Paracrine factors from cumulus-enclosed oocytes ensure the successful maturation and fertilization in vitro of denuded oocytes in the cat model

ObjectiveTo better characterize cumulus-oocyte interactions during oocyte maturation and fertilization in the cat model.DesignExperimental in vitro study.SettingSmithsonian Institution.Animal(s)Domestic shorthair cats.Intervention(s)Groups of denuded oocytes (DOs) and cumulus-oocyte complexes (COCs) were subjected to in vitro maturation (with or without FSH and LH, with or without the gap junction disruptor 1-heptanol, in separated groups or in coculture) and inseminated in vitro (IVF; in separated groups or in coculture).Main Outcome Measure(s)Nuclear maturation, pronuclear formation, kinetics of early embryo cleavage, and blastocyst formation and quality after different in vitro conditions were compared between DOs cultured separately and DOs cocultured with COCs.Result(s)Without FSH and LH, the removal of cumulus cells prevented spontaneous meiotic resumption in DOs. With FSH and LH, groups of DOs progressed to the metaphase I stage but fully advanced to metaphase II only in coculture with intact (nondisrupted) COCs. Groups of DOs cultured separately were fertilized poorly and exhibited no blastocyst formation. In contrast, DOs cocultured with intact COCs during in vitro maturation and IVF recovered fertilizability, and approximately 35% formed blastocysts.Conclusion(s)Paracrine factors produced by cumulus-enclosed oocytes in the cat model will help to develop synthetic media for successful in vitro culture of DOs.