Igf-2r expression regulated by epigenetic modification and the locus of gene imprinting disrupted in cloned cattle.

Epigenetic reprogramming has a crucial role in establishing nuclear totipotency in normal development and in cloned animals. Insulin-like growth factor-2 receptor (Igf-2r) is a tissue-specifically and species-dependently imprinted gene, regulated by epigenetic modifications. The diversity of Igf-2r imprinting suggests that the success of animal cloning may be species-dependent. To determine the relation between epigenetic modifications and Igf-2r expression in cattle, and explore whether this gene was correctly imprinted and reprogrammed after nuclear transfer, we quantified Igf-2r mRNA in a cattle cell line after treated with an inhibitor of DNA methylation transferase or an inhibitor of histone deacetylase, and confirmed that DNA methylation and histone acetylation could regulate this gene expression. CpG island searching showed that there is a conservative imprinting control region (ICR) within the second intron of Igf-2r in cattle, analogous to mice and sheep, regulating this gene imprinting. DNA methylation analysis in sperm and blood cells showed that DNA methylation at Igf-2r ICR2 was reprogrammed in normal cattle. The methylation at Igf-2r ICR2 showed significant variation in tissues, such as blood, liver, brain, heart and heart. It suggested that Igf-2r imprinting was tissue-specifically regulated. In cloned cattle, DNA methylation at Igf-2r ICR2 was markedly altered in comparison with normal fetus, while patterns of DNA methylation at Igf-2r 3'-UTR (3-terminal untranslated region) were similar to normal fetus, it indicated that 3'-UTR was not significantly altered by cloning procedures, but DNA methylation at the locus of gene imprinting was disrupted and not completely reprogrammed after nuclear transfer.