Project description:Evolutionary engineering strategy was used for selection of ethanol-tolerant Saccharomyces cerevisiae clones under gradually increasing ethanol stress levels. Clones B2 and B8 were selected based on their higher ethanol-tolerance and higher ethanol production levels. Whole genome microarray analysis was used for identifying the gene expression levels of these two evolved clones compared to the reference strain.
Project description:Aneuploidy is a hallmark of tumor cells, and yet the precise relationship between aneuploidy and a cell’s proliferative ability, or cellular fitness, has remained elusive. In this study, we have combined a detailed analysis of aneuploid clones isolated from laboratory-evolved populations of Saccharomyces cerevisiae with a systematic, genome-wide screen for the fitness effects of telomeric amplifications to address the relationship between aneuploidy and cellular fitness. We found that aneuploid clones rise to high population frequencies in nutrient-limited evolution experiments and show increased fitness relative to wild type. Direct competition experiments confirmed that three out of four aneuploid events isolated from evolved populations were themselves sufficient to improve fitness. To expand the scope beyond this small number of exemplars, we created a genome-wide collection of >1,800 diploid yeast strains, each containing a different telomeric amplicon (Tamp), ranging in size from 0.4 to 1,000 kb. Using pooled competition experiments in nutrient-limited chemostats followed by high-throughput sequencing of strain-identifying barcodes, we determined the fitness effects of these >1,800 Tamps under three different conditions. Our data revealed that the fitness landscape explored by telomeric amplifications is much broader than that explored by single-gene amplifications. As also observed in the evolved clones, we found the fitness effects of most Tamps to be condition specific, with a minority showing common effects in all three conditions. By integrating our data with previous work that examined the fitness effects of single-gene amplifications genome-wide, we found that a small number of genes within each Tamp are centrally responsible for each Tamp’s fitness effects. Our genome-wide Tamp screen confirmed that telomeric amplifications identified in laboratory-evolved populations generally increased fitness. Our results show that Tamps are mutations that produce large, typically condition-dependent changes in fitness that are important drivers of increased fitness in asexually evolving populations.
Project description:Aneuploidy is a hallmark of tumor cells and yet the precise relationship between aneuploidy and a cell’s proliferative ability, or cellular fitness, has remained elusive. In this study we have combined a detailed analysis of aneuploid clones isolated from laboratory-evolved populations of Saccharomyces cerevisiae with a systematic, genome-wide screen for the fitness effects of telomeric amplifications to address the relationship between aneuploidy and cellular fitness. We found that aneuploid clones rise to high population frequencies in nutrient-limited evolution experiments and show increased fitness relative to wild-type. Direct competition experiments confirmed that three out of four aneuploid events isolated from evolved populations were themselves sufficient to improve fitness. To expand the scope beyond this small number of exemplars, we created a genome-wide collection of >1,800 diploid yeast strains each containing a different telomeric amplicon (Tamp) ranging in size from 0.4 to 1,000kb. Using pooled competition experiments in nutrient-limited chemostats followed by high-throughput sequencing of strain-identifying barcodes, we determined the fitness effects of these >1,800 Tamps under three different conditions. Our data revealed that the fitness landscape explored by telomeric amplifications is much broader than that explored by single-gene amplifications. As also observed in the evolved clones, we found the fitness effects of most Tamps to be condition specific with a minority showing common effects in all three conditions. By integrating our data with previous work that examined the fitness effects of single-gene amplifications genome wide, we found that a small number of genes within each Tamp are centrally responsible for each Tamp’s fitness effects. Our genome-wide Tamp screen confirmed that telomeric amplifications identified in laboratory-evolved populations generally increased fitness. Our results show that Tamps are mutations that produce large, typically condition-dependent changes in fitness that are important drivers of increased fitness in asexually evolving populations. Each of these arrays is a Comparative Genomic Hybridization experiment to detect copy number differences between a reference strain and a strain of interest.
Project description:Evolutionary engineering strategy was used for selection of ethanol-tolerant Saccharomyces cerevisiae clones under gradually increasing ethanol stress levels. Clones B2 and B8 were selected based on their higher ethanol-tolerance and higher ethanol production levels. Whole genome microarray analysis was used for identifying the gene expression levels of these two evolved clones compared to the reference strain. Two evolved ethanol-tolerant strains B2 and B8, which were selected by evolutionary engineering under gradually increasing ethanol stress, were used for whole genome transcriptomic analysis in comparison with the reference strain. Cells were grown in yeast minimal media until they reach a final OD600 of 1. Following total RNA isolation, gene expression levels were analyzed using One-color microarray-based gene expression analysis (Agilent Technologies). Experiments were done in triplicates.
Project description:CGH arrays for Smukowski Heil, et al MBE 2017. Hybridization is often considered maladaptive, but sometimes hybrids can invade new ecological niches and adapt to novel or stressful environments better than their parents. The genomic changes that occur following hybridization that facilitate genome resolution and/or adaptation are not well understood. Here, we address these questions using experimental evolution of de novo interspecific hybrid yeast Saccharomyces cerevisiae x Saccharomyces uvarum and their parentals. We evolved these strains in nutrient limited conditions for hundreds of generations and sequenced the resulting cultures to identify genomic changes. Analysis of 16 hybrid clones and 16 parental clones identified numerous point mutations, copy number changes, and loss of heterozygosity events, including species biased amplification of nutrient transporters. We focused on a particularly interesting example, in which we saw repeated loss of heterozygosity at the high affinity phosphate transporter gene PHO84 in both intra- and interspecific hybrids. Using allele replacement methods, we tested the fitness of different alleles in hybrid and S. cerevisiae strain backgrounds and found that the loss of heterozygosity is indeed the result of selection on one allele over the other in both S. cerevisiae and the hybrids. This is an example where hybrid genome resolution is driven by positive selection on existing heterozygosity, and demonstrates that even infrequent outcrossing may have lasting impacts on adaptation.
Project description:Elevated thermotolerance is an important desired property of Saccharomyces cerevisiae for its industrial applications. Here, adaptive laboratory evolution experiments were employed to further improve the thermotolerance of an industrial strain ScY. The resulting evolved strain showing enhanced thermotolerance was named ScY01. We sequenced mRNA from the cultures of the evolved strain ScY01 and the parental strain ScY grown on YP medium containing 200 g/l glucose at 40ºC at 200 rpm for 14 h ~ 16 h to the early-log phase. Differences in gene expression in ScY01 versus ScY revealed by RNA deep sequencing revealled that genes involved into glycolysis, amino acid biosynthesis and translation showed increased gene expressions, whereas mitochondrial translation and respiration associated genes showed decreased gene expressions. This suggested that the evolved strain might suppress its mitochondrial respiratory activity but boost its fermentation capacity, thereby providing enough ATP required for its more active energy-consuming pathways including amino acid and protein biosynthetic pathways.
Project description:Saccharomyces cerevisiae has been used as a secretion host for production of various products, including pharmaceuticals. However, few antibody molecules have been functionally expressed in S. cerevisiae due to the incompatible surface glycosylation. Our laboratory previously isolated a group of yeast mutant strains with different α-amylase secretory capacities, and these evolved strains have showed advantages for production of some heterologous proteins. However, it is not known whether these secretory strains are generally suitable for pharmaceutical protein production. Here, three non-glycosylated antibody fragments with different configurations (Ran-Fab fragment Ranibizumab, Pex-the scFv peptide Pexelizumab, and Nan-a single V-type domain) were successfully expressed and secreted in three background strains with different secretory capacities, including HA (wild type), MA (evolved strain), and LA (evolved strain). However, the secretion of Ran and Nan were positively correlated with the strains’ secretory capacity, while Pex was most efficiently secreted in the parental strain. Therefore, transcriptional analysis was performed to explore the fundamental changes triggered by the expression of the different pharmaceutical proteins in these selected yeast strains.