Transcription-induced formation of extrachromosomal DNA during yeast ageing
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ABSTRACT: Extrachromosomal circular DNA (eccDNA) facilitates adaptive evolution by allowing rapid and extensive gene copy number variation, and is implicated in the pathology of cancer and ageing. Here, we demonstrate that yeast aged under environmental copper accumulate high levels of eccDNA containing the copper resistance gene CUP1. Transcription of CUP1 causes CUP1 eccDNA accumulation, which occurs in the absence of phenotypic selection. We have developed a sensitive and quantitative eccDNA sequencing pipeline that reveals CUP1 eccDNA accumulation on copper exposure to be exquisitely site specific, with no other detectable changes across the eccDNA complement. eccDNA forms de novo from the CUP1 locus through processing of DNA double-strand breaks (DSBs) by Sae2 / Mre11 and Mus81, and genome-wide analyses show that other protein coding eccDNA species in aged yeast share a similar biogenesis pathway. Although abundant we find that CUP1 eccDNA does not replicate efficiently, and high copy numbers in aged cells arise through frequent formation events combined with asymmetric DNA segregation. The transcriptional stimulation of CUP1 eccDNA formation shows that age-linked genetic change varies with transcription pattern, resulting in gene copy number profiles tailored by environment.
Project description:The effect of the heavy metal copper on the expression of a wide spectrum of genes was analyzed by using a DNA microarray. Gene expression profile of baker’s yeast Saccharomyces cerevisiae grown in a media containing sub-lethal concentration of cupric sulfate was compared with those of yeast grown in a normal media. Among about 6200 ORFs of yeast, 143 ORFs were induced more than two-fold to resist against copper toxicity after exposure to copper. As was expected, FRE1, FRE7, and CTR1, genes controlled by Mac1p, were strongly down-regulated. Copper metallothionein CUP1-1 and CUP1-2 were induced more than 20-fold. Some genes related to sulfur metabolism and oxidative stress response were also up-regulated. This DNA microarray technology indicated that plasma membrane, cell wall, protein, and DNA, were molecular targets of copper toxicity. Keywords: stress response
Project description:Copper tolerance and sulfite tolerance are two well-studied phenotypic traits of Saccharomyces cerevisiae. The genetic bases of these traits are derived from allelic expansion at the CUP1 locus and reciprocal translocation at the SSU1 locus, respectively. Previous work identified a negative association between sulfite and copper tolerance in S. cerevisiae wine yeasts. Here we probe the relationship between sulfite and copper tolerance and show that an increase in CUP1 copy number does not impart copper tolerance in all S. cerevisiae wine yeast. Bulk-segregant QTL analysis was used to identify variance at SSU1 as a causative factor in copper sensitivity, which was verified by reciprocal hemizygosity analysis in a strain carrying 20 copies of CUP1. Transcriptional and proteomic analysis demonstrated that SSU1 over-expression did not suppress CUP1 transcription or constrain protein production but suggested that SSU1 overexpression induced sulfur limitation during exposure to copper. Finally, an SSU1 over-expressing strain exhibited increased sensitivity to moderately elevated copper concentrations in sulfur-limited medium, demonstrating that SSU1 over-expression burdens the sulfate assimilation pathway. Over-expression of MET 3/14/16, genes upstream of H2S production in the sulfate assimilation pathway increased the production of SO2 and H2S but did not improve copper sensitivity in an SSU1 overexpressing background. We conclude that copper and sulfite tolerance are conditional traits in S. cerevisiae and provide evidence of the metabolic basis for their mutual exclusivity. These findings suggest an evolutionary basis for the extreme amplification of CUP1 observed in some yeasts.
Project description:In Saccharomyces cerevisiae, copper ions regulate gene expression through the two transcriptional activators, Ace1 and Mac1. Ace1 mediates Cu-induced gene expression in cells exposed to stressful levels of copper salts, whereas Mac1 activates a subset of genes under copper-deficient conditions. DNA microarray hybridization experiments revealed a limited set of yeast genes differentially expressed under growth conditions of excess copper or copper deficiency. Mac1 activates the expression of six S. cerevisiae genes, including CTR1, CTR3, FRE1, FRE7, YJL217w and YFR055w. Two of the last three newly identified Mac1 target genes have no known function, the third, YFR055w, is homologous to cystathionine gamma-lyase encoded by CYS3. Several genes that are differentially expressed in cells containing a constitutively active Mac1, designated Mac1up1, are not direct targets of Mac1. Induction or repression of these genes is likely a secondary effect of cells due to constitutive Mac1 activity. Elevated copper levels induced the expression of the metallothioneins CUP1 and CRS5, and two genes, FET3 and FTR1, in the iron uptake system. Cu-induced FET3 and FTR1 expression arises from an indirect Cu effect on cellular Fe pools. This study is described in more detail in Gross C et al.(2000) J Biol Chem 275:32310-6 Keywords: other
Project description:DNA repair by homologous recombination is under stringent cell cycle control. This includes the last step of the reaction, disentanglement of DNA joint molecules (JMs). Previous work has established that JMs resolving nucleases are activated specifically at the onset of mitosis. In case of budding yeast Mus81-Mms4, this cell cycle stage-specific activation is known to depend on phosphorylation by CDK and Cdc5 kinases. Here, we show that a third cell cycle kinase, Cdc7-Dbf4 (DDK), targets Mus81-Mms4 in conjunction with Cdc5 - both kinases bind to as well as phosphorylate Mus81-Mms4 in an interdependent manner. Moreover, DDK-mediated phosphorylation of Mms4 is strictly required for Mus81 activation in mitosis, establishing DDK as a novel regulator of homologous recombination. The scaffold protein Rtt107, which is part of the Mus81-Mms4 complex, interacts with Cdc7 and thereby targets DDK and Cdc5 to the complex enabling full Mus81 activation. Therefore, Mus81 activation in mitosis involves at least three cell cycle kinases, Cdk1, Cdc5 and DDK. Furthermore, tethering of the kinases in a stable complex with Mus81 is critical for efficient JM resolution
Project description:1) The Pgal-3HA cup1 yeast strain, in which all CUP1 ORFs are replaced with 3HA and all CUP1 promoters are replaced by GAL1-10 promoters (PMID: 28654659, which carries ~17 tandem repeats of the modified Pgal-3HA cup1 repeat) undergoes extensive CNV when shifted to galactose. Here we use TrAEL-seq to look for replication fork stalling in this strain with and without induction. 2) We also profile the impact on replication of integrating an ARSH4 origin upstream of the RSC30 gene (so outside the CUP1 locus), using the 3xCUP1 strain which carries 3 repeats of CUP1 (PMID: 28654659). The origin was integrated with a URA3 marker, the control strain has the URA3 marker but no origin.
Project description:When using YPM media, the carotenoid yield was increased 10-fold compared to using the YPD media. To elucidate the hidden mechanism, the transcriptome analysis was performed and showed that 464 genes changed significantly in YPM media. Furthermore, inspired by the differential gene expression analysis which indicated that ADY2, HES1, and CUP1 showed the most remarkable changes, we found that the improvement of carotenoid accumulation in YPM media was mainly due to the copper, since supplementation of 80 µM CuSO4 in YPD media could increase carotenoid yield 9.2-fold
Project description:Extrachromosomal circular DNA (eccDNA) is double-stranded circular DNA that is derived from but independent of chromosomal DNA. Owing to its nonchromosomal inheritance, eccDNA facilitates the amplification of oncogenes and expedites the process of genome evolution in tumor. However, the role of eccDNA in RB remains enigmatic. We combined Circle-Seq and RNA-Seq to identified crucial extrachromosomal circular oncogene amplicons. Herein, we revealed that extrachromosomal circular SUZ12 amplicon regulates H3K27me3 modification during the oncogenic progression of retinoblastoma. Conclusively, our study initially delineated an integrated picture of the eccDNA landscape in retinoblastoma and unveiled a novel SUZ12-containing eccDNA/H3K27me3 oncogenic mechanism where eccDNA dictates retinoblastoma progression through regulating transcription levels of linear DNA.