A global analysis of ploidy maintenance in S. cerevisiae

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A Global Analysis of Ploidy Maintenance in S. cerevisiae******Ploidy, the number of complete sets of chromosomes in an organism, is tightly regulated in eukaryotic cells, and is critical for cell function and survival. Cells must coordinate multiple pathways to ensure that replicated DNA is segregated accurately and in a timely fashion to prevent changes in chromosome number. We are taking a two-pronged approach to develop a mechanistic understanding of the pathways that maintain ploidy in the model eukaryote Saccharomyces cerevisiae. First, we discovered an unanticipated role for the SWI/SNF family chromatin remodeler RSC in ploidy maintenance. Second, we conducted a genome-scale screen to identify the complement of ploidy maintenance genes in budding yeast. This screen identified a novel relationship between protein translation and ploidy maintenance and we discovered that the loss of genes in this pathway caused a quadrupling in genome size. We are now poised to delve into the molecular mechanism by which RSC regulates ploidy, to explore the relationship between cell morphology and ploidy, and to define the relationships between protein translation and ploidy maintenance.******Having made excellent progress in our goals of understanding the mechanism by which RSC regulates ploidy and in genome-scale analysis of ploidy maintenance pathways, we propose to build on our unique findings during the next funding period. Our current analysis has identified the nuclear pore complex as the key target of RSC in maintaining ploidy. Going forward, we will combine molecular and high-resolution microscopic analyses to understand how RSC modulates the function of the nuclear pore complex. We have also discovered a unique connection between ploidy and many aspects of cellular morphology. In collaboration with Yoshi Ohya at the University of Tokyo we will use a multi-parameter image analysis to identify new ploidy maintenance genes on the basis of morphology profile, with the ultimate goal of understanding the ways in which ploidy increase alters the shape and structure of the eukaryotic cell. Finally, our current genome-scale analysis has reached the exciting stage where we can begin to understand the mechanisms by which the SESA network of translational regulators, which comprises mRNA and ribosome binding proteins, regulates ploidy. We identified multiple components of the SESA network in our ploidy maintenance screen, indicating a strong functional relationship to follow up in future mechanistic studies.******To summarize, we will define the mechanisms by which RSC and SESA maintain ploidy in a model eukaryote, and will use morphological analysis to identify additional ploidy maintenance pathways and understand how ploidy influences the structure of the cell. We expect to derive considerable mechanistic insight into how cells maintain ploidy and accurately transmit the genome from one generation to the next.