Fertilization and early embryology: Cryopreservation of immature mouse oocytes |
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Authors: | Candy CJ; Wood MJ; Whittingham DG; Merriman JA; Choudhury N |
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Institution: | MRC Experimental Embryology and Teratology Unit, St George's Hospital Medical School Cranmer Terrace, London SW17 ORE, UK |
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Abstract: | Mouse oocytes enclosed in cumulus cells were isolated from antralfollicles at the germinal vesicle (GV) stage. They were storedin straws at 196°C by a conventional mouse embryofreezing method using dimethylsulphoxide (1.5 M) as the cryoprotectant.Overall survival assessed after removal of the cumulus cellswas 93% (299/320). A significantly greater proportion of freshoocytes remained arrested at the GV stage during culture (11versus 1%), but the rate of maturation to metaphase II was notsignificantly different between frozen and fresh oocytes (83versus 74%). The rate of fertilization in vitro was similarfor frozen and fresh oocytes matured in vitro (70 versus 81%)but significantly less than with mature ovulated oocytes (96%).Fertilization of frozen and fresh oocytes arrested after germinalvesicle breakdown was similar (77 versus 95%. No evidence ofparthenogenetic activation was found in the different groupsafter overnight incubation of metaphase II oocytes. Implantationwas similar for embryos derived from fresh and frozen GV-stageoocytes matured in vitro and mature ovulated oocytes, but theloss of embryos after implantation was significantly higherin the in-vitro matured groups (frozen, 40% and fresh, 46% versus24%). The overall survival of oocytes frozen at the GV stagewas 27%. This compares favourably with the estimated overallsurvival of mature oocytes cryopreserved by a similar procedure.We conclude that the increased post-implantation loss is dueto suboptimal conditions for maturation in vitro rather thanfreezing injury. |
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Keywords: | cryopreservation/germinal vesicle/maturation/mouse/oocyte |
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