RT Journal
A1 Suzuki, Miho M.
A1 Kerr, Alastair R.W.
A1 De Sousa, Dina
A1 Bird, Adrian
T1 CpG methylation is targeted to transcription units in an invertebrate genome
JF Genome Research 
JO Genome Research 
YR 2007 
FD May 01 
VO 17 
IS 5 
SP 625 
OP 631 
DO 10.1101/gr.6163007 
UL http://genome.cshlp.org/content/17/5/625.abstract 
AB DNA is methylated at the dinucleotide CpG in genomes of a wide range of plants and animals. Among animals, variable patterns of genomic CpG methylation have been described, ranging from undetectable levels (e.g., in Caenorhabditis elegans) to high levels of global methylation in the vertebrates. The most frequent pattern in invertebrate animals, however, is mosaic methylation, comprising domains of methylated DNA interspersed with unmethylated domains. To understand the origin of mosaic DNA methylation patterns, we examined the distribution of DNA methylation in the Ciona intestinalis genome. Bisulfite sequencing and computational analysis revealed methylated domains with sharp boundaries that strongly colocalize with ∼60% of transcription units. By contrast, promoters, intergenic DNA, and transposons are not preferentially targeted by DNA methylation. Methylated transcription units include evolutionarily conserved genes, whereas the most highly expressed genes preferentially belong to the unmethylated fraction. The results lend support to the hypothesis that CpG methylation functions to suppress spurious transcriptional initiation within infrequently transcribed genes.