Epigenetic dynamics of H4K20me3 modification during oocyte maturation and early reprogramming of somatic cell nuclear transfer goat embryos

Objective: We examined the epigenetic dynamics of histone H4K20 trimethylation (H4K20me3), a repressive signature in heterochromatin, during goat oocyte meiosis and the reprogramming of somatic cell nuclear transfer (NT) embryos through the first three cell divisions. Methods: Following NT, oocytes were treated with parthenogenetic activation (PA), by 5 mu M calcium ionophore A23187 for 5 min followed by incubation in 2.0 mM 6-dimethylaminopurine with 5 mu g/mL cycloheximide for 4 h. NT embryos up to 8-celled stage were incubated with H4K20me3 antibody. Results: Immunofluorescence microscopy revealed the existence of a persistent H4K20me3 signature during oocyte maturation from germinal vesicle phase to metaphase I, anaphase I, telophase I, and metaphase II, with a gradual reduction in staining intensity. NT embryos at the 2-, 4- and 8-celled stage showed lower H4K20me3 intensity than PA and IVF embryos (P < 0.05). Conclusion: These results indicate that NT embryos exhibit insufficient H4K20me3 modification compared with IVF and PA embryos during early reprogramming, suggesting the existence of a resistant memory of differentiated cell nuclear architecture. These findings help unravel the epigenetic mechanism of histone H4K20me3 in goat nuclear transfer reprogramming.