Golgi apparatus and endoplasmic reticulum dynamic during meiotic development in canine oocytes

The Golgi apparatus (GA) and endoplasmic reticulum (ER) play a central role in the events related to intracellular trafficking distribution. This work evaluated the dynamics and localization of the GA and ER in canine oocytes during meiotic development in vitro. Cumulus-oocytes complexes (COCs) from ovaries of adult bitches were incubated for IVM for 0, 48, 72 and 96 h. At each time, the nuclear status was determined using DAPI staining, and the GA was evaluated by immunofluorescence using two antibodies against Golgi proteins: GM130 and Giantin. ER was analysed with fluorescent lipid probes (ER-Tracker), for living cells. Golgi structures were homogeneous in the cytoplasm in non-matured oocytes, mainly in those GV-arrested oocytes. In contrast, at 48 h and from GVBD stage, the immunolocalization began to be subcortical, increasing at 72 h and 96 h. Meiotic development increased with time and the majority of oocytes at MI-MII stages showed cortical distribution of Golgi structure. Living ZP intact non-matured oocytes showed a reticular pattern of ER that covered oocyte cortex. Confocal microscopy showed that, in all levels cuts the fluorescence marks were located in the cortical region, irrespective of culture time. The changes and localization in these organelles during IVM might be related to meiotic development, but in a non-synchronous manner.