INFLUENCES OF ELECTRODE GEOMETRY AND FIELD-STRENGTH ON THE FUSION AND SUBSEQUENT DEVELOPMENT OF MOUSE 2-CELL EMBRYOS

The electrofusion and subsequent development of mouse 2-cell embryos were studied with respect to electrode geometry and field strength using a wire chamber (W-chamber) or a rectangular chamber (R-chamber) with 1-mm gaps. Field strengths of 1.0-2.5 kV cm-1 were examined. Fusion rates were high (92.6 +/- 2.4-98.9 +/- 1.1%) regardless of electrode geometry and field strength. However, when an R-chamber was used, significantly lower development rates were obtained at field strengths of 2.0 and 2.5 kV cm-1. Fusion progressed quickly using the R-chamber and applying the higher field strengths. Blastocyst formation by fused embryos in the R-chamber was faster than in the W-chamber and control embryos. In the R-chamber, the number of embryos with visible vacuoles increased, especially at 2.0-2.5 kV cm-1 (4.9-8.8%), of which 78.6% lysed at the one- or two-cell stage. Most of the fused embryos had a tetraploid chromosome constitution, but eight embryos (1.6%) were diploid. The mean cell number of tetraploid blastocysts was about half that of diploid control embryos, and was reduced with increasing field strength in the R-chamber. These results suggest that the W-chamber can be successfully applied across a relatively wide range of field strengths, providing stable conditions for fusion and subsequent development. However, when the R-chamber is used, the developmental capacity of fused embryos can be affected by an increase in field strength.