The ‘active’ histone mark H3K4me2/3 is important for transcription initiation and activity [60] and is associated with transcriptional gene reactivation after somatic cell nuclear transfer to Xenopus oocytes [61]. In agreement with this, in induced pluripotency experiments, H3K4me2 is deposited before the first cell division and prior to signs of transcriptional activation at a subset of genes [62]. It is thought that this event may increase accessibility of regulatory regions of DNA. The Trithorax protein Wdr5, an effector of H3K4 methylation, was shown to be required for the formation of iPS cells (Table 1) [63].
