title: Forced expression of DNA methyltransferases during oocyte growth accelerates the establishment of methylation imprints but not functional genomic imprinting.
abstract: In mammals, genomic imprinting governed by DNA methyltransferase DNMT3A and its cofactor DNMT3L is essential for functional gametes. Oocyte-specific methylation imprints are established during oocyte growth concomitant with DNMT3A/DNMT3L expression, although the mechanisms of oocyte-specific imprinting are not fully understood. To determine whether the presence of DNMT3A/DNMT3L in oocytes is sufficient for acquisition of methylation imprints, we produced transgenic mice to induce DNMT3A/DNMT3L expression prematurely in oogenesis and analyzed DNA methylation imprints. The results showed that 2- to 4-fold greater expression of DNMT3A/DNMT3L was achieved in non-growing (ng) oocytes versus fully grown oocytes derived from wild-type mice, but the analyzed imprint domains were not methylated. Thus, the presence of DNMT3A/DNMT3L in ng oocytes is insufficient for methylation imprints, and imprinted regions are resistant to DNMT3A/DNMT3L in ng oocytes. In contrast, excess DNMT3A/DNMT3L accelerated imprint acquisition at Igf2r, Lit1, Zac1 and Impact but not Snrpn and Mest in growing oocytes. Therefore, DNMT3A/DNMT3L quantity is an important factor for imprint acquisition. Transcription at imprinted domains is proposed to be involved in de novo methylation; however, transcription at Lit1, Snrpn and Impact was observed in ng oocytes. Thus, transcription cannot induce DNMT3A catalysis at imprinted regions even if DNMT3A/DNMT3L is present. However, the accelerated methylation imprints in oocytes, with the exception of Igf2r, were erased during embryogenesis. In conclusion, a sufficient amount of DNMT3A/DNMT3L and a shift from the resistant to permissive state are essential to establish oocyte-specific methylation imprints and that maintenance of the acquired DNA methylation imprints is essential for functional imprinting.
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hara
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Takano
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Tsugunari
authors.initials: T
authors.lastname: Fujikawa
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Munehiro
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Wakai
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kono
authors.affiliation: Department of BioScience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan y1obata@nodai.ac.jp.
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Obata
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics; D004247:DNA / Q000032:analysis; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism*; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D005260:Female; D016147:Genes, Tumor Suppressor; D018392:Genomic Imprinting; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008822:Mice, Transgenic; D009865:Oocytes / Q000254:growth & development* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D011506:Proteins / Q000235:genetics; D017527:Receptor, IGF Type 2 / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; C000715535:Dnmt3a protein, mouse; C107747:Impact protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; C498423:Plagl1 protein, mouse; D024642:Potassium Channels, Voltage-Gated; D011506:Proteins; D017527:Receptor, IGF Type 2; D014157:Transcription Factors; D004247:DNA; C498796:Dnmt3l protein, mouse; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A