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Molecular and Cellular Biology, December 2006, p. 9471-9483, Vol. 26, No. 24
0270-7306/06/$08.00+0 doi:10.1128/MCB.00898-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Arthur C.-K. Chung,
and
Austin J. Cooney*
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
Received 19 May 2006/ Returned for modification 15 June 2006/ Accepted 29 September 2006
The pluripotent factor Oct4 is a key transcription factor that maintains embryonic stem (ES) cell self-renewal and is down-regulated upon the differentiation of ES cells and silenced in somatic cells. A combination of cis elements, transcription factors, and epigenetic modifications, such as DNA methylation, are involved in the regulation of Oct4 gene expression. Here we show that the orphan nuclear receptor GCNF initiates Oct4 repression and DNA methylation by the differential recruitment of MBD (methylated CpG binding domain) factors to the promoter. Compared with wild-type ES cells and gastrulating embryos, Oct4 repression is lost and its proximal promoter is significantly hypomethylated in RA-differentiated GCNF/ ES cells. The Oct4 gene is reexpressed in some somatic cells of GCNF/ embryos, showing that it has not been properly silenced coincident with reduced DNA methylation of its promoter. Efforts to characterize mediators of GCNF's repressive function and DNA methylation of the Oct4 promoter identified methyl-DNA binding proteins, MBD3 and MBD2, as GCNF-interacting factors. In P19 and ES cells, upon differentiation, endogenous GCNF binds to the Oct4 proximal promoter and differentially recruits MBD3 and MBD2. In differentiated GCNF/ ES cells, recruitment of MBD3 and MBD2 to the Oct4 promoter is lost, and repression of Oct4 expression and DNA methylation fails to occur. RNA interference-mediated knockdown of MBD3 and/or MBD2 expression results in reduced Oct4 repression in differentiated P19 and ES cells. Repression of Oct4 expression and recruitment of MBD3 are maintained in de novo DNA methylation-deficient ES cells (Dnmt3A/3B-null cells), while MBD2 recruitment is lost. Thus, recruitment of MBD3 and MBD2 by GCNF links two events, gene-specific repression and DNA methylation, which occur differentially at the Oct4 promoter. GCNF initiates the repression and epigenetic modification of Oct4 gene during ES cell differentiation.
Published ahead of print on 9 October 2006.
Present address: INSERM, U693, Faculté de Médecine Paris-Sud, 63 rue Gabriel Péri, 94276, Le Kremlin Bicêtre Cedex, France.
Present address: Center for Inflammatory Diseases and Molecular Therapies, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong.
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