ABSTRACT
In somatic tissues, the CpG island of the imprinted Peg1/Mest gene is methylated on the maternal allele. We have examined the methylation of CpG and non-CpG sites of this differentially methylated CpG island in freshly ovulated oocytes, in vitro aged oocytes, and preimplantation embryos. The CpG methylation pattern was heterogeneous in freshly ovulated oocytes, despite the fact that they all were arrested in metaphase II. After short in vitro culture, Peg1/Mest became hypermethylated, whereas prolonged in vitro culture resulted in demethylation in a fraction of oocytes. Non-CpG methylation also occurred in a stage-specific manner. On alleles that were fully methylated at CpG sites, this modification was found, and it became reduced in two-cell stage embryos and blastocysts. These observations suggest that the process of establishment of the methylation imprint at this locus is more dynamic than previously thought.
Subject(s)
Blastocyst/metabolism , DNA Methylation , Oocytes/metabolism , Proteins/genetics , Animals , Base Sequence , Cellular Senescence , Cleavage Stage, Ovum/cytology , Cleavage Stage, Ovum/metabolism , CpG Islands , DNA/chemistry , DNA/genetics , DNA/metabolism , Female , In Vitro Techniques , Metaphase , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Molecular Sequence Data , Oocytes/cytology , PregnancyABSTRACT
BACKGROUND: Poly (ADP-ribosyl)ation is a covalent modification of many nuclear proteins. It has a strong chromatin modifying potential involved in DNA repair, transcription and replication. Its role during preimplantation development is unknown. RESULTS: We have observed strong but transient synthesis of poly ADP-ribose polymers on decondensing chromosomes of fertilized and parthenogenetically activated mouse oocytes. Inhibition of this transient upregulation with a specific enzyme inhibitor, 3-aminobenzamide, has long-term effects on the postimplantation development of the embryos. In addition, inhibition of poly (ADP-ribosyl)ation at the 4-8 cell stage selectively blocks morula compaction. CONCLUSION: These observations suggest that poly (ADP-ribosyl)ation is involved in the epigenetic chromatin remodeling in the zygote.
