抄録
The hatching ability was evaluated in diploid parthenogenetic mouse blastocysts based on the hatching rate, the embryonic contraction, the ultrastructure of the zona pellucida, and the activity of trypsin-like proteinase. The hatching rate of parthenogenetic blastocysts was 24.7% (87/350), which was significantly lower than 48.6% (184/383) in control blastocysts developed from fertilized 1-cell embryos (fertilized blastocysts). During observation for 32 h after blastocoel formation, strong contractions (20% or more volume reduction) occurred more frequently in parthenogenetic blastocysts (2.4 times) than in fertilized blastocysts (1.4 times, P<0.01). The lengths of time needed for re-expansion following both weak (less than 20% volume reduction) and strong contractions were significantly longer in parthenogenetic blastocysts (147.7 and 345.0 min) than in fertilized blastocysts (107.7 and 242.6 min). The zona pellucida showed a dense and homogeneous microgranular appearance in both parthenogenetic and fertilized blastocysts, while the zona pellucida of parthenogenetic blastocysts showed a few cracks in the outer surface. A similar morphological change was also observed in fertilized blastocysts developed following ethanol treatment, suggesting that the zona crack may be induced by ethanol treatment. The thickness of the zona pellucida and the activity of trypsin-like proteinase did not differ between parthenogenetic and fertilized blastocysts. These results suggest that the lower rate of hatching in parthenogenetic blastocysts might be due to the large number of strong contractions that require longer duration for re-expansion rather than changes in the structure of the zona pellucida or the activity of trypsin-like proteinase of the embryos.
