ABSTRACT
Nuclear behavior and cleavage pattern in partial fertilization were studied by using sea urchins,Temnopleurus toreumaticus, Anthocidaris crassispina and Hemicentrotus pulcherrimus. Partial fertilization was induced by insemination with the alkaline-treated sperm or the ultraviolet(UV)-irradiated sperm to normal eggs. When sperm were exposed to a 4. 8 mM KOH sea water, pH 9.8 for 2 min, the partial fertilization took place in a high percentage. In such cases, the first cleavage occurred without participation of the sperm nucleus. The sperm nucleus entered one of blastomeres and conjugated with its nucleus at 2-cell stage. In the second cleavage,cell division of the haploid blastomere preceded that of diploid one. Thus, the temporary 3-cell stage was formed. Irradiation of UV-dose 10 to 100 J/m to sperm did not damage the sperm mobility and fertilizabilty. Over 30 J/m -UV irradiation brought partial fertilization in high percentage. The cleavage pattern was similar to that of the fertilized eeg which has been induced by alkalinetreated sperm. The temporary 3-cell stage appeared. But in this case,the chromosome bridge was observed in one of blastomeres at anaphase of the second cleavage. This shows that the nucleus of the UV-irradiated sperm conjugated with the nucleus of one of blastomeres at 2-cell stage. Morphogenetical abnormalities of embryos derived from UV-irradiated sperm were also reported. It was suggested that UV-induced pyrimidine dimers in DNA of sperm are the primary lesions leading to abnormalities of nuclear behavior in the partial fertilization and of morphogenesis.
