Histone methyltransferases and porcine embryo development

Successful cleavage development of mammalian embryos requires precise activation and repression of transcription. Gene expression is regulated through epigenetic modifications such as DNA methylation and histone modifications. Because there is a global remodeling of epigenetic modifications in the early developing embryo, we want to gain insight into the role of these epigenetic modifiers, as it will provide information on how developmentally important genes are regulated. The early developing embryo has a window where it is sensitive to in vitro manipulation, thus resulting in compromised development. Therefore, it is essential to understand mechanisms involved in epigenetic remodeling during cleavage development in hopes of improving methods that utilize in vitro manipulations, such as in vitro fertilization, embryo culture, somatic cell nuclear transfer, and stem cell therapy. The first goal of my study was to determine the localization of the histone methyltransferases Suv39H2, G9a, and ESET in the porcine oocyte and cleavage stage porcine embryo. The localization of these proteins would provide insight into the role of these enzymes in the methylation of lysine 9 of histone H3, a modification that results in gene silencing. It appears that Suv39H2, G9a, and ESET all play an important role in the methylation of H3/K9 as they are all present in the nucleus, although ESET was also in the cytoplasm, which may suggest its lesser role during this developmental time period. The second objective was to determine the developmental requirement for the histone methyltransferase G9a by performing knockdown experiments to lower G9a transcript abundance in the oocyte and cleavage stage porcine embryo. Although our RNAi oligonucleotides were effective at reducing G9a transcript abundance, no significant effect on embryo development was detectable. Overall these results indicate that each histone methyltransferase plays a distinct role at critical time points during porcine embryo development