title: Characterization of DNA methylation in the rat.
abstract: In the rat, differentiation and cell proliferation both affect DNA methylation. We studied 5-methylcytosine at the inner cytosine of the sequence C-C-G-G, a common methylation site, using endonuclease MspI (which cleaves C-C-G-G- and C-mC-G-G), and its isoschizomer HpaII (which cleaves only C-C-G-G). DNA from all tissues and cell lines studied was methylated at C-C-G-G, at levels ranging from 45 to 80%, but the methylation sites were not distributed uniformly. Our analysis suggests a model in which cells contain variable amounts of three DNA methylation states, averaging 30-40, 70-80 and 95-100% methylation, respectively. One biological parameter that alters methylation is the proliferative state of the cell. We observed that NRK, a non-transformed cell line, increased its DNA methylation from 45 to 67% when monolayer cultures became confluent and non-dividing. We also observed that a class of repetitive DNA was completely methylated in DNA from all sources except a transformed cell line.
mesh_terms: D044503:5-Methylcytosine; D000375:Aging; D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D002454:Cell Differentiation; D002460:Cell Line; D003596:Cytosine / Q000031:analogs & derivatives* / Q000032:analysis; D004247:DNA / Q000302:isolation & purification; D004262:DNA Restriction Enzymes; D004622:Embryo, Mammalian; D007668:Kidney; D008099:Liver / Q000032:analysis; D008745:Methylation; D009928:Organ Specificity; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; D004262:DNA Restriction Enzymes