| Embryo technology needs large quantities of high quality oocytes. However, the quality of in vitro matured oocytes is generally lower than that of the in vivo matured. The poor quality of in vitro matured oocytes was thought to be due to a premature meiotic resumption without adequate cytoplasmic maturation induced by transfer of oocytes from follicles into a suitable culture medium. The distinguishing features of IVO oocytes that confer greater developmental potential remain obscure. Changes in the distribution of cortical granules (CGs) during oocyte maturation could be used as an important criterion to evaluate cytoplasmic maturation quality in vitro matured oocytes. Stydies on cortical granules migration and distribution are abundent in different mammalian spicies,such as mouse and porcine, but there are few studies in goat, especially that adopt the apparatus of Laser Scanning Confocal Microscope. In this study, chronological changes in CGs distribution and nuclear progression during maturation were compared among goat oocytes derived from different sizes of follicles. This study is significant to look into changes of cortical guanules in oocytes, probe into oocytes maturation mechanism, improve in vitro culture conditions and enhance in vitro maturation quality. The results are summarized as follows:1. The timeing of nuclear process differed between oocytes derived from different sizes of follicles. Only minority of oocytes from diametre≤0.5mm follicles could resume meiotic maturation but reach MI at most. Most oocytes from diametre 0.8-1.2mm follicles could resume meiotic maturation, but only 27% could reach MII. Oocytes from diametre 1.5-2.5mm and 3-5mm follicles could resume meiotic maturation and kept on development to the stage of MII(percentage is 64.5% and 82.4% at 24h,respectively). 2. Three stages of CGs distribution were observed during goat oocytes maturation, named no migration(NG),part migration(PG) and full migration(FG). First CGs neighbouring cortical area clustered to cortical cytoplasm and formed a discrete race, then the others gradually migrated and at last occupied the area just beneath the oolema to form a monolayer .3. CGs migration improved along with the increase of follicle sizes in fresh oocytes just obtained form follicles. Most oocytes from preantral follicles and early antral follicles showed no CGs migration, whereas majority of those from large follicles appeared as part migration.4. There was a cortical granules-rich region around the germinal vesicle in oocytes from preantral follicles and early antral follicles. It is likely that it is the sites of CGs production.5. CGs showed advanced distribution pattern with the extention of culture time and with the increase of follicle size. After in vitro culture 24h, the percentage of full migration stage in oocytes from diametre≤0.5mm follicles was 5.4%,in oocytes from diametre 0.8-1.2mm 1.5-2.5mm and 3-5mm follicles this number was 54.8%,79.0% and 97.0% ,respectively. Oocytes from large follicles showed advanced CGs compared with those from small follicles, both in time and excent.6. Cortical granule free domain(CGFD) existed in goat oocytes, located in the oolema above the chromatin, amounted for 10-15% of the oocyte perimetre. CGFD appeared at the stage of MI, and persisted up to MII.7. CGs migration and nuclear progress were two seperated processes. It is more likely that CGs migration reflected cytoplasm maturation. Oocytes at same stage of nuclear progress showed different CGs migration pattern.
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