267 ULTRASTRUCTURAL CHARACTERISTICS OF NON-MATURED AND IN VITRO MATURED OOCYTES COLLECTED FROM FOLLICULAR, LUTEAL, AND INACTIVE OVARIES OF DOMESTIC CAT (FELIS CATUS) DURING BREEDING AND NON-BREEDING SEASON

The aim of this experiment was to describe the ultrastructural characteristics of non-matured (NM) and in vitro matured (IVM) cumulus–oophorus complexes (COC) recovered from adult queens during the breeding season (BS; July, August, and September) and the non-breeding season (NBS; January, February, and March) in southeast Brazil. Transmission electronic microscopy was performed in NM COC immediately after harvest, and IVM COC were matured for 36 h before transmission electronic microscopy. All IVM COC during both seasons were at metaphase II stage. Specimens were divided into COC from inactive ovaries, follicular ovaries, and luteal ovaries recovered during BS and NBS. During NBS, NM follicular and inactive COC presented a narrow perivitelline space covered with microvilli, which were less evident in NM luteal COC. Cumulus-cell projections penetrated the zona pellucida forming gap junctions with the oolemma in all NM COC. In the cytoplasm of NM inactive COC, lipid droplets and vesicles were evenly distributed in the ooplasm except for in the cortical zone, where clusters of mitochondria were observed. Non-matured luteal COC were also characterised by peripheral mitochondrial clusters, but greater clusters could also be seen centrally in the cytoplasm. In contrast, NM follicular COC were characterised by evenly distributed mitochondria within the ooplasma. In NM inactive and follicular COC, cortical granules were seen only in the central region of the cytoplasm, but the electron density of these organelles appeared to be low and Golgi complexes were often seen in association with these granules. The density of cortical granules in NM follicular COC was higher, but they were also present in central regions of the ooplasm. In all NM COC, a well-developed Golgi complex was observed. In all IVM COC, mitochondria clusters were no longer observed, and these organelles presented an even distribution toward the ooplasm. High-density cortical granules were present in the peripheral region of all IVM COC, although a small number could still be observed in central region of the ooplasm of IVM follicular COC. The perivitelline space was more prominent in IVM COC. During BS, COC characteristics were similar to NM COC during NBS; the presence of mitochondrial clusters associated with lipid droplets, well-developed cortical granules, and the presence of nuage could be observed, except that all cortical granules located in the central region of the cytoplasm of NM follicular COC during BS. A great amount of smooth endoplasmic reticulum could be verified in NM follicular and luteal COC. During BS, all IVM COC presented uniform distribution of mitochondria and peripheral distribution of cortical granules in the ooplasma. These results indicate that IVM was efficient in inducing the morphological changes necessary for cytoplasmic maturation of cat COC, independently of the ovarian status. The authors acknowledge FAPESP.