Direct Effect of Controlled Osmotic Stress on Nuclear Maturation of Bovine Oocytes

Background: Recent studies have indicated that a well-defined and properly applied stress treatment of oocytes may induce general their adaptation, improve survival, and in vitro develop-ment. The current study was designed to understand the effect of controlled and sublethal osmotic stress on nuclear in vitro maturation of bovine oocytes as a fiirst step toward improving tolerance to various in vitro procedures such as cryopreserva-tion, enucleation and SCNT.Materials and Methods: Bovine immature aspirated oocytes from abattoir-derived ovaries were initially cultured in isosmot-ic IVM medium (bicarbonate –TCM 199 supplemented with 10% FCS and 0.1IU/ml FSH) (osmolality was 280-285mOsm) for 1h adaptation. After that, the oocytes of treatment group were exposed to hyperosmotic medium (500-510mOsm IVM medium contained sorbitol) for 4h and then transferred to IVM medium. All of the maturation procedure was carried out at 38.5ºC with a 5% CO2/air atmosphere for 22-24h. Eventu-ally nuclear maturation of oocytes was evaluated with 5µg/ml H33342 for 5min under an epifluorescent microscope.Results: The results showed that exposure of bovine oocytes to high osmolality had not any effect on nuclear maturation po-tential of osmotic stress-treated oocytes (12.05% MI stage and 86.14% MII stage versus 11.36% MI stage and 84.42% MII stage for control and treatment groups, respectively)(P> 0.05). Conclusion: Treatment with sublethal doses of high osmotic stress couldn’t induce any detrimental effect on in vitro matura-tion ability of bovine oocytes and oocytes could tolerate hy-perosmotic stress for up to 4h. In this study osmotic stress was carried out in the first quarter of bovine oocyte maturation pe-riod wherein the transcription potential of oocyte is still active. Accordingly, this controlled osmotic stress can induce efficient changes in the gene expression programs by intracellular sign-aling networks and may outline a completely new strategy in mammalian embryology.

کلیدواژه ها:

Osmotic Stress ، Nuclear Maturation ، Bovine ، Oo-cytes