Mitochondrial distribution after fast embryo freezing.
Mitochondrial distribution pattern after ultrarapid freezing in dimethylsulphoxide was assessed in human multipronucleate zygotes, 2-cell and 4-cell stage embryos using rhodamine 123. The mitochondrial distribution pattern was evaluated at 37 degrees C after a 30 min incubation in rhodamine 123 solution, 4 h and 24 h after thawing. Non-frozen human unfertilized oocytes, 2-cell and 4-cell embryos used as a control showed a homogeneous distribution of mitochondria throughout the cytoplasm, while there was sequestration of mitochondria from the cortex to the region surrounding the pronuclei in multipronucleate zygotes. Morphologically intact multipronucleate zygotes, 2-cell and 4-cell stage embryos after quick freeze-thawing showed the same mitochondrial distribution pattern found in the unfrozen controls. Mitochondria exhibited a typical severe aggregation (clumping) throughout the cytoplasm when non-viable single blastomeres or embryos at thawing were exposed to rhodamine 123. Our study indicates that quick freezing does not affect subcellular structures. The well-organized and specific mitochondrial distribution appeared still to be present after frozen storage, and subcellular structures seemed to be rather resistant targets for cryo-injury.
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Medical Centre for Fertility Diagnostics and In Vitro Fertilization and Embryo Transfer, Leuven, Belgium.
Campo
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Roziers
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Swinnen
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Vercruyssen
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Gordts
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D002970:Cleavage Stage, Ovum / Q000648:ultrastructure*; D015925:Cryopreservation; D005260:Female; D006801:Humans; D008928:Mitochondria / Q000648:ultrastructure*; D009865:Oocytes / Q000648:ultrastructure*; D013997:Time Factors; D015053:Zygote / Q000648:ultrastructure*