Selective chemical labeling reveals intragenic enrichment of 5-hydroxymethylcytosine in mouse cerebellum

5-Methylcytosine (5-mC) is an important DNA modification found in eukaryotes that impacts gene regulation and disease pathogenesis. Recently, 5-hydroxymethylcytosine (5-hmC), another form of DNA modification, has been identified in substantial amounts in certain mammalian cell types; however, its roles as well as its distribution in mammalian genomes are unknown. Here we present a selective chemical labeling method for 5-hmC by utilizing T4 bacteriophage BGT-glucosyltransferase to transfer an engineered glucose moiety containing an azide group onto the hydroxyl group of 5-hmC, which in turn can chemically incorporate a biotin group for detection, affinity enrichment, and sequencing of 5-hmC in mammalian genomes. Using this highly effective method, we demonstrate that 5-hmC is present in human cell lines beyond those previously recognized. We also find a gene expression level-dependent enrichment of intragenic 5-hmC in mouse cerebellum and an age-dependent acquisition of this modification in specific gene bodies linked to neurodegenerative disorders Overall design: Identification of 5hmC enriched genmoic regions in mouse cerebellum