An improved method for destroying mouse blastomeres electrically inside the zona pellucida and the in vitro development of the surviving blastomeres.

An improved method for isolating mouse blastomeres by electrically destroying the other blastomeres inside the zona pellucida is described. Instruments required are two micromanipulators connected to an inverted microscope and an electronic stimulator equipped with an isolator. The target blastomere in which a glass microelectrode is inserted disintegrates completely within a few seconds after a direct current is applied. Complete destruction of a blastomere requires more than 60 microA delivered at 8 V. Destruction of blastomeres occurred mainly as a result of the medium penetrating the blastomere due to the change of membrane potential in both the zona and the blastomere. Most one-half, two-quarter, and three-quarter embryos obtained in this way developed in vitro into normal blastocysts (76.4--86.2%). By contrast, there was a marked decrease (35.3%) of developmental potential in one-quarter embryos. The results indicate that the present method is an improvement over previous methods of obtaining mammalian blastomeres inside the zona pellucida.