Manipulation of chromosome condensation by protein synthesis inhibitors and cyclic AMP during maturation of bovine oocytes

We investigated the effects of cycloheximide on bovine oocyte chromosomes during meiotic maturation in vitro. Bovine oocytes at Metaphase I (MI) of the meiotic maturation were treated with 10 μg/ml cycloheximide alone or in addition to 5 mM dibutyrylcAMP (dbcAMP) plus 1 mM isobutylmetylxantine (IBMX). A maturation period of 15 to 18 h followed by 12-h treatment with cycloheximide appeared to be most efficient to induce interphase (86% with 16 h maturation). About 60% of oocytes returned to a metaphase state 12 h after the oocytes were transferred to cycloheximide-free medium. In contrast, up to 73% of cycloheximide-treated oocytes at 17 h of maturation remained in interphase if dbcAMP plus IBMX was included in the cycloheximide-free medium. This shows that dbcAMP plus IBMX can inhibit the development of conditions in the oocytes that are required for the transition to metaphase. The chromosome decondensation induced by protein synthesis inhibition at Metaphase I is reversible. This study shows that transition to interphase in bovine oocyte depends on the stage of maturation of oocytes and is sensitive to cAMP levels.