Increased ploidy and KAR3 and SIR3 disruption alter the dynamics of meiotic chromosomes and telomeres

We investigated the sequence of chromosomal events during meiotic prophase in haploid, diploid and autotetraploid SK1 strains of Saccharomyces cerevisiae. Using molecular cytology, we found that meiosis-specific nuclear topology (i.e. dissolution of centromere clustering, bouquet formation and meiotic divisions) are significantly delayed in polyploid SK1 meiosis. Thus, and in contrast to the situation in plants, an increase in ploidy extends prophase I in budding yeast. Moreover, we found that bouquet formation also occurs in haploid and diploid SK1 meiosis deficient in the telomeric heterochromatin protein Sir3p. Diploid sir3 SK1 meiosis showed pleiotropic defects such as delayed centromere cluster resolution in a proportion of cells and impeded downstream events (i.e. bouquet formation, homologue pairing and meiotic divisions). Meiotic telomere clustering occurred in diploid and haploid sir3 strains. Using the haploid system, we further show that a bouquet forms at the kar3 SPB. Comparison of the expression of meiosis-specific Ndj1p-HA and Zip1p in haploid control and kar3 time courses revealed that fewer cells enter the meiotic cycle in absence of Kar3p. Elevated frequencies of bouquets in kar3 haploid meiosis suggest a role for Kar3p in regulation of telomere dynamics.