Distal regulatory elements identified by methylation and hydroxymethylation haplotype blocks from mouse brain

Epigenetics Chromatin. 2018 Dec 29;11(1):75. doi: 10.1186/s13072-018-0248-3.


Background: 5-Hydroxymethylcytosine (5hmC) is an oxidation product of 5-methylcytosine (5mC), and adjacent CpG sites in mammalian genome can be co-methylated and co-hydroxymethylated due to the processivity of DNMT and TET enzymes.

Results: We applied TAB-seq and oxBS-seq to selectively detect 5hmC and 5mC at base resolution in the mouse cortex, olfactory bulb and cerebellum tissues. We found that majority of the called 5hmC CpG sites frequently have 5mC modification simultaneously and are enriched in gene body regions of neuron development-related genes in brain tissues. Strikingly, by a systematic search of regions that show highly coordinated methylation and hydroxymethylation (MHBs and hMHBs), we found that MHBs significantly overlapped with hMHBs in gene body regions. Moreover, using a metric called methylation haplotype load, we defined a subset of 1361 tissue-specific MHBs and 3818 shared MHBs. Shared MHBs with low MHL correspond with developmental enhancers, and tissue-specific MHBs resemble the regulatory elements for tissue identity.

Conclusions: Our results provide new insights into the role of coordinately oxidized 5mC to 5hmC as distal regulatory elements may involve in regulating tissue identity.

Keywords: 5hmC; 5mC; Hydroxymethylation haplotype block; Methylation haplotype block; Methylation haplotype load.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Methylcytosine / analogs & derivatives*
  • 5-Methylcytosine / metabolism
  • 5-Methylcytosine / physiology
  • Animals
  • Brain / metabolism
  • Cerebellar Cortex / physiology
  • Cerebellum / physiology
  • Chromosome Mapping / methods
  • CpG Islands / genetics
  • Cytosine / metabolism
  • DNA Methylation / physiology*
  • Female
  • Genome / genetics
  • Haplotypes / genetics
  • Mice
  • Mice, Inbred C57BL
  • Olfactory Bulb / physiology
  • Regulatory Sequences, Nucleic Acid / genetics
  • Sequence Analysis, DNA / methods*


  • 5-hydroxymethylcytosine
  • 5-Methylcytosine
  • Cytosine