Neural stem cells differentiated from iPS cells spontaneously regain pluripotency

Area of Science:

• Stem Cell Biology
• Epigenetics
• Developmental Biology

Background:

• Differentiated somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) using exogenous factors.
• Exogenous genes introduced during reprogramming are typically silenced epigenetically in pluripotent cells.
• Understanding the stability of silenced genes during differentiation and potential reactivation is crucial.

Purpose of the Study:

• To investigate whether exogenous genes remain silenced or are reactivated upon loss of pluripotency or differentiation.
• To examine the epigenetic regulation and potential for pluripotency restoration in differentiated iPSCs.

Main Methods:

• Induced differentiation of iPSCs into neural stem cells (NSCs) in vitro.
• Morphological and marker analysis (Nestin, Sox2) of iPSC-derived NSCs (iPS-NSCs).
• Long-term culture of iPS-NSCs to observe spontaneous changes and gene reactivation (Oct4-GFP).
• Analysis of DNA methyltransferase (Dnmt) levels during differentiation.
• Comparison with doxycycline-inducible iPSC systems.

Main Results:

• iPS-NSCs were morphologically and marker-wise indistinguishable from brain-derived NSCs and could differentiate into neural subtypes.
• Long-term culture of iPS-NSCs led to spontaneous aggregate formation and reactivation of the Oct4-GFP marker, forming ESC-like colonies.
• Reactivated cells (iPS-NSC-GFP(+)) expressed high pluripotency markers (Oct4, Nanog), formed germline chimeras, and regained pluripotency.
• Exogenous gene reactivation correlated with DNA methyltransferase (Dnmt) downregulation during iPSC differentiation.
• Reactivation was not observed in doxycycline-inducible iPSCs without induction.

Conclusions:

• Pluripotency can be regained in differentiated cells through the reactivation of silenced exogenous genes.
• This pluripotency restoration is associated with dynamic changes in DNA methyltransferase (Dnmt) levels during differentiation.
• Epigenetic regulation of silenced reprogramming factors plays a key role in maintaining or regaining pluripotency.