Effects of different electrofusion parameters on activation and early development of mouse embryos reconstructed by cumulus cell nuclear transfer

OBJECTIVE: To study the effects of different parameters for electrofusion on the activation and early development of mouse embryos reconstructed by cumulus cell nuclear transfer, and explore optimal parameters for electrofusion. METHODS: A C57BL/6j mouse cumulus cell nucleus 10-12 mm in diameter was inserted into the perivitelline space of an enucleated oocyte. The fusion of donor-recipient pairs was induced with different parameters for electrofusion (with variation in electric field intensity, pulse duration and pulse times). Successful formation of the reconstructed embryos from donor-recipient pairs and the reconstructed embryos developing into the early embryonic stages (2-cell, 4-8-cell and morula stages) were observed and counted. RESULTS: The electric field intensity and pulse duration allowed variation during electrofusion within the range of 1 000-2 000 kV/cm and 40-160 ms, respectively. The donor-recipient pairs fused at very low rate when the parameters were below the allowed ranges, and disintegration or even death might occur when the parameters were above the ranges. Within these allowed ranges, variation of the electrofusion parameters did not produce significant impact on the ratio of the reconstructed embryos in 2-cell, 4-8-cell or morula stages (P<0.05). In addition, we suggested that pulse times be limited to 1-2. CONCLUSION: Optimal parameters for electrofusion are crucial for the fusion of donor-recipient pairs and the activation of the reconstructed embryo.