Tissue- and gene-specific DNA methylation patterns are hallmarks of vertebrate genomes and have been suggested to play a critical role in regulating genome functions. There is remarkable diversity of DNA methylation patterns. However, it is yet unclear what is responsible for this diversity. / In this dissertation, Chapters Two and Three, we test the hypothesis that multiple forms of DNA (cytosine-5) methyltransferase are generated from a single DNA methyltransferase gene (Dnmt1) in vertebrates in vivo. We show that diversification of the N-terminus of Dnmt1 occurs by two mechanisms, multiple transcription initiations and alternative splicing. The rat Dnmt1 initiates transcription from three sites at least: a distal promoter, and a downstream promoter in exon 3 and exon 4. In addition to alternative initiations, alternatively spliced N-terminus domains are also present in rat brain. Similarly, we show that the DNA methyltransferase domain of rat Dnmt1 is alternatively spliced in vivo, generating different in-frame variants of DNA methyltransferase in specific tissues. This process is developmentally regulated, and is induced in PC12 cells by nerve growth factor (NGF). / Using this PC12 differentiation model, in Chapter Four, we further test the hypothesis that the expression of Dnmt1 is regulated with the developmental state of neuronal cells. We show that DNA methyltransferase (Dnmt1) activity is sharply reduced 4 days after NGF treatment. Similarly, the adult brain expresses reduced levels of Dnmt1 activity. The abundance of Dnmt1 mRNA as well as the Dnmt1 polypeptide is down regulated. Downregulation of Dnmt1 parallels other indicators of withdrawal from the cell cycle such as p21 and prolife rating cell nuclear antigen (PCNA), and may not be required for initiation of PC12 differentiation. This temporal pattern is different from myotube differentiation where down regulation of DNA methyltransferase and demethylation is an early event and is proposed to play a causal role in differentiation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36001 |
| Date | January 1999 |
| Creators | Deng, Jing, 1966- |
| Contributors | Szyf, Moshe (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Pharmacology & Therapeutics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001681941, proquestno: NQ55320, Theses scanned by UMI/ProQuest. |
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