DNA demethylation in zebrafish involves the coupling of a deaminase, a glycosylase, and gadd45

Cell. 2008 Dec 26;135(7):1201-12. doi: 10.1016/j.cell.2008.11.042.


Evidence for active DNA demethylation in vertebrates is accumulating, but the mechanisms and enzymes remain unclear. Using zebrafish embryos we provide evidence for 5-methylcytosine (5-meC) removal in vivo via the coupling of a 5-meC deaminase (AID, which converts 5-meC to thymine) and a G:T mismatch-specific thymine glycosylase (Mbd4). The injection of methylated DNA into embryos induced a potent DNA demethylation activity, which was attenuated by depletion of AID or the non enzymatic factor Gadd45. Remarkably, overexpression of the deaminase/glycosylase pair AID/Mbd4 in vivo caused demethylation of the bulk genome and injected methylated DNA fragments, likely involving a G:T intermediate. Furthermore, AID or Mbd4 knockdown caused the remethylation of a set of common genes. Finally, Gadd45 promoted demethylation and enhanced functional interactions between deaminase/glycosylase pairs. Our results provide evidence for a coupled mechanism of 5-meC demethylation, whereby AID deaminates 5-meC, followed by thymine base excision by Mbd4, promoted by Gadd45.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cytidine Deaminase / metabolism
  • DNA (Cytosine-5-)-Methyltransferases / metabolism*
  • DNA Glycosylases / metabolism*
  • DNA Methylation*
  • Embryo, Nonmammalian / metabolism
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Neuropeptides / metabolism
  • Thymine DNA Glycosylase / metabolism*
  • Up-Regulation
  • Zebrafish / metabolism*
  • Zebrafish Proteins / metabolism*


  • GADD45 protein
  • Intracellular Signaling Peptides and Proteins
  • Neuropeptides
  • Zebrafish Proteins
  • DNA (Cytosine-5-)-Methyltransferases
  • DNA Glycosylases
  • MBD4 protein, zebrafish
  • Thymine DNA Glycosylase
  • Cytidine Deaminase