Induced pluripotent stem cells (iPSCs), generated by the overexpression of transcription factors Oct4, Sox2, Klf4 and c‐Myc in somatic cells, are pluripotent. iPSCs reprogrammed from differentiated cells get through a epigenetic modification during reprogramming and finally have the similar epigenetic state to embryonic stem cells (ESCs). In this study, these epigenetic changes were observed in reprogramming of uni‐parental parthenogenetic somatic cells. Furthermore, we have shown that parthenogenetic pattern of imprinted genes were changed during pluripotential reprogramming. Parthenogenetic neural stem cells (pNSCs) containing only maternal alleles regain the biparental imprinting patterns after reprogramming. However, we have yet to define whether the changed imprinted genes are maintained or reverted to the parthenogenetic state when the reprogrammed cells are differentiated into specialized cell types. To address this question, we compared genome‐wide expression profiles of biparental female neural stem cells (fNSCs), parthenogenetic neural stem cells (pNSCs), and NSCs differentiated from parthenogenetic maternal iPSC (miPS‐NSCs). Furthermore, this study establishes the correlation between the alteration of genome methylation and activation of imprinting genes in the parthenogenetic cells and reports for the first time that the silenced PWS‐related imprinted genes are activated in miPS‐NSCs. Our data demonstrated that pluripotential reprogramming of parthenogenetic somatic cells were able to reset the parthenogenetic imprinting patterns; reprogrammed miPSCs showed erasure of maternal methylation imprints and acquisition of methylation in paternally imprinted genes. Furthermore, the changed imprinting patterns were maintained when the reprogrammed cells are differentiated into specialized cell type. * This work was supported by the Next‐Generation BioGreen 21 program (Grant PJ008- 009) funded by the Rural Development Administration, Republic of Korea.

Pluripotent stem cells can be derived from both pre- and post-implantation embryos. Embryonic stem cells (ES cells), derived from inner cell mass (ICM) of blastocyst are naïve pluripotent and epiblast stem cells (EpiSCs) derived from post-implantation epiblast are primed pluripotent. The phenotypes and gene expression patterns of the two pluripotent stem cells are different each other and EpiSCs thought to be in a more advanced pluripotent (primed pluripotent state) than mouse ES cells (naïve pluripotent state). Therefore, we questioned whether EpiSCs are less potential to be differentiated into specialized cell types in vitro. EpiSCs were isolated from 5.5～6.5 day post coitum mouse embryos of the post-implantation epiblast. The EpiSCs could differentiate into all tree germ layers in vivo, and expressed pluripotency markers (Oct4, Nanog). Interestingly, EpiSCs also were able to efficiently differentiate into neural stem cells (NSCs). The NSCs differentiated from EpiSCs (EpiSC-NSCs) expressed NSC markers (Nestin, Sox2, and Musasi), self-renewed over passage 20, and could differentiate into two neural subtypes, neurons, astrocytes and oligodendrocytes. Next, we compared global gene expression patterns of EpiSC-NSCs with that of NSCs differentiated from ES cells and brain tissue. Gene expression pattern of brain tissue derived NSCs were closer to ES cell-derived NSCs than EpiSC-NSCs, indicating that the pluripotent stem cell-derived somatic cells could have different characteristics depending on the origin of pluripotent stem cell types. * This work was supported by the Next Generation Bio-Green 21 Program funded by the Rural Development Administration (Grant PJ 008009).

Neural stem cells (NSCs) are self-renewing tripotent cell populations and have capacity of neuronal (neurons) and glial (astrocytes and oligodendrocytes) differentiation. Many researchers have reported that NSCs have therapeutic effects in neurological disease by transplantation. However, it is not easy to obtain NSCs in vitro. Recently, Yamanaka and colleagues showed that somatic cells could be reprogrammed into pluripotent state by enforcing reprogramming factors. Induced pluripotent stem (iPS) cells undergo unlimited self-renewal and have differentiation potential into various types of cells like embryonic stem cells. Direct differentiation into a specialized cell types from iPS cells hold considerable promise for regenerative medicine as well as basic research. Here, we induced differentiation of iPS cells into NSCs in vitro and in vivo, which were compared with embryonic stem (ES) cell-derived NSCs and brain derived NSCs. NSCs from ES and iPS cells were morphologically indistinguishable from brain derived NSCs and stained positive for NSCs markers Nestin and Sox2. ES cells derived NSCs were transcriptionally distinguishable from brain derived NSCs. However, global gene expression pattern were similar but distinct between iPS derived NSCs and brain derived NSCs. Moreover, iPS derived NSCs were spontaneously aggregated upon passaging, formed ES cell like colonies, and finally reactivated Oct4-GFP. The spontaneously reverted GFP-positive cells (iPS-NSC-iPS) expressed similar levels of pluripotency markers (Oct4,Nanog) to ES and iPS cells, and could form germ line chimera. One possible explanation for this phenomenon is that spontaneously re-reprogramming was associated with transgene re-activation when iPS cells were differentiated into NSCs. However, NSCs from dox-inducible iPScells could not be reprogrammed into pluripotent state without doxycycline. Taken together, iPS derived NSCs were morphologically and similar to brain derived NSCs, but differ in gene expression pattern and maintenance. * This work was supported by the Next Generation Bio-Green21 Program funded by the Rural Development Administration (Grant PJ008009).