Effects of extremely low osmolarity on fertilized mouse eggs

Abstract

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 blasto-cyst. 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.