The Regulation of Imprinting Instability in Human Pluripotent Stem Cells.

The instability of genomic imprinting in pluripotent stem cells plants risk of cancer formation after stem cell based regenerative medical treatment, as many imprinted genes, such as Igf2, H19, and Igf2r, are involved in growth control and their deregulation is highly associated with carcinogenesis. Furthermore, imprinting defects at Dlk1-Dio3 locus have been shown to correlate with loss of "full" pluripotency in mouse ES (embryonic stem) and iPS (induced pluripotent stem) cells. Our data from analyzing different passages of NTU1 human embryonic stem (ES) cell line indicated that Dlk1-Dio3 imprinted locus is one of the first imprinted loci to acquire hypermethylation associated with dramatically altered dosages of imprinted genes at later passages. Some of these aberrantly silenced imprinted genes are microRNAs that were predicted to target some histone modifiers which regulate different histone modifications. Intriguingly, some miRNAs in the same locus that were predicted to target pluripotent genes such as Sox2 and Oct4, were consistently undetectable through different passages. Taken together, according to the preliminary data, we speculate that the down regulation of the miRNAs including non-coding RNAs on the Dlk1-Dio3 locus may be the first sign of epigenetic instability. Consequently, the lack of reduction for the target histone modifiers may affect the levels of specific histone modifications in the entire genome, including Dlk1-Dio3 locus, some other imprinted loci and even some important developmentally regulated genes that are associated with differentiation potential during prolonged pluripotent stem cell culture. (platform)