Doctor of Philosophy (PhD)


School of Animal Science

Document Type



Histone proteins are proteins found in eukaryotic cells that associate with DNA to form the most basic structural unit of chromatin, called nucleosomes. The post-translational modifications of histones regulate developmental competence in bovine oocytes and early embryos. The difference in developmental competence between in vitro matured oocytes and in vivo matured oocytes was used to investigate the accumulation of transcripts for histone methyltransferases (HMTs) during oocyte maturation. Methyltransferases ASH1L, EHMT2, SUV39H1 and KDM6B were selected as genes of interest. Transvaginal ultrasound-guided aspiration (TUGA) was used to collect immature and in vivo matured bovine cumulus-oocyte complexes (COCs). Immature COCs collected via TUGA were randomly assigned to either the immature or the in vitro mature treatments. Transcriptome analysis was performed in COCs, oocytes, and cumulus cells. Results showed no differences in transcriptome levels between immature and in vivo treatments, suggesting that there are no major accumulations of transcripts for HMTs during the antral phase of oocyte maturation in vivo. Higher accumulations of transcripts for the EHMT2 and ASH1L genes were found in the in vitro maturation Treatment for COCs and oocytes (p = 0.005 and p = 0.001, respectively). Immunocytochemistry was used to investigate the consequences of this increase in transcripts accumulation for HMTs during in vitro maturation of oocytes. Methylation levels of lysine 9 in histone 3 measured in both oocytes at the metaphase II stage and early embryos showed that the increase in the accumulation of transcripts coding for HMTs during in vitro maturation correlates with a decrease in the level of methylation of lysine 9 in histone 3 in oocytes at the metaphase II stage, as well as a decrease in the levels of methylation of lysine 9 in histone 3 in the blastomeres of early cleaving embryos. The decrease in the levels of tri-methylation of lysine 9 in histone 3 potentially affect the capacity of the oocyte and early embryo to silence gene and stabilize heterochromatic regions and potentially compromise the developmental potential of the embryo.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Bondioli, Kenneth