| During development cells undergo major transcriptional changes. Once established, specific gene expression patterns are maintained in the cell and its progeny by epigenetic mechanisms, which affect the structure of chromatin. When a cell divides, parental chromatin proteins, such as histones, containing their epigenetic marks and newly synthesized chromatin proteins are somehow assembled onto the daughter DNA strands in a manner that faithfully reproduces the transcriptional states of chromatin. However, the molecular mechanisms by which histone modifications contribute to gene regulation and transcriptional memory are unclear. In yeast, we recently identified an unusual epigenetic regulator, Dot1, which methylates lysine 79 on histone H3. Dot1 is conserved from yeast to humans. In yeast, Dot1 and is important for silent chromatin formation. However, Dot1 primarily methylates histones in active chromatin. Our findings indicate that Dot1 promotes silencing by preventing promiscuous interactions of silencing proteins with euchromatin. To understand how this unusual form of regulation works, we propose to perform suppressor analysis and genomic screens to find genes that interact with DOT1 and identify functional pathways in which DOT1 is involved. To investigate if and how histone methylation serves as an epigenetic memory mark to promote reproduction of parental chromatin structures in the daughter cells, we have developed a new system to study the inheritance of histones and epigenetic marks in vivo at a whole- genome level as well as a gene-specific level. We will use this system to examine the molecular principles of chromatin duplication and determine the inheritance of methyl groups on histones introduced by Dot1 and other histone methyltransferases. We expect that our studies will critically improve our understanding of the molecular mechanisms of epigenetic regulation and memory. This knowledge will be essential for the identification of drug targets to prevent or correct aberrant epigenetic regulation in diseases such as cancer. |
