Loss of the SUMO Protease Ulp2 Triggers a Specific Multi-Chromosome Aneuploidy

Post-translational protein modification by the small ubiquitin-related modifier (SUMO) protein regulates numerous cellular pathways, including transcription, cell division and genome maintenance. The SUMO protease Ulp2 modulates many of these SUMO-dependent processes in budding yeast. To investigate changes to the transcriptome of cells lacking Ulp2, whole-genome RNA sequencing (RNA-seq) was employed. Unexpectedly, ulp2? cells display a general two-fold increase in transcript levels across two particular chromosomes, Chromosome I (ChrI) and Chromosome XII (ChrXII). Quantification of relative DNA levels showed that ChrI and ChrXII are present at twice their normal copy number in ulp2? cells. This double disomy occurs in mutants in multiple genetic backgrounds and does not require passage through meiosis. An abnormal number of chromosomes in a cell, termed aneuploidy, is usually deleterious. However, development of specific aneuploidies allows rapid adaptation to cellular stresses in yeast and other species, and aneuploidy characterizes most tumors. Extra copies of ChrI and ChrXII appear quickly following loss of active Ulp2, suggesting aneuploidy is an adaptive mechanism in cells lacking the functional SUMO protease. The specific aneuploidy in ulp2? cells highlights a unique example of a homogeneous, multi-chromosome aneuploidy in response to mutation of a single gene. Overall design: three mutants and one WT control each with 3 replicates

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