GSE202875
Transcription Across the H19/Igf2 Imprinting Control Region Initiates Paternally Methylated Imprinting in Mouse Prospermatogonia (RNA-Seq)
Silver-Russell syndrome(SRS, OMIM 180860) is an imprinting disordermanifesting in fetal and postnatal growth retardation. Loss of methylation (LOM) is detected in the imprinting control region 1 (ICR1) that controls the H19/IGF2 domain, in about 65% of SRS cases. The cause of this epigenetic deficiency is unknown. It may affect the process of imprint establishment --de novo methylation of ICR1 in the male germ line. In the paralogous mouse locus this process involves DNA methyltransferase DNMT3A and H3K36me2 histone methyltransferase NSD1, but the mechanism that targets these enzymes to this ICR is unknown. Based on our genome-wide deep-sequencing data of transcription and DNA methylation, we hypothesized that low-level transcription is required in prospermatogonia for targeting H3K36me2 and de novo methylation to ICR. We truncated this transcript at the entry point to ICR by gene-targeting. In response, the establishment of DNA methylation imprint was incomplete. The sporadic LOM persisted from the male germ line into the paternal allele of the soma, resulting in reduced Igf2, and increased, biallelic H19 RNA in the fetal organs, consistent with the insulator model. Fetus weight was also variably reduced upon paternal transmission of this mutation, consistent with the role of IGF2 as a fetal growth factor. We identify low-level transcription-through as the mechanism that initiates paternal imprint establishment at the H19/Igf2 ICR in the male germ line. The findings predict that RNA-dependent imprint establishment may be affected in human fetuses resulting in sporadic hypomethylation of the ICR1 in SRS. Overall design: We truncated this transcript at the entry point to ICR by gene-targeting.