Epigenetic Factors Are Dynamically Regulated Throughout The Cell Cycle And Are Required For Efficient DNA Replication Public Deposited

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  • March 19, 2019
Creator
  • Rizzardi, Lindsay Faircloth
    • Affiliation: School of Medicine, Curriculum in Genetics and Molecular Biology
Abstract
  • Chromatin consists of DNA wrapped around a core of histone proteins that can be modified to elicit distinct cellular responses. All DNA-templated processes including DNA replication must function within the context of chromatin. The focus of this study is the interaction between the replication machinery and the chromatin structure it must traverse to faithfully replicate the genome. Individual histone modifications can promote recruitment of replication proteins directly or recruit chromatin remodelers that increase the accessibility of the underlying DNA. Our studies in budding yeast, Saccharomyces cerevisiae, have identified a specific histone modification, H3K4me2, that promotes efficient DNA replication; although, the mechanism of this regulation remains unclear. Additionally, we found that the enzyme responsible for depositing H3K4me2 is cell cycle regulated, being most abundant during G1 when cells prepare the genome for DNA replication. Another histone modification required during G1 for proper DNA replication is H4K20me1. As this modification is not found in budding yeast, our studies were undertaken in a mammalian cell culture system. The enzyme responsible for this modification had previously been identified as Set8 (a.k.a. PR-Set7) and we have begun investigating the regulation of this enzyme throughout the cell cycle and during a cellular stress response. This enzyme is degraded both during S phase and after UV-induced DNA damage by the CRL4Cdt2 E3 ubiquitin ligase complex. We discovered that this degradation after DNA damage is abrogated during mitosis and after osmotic stress. This mechanism is conserved for at least one other CRL4Cdt2 substrate, Cdt1, that is an essential replication factor. Protection from UV-induced degradation requires active Cdk1 during mitosis as inhibition of this kinase leads to degradation of both Set8 and Cdt1. We are currently investigating whether this is a direct or indirect effect. During osmotic stress in asynchronous cells, the stress MAPKs p38 and JNK may play a more important role than Cdk1. It is clear that the histone modifications and the enzymes responsible for their deposition are critical components ensuring proper DNA replication and as such are tightly regulated. Future work will elucidate the exact mechanisms by which these chromatin factors influence DNA replication.
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  • In Copyright
Advisor
  • Errede, Beverly
  • Baldwin, Albert
  • Strahl, Brian
  • Cook, Jean
  • Duronio, Robert
Degree
  • Doctor of Philosophy
Graduation year
  • 2013
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