The effect of ovine oocyte vitrification on expression of subset of genes involved in epigenetic modifications during oocyte maturation and early embryo development.

Apart from ultrastructural damages in oocytes subjected to cryopreservation procedures, little is known about the status of epigenetic modification and chromatin remodeling in vitrified oocytes. In present study, the expression patterns of eight genes involved in epigenetic modification (HAT1, HDAC1, SUV39H1, DNMT1, and DNMT3b), chromatin remodeling (HMGN3a and SMARCAL1), and transcription (STAT3), were investigated in fresh and vitrified germinal vesicle and metaphase II oocytes and their resulting embryos at 2 to 7 cells, 8 to 16 cells, morula, and blastocyst stages. The mRNA relative abundance was quantified by reverse transcriptase real-time polymerase chain reaction, as fold change relative to the value obtained for fresh germinal vesicle oocytes. Vitrified oocytes showed lower cleavage (38.1% vs. 95.5%, P < 0.001) and development to blastocyst (8.2% vs. 50.8%, P < 0.001) compared with controls. In both fresh and vitrified groups, the genes expressions in oocytes were lower than cleaving embryos, with an exception of HMGN3a. Compared with fresh derived embryos, in vitrified groups, the overall expressions of HMGN3a and HDAC1 were decreased, whereas the expressions of STAT3, SMARCAL1, and DNMT3B were increased. Altogether, despite some differences in expression pattern of some genes, the overall pattern of increase and/or decrease in gene expression was almost the same in most of the genes studied between vitrified and fresh groups. Thus, apart from some mismatch in pattern of genes expression in a number of cases, the difference in magnitude and/or primacy and recency in reaching to the maximum expression, in association to embryonic genome activation, between fresh and vitrified groups, might be the reason for the lower developmental competence of vitrified-warmed oocytes compared with fresh ones.