Effect of follicle cells on the maturation and developmental competence of ovine oocytes matured outside the follicle

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Abstract
The hypothesis that follicle cells play a central role in endowing the oocyte with developmental competence during maturation has been tested in coculture studies. Oocytes and follicle cells in various combinations were cultured for 24 h with gonadotrophins and estrogen in a nonstatic culture system. Developmental competence was assessed by transfer of oocytes to inseminated receipient ewes followed by embryonic examination 12 days later or at parturition.Denuded and corona‐enclosed oocytes resume meiosis in culture but remain immature and developmentally incompetent. By contrast, oocytes supported by the cumulus and underlying granulosa (cumulus‐oocyte complexes) undergo full maturation and normal subsequent embryonic development (42.6% to embryos). Addition of supplementary follicle cells during culture (5 × 106 cells/ml medium) is without beneficial effect on denuded oocytes. However, supplementary cells confer competence on corona‐enclosed oocytes (37% to embryos).A dual cellular requirement for full maturation involving both cell numbers and some direct cell‐oocyte contact is highlighted by our experiments. The results demonstrate further that the nonstatic system provides a simple but reliable method of producing large numbers of fully matured oocytes for both research and clinical purposes.

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