One-pot trimodal mapping of unmethylated, hydroxymethylated, and open chromatin sites unveils distinctive 5hmC roles at dynamic chromatin loci.

We present a method, named Mx-TOP, for profiling of three epigenetic regulatory layers-chromatin accessibility, general DNA modification, and DNA hydroxymethylation-from a single library. The approach is based on chemo-enzymatic covalent tagging of unmodified CG sites and hydroxymethylated cytosine (5hmC) along with GC sites in chromatin, which are then mapped using tag-selective base-resolution TOP-seq sequencing. Our in-depth validation of the approach revealed its sensitivity and informativity in evaluating chromatin accessibility and DNA modification interactions that drive transcriptional regulation. We employed the technology in a study of chromatin and DNA demethylation dynamics during in vitro neuronal differentiation. The study highlighted the involvement of gene body 5hmC in modulating an extensive decoupling between promoter accessibility and transcription. The importance of 5hmC in chromatin remodeling was further demonstrated by the observed resistance of the developmentally acquired open loci to the global 5hmC erasure in neuronal progenitors.