神经干细胞恢复为诱导多能干细胞

yigang

Differentiated somatic cells can be reprogrammed into pluripotent stem cells by transduction of exogenous reprogramming factors. After induced pluripotent stem (iPS) cells are established, exogenous genes are silenced. In the pluripotent state, retroviral genes integrated in the host genome are kept inactive through epigenetic transcriptional regulation. In the present study, we tried to determine whether exogenous genes remain silenced or are reactivated upon loss of pluripotency or on differentiation by using an in vitro system. We induced differentiation of iPS cells into neural stem cells (NSCs) in vitro; the NSCs appeared morphologically indistinguishable from brain‐derived NSCs and stained positive for the NSC markers Nestin and Sox2. These iPS cell‐derived NSCs (iPS‐NSCs) were also capable of differentiating into all three neural subtypes. Interestingly, iPS‐NSCs spontaneously formed aggregates on long‐term culture and showed reactivation of the Oct4‐GFP marker, which was followed by the formation of ES celllike colonies. The spontaneously reverted GFP‐positive (iPS‐NSC‐GFP+) cells expressed high levels of pluripotency markers (Oct4 and Nanog) and formed germline chimeras, indicating that iPS‐NSC‐GFP+ cells had the same pluripotency as the original iPS cells. The reactivation of silenced exogenous genes was tightly correlated with the downregulation of DNA methyltransferases (Dnmts) during differentiation of iPS cells. This phenomenon was not observed in doxycycline‐inducible iPS cells, where the reactivation of exogenous genes could be induced only by doxycycline treatment. These results indicate that pluripotency can be regained through reactivation of exogenous genes, which is associated with dynamic change of Dnmt levels during differentiation of iPS cells
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作者发现为什么ipsc体外诱导分化为神经干细胞后的传代培养过程中，部分神经干细胞可以恢复诱导干细胞特性。并对诱导干细胞的临床应用的安全性提供指导意见。