Effect of Treatment to Temporarily Block Germinal Vesicle Breakdown on Porcine Oocyte Maturation and Subsequent Parthenogenetic Development

In order to achieve developmental competence, porcine oocytes must undergo both nuclear and cytoplasmic maturation. Nuclear maturation results from breakdown of the germinal vesicle (GV) and progression of meiosis to metaphase II (MII). Cytoplasmic maturation is the accumulation, within the oocyte’s cytoplasm, of products necessary for fertilization, cleavage and development, prior to activation of the embryonic genome. In vitro studies show that porcine oocytes require a maturation period of about 44 h in vitro to achieve adequate cytoplasmic maturation for developmental competence. However, nuclear maturation to metaphase II occurs within the first 24 h of culture (Day & Funahashi, 1996). This suggests that nuclear maturation events undergo aging while awaiting adequate cytoplasmic maturation, which in turn may decrease developmental competence. Better synchrony between nuclear and cytoplasmic maturation might be achieved by temporarily blocking the spontaneous nuclear maturation that occurs when oocytes are removed from follicles and placed into culture. This might be achieved through the use of chemical blocking agents or altering the timing of addition of hormones to maturation medium. The present studies were conducted to determine if the presence or absence of gonadotropins (FSH and LH) during the first or second half of in vitro maturation affected porcine oocyte maturation to M II and subsequent cleavage. Also, the studies assessed the effectiveness of various chemical treatments to prevent porcine oocyte germinal vesicle breakdown (GVBD) for a period of 20 h without detrimental effects to subsequent maturation and cleavage.