5-hmC in the brain is abundant in synaptic genes and shows differences at the exon-intron boundary

The 5-hydroxymethylcytosine (5-hmC) nucleoside is abundant in the brain for unknown reasons. Genome-wide analysis of the distribution of 5-hmC versus 5-methylcytosine (5-mC) in human and mouse tissues now shows that 5-hmC is enriched in genes with synaptic functions. The differential distribution of 5-hmC versus 5-mC at exon-intron boundaries in both human and mouse tissues further suggests a possible role for 5-hmC in pre-mRNA splicing.