Disease relevance of 5-Methylcytosine

• DME can excise 5-methylcytosine in vitro and when expressed in E. coli [1].
• The 5-methylcytosine content of mouse mammary tumor virus (MMTV)-specific DNA sequences acquired by both milk-borne infection and genetic transmission was determined for both normal and neoplastic tissues of the mouse [2].
• Amplified ribosomal RNA genes in a rat hepatoma cell line are enriched in 5-methylcytosine [3].
• The DNA of hamster cells transformed by adenovirus type 12 contains 3.11 and 3.14% 5-methycytosine (HA12/7 and T627 cells, respectively), whereas the DNA from untransformed hamster cells (BHK21 cells) contains 2.22% 5-methylcytosine [4].
• The majority of genomic 5-methylcytosine is now known to enforce the transcriptional silence of the enormous burden of transposons and retroviruses that have accumulated in the mammalian genome [5].

High impact information on 5-Methylcytosine

• The nucleotide 5-methylcytosine is involved in processes crucial in mammalian development, such as X-chromosome inactivation and gene imprinting [6].
• Epigenetic events can also facilitate genetic damage, as illustrated by the increased mutagenicity of 5-methylcytosine and the silencing of the MLH1 mismatch repair gene by DNA methylation in colorectal tumours [7].
• In vertebrate DNA, 3% to 5% of cytosine residues are present as 5-methylcytosine, and it is generally accepted that essentially all of this methylation occurs at cytosines which are contained in the symmetrical dinucleotide CpG [8].
• In mouse, for example, MeCP2 is concentrated in pericentromeric heterochromatin, which contains a large fraction (about 40%) of all genomic 5-methylcytosine [9].
• Mismatches arise during recombination, as errors of DNA replication, and from deamination of 5-methylcytosine to thymine [10].

Chemical compound and disease context of 5-Methylcytosine

• Multicopy clones of Escherichia coli cytosine methyltransferases Dcm and EcoRII methylase (M. EcoRII) cause an approximately 50-fold increase in C --> T mutations at their canonical site of methylation, 5'-CmeCAGG (meC is 5-methylcytosine) [11].
• Bacteriophage XP-12, whose DNA contains 34 mol% 5-methylcytosine, induces the synthesis of a unique enzyme, 5-methyl-dCTP deaminase [12].
• The Vsr endonuclease of Escherichia coli initiates the repair of T/G mismatches caused by deamination of 5-methylcytosine to thymine [13].
• The Escherichia coli K-12 restriction enzyme Mrr recognizes and cleaves N6-methyladenine- and 5-methylcytosine-containing DNA [14].
• The distribution of labeled 5-methylcytosine in DNA pyrimidine tracts was identical for phage grown in mec+ and mec minus (N-3) cells [15].

Biological context of 5-Methylcytosine

• These results attest to a specific mismatch repair pathway that restores G/C pairs lost through deamination of 5-methylcytosine residues [16].
• In all the above chromosomes, especially chromosome 15, additional 5-methylcytosine residues were detected as isolated foci along the arms [17].
• Localization of 5-methylcytosine in human metaphase chromosomes by immunoelectron microscopy [17].
• A helical arrangement of 5-methylcytosine residues was seen below the centromere of chromosome 1 [17].
• Our results demonstrate that this lower eukaryote normally maintains only very low levels of 5-methylcytosine in its genome, but possesses a mechanism for substantial methylation of DNA de novo [18].

Anatomical context of 5-Methylcytosine

• We found, by representational difference analysis, that expression of DNA 5-methylcytosine transferase (dnmt1) in fos-transformed cells is three times the expression in normal fibroblasts and that fos-transformed cells contain about 20 percent more 5-methylcytosine than normal fibroblasts [19].
• The analysis of modified base composition revealed the presence of methylated bases in chromoplast DNA, in which 5-methylcytosine was most abundant [20].
• G.T mispairs, the sole mismatch type that can arise in "resting" mammalian DNA (through spontaneous hydrolytic deamination of 5-methylcytosine), are corrected in vivo with high efficiency and mostly to a G.C. We identified a protein factor, present in HeLa cell extracts, that binds selectively to DNA substrates containing this mismatch [21].
• The extent of methylation of 18 sites in the PEPCK gene in adult liver, kidney, spleen, and heart muscle and in fetal liver has been analyzed using the 5-methylcytosine sensitive enzymes Hpa II and Hha I [22].
• Patients have immunodeficiency, chromosome 1 (Chr1) and Chr16 pericentromeric anomalies in mitogen-stimulated lymphocytes, a small decrease in overall genomic 5-methylcytosine levels and much hypomethylation of Chr1 and Chr16 juxtacentromeric heterochromatin [23].

Associations of 5-Methylcytosine with other chemical compounds

• DNA methylation (5-methylcytosine) in mammalian genomes predominantly occurs at CpG dinucleotides, is maintained by DNA methyltransferase1 (Dnmt1), and is essential for embryo viability [24].
• To ascertain whether DNA methylation might play a role at mammalian replication origins, the methylation status of these sites was examined with bisulfite to chemically distinguish cytosine (C) from 5-methylcytosine (mC) [25].
• DNA synthesized during this interval was methyl deficient as judged by the reduced incorporation of radioactivity from L-[methyl-3H]methionine into 5-methylcytosine residues of DNA [26].
• The double-stranded oligonucleotides incorporating 5-methylcytosine (5mC) and O6-methylguanine (O6mG) in various combinations in a CpG site were 5' labeled with 32P and incubated with recombinant O6-methylguanine-DNA methyltransferase [27].
• Compared with the paired non-HCC liver tissues, genome-wide 5-methylcytosine content in HCC was reduced in all of the tested HCC samples (P < 0.001) [28].

Gene context of 5-Methylcytosine

• The plant genome also has 5-methylcytosine at CpG dinucleotides, which is maintained by METHYLTRANSFERASE1 (MET1), a homolog of Dnmt1 [24].
• This residual 5-methylcytosine may be the product of a candidate second DNA methyltransferase, Dnmt2, that has now been identified in human and mouse [29].
• Comparison of kinetic profiles revealed that the MED1 5-methylcytosine binding domain and methylation of the mismatched CpG site are not required for efficient catalysis [30].
• Furthermore, overexpression of DNMT1 with this deleted destruction domain in HMECs resulted in significantly increased genomic 5-methylcytosine levels relative to overexpression of the full-length protein [31].
• In vivo, MBD3L1 associates with and colocalizes with MBD2 but not with MBD3 and is recruited to 5-methylcytosine-rich pericentromeric heterochromatin in mouse cells [32].

Analytical, diagnostic and therapeutic context of 5-Methylcytosine

• Also, after about 150 cell generations after treatment, reactivants from both temperature-induced tsm and cells exposed to demethylating agents gained 60% and 23%, respectively, in 5-methylcytosine (5mC) [33].
• The DNA is degraded to nucleosides, 5-methylcytosine purified by HPLC and, for detection by 1D- and 2D-TLC, radiolabeled using deoxynucleoside kinase and [gamma-(32)P]ATP [34].
• Estimation of the amount of 5-methylcytosine in Drosophila melanogaster DNA by amplified ELISA and photoacoustic spectroscopy [35].
• The positions of all 5-methylcytosine (mC) residues in bovine satellite I DNA were determined by sequence analysis of native purified satellite I DNAs from three bovine tissues as well as from cloned DNA [36].
• The sequence under investigation is then amplified by PCR with two sets of strand-specific primers to yield a pair of fragments, one from each strand, in which all uracil and thymine residues have been amplified as thymine and only 5-methylcytosine residues have been amplified as cytosine [37].

References