TRANSIENT EXPOSURE OF RHESUS MACAQUE OOCYTES TO CALYCULIN-A AND OKADAIC ACID STIMULATES GERMINAL VESICLE BREAKDOWN PERMITTING SUBSEQUENT DEVELOPMENT AND FERTILIZATION

Exposure of mammalian oocytes to the protein phosphatase (PP)-1 (PP1) and PP2A inhibitor okadaic acid (OA) stimulates oocyte meiosis. Howeve r, treated oocytes do not develop beyond metaphase I (MI), and they di splay morphological aberrations. Experiments were conducted to define inhibitor treatment conditions for macaque oocytes that would result i n germinal vesicle breakdown (GVB) stimulation and completion of meios is without significant cytoplasmic abnormalities. As described above f or OA, continual exposure of macaque oocytes to 50 nM calyculin-a (CL- A) significantly enhanced GVB at 24 h compared to that in controls, an d the majority of the treated oocytes displayed cytoplasmic abnormalit ies. However, transient exposure (10 min) of rhesus macaque oocytes to -either 50 nM CL-A or 1.0 mu M OA enhanced GVB rates compared to that in controls and did not increase the incidence of cytoplasmic abnormal ities. Meiotic maturation from germinal vesicle-intact oocytes to MII was enhanced following transient treatment with CL-A or OA compared to that in controls; however, development from MI to MII occurred at a s imilar frequency. In vitro-matured oocytes transiently exposed to OA a nd CL-A were capable of fertilization. In addition, ovarian immunohist ochemical analysis revealed that both PP1 and PP2A were present in mac aque oocytes. PP1 was localized throughout the cytoplasm with a predom inance in the nucleus, whereas PP2A was evenly distributed throughout the cytoplasm with a reduction in the nuclear area. These results take n together-differential developmental responses to inhibitor treatment and intracellular enzyme localizations-may be indicative of multiple regulatory roles of PP1 and/or PP2A during meiosis.