Active and Passive Demethylation of Male and Female Pronuclear DNA in the Mammalian Zygote

Fan Guo, Xianlong Li, Dan Liang, Tong Li, Ping Zhu, Hongshan Guo, Xinglong Wu, Lu Wen, Tian-Peng Gu, Boqiang Hu, Colum Walsh, Jinsong Li, Fuchou Tang, Guo-Liang Xu

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291 Citations (Scopus)


The epigenomes of mammalian sperm and oocytes, characterized by gamete-specific 5-methylcytosine (5mC) patterns, are reprogrammed during early embryogenesis to establish full developmental potential. Previous studies have suggested that the paternal genome is actively demethylated in the zygote while the maternal genome undergoes subsequent passive demethylation via DNA replication during cleavage. Active demethylation is known to depend on 5mC oxidation by Tet dioxygenases and excision of oxidized bases by thymine DNA glycosylase (TDG). Here we show that both maternal and paternal genomes undergo widespread active and passive demethylation in zygotes before the first mitotic division. Passive demethylation was blocked by the replication inhibitor aphidicolin, and active demethylation was abrogated by deletion of Tet3 in both pronuclei. At actively demethylated loci, 5mCs were processed to unmodified cytosines. Surprisingly, the demethylation process was unaffected by the deletion of TDG from the zygote, suggesting the existence of other demethylation mechanisms downstream of Tet3-mediated oxidation.
Original languageEnglish
Pages (from-to)447-459
Number of pages12
JournalCell Stem Cell
Issue number4
Publication statusPublished (in print/issue) - 11 Sept 2014


  • Active demethylation
  • Passive demethylation
  • Zygote
  • 5hmC
  • Pronuclear DNA
  • TETs


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