variation contributes to cell state transitions and phenotypic heterogeneity, thereby providing a substrate for somatic evolution. Nonetheless, the genetic mechanisms underlying phenotypic heterogeneity are still poorly understood. Here, we show that extrachromosomal DNA (ecDNA) is a major source of high-level focal amplification in key oncogenes and a major contributor of MYC heterogeneity in pancreatic ductal adenocarcinoma (PDAC). We demonstrate that ecDNAs drive varying levels of MYC dosage, depending on their regulatory landscape, enabling cancer cells to rapidly and reversibly adapt to microenvironmental changes. In absence of selective pressure, a high ecDNA copy number imposes a substantial fitness cost on PDAC cells. We also show that MYC dosage affects cell morphology and dependence of cancer cells on stromal niche factors. Our work provides the first detailed analysis of ecDNAs in PDAC and describes a new genetic mechanism driving MYC heterogeneity in PDAC.
Project description:Intratumor heterogeneity and phenotypic plasticity drive tumour progression and therapy resistance. Oncogene dosage variation contributes to cell state transitions and phenotypic heterogeneity, thereby providing a substrate for somatic evolution. Nonetheless, the genetic mechanisms underlying phenotypic heterogeneity are still poorly understood. Here, we show that extrachromosomal DNA (ecDNA) is a major source of high-level focal amplification in key oncogenes and a major contributor of MYC heterogeneity in pancreatic ductal adenocarcinoma (PDAC). We demonstrate that ecDNAs drive varying levels of MYC dosage, depending on their regulatory landscape, enabling cancer cells to rapidly and reversibly adapt to microenvironmental changes. In absence of selective pressure, a high ecDNA copy number imposes a substantial fitness cost on PDAC cells. We also show that MYC dosage affects cell morphology and dependence of cancer cells on stromal niche factors. Our work provides the first detailed analysis of ecDNAs in PDAC and describes a new genetic mechanism driving MYC heterogeneity in PDAC.
Project description:Isolation of copy number variations and chromosomal duplications at high frequency in Caenorhabditis elegans suggested that this organism tolerates dosage problems. Here we addressed if this tolerance is due to a genome-wide compensation mechanism acting at the level of mRNA expression. We characterized several chromosomal duplication strains using DNA-seq and analyzed gene expression in two duplication and a fosmid integration strain using mRNA-seq. Our results show that on average, increased gene dosage leads to increased mRNA expression, pointing to a lack of genome-wide dosage compensation. Different genes within the same duplicated region show variable changes in mRNA expression, suggesting feedback regulation of individual genes. Transcriptional repression by somatic dosage compensation and germline silencing contribute to the level of mRNA increase from a large X chromosomal duplication. In sum, our results show a lack of genome-wide dosage compensation mechanism acting at the mRNA level in C. elegans and highlight the role of epigenetic and individual gene regulation contributing to the varied consequences of increased gene dosage.
Project description:Gene copy-number variation, which provides the raw material for the evolution of novel genes, is surprisingly widespread in natural populations. Experimental evolution studies have demonstrated an extremely high spontaneous rate of origin of gene duplications. When organisms are suboptimally adapted to their environment, gene duplication may compensate for reduced fitness by amplifying promiscuous activity of a gene, or increasing dosage of a suboptimal gene. The overarching goal of this study is to inverstigate whether CNVs constitute a common mechanism of adaptive genetic change during compensatory evolution and to further characterize the role of natural selection in dictating their evolutionary spread at a population-genomic level. Outcrossing populations of C. elegans with low fitness were evolved for >200 generations and the frequencies of CNVs in these populations were analyzed by oligonucleotide array comparative genome hybridization, quantitative PCR, and single-worm PCR. Multiple duplications and deletions were detected in intermediate to high frequencies and several lines of evidence suggest that the changes in frequency were adaptive. 1) Many copy-number changes reached high frequency, were near fixation, or were fixed in a short time. 2) Many independent duplications and deletions in high frequency harbor overlapping regions which likely include genes that are under selection for either higher or lower rates of expression. 3) The size spectrum of deuplications and deletions in the adaptive recovery populations is significantly larger than that of spontaneous copy-number variants in mutation accumulation experiments. This is expected if larger CNVs are more likely to encompass genes that are being selected for altered gene dosage. Out results validate the great potential borne by gene copy-number changes for compensatory evolution and adaptation. Experimental genome evolution of copy-number variants in 25 experimental lines compared to 5 ancestral control lines.