Effects of extremely low osmolarity on fertilized mouse eggs.

When fertilized one-cell eggs are subjected to distilled water treatment for 2-6 min, cytoplasm bulges through the sperm-slit in the zona pellucida and forms a cytoplasmic fragment (CF). CFs were observed in 86-5% of eggs; in 20-9% of cases CFs contained a pronucleus (or pronuclei). In 53-4% of eggs permanent incorporation of the second polar body (2 P.B.) into the egg cytoplasm occurred. These phenomena occurring in different combinations produced 6-2% of haploid eggs, 10-3% of diploid eggs with a pronucleus replaced by 2 P.B. nucleus, and 43-1% of triploid eggs. 4-4% of eggs were enucleated. The remaining group comprised diploid eggs which were either not affected by the treatment (6-4%) or lost a certain amount of cytoplasm by formation of an anucleate CF (29-6%). The frequencies of the types of reaction were related to the post-fertilization stage of eggs. All eggs except the enucleated ones were able to develop to the stage of morula or blastocyst. Triploids developed until the 12th day of pregnancy and diploids that had lost up to 15% of the cytoplasm developed to term. There was a twofold reduction in the percentage of preimplantation development when treated eggs originated from induced rather than spontaneous ovulation.