Effect of encapsulation on development of mouse pronuclear stage embryos in vitro.

Pronuclear stage embryos with intact (ZI), slit (ZS) or completely removed (ZF) zona pellucida were encapsulated with an artificial zona pellucida (AZP) made of 1.5% sodium alginate. Embryos were cultured in KSOM medium with or without protein and their development in vitro to the blastocyst stage was recorded. AZP significantly (P < 0.05) improved the development of embryos to the blastocyst stage regardless of the presence of the natural zona pellucida. The encapsulated embryos developed at a higher rate (P < 0.05) in the absence of protein as compared with non-encapsulated embryos. Furthermore, the cell contacts at the 4-cell stage were significantly improved (P < 0.05) with encapsulation. AZP improved (P < 0.05) the development of pronuclear stage embryos with a slit zona pellucida to morula and blastocyst stages as compared with ZS embryos. It is concluded that AZP improves the in vitro development of pronuclear stage embryos with intact or completely removed zona pellucida as well as micromanipulated embryos to the blastocyst stage.

Preparation of young preactivated oocytes with high enucleation efficiency for bovine nuclear transfer.

To improve the enucleation rate in newly matured bovine oocytes, we investigated the position of cytoplasmic chromatin in relation to the polar body and the consequent enucleation efficiency before and after sequential activation with calcium ionophore A23187 and cycloheximide. Oocytes aspirated from the follicles of slaughterhouse-collected ovaries were cultured for 18 to 20 h. With Hoechst staining, only 40.7% of the chromatin material was found adjacent to the first polar body in metaphase II oocytes, while 100% was located adjacent to the second polar body in oocytes after the activation. Enucleation trials after activation showed a higher enucleation rate (91.5%) than that before activation (59.9%). The following experiment determined the effect of using both kinds of cytoplast on the in vitro development of nuclear transfer embryos. Blastomeres of the 32-cell-stage in vitro-produced embryos were transferred, fused to the activated cytoplasts and cultured in vitro. No significant difference was detected in fusion, cleavage or development to blastocysts obtained 7 d (174 h) post fusion. In conclusion, this study showed that young in vitro-matured bovine oocytes sequentially activated with calcium ionophore and cycloheximide have cytoplasmic chromatin material adjacent to the second polar body, leading to a high enucleation rate.

In vitro developmental potential of bovine nuclear transfer embryos derived from primary cultured cumulus cells.

The in vitro development and the quality of blastocysts produced from the nuclear transfer (NT) embryos reconstituted from primary cultured cumulus cells (NT-cumulus) were examined compared to in vitro fertilized embryos (IVF) and NT embryos reconstituted from the embryonic blastomeres (NT-blastomere). The cleavage rate, and the development to blastocyst were the same for all three sets of embryos. The time required for blastocoel formation starting from the time of the initial cleavage was shorter for NT embryo groups than IVF ones. All experimental groups produced morphologically similar and normal blastocysts containing the same cell number. The percentage of the blastocysts with normal chromosomal complements were the same for NT-cumulus and IVF.