Cooperativity between DNA methyltransferases in the maintenance methylation of repetitive elements.
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.
Liang
Gangning
G
USC/Norris Comprehensive Cancer Center, Department of Urology, Keck School of Medicine of the University of Southern California, Los Angeles, California 90089-9181, USA.
Chan
Matilda F
MF
Tomigahara
Yoshitaka
Y
Tsai
Yvonne C
YC
Gonzales
Felicidad A
FA
Li
En
E
Laird
Peter W
PW
Jones
Peter A
PA
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
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