Aneuploidy drives genomic instability in yeast

Abstract

Aneuploidy decreases cellular fitness, yet it is also associated with cancer, a disease of enhanced proliferative capacity. To investigate one mechanism by which aneuploidy could contribute to tumorigenesis, we examined the effects of aneuploidy on genomic stability. We analyzed 13 budding yeast strains that carry extra copies of single chromosomes and found that all aneuploid strains exhibited one or more forms of genomic instability. Most strains displayed increased chromosome loss and mitotic recombination, as well as defective DNA damage repair. Aneuploid fission yeast strains also exhibited defects in mitotic recombination. Aneuploidy-induced genomic instability could facilitate the development of genetic alterations that drive malignant growth in cancer.

Fig. 1

Aneuploidy induces chromosome missegregation. (A) YAC loss is increased in disomes and kinetochore mutants. The means ± SD of at least 12 cultures are displayed. **P < 0.005; ***P < 0.0005 (Student’s t test). (B) Proliferation of disomes is decreased in the presence of benomyl. 10-fold serial dilutions of the indicated strains are shown. (C) Pds1 levels and cell cycle progression in wild-type and disome XV cells after release from a G₁ arrest (7).

Fig. 2

Aneuploidy increases the mutation rate and sensitivity to genotoxins. (A) Mutation rate in disomic strains. Note that the CAN1 and URA3 reporters are located on chromosome V; we therefore measured the mutation rate of disome V at LYP1 and of URA3 integrated on chromosome VI (7). (B) Tenfold serial dilutions of the indicated strains were spotted on medium supplemented or treated with a genotoxic agent. CPT, camptothecin; HU, hydroxyurea; MMS, methyl methanesulfonate. (C) Tenfold serial dilutions of cells on medium containing phleomycin (Phleo) or bleomycin (Bleo).

Fig. 3

Aneuploidy induces recombination defects. (A) The fraction of wild-type and disomic cells displaying Rad52-GFP foci after release from a G₁ arrest or arrested with nocodazole. Images display wild-type, disome VIII, and disome XIV cells arrested with nocodazole. Means ± SD of three experiments are shown. (B) Rad52-GFP foci were scored in spores from triploid or diploid strains (7). The mean (black bar) of 15 spore-derived colonies (dots) are displayed. ***P < 0.0005 (Student’s t test). (C) Mitotic recombination between truncated alleles of ade2 (7). (D) Wild-type and disome XI cells treated with phleomycin were released into medium containing nocodazole. Chromosome integrity was analyzed by pulse-field gel electrophoresis (7). (E) Fivefold serial dilutions of fission yeast cells on medium supplemented with hydroxyurea or phleomycin. Rhp51 is the fission yeast Rad51 homolog. (F) The fraction of cells displaying SpRad22-GFP foci in aneuploid and euploid microcolonies resulting from sporulation of a triploid strain. Images are representative euploid and aneuploid microcolonies.

Fig. 4

Stoichiometric imbalances drive genomic instability. (A) Tenfold serial dilutions of strains harboring YACs on the indicated media. (B) The mutation rate at CAN1. Median and 95% confidence intervals of at least 12 independent cultures are shown. ***P < 0.0005 (Wilcoxon rank-sum test). (C) Fraction of nocodazole-arrested cells displaying Rad52-GFP foci. Means ± SD of three experiments are shown. **P < 0.005 (Student’s t test ). (D) Tenfold serial dilutions of trisomic and corresponding disomic strains on the indicated medium. (E) YAC loss rates in diploid and trisomic strains. Means ± SD of at least 12 independent cultures are shown. (F) YAC loss rates normalized to either haploid or diploid controls. *P < 0.05; **P < 0.005; ***P < 0.0005 (Student’s t test).