Fig. 8. Summary of histone H3 methylation events and the role of Ezh2 at the onset of mouse development. Shortly after fertilisation, Ezh2/Eed and H3 methylation are predominantly associated with the female pronucleus, and establish an epigenetic asymmetry between the two parental genomes. When this asymmetry is disturbed after depletion of the maternally inherited Ezh2, there is a long-term effect resulting in severe growth retardation of neonates even when the embryonic transcription occurs at the four-cell stage. The epigenetic asymmetry therefore has a significant effect on development and fetal growth. During cleavage stages, Ezh2/Eed and H3 methylation levels are high. At this stage, all cells are pluripotent. During differentiation of TE cells, there are significant changes in the subnuclear localisation and levels of Ezh2/Eed and H3 histone methylation. The pluripotent epiblast cells that continue to express Oct4 retain a characteristic and a distinct histone methylation pattern consistent with the epigenetic plasticity of these cells.

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