Pluripotential Reprogramming of the Somatic Genome in Hybrid Cells Occurs with the First Cell Cycle

¹ Department of Cell and Developmental Biology, Max Planck Institute for Molecular Biomedicine, Röntgenstrasse 20, 48149 Münster, Germany.; Department of Bioscience and Biotechnology, Bio-Organ Research Center, Konkuk University; Hwayang-dong, Gwangjin-Gu, Seoul 143-701, South Korea
² Department of Cell and Developmental Biology, Max Planck Institute for Molecular Biomedicine, Röntgenstrasse 20, 48149 Münster, Germany.

^* To whom correspondence should be addressed. E-mail: schoeler{at}mpi-muenster.mpg.de.

	Abstract

The fusion of pluripotent embryonic cells with somatic cells results in reprogramming of the somatic cell genome. Oct4-GFP transgenes that do not contain the proximal enhancer (PE) region are widely used to visualize reprogramming of the somatic to the pluripotent cell state. The temporal onset of Oct4-GFP activation has been found to occur 40-48 hrs post-fusion. We asked whether activation of the transgene actually reflects activation of the endogenous Oct4 gene. In the current study, we show that activation of an Oct4-GFP transgene that contains the PE region occurs within 22 hrs of fusion. In addition, demethylation of the Oct4-GFP transgene and that of the endogenous Oct4 and Nanog genes was found to occur within 24 hrs of fusion. As this timing corresponds with the timing of cell cycle completion in ES cells and fusion hybrids (22 hrs), we postulate that pluripotential reprogramming of the somatic cell genome begins during the first cell cycle after the fusion of a somatic cell with a pluripotent cell and has been completed by day 2 post-fusion.