title: Cooperativity between DNA methyltransferases in the maintenance methylation of repetitive elements.
abstract: We used mouse embryonic stem (ES) cells with systematic gene knockouts for DNA methyltransferases to delineate the roles of DNA methyltransferase 1 (Dnmt1) and Dnmt3a and -3b in maintaining methylation patterns in the mouse genome. Dnmt1 alone was able to maintain methylation of most CpG-poor regions analyzed. In contrast, both Dnmt1 and Dnmt3a and/or Dnmt3b were required for methylation of a select class of sequences which included abundant murine LINE-1 promoters. We used a novel hemimethylation assay to show that even in wild-type cells these sequences contain high levels of hemimethylated DNA, suggestive of poor maintenance methylation. We showed that Dnmt3a and/or -3b could restore methylation of these sequences to pretreatment levels following transient exposure of cells to 5-aza-CdR, whereas Dnmt1 by itself could not. We conclude that ongoing de novo methylation by Dnmt3a and/or Dnmt3b compensates for inefficient maintenance methylation by Dnmt1 of these endogenous repetitive sequences. Our results reveal a previously unrecognized degree of cooperativity among mammalian DNA methyltransferases in ES cells.
authors.affiliation: USC/Norris Comprehensive Cancer Center, Department of Urology, Keck School of Medicine of the University of Southern California, Los Angeles, California 90089-9181, USA.
authors.forename: Gangning
authors.initials: G
authors.lastname: Liang
authors.forename: Matilda F
authors.initials: MF
authors.lastname: Chan
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Tomigahara
authors.forename: Yvonne C
authors.initials: YC
authors.lastname: Tsai
authors.forename: Felicidad A
authors.initials: FA
authors.lastname: Gonzales
authors.forename: En
authors.initials: E
authors.lastname: Li
authors.forename: Peter W
authors.initials: PW
authors.lastname: Laird
authors.forename: Peter A
authors.initials: PA
authors.lastname: Jones
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001483:Base Sequence; D002460:Cell Line; D018899:CpG Islands; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D020084:Long Interspersed Nucleotide Elements; D051379:Mice; D018345:Mice, Knockout; D012091:Repetitive Sequences, Nucleic Acid; D000097584:DNA Methyltransferase 3B
chemical_list: D001374:Azacitidine; D004247:DNA; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D000077209:Decitabine; D004791:Enzyme Inhibitors; D000097584:DNA Methyltransferase 3B; C000715535:Dnmt3a protein, mouse; C000619381:Dnmt1 protein, mouse