Role of PRMT7 in Genomic Imprinting

PROJECT SUMMARY/ABSTRACT Genomic imprinting is an epigenetic gene-marking phenomenon that causes a subset of mammalian genes (i.e. imprinted genes) to be expressed from only one of the two parental copies. The majority of imprinted genes are arranged in chromosomal clusters. Each cluster has an imprinting control region (ICR) with one or more differentially methylated regions (DMRs) - regions marked by DNA methylation on only one allele - which act as the epigenetic signal that controls monoallelic expression. Imprinted DMRs are classified as germline (primary) DMRs (gDMRs) and somatic (secondary) DMRs (sDMRs). gDMRs are established during gametogenesis, resulting from differential de novo methylation of male and female germ cells. sDMRs represents allele-specific methylation acquired during embryonic development. Genetic studies have demonstrated that the de novo DNA methyltransferase DNMT3A is responsible for the establishment of methylation imprints at gDMRs during germ cell development and that the maintenance enzyme DNMT1 is responsible for maintaining methylation imprints during embryonic development and in adult tissues. Despite these advances, fundamental questions remain to be answered, e.g. How sexually dimorphic patterns of DNA methylation in gametes are regulated? And how gDNAs control sDMRs? Preliminary studies in the applicant’s laboratory showed that conditional ablation of the arginine methyltransferase PRMT7 in male germ cells results in incomplete methylation of the gDMR at the H19-Igf2 imprinted locus in sperm. As a result, the progeny show biallelic repression of Igf2 and allelic switch in H19 and Gtl2 expression (Gtl2 is also a paternally imprinted gene). The applicant’s laboratory also showed that PRMT7 catalyzes monomethylation of DNMT3A at a conserved arginine residue in the N-terminal region that is important for functional specificity of DNMT3A. The applicant hypothesizes that PRMT7, through methylating DNMT3A, regulates DNMT3A-mediated de novo methylation, including the establishment of paternal imprints, during male germ cell development and that, in the absence of PRMT7, impaired DNA methylation on the paternal alleles causes secondary trans-effect changes on the maternal alleles after fertilization, resulting in allelic switch in the expression of some paternally imprinted genes. To test the hypothesis, the applicant proposes two specific aims: 1) Determine the role of PRMT7 in de novo DNA methylation during male germ cell development; and 2) Elucidate the mechanism underlying allelic switch of paternally imprinted genes in the offspring of PRMT7-deficient male mice. In the applicant’s opinion, the proposed research is innovative for its conceptual novelty. The project is significant, because results from the proposed studies are expected to provide novel insights into the regulation of de novo DNA methylation in the male germline and the crosstalk between the paternal and maternal alleles to control monoallelic expression of imprinted genes.