The factors required for pronuclear formation are derived from fully grown GV oocytes, and the transformation from decondensed sperm chromatin to a recondensed male pronucleus is governed by GV-derived factors.
Abstract:The process of early development in diploid parthenogenetic mouse embryos from the 2-cell to the blastocyst stages was observed by time-lapse videomicrography, and was compared with that in fertilized embryos. Parthenogenetic 2-cell embryos cleaved and developed to 8-cell embryos after 23.0 hrs of culture. Transformation of blastomeres occurred at the 8-cell stage: namely, outer blastomeres were flattened. The embryos compacted at the morula stage, and then developed to blastocysts after 54.0 hrs of culture. A slit in the zona pellucida was formed 42.7 hrs after blastocyst formation, and trophectoderm cells protruded out of the zona pellucida through the slit. Protrusion of trophectoderm cells from the zona pellucida could arise from either side, polar trophectoderm or mural trophectoderm. After 7.0 hrs, the blastocysts completely escaped from the zona pellucida in either state, expansion or contraction. Fertilized 2-cell embryos showed morphological changes similar to those of parthenogenetic embryos and developed to blastocysts after 51.9 hrs of culture. Fertilized blastocysts took a significantly shorter time, 31.1 hrs, to start hatching, but required a significantly longer time, 23.8 hrs, to complete hatching, compared with parthenogenetic blastocysts. Hatching patterns of fertilized blastocysts were consistent with those of parthenogenetic blastocysts, except that hatching began with protrusion of trophectoderm cells from small holes in zonae pellucidae of fertilized blastocysts. From these results, it was confirmed that the developmental ability of early diploid parthenogenetic embryos prepared by the treatment with ethanol and cytochalasin B is comparable to that in fertilized embryos.
Abstract. 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. Key words: Parthenogenetic mouse blastocyst, Hatching ability, Contraction, Time-lapse videomicrography.(J. Reprod. Dev. 46: [367][368][369][370][371][372][373][374] 2000) h e h a t c h i n g o f m o u s e b l a s t o c y s t s i s accompanied by regional dissolution of the zona pellucida by a trypsin-like proteinase synthesized in trophectoderm cells [1,2] and trophectoderm cells protrude from the dissolved hole of the zona pellucida [3][4][5]. Then the zona pellucida is slit as hatching proceeds due to blastocyst expansion [3][4][5]. During hatching, the blastocyst repeats contractions, leading to the enlargement of the zona slit, and finally escapes from the zona pellucida [3][4][5].In our previous study [6], however, diploid parthenogenetic mouse blastocysts formed a larger slit in the zona pellucida at the beginning of hatching than did control blastocysts developed f ro m f e rt i l i z e d 1 -c el l e m b ry o s ( f e r ti l i z ed blastocysts), and the duration of hatching in the former was significantly longer than that in the latter. Thus, it was inferred that the hatching ability of parthenogenetic blastocysts is different from that of fertilized blastocysts.In the present study, therefore, the hatching rate,
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