Differential chromosome control of ploidy in the yeastSaccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae, aneuploidy is well tolerated and stable. We analysed whether the induced loss of a disomic chromosome favours endo-reduplication of the remaining chromosome or the cells prefer to retain the acquired euploidy. Chromosome VIII disomes and trisomes were tagged with GFP (green fluorescent protein), DsRed (red fluorescent protein) and BFP (blue fluorescent protein) integrated at the thr1 locus, using our newly designed STIK (specific targeted integration of kanamycin resistance-associated, non-selectable DNA) plasmid system. A knockout cassette for centromere 8 was constructed with the hygromycin-B marker, which was transformed into the strains. The transformants lost sensitivity to hygromycin, thereby indicating the event of centromere replacement. Quantitative PCR and Southern analysis were performed for chromosome VIII copy number determination by probing the markers located on both the right (ARG4 and THR1 ) and left (GUT1 ) arm whereas, for chromosome V, markers such as HIS1, located on right arm, and URA3, on left arm, were used. The loss of an extranumerary chromosome VIII in a disome and trisome leads to stable euploidy. Furthermore, in a wild-type diploid, deletion of a copy of chromosome VIII, leads to monosomy, and restoration of euploidy after 22 generations, by reduplication of chromosome VIII, and consequent loss of heterozygosis (LOH). However, chromosome V knockouts in chromosome VIII trisome, still showed LOH and duplication of chromosome V, with return to the original aneuploid condition. These results suggest that yeast cells could control the integrity of their genetic complement acting at the individual chromosome level.

Genotypic and Physiological Characterization of Saccharomyces boulardii , the Probiotic Strain of Saccharomyces cerevisiae

“…The S. cerevisiae strain ⌺1278b, whose genetic background is apparently characterized by an overactive Ras pathway (55), is used commonly as the model organism for pseudohyphal development in yeast, a trait not observed in the strain with the background of the standard (sequenced) strain, S288C, due to a mutation in the FLO8 gene (35). Recent work indicates that S. cerevisiae can control and maintain aneuploidy at the individual chromosome level (58). One potential reason for the maintenance of aneuploidy may be the selective advantage to the cell from the presence of extra copies of gene(s) contained within the duplicated chromosome (1,52).…”

Industrial Relevance of Chromosomal Copy Number Variation in Saccharomyces Yeasts

“…Lanes 1 and 2 show two disomic knockout strains that have only a single copy of chromosome VIII, while lane 3 shows a diploid control strain. (Modified from reference 28 with permission [copyright 2005 John Wiley & Sons Ltd.].) (D) Copy number estimation of chromosome II by array comparative genomic hybridization of an evolved strain relative to its unevolved parental strain.…”

“…Southern hybridization of CHEF gels can reveal copy numbers of individual chromosomes by comparison of hybridization intensity with reference strains (Fig. 1C) (28). However, the accuracy of CCNV estimates obtained by this method is limited.…”

A Genetic Screen for Increased Loss of Heterozygosity inSaccharomyces cerevisiae

“…Neither chromosome IV nor XII appears to be able to be lost and produce a stable monosomic chromosome in a diploid cell (Alvaro et al 2006). By contrast, one copy of chromosome III can readily be lost from a diploid cell and yield a stable cell line with a monosomic III (Liras et al 1978;Waghmare and Bruschi 2005). As noted above, the MHM strain is heterozygous on the right arm of chromosome III at the MAT (MATa/MATa) locus and on the left arm at HIS4 (HIS4/his4DTHIS3 P TDH3 GFP) (Figure 2A).…”