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TISSUE-SPECIFIC STEM CELLS

G9a and Jhdm2a Regulate Embryonic Stem Cell Fusion-Induced Reprogramming of Adult Neural Stem Cells

^aInstitute for Cell Engineering,
^bThe Solomon H. Snyder Department of Neuroscience,
^cDepartment of Biomedical Engineering, and
^dDepartment of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

Key Words. Neural stem cells • Embryonic stem cells • Reprogramming • Oct4 • Histone methyltransferase • Histone demethylase • G9a • Jhdm2a

Correspondence: Correspondence: Hongjun Song, Ph.D., Institute for Cell Engineering, Department of Neurology, Johns Hopkins University School of Medicine, 733 North Broadway, BRB735, Baltimore, Maryland 21205, USA. Telephone: 443-287-7499; Fax: 410-614-9568; e-mail: shongju1{at}jhmi.edu

Received on April 18, 2008; accepted for publication on May 21, 2008.

First published online in STEM CELLS EXPRESS  June 5, 2008.

Somatic nuclei can be reprogrammed to pluripotency through fusion with embryonic stem cells (ESCs). The underlying mechanism is largely unknown, primarily because of a lack of effective approaches to monitor and quantitatively analyze transient, early reprogramming events. The transcription factor Oct4 is expressed specifically in pluripotent stem cells, and its reactivation from somatic cell genome constitutes a hallmark for effective reprogramming. Here we developed a double fluorescent reporter system using engineered ESCs and adult neural stem cells/progenitors (NSCs) to simultaneously and independently monitor cell fusion and reprogramming-induced reactivation of transgenic Oct4-enhanced green fluorescent protein (EGFP) expression. We demonstrate that knockdown of a histone methyltransferase, G9a, or overexpression of a histone demethylase, Jhdm2a, promotes ESC fusion-induced Oct4-EGFP reactivation from adult NSCs. In addition, coexpression of Nanog and Jhdm2a further enhances the ESC-induced Oct4-EGFP reactivation. Interestingly, knockdown of G9a alone in adult NSCs leads to demethylation of the Oct4 promoter and partial reactivation of the endogenous Oct4 expression from adult NSCs. Our results suggest that ESC-induced reprogramming of somatic cells occurs with coordinated actions between erasure of somatic epigenome and transcriptional resetting to restore pluripotency. These mechanistic findings may guide more efficient reprogramming for future therapeutic applications of stem cells.

Disclosure of potential conflicts of interest is found at the end of this article.

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