Poster abstracts
Poster number 11 submitted by Rebecca Bailey
Meiotic viability of telomere-free circular chromosomes in the eukaryote Saccharomyces cerevisiae
Rebecca L. Bailey (Department of biology and chemistry, Morehead State University), Devan W. Herald (Department of biology and chemistry, Morehead State University), Mark T. Wilson (Department of biology and chemistry, Morehead State University), Melissa A. Mefford (Department of biology and chemistry, Morehead State University)
Abstract:
Prokaryotes generally have a single circular chromosome, while eukaryotes have multiple linear chromosomes capped by specialized repetitive DNA sequences called telomeres. Telomeres shorten as we age because they cannot be completely replicated before the cell divides. To overcome this shortening, telomeres can be lengthened by the ribonucleoprotein enzyme telomerase. However, more than 85% of cancer cells upregulate telomerase, allowing the cancerous cells to divide uncontrollably. Since telomeres and telomerase contribute to aging and cancer, we set out to understand why eukaryotes have linear chromosomes with telomeres instead of circular chromosomes. To this end, we have used a genetic engineering strategy to circularize two individual chromosomes in the single-celled eukaryote Saccharomyces cerevisiae. In asexually dividing haploid cells, the circular chromosomes exhibit no obvious phenotypes. A current hypothesis posits that eukaryotes evolved linear chromosomes to permit meiosis and sexual reproduction. To test this hypothesis, we mated haploid yeast to form diploid cells with a single circular chromosome, as well as diploid cells with two copies of a circular chromosome. Upon starvation, the diploid cells will undergo meiosis to form four haploid cells, which can be dissected and tested for viability. We find that circular chromosomes decrease the number of viable spores by >30%, consistent with the hypothesis that linear chromosomes evolved to allow sexual reproduction. In the future, we plan to characterize the meiotic defects caused by the presence of a circular chromosome to shed further light on why linear chromosomes evolved in eukaryotes.
Keywords: telomere, chromosome, meiosis