Allele-specific methylation at the promoter-associated CpG island of mouse Copg2.

We previously reported that the mouse Copg2 (Coatomer Protein Subunit Gamma 2) gene was imprinted in the intraspecific F(1) hybrid mice between C57BL/6 and M. m. molossinus. In this study, methylation status at the promoter-associated CpG island and allele-specific expression pattern of Copg2 were investigated in the interspecific F(1) hybrid (C57BL/6 x M. spretus). We found that Copg2 was biallelically expressed in the interspecific F(1) hybrid, despite the presence of a differentially methylated region (DMR) in the CpG island. Therefore, paternal-specific methylation at the CpG island of Copg2 is not accompanied by allele-specific expression of Copg2 in the F(1) hybrid (C57BL/6 x M. spretus). The results suggest that the imprinted pattern of Copg2 expression is subject to variable epigenetic control systems of different mouse species. In addition, we identified a novel antisense transcript, Copg2AS2, at the Copg2 promoter region. The antisense transcript was expressed monoallelically, indicating that the differential expression of the antisense transcript is correlated with the differential methylation at the CpG island of Copg2.