UV irradiation of chromosomal DNA and its effect upon MPF and meiosis in mammalian oocytes.

Bovine oocytes were irradiated at germinal vesicle (GV) or metaphase II (MII) stage, after Hoechst staining, with chromosomally focused UV-C (254 nm) or UV-A ( > 330 nm). UV-C irradiation at GV stage did not inhibit germinal vesicle breakdown (GVBD) or chromosomal condensation; spindle formation was abolished and maturation promoting factor (MPF) levels failed to increase. UV-A irradiation at GV stage caused meiotic arrest at anaphase I; MPF levels were lower than control. UV-C irradiation at MII stage led to subsequent abnormal parthenogenetic activation when MPF levels failed to decrease. A normal male but no female pronucleus was formed at fertilization. UV-A irradiation at MII stage also caused abnormal activation; MPF levels declined normally. A normal male and abnormal female pronucleus formed at fertilization. UV-A irradiation results have implications for oocyte evaluation during development using Hoechst staining. UV-C irradiation is a potential means for oocyte enucleation in nuclear transfer.