Epigenetics involves heritable changes in an individual’s traits resulting from variations in gene expression without alterations to the DNA sequence. In eukaryotes, genomic DNA is usually folded with histones into chromatin. Post-translational modifications (PTMs) on histones not only play crucial roles in regulating various biological processes, including gene expression, but also store the majority of epigenetic information. A fundamental question in this field is how cells transmit these PTMs to their progeny.
Before I began my thesis research, a well-established dogma in the field was that parental histones containing PTMs are symmetrically distributed to daughter DNA strands during DNA replication. These modified histones serve as templates for PTM duplication, thereby restoring the original chromatin states on both daughter strands. Several histone chaperones have been identified as regulators of parental histone segregation. However, their impact on epigenetic inheritance is controversial, which I reasoned is due to the lack of proper systems to examine epigenetic inheritance. This prompted me to use the unique characteristics of fission yeast heterochromatin as a model of epigenetic inheritance. In this organism, heterochromatin formation involves two distinct steps: establishment and inheritance. Reporter systems have been established to allow precise examination of heterochromatin inheritance. However, parental histone segregation pathways have not been characterized in this organism, and their impact on heterochromatin inheritance is unknown.
My thesis work investigates the role of parental histone chaperones in regulating parental histone segregation and epigenetic inheritance in fission yeast. It comprises 5 chapters:
Chapter 1 introduces epigenetics, with a focus on chromatin-based epigenetic inheritance. It also highlights the unique features of fission yeast heterochromatin that make it an excellent model for studying epigenetic inheritance.Chapter 2 is the focus of my thesis work. I employed inheritance-specific reporters in fission yeast to investigate the roles of three parental histone chaperones on epigenetic inheritance. In addition, in collaboration with Dr. Zhiguo Zhang’s lab, I adapted the Enrichment and Sequencing of Protein-Associated Nascent DNA (eSPAN) method, a recently developed technique designed to quantify the bias of specific proteins at replication forks, to examine parental histone segregation in fission yeast. My analyses demonstrated a critical role for parental histone segregation in epigenetic inheritance. Moreover, I discovered that both the symmetric segregation of parental histones and their density on daughter strands are critical for this process.
Chapter 3 uncovers a novel function of a DNA replication protein Mrc1 in regulating epigenetic inheritance, distinct from its established roles in DNA replication checkpoint activation and replication speed control. I demonstrated the critical role of Mrc1 in regulating the symmetrical transfer of parental histone and the proper inheritance of heterochromatin. These results provide essential mechanistic insights into the function of Mrc1.
Chapter 4 explores the function of an additional DNA replication protein and histone chaperone, Swi7 (Pol alpha). I have found that mutations in Swi7 lead to defects in parental histone segregation and heterochromatin inheritance, laying a strong foundation to further investigate its mechanism of action.
Chapter 5 discusses potential future research directions that can build upon my thesis work.In conclusion, my thesis represents a thorough examination of parental histone chaperones in regulating epigenetic inheritance in fission yeast. By combining innovative genetic assays and advanced methodologies such as eSPAN, I have provided critical insights into the molecular mechanisms of epigenetic inheritance. In addition, the assays that I have developed during my thesis work also pave the way for future studies aimed at elucidating the mechanism of epigenetic inheritance in this important model organism.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/kvc7-5d79 |
| Date | January 2024 |
| Creators | Fang, Yimeng |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
Page generated in 0.0019 seconds