The presence of cumulus cells on nuclear maturation of sheep oocytes during in vitro maturation |
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| Institution: | 1. Research Institute of Animal Embryo Technology, Shahrekord University, P.O. Box 115, Shahrekord, Iran;2. Department of Pathobiology, Faculty of Veterinary Medicine, Shahrekord University, P.O. Box 115, Shahrekord, Iran;1. College of Life Science and Engineering, Northwest University for Nationalities, Lanzhou, PR China;2. Medicine College, Northwest University for Nationalities, Lanzhou, PR China;1. Department of Theriogenology, Faculty of Veterinary Medicine, Cairo University, Giza, Egypt;2. Department of AI and ET, Animal Reproduction Research Institute, Agriculture Research Centre, Giza, Egypt;3. Department of Obstetrics and Gynecology, McGill University, Montreal, Canada;4. Department of Surgery, Urology Research Laboratory, McGill University, Montreal, Canada;5. OrigenElle Fertility Clinic and Women Health Centre, Montreal, Canada;1. Reproductive Physiology Laboratory, Animal Physiology Division, Indian Council of Agricultural Research-National Institute of Animal Nutrition and Physiology, Bengaluru 560 030, India;2. Animal Reproduction Division, Indian Council of Agricultural Research-Indian Veterinary Research Institute, Izatnagar 243 122, India;3. Director, Indian Council of Agricultural Research-National Institute of Animal Nutrition and Physiology, Bengaluru 560 030, India |
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| Abstract: | This study was carried out to investigate the role of maturation by cumulus cells and the initial bond between the cumulus cells and the oocyte on nuclear maturation of sheep oocytes. Ovaries collected from the local abattoir were transported to the laboratory in saline at 30–35 °C within 1–3 h after collection. The oocytes of follicles, 2–6 mm in diameter, were recovered by aspiration and collected in a pre-incubated (at 38.6 °C, 5% CO2, and 100% humidity) Hepes-modified TCM 199 medium. After preliminary evaluation, the oocytes with evenly granulated cytoplasm and which were surrounded with at least two layers of cumulus cells (good quality oocytes) were selected and subjected to culture in pre-incubated bicarbonate-buffered TCM 199 supplemented with 0.05 IU/ml recombinant human follicle stimulating hormone (rhFSH), 1 IU/ml human chorionic gonadotropin (hCG), and 1 μg/ml estradiol (OCM: oocyte culture medium). Before culturing, the selected oocytes were randomly divided into four treatment groups: Group 1, cumulus enclosed oocytes cultured in OCM; Group 2, denuded oocytes cultured in OCM; Group 3, denuded oocytes co-cultured with a cumulus cell monolayer in OCM; Group 4, denuded oocytes cultured in OCM in the presence of cumulus cells-conditioned medium. After an incubation period (26–27 h), the nuclear status of the oocytes in each treatment group was assessed using a 2% orcein stain. The rate of oocytes reaching the metaphase II (MII) stage (metaphase of second stage of meiosis division) was 82%, 5%, 11%, and 47% for Groups 1, 2, 3, and 4, respectively. The differences between groups were significantly (P < 0.05) different. The percentage of MII oocytes in Group 4 (47%) was higher than that obtained in Group 3 (11%), indicating a higher efficiency in a cumulus cell-conditioned medium, compared to the cumulus cells monolayer in providing the proper condition for sheep oocyte nuclear maturation. The results suggest the ability of sheep oocytes to resume meiosis in the absence of gap junctional communication (GJC) between the cumulus cells and oocyte being drastically interrupted while for optimum oocyte nuclear maturation, the intact physical contact between the oocyte and cumulus cells is essential. |
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