Monoallelic expression of reactivated imprinted genes in embryonal carcinoma cell hybrids

Though DNA methylation is necessary to maintain monoallelic expression of imprinted genes, it is still unclear whether it represents the primary mark. Here we ask whether the imprinting mark is still present in terminally differentiated somatic cells in which the transcription of embryo-specific imprinted genes was shut off. For such analysis H19 and Igf2 genes were activated by inducing differentiation of (mouse embryonal carcinoma cell x mouse lymphocyte) hybrid cell clones. Although lymphocytes do not express H19 and Igf2, both genes are reactivated in a proper monoallelic manner in hybrid cells. Analysis of the upstream region of the H19 gene confirmed maintenance of differential methylation of the active and inactive H19 genes of lymphocyte origin, although a tendency toward in vitro induced hypermethylation was apparent. We conclude that the imprints of the H19, U2af1-rs1, and Igf2 genes are maintained in lymphocytes in adult mice.