P-131: Effects of Heat Shock during Early Stage of Oocyte Maturation on Meiotic Progression and Subsequent Embryonic Development and Gene Expressionin Ovine

Background: Heat shock may affect different aspects of oocyte maturation and its subsequent development to the blastocyst stage. A series of in vitro experiments was performed to determine whether physiologically heat shock (41°C) disrupts the progression of the ovine oocytes through meiosis, activation and blastocyst formation. Materials and Methods: The cumulus-oocyte complexes (COCs) were aspirated from 2-6 mm follicles and cultured at 38.5°C (control) or 41°C (heat shock) for the first 12 hours of maturation. The oocytes were incubated at 38.5°C during the last 10 hours of maturation and 8 days after activation. Results: Results showed that most of the oocytes matured in heat shock condition remained at GVBD stage and they showed an aberrant chromatin configuration. After heat shock, oocyte diameter and time spent for zona pellucida dissolution increased (p<0.05). Heat shock condition decreased (p<0.05) cleavage rates (56.19 vs. 89.28%) and morula formation (26.85 vs. 37.81%). However, there was no significant difference in blastocyst formation and percentage of hatched blastocysts. 12 hours heat shock had an adverse effect on embryo quality and reduced inner cell mass number (p<0.05). Quantitative gene expression analysis showed a greater transcripts (p<0.05) for Na/K-ATPase mRNA in heat shocked oocytes Conclusion: To sum up, heat shock has disruptive effects on ovine oocyte maturation and it can impair cellular and molecular factors which are important for embryo development.