Dynamic changes of the Golgi apparatus during bovine in vitro oocyte maturation

For successful fertilization by the male gamete, oocyte cytoplasmic organelles such as the Golgi apparatus have to undergo specific changes; the entire process is known as cytoplasmatic maturation. The goal of this study was to unravel the dynamics of the Golgi apparatus in bovine oocytes at critical stages of in vitro maturation (IVM), i.e. germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I (MI) and metaphase II (MII), and to investigate the role of various molecules critically involved therein. The cytoplasmatic distribution of proteins was assessed by immunocytochemistry and laser confocal microscopy. We applied specific inhibitors, including nocodazole (NOC) to unravel the functional role of the microtubular elements, sodium-orthovanadate (SOV), which primarily inhibits cytoplasmic dynein ATPase activity, monastrol (MON) which inhibits the kinesin Eg5 and roscovitine (ROS) to inhibit the kinase CDC2A. Prior to GVBD, the Golgi apparatus was translocated from the centre of the cytoplasm to the cortical area in the periphery, where it underwent fragmentation. A second translocation was observed between GVBD and MI stages, when the Golgi apparatus was moved from the cortex to the centre of the cytoplasm. Incubation with the specific inhibitors revealed that microtubules played an active role in the final localization at GVBD, while CDC2A was essential for Golgi fragmentation at GVBD stage. This partitioning was a precondition for the second movement. In conclusion, for the first time we show basic mechanisms critically involved in the regulation of the dynamic changes of Golgi during meiosis of the bovine oocyte.