258 MESSENGER RNA EXPRESSION PATTERNS OF HISTONE MODIFICATION GENES IN BOVINE EMBRYOS DERIVED FROM DIFFERENT ORIGINS

Abstract

Epigenetic modifications of the genome, such as covalent modifications of histones, are crucial for transcriptional regulation during development. The N-terminal tails of the histones are subject to post-translational modifications, including acetylation, deacetylation and methylation. histone acetylation loosens chromatin packing and correlates with transcriptional activation. The enzymes Histone acetyltransferases (HATs) transfer acetyl moieties to the lysine residues of histones H2A, H2B, H3, and H4. Histone acetylation is a reversible process which is catalyzed by the histone deacetylase (HDAC) and results in transcriptional repression. Histone methyltransferase (HMT) is responsible for the methylation of arginine in histones 3 and 4, playing an important role in transcriptional activation of genes. In contrast, the H3 Lys 9 methylation is associated with a transcriptionally repressive heterochromatin. The objective of the present study was to determine the effects of different origins of embryos on the relative abundance of transcripts for the histone acetyltransferase 1 (HAT1), histone deacetylase 2 (HDAC2), histone metyltransferases (SUV39H1 and G9A), and heterochromatin protein 1 (HP1). Messenger RNA expression profiles of these genes were investigated in bovine oocytes and pre-implantation embryos up to the blastocyt stage produced either in vitro by two different culture systems, i.e. SOF+BSA or TCM+SERUM, by somatic cloning using adult male and female fibroblasts, parthenogenetic activation, and androgenetic construction, or in vivo, employing semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Significant differences are described below. HAT1, SUV39H1, G9A, and HP1 mRNA transcripts decreased in enucleated oocytes, compared with immature oocytes. The relative abundance of HAT1 and SUV39H1 transcripts was significantly increased in NT-derived zygotes produced from adult female fibroblasts, compared to their in vitro fertilized and parthenogenetic counterparts. No differences were found in the relative abundances of gene transcripts at the 8-16-cell stage, except for parthenogenetic embryos in which SUV39H1 transcripts were significantly higher than in all other 8-16 cell groups. The relative abundance of SUV39H1, G9A, and HP1 transcripts were significantly higher in NT-derived blastocysts derived from adult male fibroblasts than in their in vivo-generated counterparts. HP1 and G9A transcript levels were significantly increased in NT-derived blastocysts derived from male fibroblasts compared to NT-derived embryos produced from female fibroblasts. The results show that the in vitro environment and the nuclear transfer protocol affect mRNA expression patterns of histone modification genes in pre-implantation bovine embryos.