Influence of oocyte aging on developmental ability of reconstituted embryos produced from oocyte cytoplast and single blastomeres of two-cell stage embryos

The present study was conducted to investigate the influence of aging of recipient oocyte on the developmental ability of reconstituted mouse embryos produced from the cytoplast of oocytes and single blastomeres of early or late 2-cell stage embryos by electrofusion. Oocytes were obtained at 14 (newly ovulated oocytes), 18, 22 (oocyte that time passed after ovulation; aged oocyte) hr after hCG injection and oocyte cytoplast was produced by manual enucleation using a fine glass needle under the dissecting microscope. The aging of the oocytes significantly influenced on the fusion rate of the reconstituted embryos (14hr: 42.7-47.2% vs. 22hr: 75.3-77.6%). Similarly, the cleavage rate of reconstituted embryos increased with aging of the oocytes (14hr: 50.8-56.3% vs. 22hr: 82.2-90.7%). The percentage of reconstituted embryos produced from cytoplast of aged oocytes (22hr post hCG) and single blastomeres of late 2-cell stage embryos developing to the blastocyst (20.8%) was significantly higher than that of reconstituted embryos produced by other combinations (2.0-8.2%: P