Human Molecular Genetics Advance Access published online on July 21, 2005
Human Molecular Genetics, doi:10.1093/hmg/ddi255
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1 Department of Human Genetics, Nagasaki University, Nagasaki 852-8523, Japan; Department of Obstetrics and Gynecology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8523, Japan; CREST, Japan Scence and Technology Agency, Kawaguchi 332-0012, Japan
* To whom correspondence should be addressed. The mouse Igf2r gene and its antisense transcript Air are reciprocally imprinted in most tissues, but in the brain, Igf2r is biallelically expressed despite imprinted Air expression. To investigate the molecular mechanisms of such brain-specific relaxation of Igf2r imprinting, we analyzed its expression and epigenetic modifications in neurons, glial cells and fibroblasts by the use of primary cortical cell cultures. In glial cells and fibroblasts, Igf2r was maternally expressed and Air was paternally expressed, whereas in the primary cultured neurons, Igf2r was biallelically expressed and Air was not expressed. In the differentially methylated region 2 (DMR2) that includes the Air promoter, allele-specific DNA methylation and differential H3 and H4 acetylation and H3K4 and K9 di-methylation were maintained in each cultured cell type. In DMR1, which include the Igf2r promoter, maternal-allele-specific DNA hypomethylation, histone H3 and H4 acetylation, and H3K4 di-methylation were apparent in glial cells and fibroblasts. However, in neurons, biallelic DNA hypomethylation and biallelic histone H3 and H4 acetylation and H3K4 di-methylation were detected. These data indicate that lack of reciprocal imprinting of Igf2r and Air in the brain results from neuron-specific relaxation of Igf2r imprinting associated with neuron-specific histone modifications in DMR1 and lack of Air expression. Our observation of biallelic Igf2r expression with no Air expression in neurons sheds light on the function of Air as a critical effector in Igf2r silencing and suggests that neuron-specific epigenetic modifications related to the lineage determination of neural stem cells play a critical role in controlling imprinting by antisense transcripts.
Received May 11, 2005
Revised July 8, 2005
Accepted July 8, 2005
Article
Neuron-specific relaxation of Igf2r imprinting is associated with neuron-specific histone modifications and lack of its antisense transcript Air
2 Department of Human Genetics, Nagasaki University, Nagasaki 852-8523, Japan
3 Department of Biomolecular Sciences, Saga University School of Medicine, Saga 849-8501, Japan
4 Department of Human Genetics, Nagasaki University, Nagasaki 852-8523, Japan; CREST, Japan Scence and Technology Agency, Kawaguchi 332-0012, Japan
5 Division of Functional Genomics, Center for Frontier Life Sciences, Nagasaki University, Nagasaki 852-8523, Japan; CREST, Japan Scence and Technology Agency, Kawaguchi 332-0012, Japan
6 Departments of Biochemistry II, Graduate School of Medicine, Nagoya University, Nagoya 466-8550, Japan
7 Department of Obstetrics and Gynecology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8523, Japan
8 Division of Functional Genomics, Center for Frontier Life Sciences, Nagasaki University, Sakamoto 1-12-4, Nagasaki 852-8523, Japan; CREST, Japan Scence and Technology Agency, Kawaguchi 332-0012, Japan
Tatsuya Kishino, E-mail: kishino{at}net.nagasaki-u.ac.jp
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