[The effectiveness of the microsurgical removal of the nuclei in early mouse embryos depending on the time before cleavage division].

The efficiency of microsurgical enucleation of zygote and two-cell mice embryos was found to increase sharply 1-1.5 h before cleavage in "late" embryos, and 5-6 h before cleavage in "early" embryos. In "late" embryos, the share of successful enucleations constitutes 80-90%, and in "early" ones, 10-30%. This phenomenon is not connected with cytoskeleton restructuring during the cell cycle, but is determined by the increase in intracellular osmotic pressure at late stages of cell cycle. This process results in the increased elasticity of the embryo and, consequently, the penetration of surgical instruments and removal of karyoplast occurs more efficiently. The artificial increase in the intracellular pressure by addition of distilled water to culture medium also increases the efficiency of microsurgical enucleation.