McBurney, Michael W.,Tai, Helen H.2009-03-232009-03-2320002000Source: Dissertation Abstracts International, Volume: 62-02, Section: B, page: 0708.9780612570702http://hdl.handle.net/10393/9048http://dx.doi.org/10.20381/ruor-16120Gene silencing is a stable and heritable form of repression of gene expression that is thought to be mediated by higher order chromatin structures. This thesis consists of two separate studies on gene silencing. The first chapter deals with X chromosome inactivation which is a particular case of gene silencing where almost all the genes one X chromosome are inactivated early in the development of female mammals. The Xist gene is a candidate gene for controlling X chromosome inactivation because the Xist gene resides on the X chromosome near the XIC (X inactivation center) and is expressed from the inactive X in female somatic cells. Chapter 1 describes an investigation of the expression of Xist in diploid P10 female embryonal carcinoma cells that have two active X chromosomes. The transcripts expressed from Xist alleles in P10 cells could be distinguished by restriction enzyme digestion of their cDNAs. It was found that both alleles Xist are expressed; thus, Xist transcripts are expressed prior to X chromosome inactivation and are not always derived from the inactive X chromosome. Therefore, Xist expression per se cannot be a sufficient signal to inactivate an X chromosome. The second chapter is a study of CHD-1, a mouse protein with two chromodomains, a helicase/ATPase domain, and a DNA binding domain. The chromodomain connects CHD-1 to gene silencing because the chromodomain, also present in the Drosophila proteins HP-1 and Polycomb, is required for the gene silencing function of these proteins. Therefore, CHD-1 was further examined in Chapter 11. In part A of Chapter 11, the finding that CHD-1 was associated with the nuclear matrix, a protein structure in the nucleus, is reported. Part B of Chapter 11 describes a study investigating proteins that interact with the chromodomain of CHD-1 in a yeast two hybrid screen. One of the protein identified as interacting with CHD-1 was N-CoR which is a protein that is associated with histone deacetylation. Since deacetylated histones are associated with chromatin containing silenced genes, it was concluded that CHD-1 can function in gene silencing as part of a complex with histone deacetylase.180 p.Biology, Molecular.Thesis