Tissue specificity of methylation and expression of human genes coding for neuropeptides and their receptors, and of a human endogenous retrovirus K family.
The purpose of the present study was to understand the tissue specificity of DNA methylation and the relationship between methylation and expression of genes with essential roles in neurodevelopment and brain function. We chose dopamine receptor genes (DRD1 and DRD2), NCAM, and COMT as examples of genes with CpG islands around the promoter region, and serotonin receptor genes (HTR2A and HTR3A), HCRT, and DRD3 as genes without CpG islands. Methylation states were investigated in fetal brain, fetal liver, placenta, and in adult peripheral leukocytes from three individuals by Southern blot and bisulfite-modified DNA sequencing. A repetitive sequence, human endogenous retrovirus (HERV)-K was also examined. All genes examined were almost completely unmethylated in brains. The genes with CpG islands were unmethylated regardless of their expression state. In contrast, genes without CpG islands showed various methylation patterns, which did not necessarily reflect the transcriptional activity of the genes. Most HERV-K loci were methylated, but some loci showed relatively low methylation in the placenta and liver. Interestingly, we found inter-individual differences in methylation levels in HTR2A and HCRT in the placenta and in some loci of HERV-K in the placenta and liver. The sample with the lowest methylation levels in the two unique genes showed higher methylation of HERV-K loci than the other samples. These results provide detailed information about the methylation states of the genes analyzed and evidence for inter-individual variations in methylation in both unique and repetitive sequences.
Department of Molecular Biology, Ryukyu University School of Medicine, 207 Nishihara, Okinawa 903-0215, Japan.
Hong-Mei
HM
Shen
Department of Molecular Biology, Ryukyu University School of Medicine, 207 Nishihara, Okinawa 903-0215, Japan.|Department of Neuropsychiatry, Ryukyu University School of Medicine, Okinawa, Japan.
Akifumi
A
Nakamura
Department of Molecular Biology, Ryukyu University School of Medicine, 207 Nishihara, Okinawa 903-0215, Japan.
Jun
J
Sugimoto
Department of Neuropsychiatry, Ryukyu University School of Medicine, Okinawa, Japan.
Noboru
N
Sakumoto
Department of Molecular Biology, Ryukyu University School of Medicine, 207 Nishihara, Okinawa 903-0215, Japan.
Takaya
T
Oda
Department of Molecular Biology, Ryukyu University School of Medicine, 207 Nishihara, Okinawa 903-0215, Japan. sirius@med.u-ryukyu.ac.jp.
Yoshihiro
Y
Jinno
Department of Neuropsychiatry, Mie University School of Medicine, Mie, Japan.
Yuji
Y
Okazaki
D001921:Brain / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D002394:Catechol O-Methyltransferase / Q000235:genetics / Q000378:metabolism; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D020077:Endogenous Retroviruses / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D008957:Models, Genetic; D019006:Neural Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics*; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D017982:Receptors, Biogenic Amine / Q000235:genetics*; D011954:Receptors, Dopamine / Q000235:genetics / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D020133:Reverse Transcriptase Polymerase Chain Reaction
D019006:Neural Cell Adhesion Molecules; D009479:Neuropeptides; D017982:Receptors, Biogenic Amine; D011954:Receptors, Dopamine; D011985:Receptors, Serotonin; D002394:Catechol O-Methyltransferase