Abstract
Cysteine is considered to promote MPN formation in pigs through synthesis of oocyte GSH which has an important role in providing cells with a redox state to avoid toxic effects of oxidative damage. However, such previous investigations were carried out under high oxygen tension (20% O2). In this study, we evaluated the effects of cysteine concentrations in IVM medium under low oxygen tension (5% O2) on their intercellular content of GSH after IVM, their subsequent status after IVF and embryonic development ability. COCs were collected and cultured in IVM medium supplemented with 0 (C), 0.05, 0.1, 0.2 or 0.6 mM cysteine for 44-46 h, fertilized in vitro and subsequently cultured for 6 days. GSH content of IVM oocytes exposed to 0, 0.05, 0.1, 0.2 or 0.6 mM cysteine increased significantly (P<0.05) as the concentration of cysteine increased (12.2, 14.0, 15.1, 16.4, and 16.4 pmol/oocyte, respectively). However, the rates of oocyte maturation, sperm penetration, MPN formation, monospermy, cleavage, and blastocyst formation on Day 6 were not different among the groups. Moreover, the cell numbers of blastomeres in blastocysts were uniform among the groups. These results indicate that supplementation of 0.05-0.6 mM cysteine during IVM under 5% O2 tension significantly increased intracellular GSH contents of IVM oocytes; however, it had no promoting effects on nuclear maturation, fertilization and MPN formation and subsequent embryonic development to the blastocyst stage. Therefore, O2 tension during IVM of oocytes is suggested to play an important role in IVP of porcine embryos.
Supported by JSPS-VAST 2005-2007 project and Monbukagakusho scholarships.
