| Formation of gametes capable of supporting development is dependent on a number of genetic and epigenetic events. DNA methylation is an epigenetic modification catalyzed by enzymes named DNA methyltransferases (DNMTs). In the mouse, methylation of DNA is associated with the control of gene expression and proper embryo development. Methylation patterns are established in a sex- and sequence-specific manner during male and female germ cell development and further modified during early embryonic development. Even though new DNMTs have recently been identified, little information is known on the origin of the methylation marks during male germ cell development (spermatogenesis). The main goal of the work presented in this thesis was to gain a better understanding of the enzymes involved in creating the epigenetic program of the male genome. The first step in doing so involved comparing the temporal expression profiles of DNA methyltransferases in the developing testis and ovary. The expression profiles obtained indicated that in the male, DNMT3a and DNMT3L could be involved in de novo methylation while DNMT3b and DNMT1 could be responsible for maintaining methylation patterns following DNA replication. Next, characterization of Dnmt3a and Dnmt3b expression in isolated postnatal male germ cells revealed how tightly regulated the expression of these genes is during spermatogenesis: specific transcript variants and protein isoforms of each DNMT are differentially expressed during male germ cell development. Finally, assessing the effect of Dnmt3L inactivation on the male germ line exposed the presence of a mitotic defect in germ cells lacking this protein. DNA methylation analyses revealed that many loci throughout the genome are marked for methylation by DNMT3L, indicating a more global role for this enzyme than that previously reported in genomic methylation patterning in the male germ line. As methylation patterns instituted during spermatogenesis have to be properly established for accurate transmission of epigenetic information to the next generation, the studies presented here contribute to our knowledge of the events leading to the creation of the epigenetic program necessary for the formation of healthy gametes. |
