Figure 1
From: Active demethylation in mouse zygotes involves cytosine deamination and base excision repair
Paternal loss of DNA methylation occurs in two phases. (A) Diagrammatic illustration and representative two-dimensional (2D) projections of Z-stack images of control (B6 x B6) pronuclear stage embryos (PN0 to PN5) simultaneously stained for DNA methylation (5mC) and hydroxymethylation (5hmC) clearly showing two phases of paternal loss of methylation, Phase I, corresponding to a pre-replicative state with no observable change in DNA hydroxymethylation, and Phase II, when DNA replication is taking place, and during which a very significant increase in DNA hydroxymethylation in the paternal pronucleus takes place. Scale bar 25 μm. f, female pronucleus; m, male pronucleus; pb, polar body. (B) The dynamic changes of DNA methylation and hydroxymethylation during the first cell cycle can be represented by the ratio of the total immunofluorescence signal (3D imaging) between the maternal and paternal pronuclei (male/female ratio) for 5mC and 5hmC, respectively. Values at time of fertilisation are hypothetical (dashed lines), calculated considering a minimum initial total 5mC and 5hmC for sperm and oocytes (see text for explanation). Values plotted for stages between PN1 and PN5 (minimum 10 embryos per stage). Bars indicate standard deviation.