DNA Maintainer Dependent Epigenetic Inheritance of Gene Silencing and Histone H3K9 Methylation
CitationWang, Xiaoyi. 2019. DNA Maintainer Dependent Epigenetic Inheritance of Gene Silencing and Histone H3K9 Methylation. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractEpigenetic inheritance is critical for maintenance of gene expression patterns to safeguard cell identity. From fission yeast to mammals, histone H3 lysine 9 is methylated (H3K9me) to mediate gene silencing and heterochromatin formation. After DNA replication, parental histones are distributed randomly onto the two newly synthesized DNA strands and H3K9 methyltransferases, such as Clr4 in fission yeast, are thought to recognize the old histones with H3K9me and methylate the newly deposited histones. However, this “read-write” mechanism is opposed by H3K9me demethylation as, by itself, it can only mediate stable epigenetic inheritance in the absence of the gene encoding the putative H3K9 demethylase epe1+. This is in contrast to the native heterochromatin domain at the mating type (mat) locus in which genetic manipulation results in metastable ON and OFF expression states of a reporter gene that can be transmitted in cis through meiosis. It was therefore not clear how epigenetic states of gene silencing and H3K9me are inherited in epe1+ cells at native heterochromatic regions. My thesis research focused on exploring possible roles for local DNA sequences that may act together with the read-write mechanism to maintain epigenetic states in fission yeast.
I found that, in epe1+ cells, stable epigenetic inheritance of H3K9me and gene silencing require two binding sites of the ATF/CREB family transcription factors Atf1/Pcr1 within their native chromosomal context. Therefore, stable epigenetic inheritance of H3K9me requires input from both genetic elements and the “read-write” mechanism of Clr4.
Using a combination of genetic and biochemical approaches, I discovered a minimal DNA element that mediates epigenetic inheritance but not de novo establishment of gene silencing and H3K9me. This minimal element, which we term a “maintainer”, has binding sites for another DNA binding protein, Deb1, and the origin recognition complex (ORC), in addition to the Atf1/Pcr1 binding sites. Deletion of epe1+ converts the maintainer to a silencer, suggesting that maintainer binding proteins can initiate silencing by recruiting Clr4. Together, these results have delineated the mechanisms of the contribution of genetic elements to stable cis epigenetic inheritance of histone modifications.
Citable link to this pagehttp://nrs.harvard.edu/urn-3:HUL.InstRepos:42106934
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