Other histone marks are associated with gene repression and undergo large changes during nuclear reprogramming. The maintenance of large chromatin blocks containing H3K9me2 (LOCKs) is associated with epigenetic memory, which increases resistance to nuclear reprogramming [64,65]. The H3K9me2/3 methyltransferase G9a has been shown to restrict reprogramming in part through DNA methylation [66]. In agreement, the expression of the H3K9me3 demethylase Kdm3a or G9a removal, both increase the efficiency of reprogramming following nuclear transfer and cell fusion (Table 1) [66,67]. H3K9me3 inhibitors, such as BIX-01294, also increase the efficiency of iPS cells derivation [68].
