Mechanisms of activation of the paternally expressed genes by the Prader-Willi imprinting center in the Prader-Willi/Angelman syndromes domains

• Published in: Proceedings of the National Academy of Sciences - PNAS 2012-05, Vol.109 (19), p.7403-7408
• Main Authors: Rabinovitz, Shiri, Kaufman, Yotam, Ludwig, Guy, Razin, Aharon, Shemer, Ruth
• Format: Article
• Language: English
• Subjects: Alleles; Angelman Syndrome - genetics; Animals; Apolipoprotein A-I - genetics; Base Sequence; Binding Sites - genetics; Biological Sciences; Blotting, Southern; Brain - metabolism; Chromatin; Chromosomes; Deoxyribonucleic acid; DNA; DNA Methylation; embryogenesis; Fathers; Female; Fibroblasts - metabolism; Gametes; gametogenesis; Gene Expression; gene silencing; Genes; Genetic disorders; Genomic Imprinting; germ cells; Humans; Male; Methylation; Mice; Mice, Transgenic; Models, Genetic; Molecular Sequence Data; Mutation; Nerve Tissue Proteins - genetics; Nuclear Proteins - genetics; Prader-Willi Syndrome - genetics; Promoter Regions, Genetic - genetics; Small nucleolar RNA; snRNP Core Proteins - genetics; Spermatozoa - metabolism; Transgenes; Transgenic animals; Transmission lines
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1116661109

The Prader-Willi syndrome/Angelman syndrome (PWS/AS) imprinted domain is regulated by a bipartite imprinting control center (IC) composed of a sequence around the SNRPN promoter (PWS-IC) and a 880-bp sequence located 35 kb upstream (AS-IC). The AS-IC imprint is established during gametogenesis and confers repression upon PWS-IC on the maternal allele. Mutation at PWS-IC on the paternal allele leads to gene silencing across the entire PWS/AS domain. This silencing implies that PWS-IC functions on the paternal allele as a bidirectional activator. Here we examine the mechanism by which PWS-IC activates the paternally expressed genes (PEGs) using transgenes that include the PWS-IC sequence in the presence or absence of AS-IC and NDN, an upstream PEG, as an experimental model. We demonstrate that PWS-IC is in fact an activator of NDN. This activation requires an unmethylated PWS-IC in the gametes and during early embryogenesis. PWS-IC is dispensable later in development. Interestingly, a similar activation of a nonimprinted gene (APOA1) was observed, implying that PWS-IC is a universal activator. To decipher the mechanism by which PWS-IC confers activation of remote genes, we performed methylated DNA immunoprecipitation (MeDIP) array analysis on lymphoblast cell lines that revealed dispersed, rather than continued differential methylation. However, chromatin conformation capture (3c) experiments revealed a physical interaction between PWS-IC and the PEGs, suggesting that activation of PEGs may require their proximity to PWS-IC.