Distribution of DNA methylation, CpGs, and CpG islands in human isochores.
DNA methylation is a major epigenetic modification of the genome that affects basic biological functions, such as gene expression and cell development. We used the human genome sequences and the DNA methylation data that are available in order to establish a map of the levels of GC and methylation in isochores. We also looked for the correlations that hold between GC levels and the distribution of the (1) dinucleotide CpG, (2) ratio 5mC/CpG, and (3) CpG islands. Our results show that methylation levels, CpG frequencies, and the density of CpG islands are positively correlated with the GC level of isochores. In contrast, the correlation between the 5mC/CpG ratio and GC is a negative one because the increase in methylation lags behind that of CpG, to reach a plateau in the GC-richest, gene-richest isochore families H2 and H3. In conclusion, there are more CpG targets that remain unmethylated in the GC-richest, gene-richest isochores in comparison with the other isochores. This conclusion supports the idea that the widespread methylation under consideration here has a general inhibitory effect on gene expression.
Laboratory of Molecular Evolution, Stazione Zoologica Anton Dohrn, 80121 Naples, Italy.
Annalisa
A
Varriale
Giorgio
G
Bernardi
D044503:5-Methylcytosine / Q000032:analysis / Q000737:chemistry; D001482:Base Composition; D018899:CpG Islands; D004247:DNA / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D019175:DNA Methylation; D015226:Dinucleoside Phosphates / Q000032:analysis* / Q000737:chemistry; D044127:Epigenesis, Genetic; D005786:Gene Expression Regulation; D015894:Genome, Human; D006801:Humans; D032085:Isochores / Q000737:chemistry / Q000235:genetics; D017422:Sequence Analysis, DNA
D044503:5-Methylcytosine; D004247:DNA; D015226:Dinucleoside Phosphates; D032085:Isochores; C015772:CpG dinucleotide