title: Persistence of cytosine methylation of DNA following fertilisation in the mouse.
abstract: Normal development of the mammalian embryo requires epigenetic reprogramming of the genome. The level of cytosine methylation of CpG-rich (5meC) regions of the genome is a major epigenetic regulator and active global demethylation of 5meC throughout the genome is reported to occur within the first cell-cycle following fertilization. An enzyme or mechanism capable of catalysing such rapid global demethylation has not been identified. The mouse is a widely used model for studying developmental epigenetics. We have reassessed the evidence for this phenomenon of genome-wide demethylation following fertilisation in the mouse. We found when using conventional methods of immunolocalization that 5meC showed a progressive acid-resistant antigenic masking during zygotic maturation which gave the appearance of demethylation. Changing the unmasking strategy by also performing tryptic digestion revealed a persistence of a methylated state. Analysis of methyl binding domain 1 protein (MBD1) binding confirmed that the genome remained methylated following fertilisation. The maintenance of this methylated state over the first several cell-cycles required the actions of DNA methyltransferase activity. The study shows that any 5meC remodelling that occurs during early development is not explained by a global active loss of 5meC staining during the cleavage stage of development and global loss of methylation following fertilization is not a major component of epigenetic reprogramming in the mouse zygote.
authors.affiliation: Sydney Medical School, Centre for Developmental and Regenerative Medicine, Kolling Institute for Medical Research, University of Sydney, Sydney, Australia.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Chris
authors.initials: C
authors.lastname: O'Neill
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D065150:Cellular Reprogramming / Q000235:genetics / Q000502:physiology; D003596:Cytosine / Q000378:metabolism*; D019175:DNA Methylation / Q000502:physiology*; D004622:Embryo, Mammalian; D044127:Epigenesis, Genetic / Q000502:physiology; D005260:Female; D005306:Fertilization / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D011247:Pregnancy; D013997:Time Factors; D015053:Zygote / Q000378:metabolism*
chemical_list: D003596:Cytosine