G9a/GLP complexes independently mediate H3K9 and DNA methylation to silence transcription.
Methylation of DNA and lysine 9 of histone H3 (H3K9) are well-conserved epigenetic marks for transcriptional silencing. Although H3K9 methylation directs DNA methylation in filamentous fungi and plants, this pathway has not been corroborated in mammals. G9a and GLP/Eu-HMTase1 are two-related mammalian lysine methyltransferases and a G9a/GLP heteromeric complex regulates H3K9 methylation of euchromatin. To elucidate the function of G9a/GLP-mediated H3K9 methylation in the regulation of DNA methylation and transcriptional silencing, we characterized ES cells expressing catalytically inactive mutants of G9a and/or GLP. Interestingly, in ES cells expressing a G9a-mutant/GLP complex that does not rescue global H3K9 methylation, G9a/GLP-target genes remain silent. The CpG sites of the promoter regions of these genes were hypermethylated in such mutant ES cells, but hypomethylated in G9a- or GLP-KO ES cells. Treatment with a DNA methyltransferase inhibitor reactivates these G9a/GLP-target genes in ES cells expressing catalytically inactive G9a/GLP proteins, but not the wild-type proteins. This is the first clear evidence that G9a/GLP suppresses transcription by independently inducing both H3K9 and DNA methylation.
Tachibana
Makoto
M
Experimental Research Center for Infectious Diseases, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto, Japan. mtachiba@virus.kyoto-u.ac.jp
Matsumura
Yasuko
Y
Fukuda
Mikiko
M
Kimura
Hiroshi
H
Shinkai
Yoichi
Y
D000818:Animals; D002384:Catalysis; D018899:CpG Islands; D019175:DNA Methylation; D053595:Embryonic Stem Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D011495:Histone-Lysine N-Methyltransferase / Q000378:metabolism / Q000502:physiology*; D006657:Histones / Q000737:chemistry*; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009154:Mutation; D014158:Transcription, Genetic
D006657:Histones; C533711:G9a protein, mouse; D011495:Histone-Lysine N-Methyltransferase