Time-Lapse Videomicrographic Observations of Parthenogenetic Mouse Embryos during Early Development.

Abstract

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.

Roles of Embryonic Contractions in Hatching of Parthenogenetic Mouse Blastocysts.

“…We have confirmed that the initial mode of hatching in parthenogenetic mouse blastocysts is different from that of fertilized blastocysts, and that such parthenogenetic blastocysts take a significantly longer time to start hatching than fertilized blastocysts [6].…”

“…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.…”

“…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.…”

Spindle shape and volume differ in high- and low-quality metaphase II oocytes

“…We used cytochalasin D to ensure diploidization of the parthenogenotes and SrCl 2 to induce oscillatory pattern of the activating Ca 2+ signal, very similar to the sperm-triggered Ca 2+ response (Zhang et al 2005). Although parthenogenotes are unable to achieve full term development, they are perfectly able to complete preimplantation development and form properly build blastocysts (Niimura & Futatsumata 1999). Therefore, we believe that the relationships we observed here for parthenogenotes are also true for embryos derived from fertilization.…”