Octaploid mouse embryos produced by electrofusion polarize and cavitate at the same time as normal embryos

We created enlarged octaploid mouse blastomeres by subjecting four-cell embryos to a large (greater than 2,000 V/cm) dc field of brief duration (10 microseconds). This electrofusion pulse caused three to four of the blastomeres to fuse in 60% of the embryos tested. Modifications of fusion chamber and medium enabled fusion of up to 20 embryos per pulse, greatly increasing the yield for this fusion method. The effectiveness of the electrofusion pulse depended upon such parameters as embryonic cell cycle time and the pH and temperature of the electrofusion medium. There was no discernable lag in the onset of the third cleavage division or the time of cavitation in fused blastomeres. These fused blastomeres also underwent polarization of their apical surfaces at the same time as controls in spite of their increased cell size. These results suggest that octaploid mouse blastomeres created via electrofusion divide normally through the blastocyst stage and polarize at the same time and in the same sequence as smaller control blastomeres. This suggests that the mechanisms underlying cell division, cavitation, and cortical polarization are not affected by changes in cellular size or ploidy.