Dnmt1 overexpression causes genomic hypermethylation, loss of imprinting, and embryonic lethality.
Biallelic expression of Igf2 is frequently seen in cancers because Igf2 functions as a survival factor. In many tumors the activation of Igf2 expression has been correlated with de novo methylation of the imprinted region. We have compared the intrinsic susceptibilities of the imprinted region of Igf2 and H19, other imprinted genes, bulk genomic DNA, and repetitive retroviral sequences to Dnmt1 overexpression. At low Dnmt1 methyltransferase levels repetitive retroviral elements were methylated and silenced. The nonmethylated imprinted region of Igf2 and H19 was resistant to methylation at low Dnmt1 levels but became fully methylated when Dnmt1 was overexpressed from a bacterial artificial chromosome transgene. Methylation caused the activation of the silent Igf2 allele in wild-type and Dnmt1 knockout cells, leading to biallelic Igf2 expression. In contrast, the imprinted genes Igf2r, Peg3, Snrpn, and Grf1 were completely resistant to de novo methylation, even when Dnmt1 was overexpressed. Therefore, the intrinsic difference between the imprinted region of Igf2 and H19 and of other imprinted genes to postzygotic de novo methylation may be the molecular basis for the frequently observed de novo methylation and upregulation of Igf2 in neoplastic cells and tumors. Injection of Dnmt1-overexpressing embryonic stem cells in diploid or tetraploid blastocysts resulted in lethality of the embryo, which resembled embryonic lethality caused by Dnmt1 deficiency.
Biniszkiewicz
Detlev
D
Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA.
Gribnau
Joost
J
Ramsahoye
Bernard
B
Gaudet
François
F
Eggan
Kevin
K
Humpherys
David
D
Mastrangelo
Mary-Ann
MA
Jun
Zhan
Z
Walter
Jörn
J
Jaenisch
Rudolf
R
D000483:Alleles; D000818:Animals; D015153:Blotting, Western; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D020964:Embryo Loss / Q000235:genetics*; D017353:Gene Deletion; D018628:Gene Dosage; D018507:Gene Expression Regulation, Developmental; D023061:Gene Order / Q000235:genetics; D020868:Gene Silencing; D016678:Genome; D018392:Genomic Imprinting / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D051741:Kruppel-Like Transcription Factors; D051379:Mice; D011123:Polyploidy; D011494:Protein Kinases; D011506:Proteins / Q000235:genetics; D062085:RNA, Long Noncoding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D022661:RNA, Untranslated / Q000235:genetics; D017527:Receptor, IGF Type 2 / Q000235:genetics; D013234:Stem Cells / Q000378:metabolism; D014157:Transcription Factors
C094335:H19 long non-coding RNA; D051741:Kruppel-Like Transcription Factors; C097901:Peg3 protein, mouse; D011506:Proteins; D062085:RNA, Long Noncoding; D012333:RNA, Messenger; D022661:RNA, Untranslated; D017527:Receptor, IGF Type 2; D014157:Transcription Factors; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619381:Dnmt1 protein, mouse; D011494:Protein Kinases