Abstract:
The process of maturation encompasses a complex series of molecular and structural events. Completion of the nuclear changes to produce a metaphase II (MII) oocyte does not reflect the molecular and structural maturity of an oocyte, which is sometimes termed cytoplasmic maturation. The Golgi apparatus phosphorylates, fragments, and changes the localization during oocyte maturation. GM130 and phospho-GM130 are used as markers for the Golgi apparatus and phosphorylated Golgi apparatus, respectively. The goal of this study was to analyze the dynamics of the Golgi apparatus and its association with microtubules in bovine oocytes at different stages of in vitro maturation [IVM; i.e. germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I (MI), and MII]. The roles of CDC2A kinase (also known as p34cdc2) and cytoplasmic-dynein ATPase on Golgi dynamics were studied by using specific inhibitors. The distribution of the markers was assessed by immunocytochemistry and laser confocal microscopy. To unravel the role of CDC2A and cytoplasmic dynein ATPase on the dynamics of the Golgi apparatus, the inhibitors roscovitine (ROS) and sodium-orthovanadate (SOV), respectively, were used. In the first experiment, the nuclear maturation rate was checked in the presence of the inhibitors at different times and for different incubation times to explore whether oocytes were able to reach the MII stage. At the GV and GVBD stages, the Golgi apparatus is observed as fragments named mini-Golgies and at the MI and MII stages as punctate foci throughout the cytoplasm. Our results showed 2 well-defined movements of the Golgi apparatus toward opposite directions, depending on the maturation stage. The first movement was observed between 5 and 9 h of IVM (i.e. the GVBD stage), when the Golgi apparatus relocalized from the ooplasm to the periphery. The second movement was observed between 9 and 15 h of IVM (i.e. the MI stage), when the Golgi apparatus moved from the cortex to throughout the cytoplasm and remained there up to the MII stage. The use of inhibitors on CDC2A and cytoplasmic-dynein ATPase at selected time points revealed that CDC2A played a crucial role on the distribution of this organelle during the first movement, whereas the final localization at the GVBD stage was dependent on cytoplasmic-dynein transport. The second movement of the Golgi apparatus was disturbed by the SOV treatment, but not by the use of ROS, suggesting a role of cytoplasmic-dynein-dependent transport during the distribution and organization of the punctate foci at the MI stage. The phosphorylation status of Golgi was not affected at the different incubation times with inhibitors, except in those oocytes incubated with ROS for 24 h, suggesting a role of CDC2A. In conclusion, we describe the involvement of CDC2A during the first movement of the Golgi apparatus and the importance of cytoplasmic-dynein ATPase activity in the first and second relocalization of Golgi during bovine oocyte maturation.<fn-group><fn>DAAD.</fn></fn-group>