Gene expression and distribution of Swi6 in partial aneuploids of the fission yeast Schizosaccharomyces pombe

Imbalances of gene expression in aneuploids containing an abnormal number of chromosomes cause a variety of growth and developmental defects. Aneuploid cells of the fission yeast Schizosaccharomyces pombe are inviable, or very unstable, during mitotic growth. However, S. pombe haploid cells bearing a small portion (less than 20%) of the third chromosome can grow stably as a partial aneuploid. We compared the gene expression profiles of partial aneuploid strains with those of the normal haploid strain using DNA microarray analysis. The expression of genes in disomic or trisomic cells was found to increase approximately in proportion to their copy number. We also found that some genes in the monosomic regions of partial aneuploid strains changed their expression level despite there being no change in copy number. We initially speculated that this change in gene expression was a secondary effect resulting from increased expression of the genes in the disomic or trisomic regions. However, even in an aneuploid strain that bears a minichromosome containing no protein coding genes, genes located within about 50kb of the telomere showed similar increases in expression. This result indicates that the change in expression of the genes in the telomere-adjacent region is not a secondary effect of the increased gene dosage. Examining the distribution of the heterochromoatin protein Swi6 using DNA microarray analysis, we found that binding of Swi6 within ~50kb from the telomere occurred less in partial aneuploid strains compared to euploid strains. These results suggest that additional chromosomes in aneuploid strains could lead to imbalances in gene expression through derepression of heterochromatin. Keywords: Type of experiment: Comparing between partial aneuploid strains and normal haploid strains. Gene expression profile and distribution of Swi6 in partial anueploids bearing mini chromosomes of the fission yeast Schizosaccharomyces pombe