Protective effects of melatonin on oocyte competence in vitro

Abstract

Aiming to reduce the impact of heat stress on the oocyte quality, this study will be conducted with the overall goal to evaluate the effectiveness of melatonin supplementation on bovine oocytes exposed to high temperatures on in vitro maturation. For this purpose, cumulus-oocytes complexes (COCs) will be assigned in a 2 x 6 factorial arrangement experiment with two maturation temperatures (38.5ºC or 40oC) and 6 concentrations of melatonin (0, 0.5, 1.0, 2.0, 5 and 10 nM). COCs will be placed in maturation medium containing various concentrations of melatonin and matured for either 22 h at 38.5ºC in an atmosphere of 5% CO2 (control) or 40ºC for 12 h in an atmosphere of 6% CO2 in humidified air followed by 38.5ºC in an atmosphere of 5% CO2 for 10 h. Matured oocytes will be assessed for levels of reactive oxygen species (ROS), and nuclear and cytoplasmic maturation status. After maturation, COCs will be fertilized and the resultant embryos cultured at 38.5ºC for all treatments. Endpoints will be percent of oocytes that cleave at 42-44 h post-fertilization and percent of oocytes and cleaved embryos that become blastocysts at Day 7 and 8 post-fertilization. The effects of melatonin supplementation on the oocyte competence to be fertilized and support development to the blastocyst stage will be evaluated, and also whether beneficial effects of melatonin on oocyte quality represent prevention of damage caused by heat stress. However, it should be clear that the methods of analysis, research project and work plan can be changed as needed, during the scholarship period. (AU)