During cell division the cell undergoes a complex and timely set of events necessary to segregate the replicated chromosomes into daughter cells. An important component of the process is the centromere, the specialized DNA region of the chromosome that serves as anchor to the kinetochore, a large protein structure that assembles onto centromeres and attaches sister chromatids to microtubules. Proper biorientation of sister kinetochores is essential for capturing the spindle microtubules that extend from opposite poles of the dividing cell, as defects in the process lead to missegregation of chromosomes and often cell death. Many studies have provided evidence that chromatin structure is critical in maintaining the fidelity of chromosome transmission, but its roles are not well understood. In many eukaryotes, including metazoans, the centromere is surrounded by pericentric heterochromatin, consisting of specialized nucleosomes that maintain and epigenetic transcriptionally silent state formed by covalently modified histones. Although the association between pericentric chromatin and deacetylated histones has long existed, the specific function that this modifications have in mitosis remain unknown. The long-term goal of this project is to understand how chromatin structure affects chromosome segregation, in particular the role that histones have in this process. This study uses the budding yeast Saccharomyces cerevisiae as a model eukaryote. In contrast with the long heterochromatic regions characteristic of higher eukaryotes, S. cerevisiae relies on a point centromere, consisting of a short DNA element (125 bp), which shares with all eukaryotes its association with the evolutionarily conserved histone H3 variant Cse4/CENP-A. In spite of the lack of a defined centromeric heterochromatin, many studies suggest that histones perform critical functions in S. cerevisiae mitosis. Previous work of this laboratory has shown that histone H2A affects centromere function, and that chromosome segregation defects caused by mutations in this histone can be reverted by mutations in the Hda1 deacetylase complex. This complex associates with centromeric-pericentromeric chromatin, and correlates with the deacetylation state of histones H3 and H2B. This project focuses on elucidating the role that the Hda1 complex has at the centromere. The research will use a combination of genetic, molecular, and biochemical approaches to address the following specific aims: To understand the role that deacetylation plays in centromere function. Second, to determine the function that Hda3, a subunit of the Hda1 complex, has in mitosis. Third, to characterize a newly identified interaction between the Hda1 complex and the aurora kinase Ipl1 complex, which is involved in monitoring the attachment of chromatids to microtubules.
Thus, this research uses several approaches aimed to gain new insights into the function that chromatin has in the process of chromosome segregation during cell division. This knowledge will increase our understanding of a basic cellular process common to all eukaryotes. In addition, this research provides opportunities for training and education of undergraduate and graduate students. As in the past, undergraduate students will become important contributors to the research activities in the P.I.''s lab. Also, the P.I. will continue to incorporate aspects of this research in the laboratory-based graduate class taught each year, concomitantly with the outreach and recruiting efforts to increase student diversity and the number of students interested in the sciences at the University of Arkansas.
