| The development of healthy gametes is paramount to the health of progeny and to the survival of a species. Epigenetic information contained within gametic DNA in the form of DNA methylation is essential for germ cell and embryo development. DNA methylation is a genome-wide phenomenon involved in the control of gene expression and chromosome structure and stability. During germ line development, patterns of DNA methylation are established in a sex- and sequence-specific manner. The primary goal of the work presented in this thesis is to gain an understanding of the nature of the genome-wide pattern of DNA methylation in germ cells and to study its progression during germ cell development. The complexity of male germ cell development has been well studied in mice and thus makes an excellent system in which to study germ cell DNA methylation. Firstly, genome-wide patterns of DNA methylation in adult male germ cells were determined using a variety of techniques. Results from these studies demonstrate that the DNA methylation pattern in male germ cells is highly distinct from that of somatic cells. The reorganization of the germ cell pattern is associated with chromosomal features such as the chromosomal banding pattern and regional GC content. Secondly, by examining purified populations of male germ cells, we have determined that patterns of DNA methylation are being acquired during spermatogenesis. De novo methylation and demethylation events occur in a sequence-specific manner prior to the meiotic phase of germ cell development. Finally, the stability of these patterns was studied by perturbing DNA methyltransferase activity. The study of germ cells lacking a functional Dnmt3L gene demonstrates that the abnormalities displayed in these cells are associated with a failure to acquire normal levels of DNA methylation. In addition, the treatment of mice with the hypomethylating agent, 5-aza-2'-deoxycytidine, results in adverse effects on sperm function and is associated with sequence-specific hypomethylation. Collectively, these studies have uncovered several novel aspects of DNA methylation in male germ cells and contribute to our understanding of the roles) for epigenetic phenomena in the development and maintenance of healthy gametes. |
